SSH CRC attack detector now uses a dynamically allocated context.

[u/mdw/putty] / ssh.c

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <assert.h>

#include "putty.h"
#include "tree234.h"
#include "ssh.h"

#ifndef FALSE
#define FALSE 0
#endif
#ifndef TRUE
#define TRUE 1
#endif

#define logevent(s) { logevent(s); \
                      if ((flags & FLAG_STDERR) && (flags & FLAG_VERBOSE)) \
                      { fprintf(stderr, "%s\n", s); fflush(stderr); } }

/* logevent, only printf-formatted. */
void logeventf(char *fmt, ...)
{
    va_list ap;
    char stuff[200];

    va_start(ap, fmt);
    vsprintf(stuff, fmt, ap);
    va_end(ap);
    logevent(stuff);
}

#define bombout(msg) ( ssh->state = SSH_STATE_CLOSED, \
                          (ssh->s ? sk_close(ssh->s), ssh->s = NULL : 0), \
                          logeventf msg, connection_fatal msg )

#define SSH1_MSG_DISCONNECT                       1     /* 0x1 */
#define SSH1_SMSG_PUBLIC_KEY                      2     /* 0x2 */
#define SSH1_CMSG_SESSION_KEY                     3     /* 0x3 */
#define SSH1_CMSG_USER                            4     /* 0x4 */
#define SSH1_CMSG_AUTH_RSA                        6     /* 0x6 */
#define SSH1_SMSG_AUTH_RSA_CHALLENGE              7     /* 0x7 */
#define SSH1_CMSG_AUTH_RSA_RESPONSE               8     /* 0x8 */
#define SSH1_CMSG_AUTH_PASSWORD                   9     /* 0x9 */
#define SSH1_CMSG_REQUEST_PTY                     10    /* 0xa */
#define SSH1_CMSG_WINDOW_SIZE                     11    /* 0xb */
#define SSH1_CMSG_EXEC_SHELL                      12    /* 0xc */
#define SSH1_CMSG_EXEC_CMD                        13    /* 0xd */
#define SSH1_SMSG_SUCCESS                         14    /* 0xe */
#define SSH1_SMSG_FAILURE                         15    /* 0xf */
#define SSH1_CMSG_STDIN_DATA                      16    /* 0x10 */
#define SSH1_SMSG_STDOUT_DATA                     17    /* 0x11 */
#define SSH1_SMSG_STDERR_DATA                     18    /* 0x12 */
#define SSH1_CMSG_EOF                             19    /* 0x13 */
#define SSH1_SMSG_EXIT_STATUS                     20    /* 0x14 */
#define SSH1_MSG_CHANNEL_OPEN_CONFIRMATION        21    /* 0x15 */
#define SSH1_MSG_CHANNEL_OPEN_FAILURE             22    /* 0x16 */
#define SSH1_MSG_CHANNEL_DATA                     23    /* 0x17 */
#define SSH1_MSG_CHANNEL_CLOSE                    24    /* 0x18 */
#define SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION       25    /* 0x19 */
#define SSH1_SMSG_X11_OPEN                        27    /* 0x1b */
#define SSH1_CMSG_PORT_FORWARD_REQUEST            28    /* 0x1c */
#define SSH1_MSG_PORT_OPEN                        29    /* 0x1d */
#define SSH1_CMSG_AGENT_REQUEST_FORWARDING        30    /* 0x1e */
#define SSH1_SMSG_AGENT_OPEN                      31    /* 0x1f */
#define SSH1_MSG_IGNORE                           32    /* 0x20 */
#define SSH1_CMSG_EXIT_CONFIRMATION               33    /* 0x21 */
#define SSH1_CMSG_X11_REQUEST_FORWARDING          34    /* 0x22 */
#define SSH1_CMSG_AUTH_RHOSTS_RSA                 35    /* 0x23 */
#define SSH1_MSG_DEBUG                            36    /* 0x24 */
#define SSH1_CMSG_REQUEST_COMPRESSION             37    /* 0x25 */
#define SSH1_CMSG_AUTH_TIS                        39    /* 0x27 */
#define SSH1_SMSG_AUTH_TIS_CHALLENGE              40    /* 0x28 */
#define SSH1_CMSG_AUTH_TIS_RESPONSE               41    /* 0x29 */
#define SSH1_CMSG_AUTH_CCARD                      70    /* 0x46 */
#define SSH1_SMSG_AUTH_CCARD_CHALLENGE            71    /* 0x47 */
#define SSH1_CMSG_AUTH_CCARD_RESPONSE             72    /* 0x48 */

#define SSH1_AUTH_TIS                             5     /* 0x5 */
#define SSH1_AUTH_CCARD                           16    /* 0x10 */

#define SSH1_PROTOFLAG_SCREEN_NUMBER              1     /* 0x1 */
/* Mask for protoflags we will echo back to server if seen */
#define SSH1_PROTOFLAGS_SUPPORTED                 0     /* 0x1 */

#define SSH2_MSG_DISCONNECT                       1     /* 0x1 */
#define SSH2_MSG_IGNORE                           2     /* 0x2 */
#define SSH2_MSG_UNIMPLEMENTED                    3     /* 0x3 */
#define SSH2_MSG_DEBUG                            4     /* 0x4 */
#define SSH2_MSG_SERVICE_REQUEST                  5     /* 0x5 */
#define SSH2_MSG_SERVICE_ACCEPT                   6     /* 0x6 */
#define SSH2_MSG_KEXINIT                          20    /* 0x14 */
#define SSH2_MSG_NEWKEYS                          21    /* 0x15 */
#define SSH2_MSG_KEXDH_INIT                       30    /* 0x1e */
#define SSH2_MSG_KEXDH_REPLY                      31    /* 0x1f */
#define SSH2_MSG_KEX_DH_GEX_REQUEST               30    /* 0x1e */
#define SSH2_MSG_KEX_DH_GEX_GROUP                 31    /* 0x1f */
#define SSH2_MSG_KEX_DH_GEX_INIT                  32    /* 0x20 */
#define SSH2_MSG_KEX_DH_GEX_REPLY                 33    /* 0x21 */
#define SSH2_MSG_USERAUTH_REQUEST                 50    /* 0x32 */
#define SSH2_MSG_USERAUTH_FAILURE                 51    /* 0x33 */
#define SSH2_MSG_USERAUTH_SUCCESS                 52    /* 0x34 */
#define SSH2_MSG_USERAUTH_BANNER                  53    /* 0x35 */
#define SSH2_MSG_USERAUTH_PK_OK                   60    /* 0x3c */
#define SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ        60    /* 0x3c */
#define SSH2_MSG_USERAUTH_INFO_REQUEST            60    /* 0x3c */
#define SSH2_MSG_USERAUTH_INFO_RESPONSE           61    /* 0x3d */
#define SSH2_MSG_GLOBAL_REQUEST                   80    /* 0x50 */
#define SSH2_MSG_REQUEST_SUCCESS                  81    /* 0x51 */
#define SSH2_MSG_REQUEST_FAILURE                  82    /* 0x52 */
#define SSH2_MSG_CHANNEL_OPEN                     90    /* 0x5a */
#define SSH2_MSG_CHANNEL_OPEN_CONFIRMATION        91    /* 0x5b */
#define SSH2_MSG_CHANNEL_OPEN_FAILURE             92    /* 0x5c */
#define SSH2_MSG_CHANNEL_WINDOW_ADJUST            93    /* 0x5d */
#define SSH2_MSG_CHANNEL_DATA                     94    /* 0x5e */
#define SSH2_MSG_CHANNEL_EXTENDED_DATA            95    /* 0x5f */
#define SSH2_MSG_CHANNEL_EOF                      96    /* 0x60 */
#define SSH2_MSG_CHANNEL_CLOSE                    97    /* 0x61 */
#define SSH2_MSG_CHANNEL_REQUEST                  98    /* 0x62 */
#define SSH2_MSG_CHANNEL_SUCCESS                  99    /* 0x63 */
#define SSH2_MSG_CHANNEL_FAILURE                  100   /* 0x64 */

/*
 * Packet type contexts, so that ssh2_pkt_type can correctly decode
 * the ambiguous type numbers back into the correct type strings.
 */
#define SSH2_PKTCTX_DHGROUP1         0x0001
#define SSH2_PKTCTX_DHGEX            0x0002
#define SSH2_PKTCTX_PUBLICKEY        0x0010
#define SSH2_PKTCTX_PASSWORD         0x0020
#define SSH2_PKTCTX_KBDINTER         0x0040
#define SSH2_PKTCTX_AUTH_MASK        0x00F0

#define SSH2_DISCONNECT_HOST_NOT_ALLOWED_TO_CONNECT 1   /* 0x1 */
#define SSH2_DISCONNECT_PROTOCOL_ERROR            2     /* 0x2 */
#define SSH2_DISCONNECT_KEY_EXCHANGE_FAILED       3     /* 0x3 */
#define SSH2_DISCONNECT_HOST_AUTHENTICATION_FAILED 4    /* 0x4 */
#define SSH2_DISCONNECT_MAC_ERROR                 5     /* 0x5 */
#define SSH2_DISCONNECT_COMPRESSION_ERROR         6     /* 0x6 */
#define SSH2_DISCONNECT_SERVICE_NOT_AVAILABLE     7     /* 0x7 */
#define SSH2_DISCONNECT_PROTOCOL_VERSION_NOT_SUPPORTED 8        /* 0x8 */
#define SSH2_DISCONNECT_HOST_KEY_NOT_VERIFIABLE   9     /* 0x9 */
#define SSH2_DISCONNECT_CONNECTION_LOST           10    /* 0xa */
#define SSH2_DISCONNECT_BY_APPLICATION            11    /* 0xb */
#define SSH2_DISCONNECT_TOO_MANY_CONNECTIONS      12    /* 0xc */
#define SSH2_DISCONNECT_AUTH_CANCELLED_BY_USER    13    /* 0xd */
#define SSH2_DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE 14       /* 0xe */
#define SSH2_DISCONNECT_ILLEGAL_USER_NAME         15    /* 0xf */

static const char *const ssh2_disconnect_reasons[] = {
    NULL,
    "SSH_DISCONNECT_HOST_NOT_ALLOWED_TO_CONNECT",
    "SSH_DISCONNECT_PROTOCOL_ERROR",
    "SSH_DISCONNECT_KEY_EXCHANGE_FAILED",
    "SSH_DISCONNECT_HOST_AUTHENTICATION_FAILED",
    "SSH_DISCONNECT_MAC_ERROR",
    "SSH_DISCONNECT_COMPRESSION_ERROR",
    "SSH_DISCONNECT_SERVICE_NOT_AVAILABLE",
    "SSH_DISCONNECT_PROTOCOL_VERSION_NOT_SUPPORTED",
    "SSH_DISCONNECT_HOST_KEY_NOT_VERIFIABLE",
    "SSH_DISCONNECT_CONNECTION_LOST",
    "SSH_DISCONNECT_BY_APPLICATION",
    "SSH_DISCONNECT_TOO_MANY_CONNECTIONS",
    "SSH_DISCONNECT_AUTH_CANCELLED_BY_USER",
    "SSH_DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE",
    "SSH_DISCONNECT_ILLEGAL_USER_NAME",
};

#define SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED     1     /* 0x1 */
#define SSH2_OPEN_CONNECT_FAILED                  2     /* 0x2 */
#define SSH2_OPEN_UNKNOWN_CHANNEL_TYPE            3     /* 0x3 */
#define SSH2_OPEN_RESOURCE_SHORTAGE               4     /* 0x4 */

#define SSH2_EXTENDED_DATA_STDERR                 1     /* 0x1 */

/*
 * Various remote-bug flags.
 */
#define BUG_CHOKES_ON_SSH1_IGNORE                 1
#define BUG_SSH2_HMAC                             2
#define BUG_NEEDS_SSH1_PLAIN_PASSWORD             4
#define BUG_CHOKES_ON_RSA                         8
#define BUG_SSH2_RSA_PADDING                     16
#define BUG_SSH2_DERIVEKEY                       32
#define BUG_SSH2_DH_GEX                          64

#define translate(x) if (type == x) return #x
#define translatec(x,ctx) if (type == x && (pkt_ctx & ctx)) return #x
char *ssh1_pkt_type(int type)
{
    translate(SSH1_MSG_DISCONNECT);
    translate(SSH1_SMSG_PUBLIC_KEY);
    translate(SSH1_CMSG_SESSION_KEY);
    translate(SSH1_CMSG_USER);
    translate(SSH1_CMSG_AUTH_RSA);
    translate(SSH1_SMSG_AUTH_RSA_CHALLENGE);
    translate(SSH1_CMSG_AUTH_RSA_RESPONSE);
    translate(SSH1_CMSG_AUTH_PASSWORD);
    translate(SSH1_CMSG_REQUEST_PTY);
    translate(SSH1_CMSG_WINDOW_SIZE);
    translate(SSH1_CMSG_EXEC_SHELL);
    translate(SSH1_CMSG_EXEC_CMD);
    translate(SSH1_SMSG_SUCCESS);
    translate(SSH1_SMSG_FAILURE);
    translate(SSH1_CMSG_STDIN_DATA);
    translate(SSH1_SMSG_STDOUT_DATA);
    translate(SSH1_SMSG_STDERR_DATA);
    translate(SSH1_CMSG_EOF);
    translate(SSH1_SMSG_EXIT_STATUS);
    translate(SSH1_MSG_CHANNEL_OPEN_CONFIRMATION);
    translate(SSH1_MSG_CHANNEL_OPEN_FAILURE);
    translate(SSH1_MSG_CHANNEL_DATA);
    translate(SSH1_MSG_CHANNEL_CLOSE);
    translate(SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION);
    translate(SSH1_SMSG_X11_OPEN);
    translate(SSH1_CMSG_PORT_FORWARD_REQUEST);
    translate(SSH1_MSG_PORT_OPEN);
    translate(SSH1_CMSG_AGENT_REQUEST_FORWARDING);
    translate(SSH1_SMSG_AGENT_OPEN);
    translate(SSH1_MSG_IGNORE);
    translate(SSH1_CMSG_EXIT_CONFIRMATION);
    translate(SSH1_CMSG_X11_REQUEST_FORWARDING);
    translate(SSH1_CMSG_AUTH_RHOSTS_RSA);
    translate(SSH1_MSG_DEBUG);
    translate(SSH1_CMSG_REQUEST_COMPRESSION);
    translate(SSH1_CMSG_AUTH_TIS);
    translate(SSH1_SMSG_AUTH_TIS_CHALLENGE);
    translate(SSH1_CMSG_AUTH_TIS_RESPONSE);
    translate(SSH1_CMSG_AUTH_CCARD);
    translate(SSH1_SMSG_AUTH_CCARD_CHALLENGE);
    translate(SSH1_CMSG_AUTH_CCARD_RESPONSE);
    return "unknown";
}
char *ssh2_pkt_type(int pkt_ctx, int type)
{
    translate(SSH2_MSG_DISCONNECT);
    translate(SSH2_MSG_IGNORE);
    translate(SSH2_MSG_UNIMPLEMENTED);
    translate(SSH2_MSG_DEBUG);
    translate(SSH2_MSG_SERVICE_REQUEST);
    translate(SSH2_MSG_SERVICE_ACCEPT);
    translate(SSH2_MSG_KEXINIT);
    translate(SSH2_MSG_NEWKEYS);
    translatec(SSH2_MSG_KEXDH_INIT, SSH2_PKTCTX_DHGROUP1);
    translatec(SSH2_MSG_KEXDH_REPLY, SSH2_PKTCTX_DHGROUP1);
    translatec(SSH2_MSG_KEX_DH_GEX_REQUEST, SSH2_PKTCTX_DHGEX);
    translatec(SSH2_MSG_KEX_DH_GEX_GROUP, SSH2_PKTCTX_DHGEX);
    translatec(SSH2_MSG_KEX_DH_GEX_INIT, SSH2_PKTCTX_DHGEX);
    translatec(SSH2_MSG_KEX_DH_GEX_REPLY, SSH2_PKTCTX_DHGEX);
    translate(SSH2_MSG_USERAUTH_REQUEST);
    translate(SSH2_MSG_USERAUTH_FAILURE);
    translate(SSH2_MSG_USERAUTH_SUCCESS);
    translate(SSH2_MSG_USERAUTH_BANNER);
    translatec(SSH2_MSG_USERAUTH_PK_OK, SSH2_PKTCTX_PUBLICKEY);
    translatec(SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ, SSH2_PKTCTX_PASSWORD);
    translatec(SSH2_MSG_USERAUTH_INFO_REQUEST, SSH2_PKTCTX_KBDINTER);
    translatec(SSH2_MSG_USERAUTH_INFO_RESPONSE, SSH2_PKTCTX_KBDINTER);
    translate(SSH2_MSG_GLOBAL_REQUEST);
    translate(SSH2_MSG_REQUEST_SUCCESS);
    translate(SSH2_MSG_REQUEST_FAILURE);
    translate(SSH2_MSG_CHANNEL_OPEN);
    translate(SSH2_MSG_CHANNEL_OPEN_CONFIRMATION);
    translate(SSH2_MSG_CHANNEL_OPEN_FAILURE);
    translate(SSH2_MSG_CHANNEL_WINDOW_ADJUST);
    translate(SSH2_MSG_CHANNEL_DATA);
    translate(SSH2_MSG_CHANNEL_EXTENDED_DATA);
    translate(SSH2_MSG_CHANNEL_EOF);
    translate(SSH2_MSG_CHANNEL_CLOSE);
    translate(SSH2_MSG_CHANNEL_REQUEST);
    translate(SSH2_MSG_CHANNEL_SUCCESS);
    translate(SSH2_MSG_CHANNEL_FAILURE);
    return "unknown";
}
#undef translate
#undef translatec

#define GET_32BIT(cp) \
    (((unsigned long)(unsigned char)(cp)[0] << 24) | \
    ((unsigned long)(unsigned char)(cp)[1] << 16) | \
    ((unsigned long)(unsigned char)(cp)[2] << 8) | \
    ((unsigned long)(unsigned char)(cp)[3]))

#define PUT_32BIT(cp, value) { \
    (cp)[0] = (unsigned char)((value) >> 24); \
    (cp)[1] = (unsigned char)((value) >> 16); \
    (cp)[2] = (unsigned char)((value) >> 8); \
    (cp)[3] = (unsigned char)(value); }

enum { PKT_END, PKT_INT, PKT_CHAR, PKT_DATA, PKT_STR, PKT_BIGNUM };

/* Coroutine mechanics for the sillier bits of the code */
#define crBegin(v)      { int *crLine = &v; switch(v) { case 0:;
#define crState(t) \
    struct t *s; \
    if (!ssh->t) ssh->t = smalloc(sizeof(struct t)); \
    s = ssh->t;
#define crFinish(z)     } *crLine = 0; return (z); }
#define crFinishV       } *crLine = 0; return; }
#define crReturn(z)     \
        do {\
            *crLine =__LINE__; return (z); case __LINE__:;\
        } while (0)
#define crReturnV       \
        do {\
            *crLine=__LINE__; return; case __LINE__:;\
        } while (0)
#define crStop(z)       do{ *crLine = 0; return (z); }while(0)
#define crStopV         do{ *crLine = 0; return; }while(0)
#define crWaitUntil(c)  do { crReturn(0); } while (!(c))
#define crWaitUntilV(c) do { crReturnV; } while (!(c))

typedef struct ssh_tag *Ssh;

extern char *x11_init(Socket *, char *, void *);
extern void x11_close(Socket);
extern int x11_send(Socket, char *, int);
extern void x11_invent_auth(char *, int, char *, int);
extern void x11_unthrottle(Socket s);
extern void x11_override_throttle(Socket s, int enable);

extern char *pfd_newconnect(Socket * s, char *hostname, int port, void *c);
extern char *pfd_addforward(char *desthost, int destport, int port);
extern void pfd_close(Socket s);
extern int pfd_send(Socket s, char *data, int len);
extern void pfd_confirm(Socket s);
extern void pfd_unthrottle(Socket s);
extern void pfd_override_throttle(Socket s, int enable);

static void ssh2_pkt_init(Ssh, int pkt_type);
static void ssh2_pkt_addbool(Ssh, unsigned char value);
static void ssh2_pkt_adduint32(Ssh, unsigned long value);
static void ssh2_pkt_addstring_start(Ssh);
static void ssh2_pkt_addstring_str(Ssh, char *data);
static void ssh2_pkt_addstring_data(Ssh, char *data, int len);
static void ssh2_pkt_addstring(Ssh, char *data);
static char *ssh2_mpint_fmt(Bignum b, int *len);
static void ssh2_pkt_addmp(Ssh, Bignum b);
static int ssh2_pkt_construct(Ssh);
static void ssh2_pkt_send(Ssh);

/*
 * Buffer management constants. There are several of these for
 * various different purposes:
 * 
 *  - SSH1_BUFFER_LIMIT is the amount of backlog that must build up
 *    on a local data stream before we throttle the whole SSH
 *    connection (in SSH1 only). Throttling the whole connection is
 *    pretty drastic so we set this high in the hope it won't
 *    happen very often.
 * 
 *  - SSH_MAX_BACKLOG is the amount of backlog that must build up
 *    on the SSH connection itself before we defensively throttle
 *    _all_ local data streams. This is pretty drastic too (though
 *    thankfully unlikely in SSH2 since the window mechanism should
 *    ensure that the server never has any need to throttle its end
 *    of the connection), so we set this high as well.
 * 
 *  - OUR_V2_WINSIZE is the maximum window size we present on SSH2
 *    channels.
 */

#define SSH1_BUFFER_LIMIT 32768
#define SSH_MAX_BACKLOG 32768
#define OUR_V2_WINSIZE 16384

const static struct ssh_kex *kex_algs[] = {
    &ssh_diffiehellman_gex,
    &ssh_diffiehellman
};

const static struct ssh_signkey *hostkey_algs[] = { &ssh_rsa, &ssh_dss };

static void *nullmac_make_context(void)
{
    return NULL;
}
static void nullmac_free_context(void *handle)
{
}
static void nullmac_key(void *handle, unsigned char *key)
{
}
static void nullmac_generate(void *handle, unsigned char *blk, int len,
                             unsigned long seq)
{
}
static int nullmac_verify(void *handle, unsigned char *blk, int len,
                          unsigned long seq)
{
    return 1;
}
const static struct ssh_mac ssh_mac_none = {
    nullmac_make_context, nullmac_free_context, nullmac_key,
    nullmac_generate, nullmac_verify, "none", 0
};
const static struct ssh_mac *macs[] = {
    &ssh_sha1, &ssh_md5, &ssh_mac_none
};
const static struct ssh_mac *buggymacs[] = {
    &ssh_sha1_buggy, &ssh_md5, &ssh_mac_none
};

static void ssh_comp_none_init(void)
{
}
static int ssh_comp_none_block(unsigned char *block, int len,
                               unsigned char **outblock, int *outlen)
{
    return 0;
}
static int ssh_comp_none_disable(void)
{
    return 0;
}
const static struct ssh_compress ssh_comp_none = {
    "none",
    ssh_comp_none_init, ssh_comp_none_block,
    ssh_comp_none_init, ssh_comp_none_block,
    ssh_comp_none_disable
};
extern const struct ssh_compress ssh_zlib;
const static struct ssh_compress *compressions[] = {
    &ssh_zlib, &ssh_comp_none
};

enum {                                 /* channel types */
    CHAN_MAINSESSION,
    CHAN_X11,
    CHAN_AGENT,
    CHAN_SOCKDATA,
    CHAN_SOCKDATA_DORMANT              /* one the remote hasn't confirmed */
};

/*
 * 2-3-4 tree storing channels.
 */
struct ssh_channel {
    Ssh ssh;                           /* pointer back to main context */
    unsigned remoteid, localid;
    int type;
    /*
     * In SSH1, this value contains four bits:
     * 
     *   1   We have sent SSH1_MSG_CHANNEL_CLOSE.
     *   2   We have sent SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION.
     *   4   We have received SSH1_MSG_CHANNEL_CLOSE.
     *   8   We have received SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION.
     * 
     * A channel is completely finished with when all four bits are set.
     */
    int closes;
    union {
        struct ssh1_data_channel {
            int throttling;
        } v1;
        struct ssh2_data_channel {
            bufchain outbuffer;
            unsigned remwindow, remmaxpkt;
            unsigned locwindow;
        } v2;
    } v;
    union {
        struct ssh_agent_channel {
            unsigned char *message;
            unsigned char msglen[4];
            int lensofar, totallen;
        } a;
        struct ssh_x11_channel {
            Socket s;
        } x11;
        struct ssh_pfd_channel {
            Socket s;
        } pfd;
    } u;
};

/*
 * 2-3-4 tree storing remote->local port forwardings. SSH 1 and SSH
 * 2 use this structure in different ways, reflecting SSH 2's
 * altogether saner approach to port forwarding.
 * 
 * In SSH 1, you arrange a remote forwarding by sending the server
 * the remote port number, and the local destination host:port.
 * When a connection comes in, the server sends you back that
 * host:port pair, and you connect to it. This is a ready-made
 * security hole if you're not on the ball: a malicious server
 * could send you back _any_ host:port pair, so if you trustingly
 * connect to the address it gives you then you've just opened the
 * entire inside of your corporate network just by connecting
 * through it to a dodgy SSH server. Hence, we must store a list of
 * host:port pairs we _are_ trying to forward to, and reject a
 * connection request from the server if it's not in the list.
 * 
 * In SSH 2, each side of the connection minds its own business and
 * doesn't send unnecessary information to the other. You arrange a
 * remote forwarding by sending the server just the remote port
 * number. When a connection comes in, the server tells you which
 * of its ports was connected to; and _you_ have to remember what
 * local host:port pair went with that port number.
 * 
 * Hence: in SSH 1 this structure stores host:port pairs we intend
 * to allow connections to, and is indexed by those host:port
 * pairs. In SSH 2 it stores a mapping from source port to
 * destination host:port pair, and is indexed by source port.
 */
struct ssh_rportfwd {
    unsigned sport, dport;
    char dhost[256];
};

struct Packet {
    long length;
    int type;
    unsigned char *data;
    unsigned char *body;
    long savedpos;
    long maxlen;
};

static void ssh1_protocol(Ssh ssh, unsigned char *in, int inlen, int ispkt);
static void ssh2_protocol(Ssh ssh, unsigned char *in, int inlen, int ispkt);
static void ssh_size(void *handle, int width, int height);
static void ssh_special(void *handle, Telnet_Special);
static int ssh2_try_send(struct ssh_channel *c);
static void ssh2_add_channel_data(struct ssh_channel *c, char *buf, int len);
static void ssh_throttle_all(Ssh ssh, int enable, int bufsize);
static void ssh2_set_window(struct ssh_channel *c, unsigned newwin);
static int ssh_sendbuffer(void *handle);

struct rdpkt1_state_tag {
    long len, pad, biglen, to_read;
    unsigned long realcrc, gotcrc;
    unsigned char *p;
    int i;
    int chunk;
};

struct rdpkt2_state_tag {
    long len, pad, payload, packetlen, maclen;
    int i;
    int cipherblk;
    unsigned long incoming_sequence;
};

struct ssh_tag {
    const struct plug_function_table *fn;
    /* the above field _must_ be first in the structure */

    SHA_State exhash, exhashbase;

    Socket s;

    unsigned char session_key[32];
    int v1_compressing;
    int v1_remote_protoflags;
    int v1_local_protoflags;
    int agentfwd_enabled;
    int X11_fwd_enabled;
    int remote_bugs;
    const struct ssh_cipher *cipher;
    void *v1_cipher_ctx;
    void *crcda_ctx;
    const struct ssh2_cipher *cscipher, *sccipher;
    void *cs_cipher_ctx, *sc_cipher_ctx;
    const struct ssh_mac *csmac, *scmac;
    void *cs_mac_ctx, *sc_mac_ctx;
    const struct ssh_compress *cscomp, *sccomp;
    const struct ssh_kex *kex;
    const struct ssh_signkey *hostkey;
    unsigned char v2_session_id[20];

    char *savedhost;
    int savedport;
    int send_ok;
    int echoing, editing;

    void *frontend;

    int term_width, term_height;

    tree234 *channels;                 /* indexed by local id */
    struct ssh_channel *mainchan;      /* primary session channel */
    int exitcode;

    tree234 *rportfwds;

    enum {
        SSH_STATE_PREPACKET,
        SSH_STATE_BEFORE_SIZE,
        SSH_STATE_INTERMED,
        SSH_STATE_SESSION,
        SSH_STATE_CLOSED
    } state;

    int size_needed, eof_needed;

    struct Packet pktin;
    struct Packet pktout;
    unsigned char *deferred_send_data;
    int deferred_len, deferred_size;

    /*
     * Gross hack: pscp will try to start SFTP but fall back to
     * scp1 if that fails. This variable is the means by which
     * scp.c can reach into the SSH code and find out which one it
     * got.
     */
    int fallback_cmd;

    /*
     * Used for username and password input.
     */
    char *userpass_input_buffer;
    int userpass_input_buflen;
    int userpass_input_bufpos;
    int userpass_input_echo;

    char *portfwd_strptr;
    int pkt_ctx;

    int version;
    int v1_throttle_count;
    int overall_bufsize;
    int throttled_all;
    int v1_stdout_throttling;
    int v2_outgoing_sequence;

    int ssh1_rdpkt_crstate;
    int ssh2_rdpkt_crstate;
    int do_ssh_init_crstate;
    int ssh_gotdata_crstate;
    int ssh1_protocol_crstate;
    int do_ssh1_login_crstate;
    int do_ssh2_transport_crstate;
    int do_ssh2_authconn_crstate;

    void *do_ssh_init_state;
    void *do_ssh1_login_state;
    void *do_ssh2_transport_state;
    void *do_ssh2_authconn_state;

    struct rdpkt1_state_tag rdpkt1_state;
    struct rdpkt2_state_tag rdpkt2_state;

    void (*protocol) (Ssh ssh, unsigned char *in, int inlen, int ispkt);
    int (*s_rdpkt) (Ssh ssh, unsigned char **data, int *datalen);
};

static int ssh_channelcmp(void *av, void *bv)
{
    struct ssh_channel *a = (struct ssh_channel *) av;
    struct ssh_channel *b = (struct ssh_channel *) bv;
    if (a->localid < b->localid)
        return -1;
    if (a->localid > b->localid)
        return +1;
    return 0;
}
static int ssh_channelfind(void *av, void *bv)
{
    unsigned *a = (unsigned *) av;
    struct ssh_channel *b = (struct ssh_channel *) bv;
    if (*a < b->localid)
        return -1;
    if (*a > b->localid)
        return +1;
    return 0;
}

static int ssh_rportcmp_ssh1(void *av, void *bv)
{
    struct ssh_rportfwd *a = (struct ssh_rportfwd *) av;
    struct ssh_rportfwd *b = (struct ssh_rportfwd *) bv;
    int i;
    if ( (i = strcmp(a->dhost, b->dhost)) != 0)
        return i < 0 ? -1 : +1;
    if (a->dport > b->dport)
        return +1;
    if (a->dport < b->dport)
        return -1;
    return 0;
}

static int ssh_rportcmp_ssh2(void *av, void *bv)
{
    struct ssh_rportfwd *a = (struct ssh_rportfwd *) av;
    struct ssh_rportfwd *b = (struct ssh_rportfwd *) bv;

    if (a->sport > b->sport)
        return +1;
    if (a->sport < b->sport)
        return -1;
    return 0;
}

static int alloc_channel_id(Ssh ssh)
{
    const unsigned CHANNEL_NUMBER_OFFSET = 256;
    unsigned low, high, mid;
    int tsize;
    struct ssh_channel *c;

    /*
     * First-fit allocation of channel numbers: always pick the
     * lowest unused one. To do this, binary-search using the
     * counted B-tree to find the largest channel ID which is in a
     * contiguous sequence from the beginning. (Precisely
     * everything in that sequence must have ID equal to its tree
     * index plus CHANNEL_NUMBER_OFFSET.)
     */
    tsize = count234(ssh->channels);

    low = -1;
    high = tsize;
    while (high - low > 1) {
        mid = (high + low) / 2;
        c = index234(ssh->channels, mid);
        if (c->localid == mid + CHANNEL_NUMBER_OFFSET)
            low = mid;                 /* this one is fine */
        else
            high = mid;                /* this one is past it */
    }
    /*
     * Now low points to either -1, or the tree index of the
     * largest ID in the initial sequence.
     */
    {
        unsigned i = low + 1 + CHANNEL_NUMBER_OFFSET;
        assert(NULL == find234(ssh->channels, &i, ssh_channelfind));
    }
    return low + 1 + CHANNEL_NUMBER_OFFSET;
}

static void c_write(Ssh ssh, char *buf, int len)
{
    if ((flags & FLAG_STDERR)) {
        int i;
        for (i = 0; i < len; i++)
            if (buf[i] != '\r')
                fputc(buf[i], stderr);
        return;
    }
    from_backend(ssh->frontend, 1, buf, len);
}

static void c_write_untrusted(Ssh ssh, char *buf, int len)
{
    int i;
    for (i = 0; i < len; i++) {
        if (buf[i] == '\n')
            c_write(ssh, "\r\n", 2);
        else if ((buf[i] & 0x60) || (buf[i] == '\r'))
            c_write(ssh, buf + i, 1);
    }
}

static void c_write_str(Ssh ssh, char *buf)
{
    c_write(ssh, buf, strlen(buf));
}

/*
 * Collect incoming data in the incoming packet buffer.
 * Decipher and verify the packet when it is completely read.
 * Drop SSH1_MSG_DEBUG and SSH1_MSG_IGNORE packets.
 * Update the *data and *datalen variables.
 * Return the additional nr of bytes needed, or 0 when
 * a complete packet is available.
 */
static int ssh1_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
{
    struct rdpkt1_state_tag *st = &ssh->rdpkt1_state;

    crBegin(ssh->ssh1_rdpkt_crstate);

  next_packet:

    ssh->pktin.type = 0;
    ssh->pktin.length = 0;

    for (st->i = st->len = 0; st->i < 4; st->i++) {
        while ((*datalen) == 0)
            crReturn(4 - st->i);
        st->len = (st->len << 8) + **data;
        (*data)++, (*datalen)--;
    }

    st->pad = 8 - (st->len % 8);
    st->biglen = st->len + st->pad;
    ssh->pktin.length = st->len - 5;

    if (ssh->pktin.maxlen < st->biglen) {
        ssh->pktin.maxlen = st->biglen;
        ssh->pktin.data = srealloc(ssh->pktin.data, st->biglen + APIEXTRA);
    }

    st->to_read = st->biglen;
    st->p = ssh->pktin.data;
    while (st->to_read > 0) {
        st->chunk = st->to_read;
        while ((*datalen) == 0)
            crReturn(st->to_read);
        if (st->chunk > (*datalen))
            st->chunk = (*datalen);
        memcpy(st->p, *data, st->chunk);
        *data += st->chunk;
        *datalen -= st->chunk;
        st->p += st->chunk;
        st->to_read -= st->chunk;
    }

    if (ssh->cipher && detect_attack(ssh->crcda_ctx, ssh->pktin.data,
                                     st->biglen, NULL)) {
        bombout(("Network attack (CRC compensation) detected!"));
        crReturn(0);
    }

    if (ssh->cipher)
        ssh->cipher->decrypt(ssh->v1_cipher_ctx, ssh->pktin.data, st->biglen);

    st->realcrc = crc32(ssh->pktin.data, st->biglen - 4);
    st->gotcrc = GET_32BIT(ssh->pktin.data + st->biglen - 4);
    if (st->gotcrc != st->realcrc) {
        bombout(("Incorrect CRC received on packet"));
        crReturn(0);
    }

    ssh->pktin.body = ssh->pktin.data + st->pad + 1;

    if (ssh->v1_compressing) {
        unsigned char *decompblk;
        int decomplen;
        zlib_decompress_block(ssh->pktin.body - 1, ssh->pktin.length + 1,
                              &decompblk, &decomplen);

        if (ssh->pktin.maxlen < st->pad + decomplen) {
            ssh->pktin.maxlen = st->pad + decomplen;
            ssh->pktin.data = srealloc(ssh->pktin.data,
                                       ssh->pktin.maxlen + APIEXTRA);
            ssh->pktin.body = ssh->pktin.data + st->pad + 1;
        }

        memcpy(ssh->pktin.body - 1, decompblk, decomplen);
        sfree(decompblk);
        ssh->pktin.length = decomplen - 1;
    }

    ssh->pktin.type = ssh->pktin.body[-1];

    log_packet(PKT_INCOMING, ssh->pktin.type, ssh1_pkt_type(ssh->pktin.type),
               ssh->pktin.body, ssh->pktin.length);

    if (ssh->pktin.type == SSH1_SMSG_STDOUT_DATA ||
        ssh->pktin.type == SSH1_SMSG_STDERR_DATA ||
        ssh->pktin.type == SSH1_MSG_DEBUG ||
        ssh->pktin.type == SSH1_SMSG_AUTH_TIS_CHALLENGE ||
        ssh->pktin.type == SSH1_SMSG_AUTH_CCARD_CHALLENGE) {
        long stringlen = GET_32BIT(ssh->pktin.body);
        if (stringlen + 4 != ssh->pktin.length) {
            bombout(("Received data packet with bogus string length"));
            crReturn(0);
        }
    }

    if (ssh->pktin.type == SSH1_MSG_DEBUG) {
        /* log debug message */
        char buf[512];
        int stringlen = GET_32BIT(ssh->pktin.body);
        strcpy(buf, "Remote debug message: ");
        if (stringlen > 480)
            stringlen = 480;
        memcpy(buf + 8, ssh->pktin.body + 4, stringlen);
        buf[8 + stringlen] = '\0';
        logevent(buf);
        goto next_packet;
    } else if (ssh->pktin.type == SSH1_MSG_IGNORE) {
        /* do nothing */
        goto next_packet;
    }

    if (ssh->pktin.type == SSH1_MSG_DISCONNECT) {
        /* log reason code in disconnect message */
        char buf[256];
        unsigned msglen = GET_32BIT(ssh->pktin.body);
        unsigned nowlen;
        strcpy(buf, "Remote sent disconnect: ");
        nowlen = strlen(buf);
        if (msglen > sizeof(buf) - nowlen - 1)
            msglen = sizeof(buf) - nowlen - 1;
        memcpy(buf + nowlen, ssh->pktin.body + 4, msglen);
        buf[nowlen + msglen] = '\0';
        /* logevent(buf); (this is now done within the bombout macro) */
        bombout(("Server sent disconnect message:\n\"%s\"", buf+nowlen));
        crReturn(0);
    }

    crFinish(0);
}

static int ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
{
    struct rdpkt2_state_tag *st = &ssh->rdpkt2_state;

    crBegin(ssh->ssh2_rdpkt_crstate);

  next_packet:
    ssh->pktin.type = 0;
    ssh->pktin.length = 0;
    if (ssh->sccipher)
        st->cipherblk = ssh->sccipher->blksize;
    else
        st->cipherblk = 8;
    if (st->cipherblk < 8)
        st->cipherblk = 8;

    if (ssh->pktin.maxlen < st->cipherblk) {
        ssh->pktin.maxlen = st->cipherblk;
        ssh->pktin.data = srealloc(ssh->pktin.data, st->cipherblk + APIEXTRA);
    }

    /*
     * Acquire and decrypt the first block of the packet. This will
     * contain the length and padding details.
     */
    for (st->i = st->len = 0; st->i < st->cipherblk; st->i++) {
        while ((*datalen) == 0)
            crReturn(st->cipherblk - st->i);
        ssh->pktin.data[st->i] = *(*data)++;
        (*datalen)--;
    }

    if (ssh->sccipher)
        ssh->sccipher->decrypt(ssh->sc_cipher_ctx,
                               ssh->pktin.data, st->cipherblk);

    /*
     * Now get the length and padding figures.
     */
    st->len = GET_32BIT(ssh->pktin.data);
    st->pad = ssh->pktin.data[4];

    /*
     * _Completely_ silly lengths should be stomped on before they
     * do us any more damage.
     */
    if (st->len < 0 || st->pad < 0 || st->len + st->pad < 0) {
        bombout(("Incoming packet was garbled on decryption"));
        crReturn(0);
    }

    /*
     * This enables us to deduce the payload length.
     */
    st->payload = st->len - st->pad - 1;

    ssh->pktin.length = st->payload + 5;

    /*
     * So now we can work out the total packet length.
     */
    st->packetlen = st->len + 4;
    st->maclen = ssh->scmac ? ssh->scmac->len : 0;

    /*
     * Adjust memory allocation if packet is too big.
     */
    if (ssh->pktin.maxlen < st->packetlen + st->maclen) {
        ssh->pktin.maxlen = st->packetlen + st->maclen;
        ssh->pktin.data = srealloc(ssh->pktin.data,
                                   ssh->pktin.maxlen + APIEXTRA);
    }

    /*
     * Read and decrypt the remainder of the packet.
     */
    for (st->i = st->cipherblk; st->i < st->packetlen + st->maclen;
         st->i++) {
        while ((*datalen) == 0)
            crReturn(st->packetlen + st->maclen - st->i);
        ssh->pktin.data[st->i] = *(*data)++;
        (*datalen)--;
    }
    /* Decrypt everything _except_ the MAC. */
    if (ssh->sccipher)
        ssh->sccipher->decrypt(ssh->sc_cipher_ctx,
                               ssh->pktin.data + st->cipherblk,
                               st->packetlen - st->cipherblk);

    /*
     * Check the MAC.
     */
    if (ssh->scmac
        && !ssh->scmac->verify(ssh->sc_mac_ctx, ssh->pktin.data, st->len + 4,
                               st->incoming_sequence)) {
        bombout(("Incorrect MAC received on packet"));
        crReturn(0);
    }
    st->incoming_sequence++;           /* whether or not we MACed */

    /*
     * Decompress packet payload.
     */
    {
        unsigned char *newpayload;
        int newlen;
        if (ssh->sccomp &&
            ssh->sccomp->decompress(ssh->pktin.data + 5, ssh->pktin.length - 5,
                                    &newpayload, &newlen)) {
            if (ssh->pktin.maxlen < newlen + 5) {
                ssh->pktin.maxlen = newlen + 5;
                ssh->pktin.data = srealloc(ssh->pktin.data,
                                           ssh->pktin.maxlen + APIEXTRA);
            }
            ssh->pktin.length = 5 + newlen;
            memcpy(ssh->pktin.data + 5, newpayload, newlen);
            sfree(newpayload);
        }
    }

    ssh->pktin.savedpos = 6;
    ssh->pktin.type = ssh->pktin.data[5];

    log_packet(PKT_INCOMING, ssh->pktin.type,
               ssh2_pkt_type(ssh->pkt_ctx, ssh->pktin.type),
               ssh->pktin.data+6, ssh->pktin.length-6);

    switch (ssh->pktin.type) {
        /*
         * These packets we must handle instantly.
         */
      case SSH2_MSG_DISCONNECT:
        {
            /* log reason code in disconnect message */
            char buf[256];
            int reason = GET_32BIT(ssh->pktin.data + 6);
            unsigned msglen = GET_32BIT(ssh->pktin.data + 10);
            unsigned nowlen;
            if (reason > 0 && reason < lenof(ssh2_disconnect_reasons)) {
                sprintf(buf, "Received disconnect message (%s)",
                        ssh2_disconnect_reasons[reason]);
            } else {
                sprintf(buf, "Received disconnect message (unknown type %d)",
                        reason);
            }
            logevent(buf);
            strcpy(buf, "Disconnection message text: ");
            nowlen = strlen(buf);
            if (msglen > sizeof(buf) - nowlen - 1)
                msglen = sizeof(buf) - nowlen - 1;
            memcpy(buf + nowlen, ssh->pktin.data + 14, msglen);
            buf[nowlen + msglen] = '\0';
            logevent(buf);
            bombout(("Server sent disconnect message\ntype %d (%s):\n\"%s\"",
                     reason,
                     (reason > 0 && reason < lenof(ssh2_disconnect_reasons)) ?
                     ssh2_disconnect_reasons[reason] : "unknown",
                     buf+nowlen));
            crReturn(0);
        }
        break;
      case SSH2_MSG_IGNORE:
        goto next_packet;
      case SSH2_MSG_DEBUG:
        {
            /* log the debug message */
            char buf[512];
            /* int display = ssh->pktin.body[6]; */
            int stringlen = GET_32BIT(ssh->pktin.data+7);
            int prefix;
            strcpy(buf, "Remote debug message: ");
            prefix = strlen(buf);
            if (stringlen > (int)(sizeof(buf)-prefix-1))
                stringlen = sizeof(buf)-prefix-1;
            memcpy(buf + prefix, ssh->pktin.data + 11, stringlen);
            buf[prefix + stringlen] = '\0';
            logevent(buf);
        }
        goto next_packet;              /* FIXME: print the debug message */

        /*
         * These packets we need do nothing about here.
         */
      case SSH2_MSG_UNIMPLEMENTED:
      case SSH2_MSG_SERVICE_REQUEST:
      case SSH2_MSG_SERVICE_ACCEPT:
      case SSH2_MSG_KEXINIT:
      case SSH2_MSG_NEWKEYS:
      case SSH2_MSG_KEXDH_INIT:
      case SSH2_MSG_KEXDH_REPLY:
      /* case SSH2_MSG_KEX_DH_GEX_REQUEST: duplicate case value */
      /* case SSH2_MSG_KEX_DH_GEX_GROUP: duplicate case value */
      case SSH2_MSG_KEX_DH_GEX_INIT:
      case SSH2_MSG_KEX_DH_GEX_REPLY:
      case SSH2_MSG_USERAUTH_REQUEST:
      case SSH2_MSG_USERAUTH_FAILURE:
      case SSH2_MSG_USERAUTH_SUCCESS:
      case SSH2_MSG_USERAUTH_BANNER:
      case SSH2_MSG_USERAUTH_PK_OK:
      /* case SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ: duplicate case value */
      /* case SSH2_MSG_USERAUTH_INFO_REQUEST: duplicate case value */
      case SSH2_MSG_USERAUTH_INFO_RESPONSE:
      case SSH2_MSG_GLOBAL_REQUEST:
      case SSH2_MSG_REQUEST_SUCCESS:
      case SSH2_MSG_REQUEST_FAILURE:
      case SSH2_MSG_CHANNEL_OPEN:
      case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
      case SSH2_MSG_CHANNEL_OPEN_FAILURE:
      case SSH2_MSG_CHANNEL_WINDOW_ADJUST:
      case SSH2_MSG_CHANNEL_DATA:
      case SSH2_MSG_CHANNEL_EXTENDED_DATA:
      case SSH2_MSG_CHANNEL_EOF:
      case SSH2_MSG_CHANNEL_CLOSE:
      case SSH2_MSG_CHANNEL_REQUEST:
      case SSH2_MSG_CHANNEL_SUCCESS:
      case SSH2_MSG_CHANNEL_FAILURE:
        break;

        /*
         * For anything else we send SSH2_MSG_UNIMPLEMENTED.
         */
      default:
        ssh2_pkt_init(ssh, SSH2_MSG_UNIMPLEMENTED);
        ssh2_pkt_adduint32(ssh, st->incoming_sequence - 1);
        ssh2_pkt_send(ssh);
        break;
    }

    crFinish(0);
}

static void ssh1_pktout_size(Ssh ssh, int len)
{
    int pad, biglen;

    len += 5;                          /* type and CRC */
    pad = 8 - (len % 8);
    biglen = len + pad;

    ssh->pktout.length = len - 5;
    if (ssh->pktout.maxlen < biglen) {
        ssh->pktout.maxlen = biglen;
#ifdef MSCRYPTOAPI
        /* Allocate enough buffer space for extra block
         * for MS CryptEncrypt() */
        ssh->pktout.data = srealloc(ssh->pktout.data, biglen + 12);
#else
        ssh->pktout.data = srealloc(ssh->pktout.data, biglen + 4);
#endif
    }
    ssh->pktout.body = ssh->pktout.data + 4 + pad + 1;
}

static void s_wrpkt_start(Ssh ssh, int type, int len)
{
    ssh1_pktout_size(ssh, len);
    ssh->pktout.type = type;
}

static int s_wrpkt_prepare(Ssh ssh)
{
    int pad, len, biglen, i;
    unsigned long crc;

    ssh->pktout.body[-1] = ssh->pktout.type;

    log_packet(PKT_OUTGOING, ssh->pktout.type, ssh1_pkt_type(ssh->pktout.type),
               ssh->pktout.body, ssh->pktout.length);

    if (ssh->v1_compressing) {
        unsigned char *compblk;
        int complen;
        zlib_compress_block(ssh->pktout.body - 1, ssh->pktout.length + 1,
                            &compblk, &complen);
        ssh1_pktout_size(ssh, complen - 1);
        memcpy(ssh->pktout.body - 1, compblk, complen);
        sfree(compblk);
    }

    len = ssh->pktout.length + 5;              /* type and CRC */
    pad = 8 - (len % 8);
    biglen = len + pad;

    for (i = 0; i < pad; i++)
        ssh->pktout.data[i + 4] = random_byte();
    crc = crc32(ssh->pktout.data + 4, biglen - 4);
    PUT_32BIT(ssh->pktout.data + biglen, crc);
    PUT_32BIT(ssh->pktout.data, len);

    if (ssh->cipher)
        ssh->cipher->encrypt(ssh->v1_cipher_ctx, ssh->pktout.data + 4, biglen);

    return biglen + 4;
}

static void s_wrpkt(Ssh ssh)
{
    int len, backlog;
    len = s_wrpkt_prepare(ssh);
    backlog = sk_write(ssh->s, ssh->pktout.data, len);
    if (backlog > SSH_MAX_BACKLOG)
        ssh_throttle_all(ssh, 1, backlog);
}

static void s_wrpkt_defer(Ssh ssh)
{
    int len;
    len = s_wrpkt_prepare(ssh);
    if (ssh->deferred_len + len > ssh->deferred_size) {
        ssh->deferred_size = ssh->deferred_len + len + 128;
        ssh->deferred_send_data = srealloc(ssh->deferred_send_data,
                                           ssh->deferred_size);
    }
    memcpy(ssh->deferred_send_data + ssh->deferred_len, ssh->pktout.data, len);
    ssh->deferred_len += len;
}

/*
 * Construct a packet with the specified contents.
 */
static void construct_packet(Ssh ssh, int pkttype, va_list ap1, va_list ap2)
{
    unsigned char *p, *argp, argchar;
    unsigned long argint;
    int pktlen, argtype, arglen;
    Bignum bn;

    pktlen = 0;
    while ((argtype = va_arg(ap1, int)) != PKT_END) {
        switch (argtype) {
          case PKT_INT:
            (void) va_arg(ap1, int);
            pktlen += 4;
            break;
          case PKT_CHAR:
            (void) va_arg(ap1, char);
            pktlen++;
            break;
          case PKT_DATA:
            (void) va_arg(ap1, unsigned char *);
            arglen = va_arg(ap1, int);
            pktlen += arglen;
            break;
          case PKT_STR:
            argp = va_arg(ap1, unsigned char *);
            arglen = strlen(argp);
            pktlen += 4 + arglen;
            break;
          case PKT_BIGNUM:
            bn = va_arg(ap1, Bignum);
            pktlen += ssh1_bignum_length(bn);
            break;
          default:
            assert(0);
        }
    }

    s_wrpkt_start(ssh, pkttype, pktlen);
    p = ssh->pktout.body;

    while ((argtype = va_arg(ap2, int)) != PKT_END) {
        switch (argtype) {
          case PKT_INT:
            argint = va_arg(ap2, int);
            PUT_32BIT(p, argint);
            p += 4;
            break;
          case PKT_CHAR:
            argchar = va_arg(ap2, unsigned char);
            *p = argchar;
            p++;
            break;
          case PKT_DATA:
            argp = va_arg(ap2, unsigned char *);
            arglen = va_arg(ap2, int);
            memcpy(p, argp, arglen);
            p += arglen;
            break;
          case PKT_STR:
            argp = va_arg(ap2, unsigned char *);
            arglen = strlen(argp);
            PUT_32BIT(p, arglen);
            memcpy(p + 4, argp, arglen);
            p += 4 + arglen;
            break;
          case PKT_BIGNUM:
            bn = va_arg(ap2, Bignum);
            p += ssh1_write_bignum(p, bn);
            break;
        }
    }
}

static void send_packet(Ssh ssh, int pkttype, ...)
{
    va_list ap1, ap2;
    va_start(ap1, pkttype);
    va_start(ap2, pkttype);
    construct_packet(ssh, pkttype, ap1, ap2);
    s_wrpkt(ssh);
}

static void defer_packet(Ssh ssh, int pkttype, ...)
{
    va_list ap1, ap2;
    va_start(ap1, pkttype);
    va_start(ap2, pkttype);
    construct_packet(ssh, pkttype, ap1, ap2);
    s_wrpkt_defer(ssh);
}

static int ssh_versioncmp(char *a, char *b)
{
    char *ae, *be;
    unsigned long av, bv;

    av = strtoul(a, &ae, 10);
    bv = strtoul(b, &be, 10);
    if (av != bv)
        return (av < bv ? -1 : +1);
    if (*ae == '.')
        ae++;
    if (*be == '.')
        be++;
    av = strtoul(ae, &ae, 10);
    bv = strtoul(be, &be, 10);
    if (av != bv)
        return (av < bv ? -1 : +1);
    return 0;
}

/*
 * Utility routines for putting an SSH-protocol `string' and
 * `uint32' into a SHA state.
 */
#include <stdio.h>
static void sha_string(SHA_State * s, void *str, int len)
{
    unsigned char lenblk[4];
    PUT_32BIT(lenblk, len);
    SHA_Bytes(s, lenblk, 4);
    SHA_Bytes(s, str, len);
}

static void sha_uint32(SHA_State * s, unsigned i)
{
    unsigned char intblk[4];
    PUT_32BIT(intblk, i);
    SHA_Bytes(s, intblk, 4);
}

/*
 * SSH2 packet construction functions.
 */
static void ssh2_pkt_ensure(Ssh ssh, int length)
{
    if (ssh->pktout.maxlen < length) {
        ssh->pktout.maxlen = length + 256;
        ssh->pktout.data = srealloc(ssh->pktout.data,
                                    ssh->pktout.maxlen + APIEXTRA);
        if (!ssh->pktout.data)
            fatalbox("Out of memory");
    }
}
static void ssh2_pkt_adddata(Ssh ssh, void *data, int len)
{
    ssh->pktout.length += len;
    ssh2_pkt_ensure(ssh, ssh->pktout.length);
    memcpy(ssh->pktout.data + ssh->pktout.length - len, data, len);
}
static void ssh2_pkt_addbyte(Ssh ssh, unsigned char byte)
{
    ssh2_pkt_adddata(ssh, &byte, 1);
}
static void ssh2_pkt_init(Ssh ssh, int pkt_type)
{
    ssh->pktout.length = 5;
    ssh2_pkt_addbyte(ssh, (unsigned char) pkt_type);
}
static void ssh2_pkt_addbool(Ssh ssh, unsigned char value)
{
    ssh2_pkt_adddata(ssh, &value, 1);
}
static void ssh2_pkt_adduint32(Ssh ssh, unsigned long value)
{
    unsigned char x[4];
    PUT_32BIT(x, value);
    ssh2_pkt_adddata(ssh, x, 4);
}
static void ssh2_pkt_addstring_start(Ssh ssh)
{
    ssh2_pkt_adduint32(ssh, 0);
    ssh->pktout.savedpos = ssh->pktout.length;
}
static void ssh2_pkt_addstring_str(Ssh ssh, char *data)
{
    ssh2_pkt_adddata(ssh, data, strlen(data));
    PUT_32BIT(ssh->pktout.data + ssh->pktout.savedpos - 4,
              ssh->pktout.length - ssh->pktout.savedpos);
}
static void ssh2_pkt_addstring_data(Ssh ssh, char *data, int len)
{
    ssh2_pkt_adddata(ssh, data, len);
    PUT_32BIT(ssh->pktout.data + ssh->pktout.savedpos - 4,
              ssh->pktout.length - ssh->pktout.savedpos);
}
static void ssh2_pkt_addstring(Ssh ssh, char *data)
{
    ssh2_pkt_addstring_start(ssh);
    ssh2_pkt_addstring_str(ssh, data);
}
static char *ssh2_mpint_fmt(Bignum b, int *len)
{
    unsigned char *p;
    int i, n = (bignum_bitcount(b) + 7) / 8;
    p = smalloc(n + 1);
    if (!p)
        fatalbox("out of memory");
    p[0] = 0;
    for (i = 1; i <= n; i++)
        p[i] = bignum_byte(b, n - i);
    i = 0;
    while (i <= n && p[i] == 0 && (p[i + 1] & 0x80) == 0)
        i++;
    memmove(p, p + i, n + 1 - i);
    *len = n + 1 - i;
    return p;
}
static void ssh2_pkt_addmp(Ssh ssh, Bignum b)
{
    unsigned char *p;
    int len;
    p = ssh2_mpint_fmt(b, &len);
    ssh2_pkt_addstring_start(ssh);
    ssh2_pkt_addstring_data(ssh, p, len);
    sfree(p);
}

/*
 * Construct an SSH2 final-form packet: compress it, encrypt it,
 * put the MAC on it. Final packet, ready to be sent, is stored in
 * ssh->pktout.data. Total length is returned.
 */
static int ssh2_pkt_construct(Ssh ssh)
{
    int cipherblk, maclen, padding, i;

    log_packet(PKT_OUTGOING, ssh->pktout.data[5],
               ssh2_pkt_type(ssh->pkt_ctx, ssh->pktout.data[5]),
               ssh->pktout.data + 6, ssh->pktout.length - 6);

    /*
     * Compress packet payload.
     */
    {
        unsigned char *newpayload;
        int newlen;
        if (ssh->cscomp &&
            ssh->cscomp->compress(ssh->pktout.data + 5, ssh->pktout.length - 5,
                                  &newpayload, &newlen)) {
            ssh->pktout.length = 5;
            ssh2_pkt_adddata(ssh, newpayload, newlen);
            sfree(newpayload);
        }
    }

    /*
     * Add padding. At least four bytes, and must also bring total
     * length (minus MAC) up to a multiple of the block size.
     */
    cipherblk = ssh->cscipher ? ssh->cscipher->blksize : 8;  /* block size */
    cipherblk = cipherblk < 8 ? 8 : cipherblk;  /* or 8 if blksize < 8 */
    padding = 4;
    padding +=
        (cipherblk - (ssh->pktout.length + padding) % cipherblk) % cipherblk;
    maclen = ssh->csmac ? ssh->csmac->len : 0;
    ssh2_pkt_ensure(ssh, ssh->pktout.length + padding + maclen);
    ssh->pktout.data[4] = padding;
    for (i = 0; i < padding; i++)
        ssh->pktout.data[ssh->pktout.length + i] = random_byte();
    PUT_32BIT(ssh->pktout.data, ssh->pktout.length + padding - 4);
    if (ssh->csmac)
        ssh->csmac->generate(ssh->cs_mac_ctx, ssh->pktout.data,
                             ssh->pktout.length + padding,
                             ssh->v2_outgoing_sequence);
    ssh->v2_outgoing_sequence++;       /* whether or not we MACed */

    if (ssh->cscipher)
        ssh->cscipher->encrypt(ssh->cs_cipher_ctx,
                               ssh->pktout.data, ssh->pktout.length + padding);

    /* Ready-to-send packet starts at ssh->pktout.data. We return length. */
    return ssh->pktout.length + padding + maclen;
}

/*
 * Construct and send an SSH2 packet immediately.
 */
static void ssh2_pkt_send(Ssh ssh)
{
    int len;
    int backlog;
    len = ssh2_pkt_construct(ssh);
    backlog = sk_write(ssh->s, ssh->pktout.data, len);
    if (backlog > SSH_MAX_BACKLOG)
        ssh_throttle_all(ssh, 1, backlog);
}

/*
 * Construct an SSH2 packet and add it to a deferred data block.
 * Useful for sending multiple packets in a single sk_write() call,
 * to prevent a traffic-analysing listener from being able to work
 * out the length of any particular packet (such as the password
 * packet).
 * 
 * Note that because SSH2 sequence-numbers its packets, this can
 * NOT be used as an m4-style `defer' allowing packets to be
 * constructed in one order and sent in another.
 */
static void ssh2_pkt_defer(Ssh ssh)
{
    int len = ssh2_pkt_construct(ssh);
    if (ssh->deferred_len + len > ssh->deferred_size) {
        ssh->deferred_size = ssh->deferred_len + len + 128;
        ssh->deferred_send_data = srealloc(ssh->deferred_send_data,
                                           ssh->deferred_size);
    }
    memcpy(ssh->deferred_send_data + ssh->deferred_len, ssh->pktout.data, len);
    ssh->deferred_len += len;
}

/*
 * Send the whole deferred data block constructed by
 * ssh2_pkt_defer() or SSH1's defer_packet().
 */
static void ssh_pkt_defersend(Ssh ssh)
{
    int backlog;
    backlog = sk_write(ssh->s, ssh->deferred_send_data, ssh->deferred_len);
    ssh->deferred_len = ssh->deferred_size = 0;
    sfree(ssh->deferred_send_data);
    ssh->deferred_send_data = NULL;
    if (backlog > SSH_MAX_BACKLOG)
        ssh_throttle_all(ssh, 1, backlog);
}

#if 0
void bndebug(char *string, Bignum b)
{
    unsigned char *p;
    int i, len;
    p = ssh2_mpint_fmt(b, &len);
    debug(("%s", string));
    for (i = 0; i < len; i++)
        debug((" %02x", p[i]));
    debug(("\n"));
    sfree(p);
}
#endif

static void sha_mpint(SHA_State * s, Bignum b)
{
    unsigned char *p;
    int len;
    p = ssh2_mpint_fmt(b, &len);
    sha_string(s, p, len);
    sfree(p);
}

/*
 * SSH2 packet decode functions.
 */
static unsigned long ssh2_pkt_getuint32(Ssh ssh)
{
    unsigned long value;
    if (ssh->pktin.length - ssh->pktin.savedpos < 4)
        return 0;                      /* arrgh, no way to decline (FIXME?) */
    value = GET_32BIT(ssh->pktin.data + ssh->pktin.savedpos);
    ssh->pktin.savedpos += 4;
    return value;
}
static int ssh2_pkt_getbool(Ssh ssh)
{
    unsigned long value;
    if (ssh->pktin.length - ssh->pktin.savedpos < 1)
        return 0;                      /* arrgh, no way to decline (FIXME?) */
    value = ssh->pktin.data[ssh->pktin.savedpos] != 0;
    ssh->pktin.savedpos++;
    return value;
}
static void ssh2_pkt_getstring(Ssh ssh, char **p, int *length)
{
    *p = NULL;
    *length = 0;
    if (ssh->pktin.length - ssh->pktin.savedpos < 4)
        return;
    *length = GET_32BIT(ssh->pktin.data + ssh->pktin.savedpos);
    ssh->pktin.savedpos += 4;
    if (ssh->pktin.length - ssh->pktin.savedpos < *length)
        return;
    *p = ssh->pktin.data + ssh->pktin.savedpos;
    ssh->pktin.savedpos += *length;
}
static Bignum ssh2_pkt_getmp(Ssh ssh)
{
    char *p;
    int length;
    Bignum b;

    ssh2_pkt_getstring(ssh, &p, &length);
    if (!p)
        return NULL;
    if (p[0] & 0x80) {
        bombout(("internal error: Can't handle negative mpints"));
        return NULL;
    }
    b = bignum_from_bytes(p, length);
    return b;
}

/*
 * Helper function to add an SSH2 signature blob to a packet.
 * Expects to be shown the public key blob as well as the signature
 * blob. Normally works just like ssh2_pkt_addstring, but will
 * fiddle with the signature packet if necessary for
 * BUG_SSH2_RSA_PADDING.
 */
static void ssh2_add_sigblob(Ssh ssh, void *pkblob_v, int pkblob_len,
                             void *sigblob_v, int sigblob_len)
{
    unsigned char *pkblob = (unsigned char *)pkblob_v;
    unsigned char *sigblob = (unsigned char *)sigblob_v;

    /* dmemdump(pkblob, pkblob_len); */
    /* dmemdump(sigblob, sigblob_len); */

    /*
     * See if this is in fact an ssh-rsa signature and a buggy
     * server; otherwise we can just do this the easy way.
     */
    if ((ssh->remote_bugs & BUG_SSH2_RSA_PADDING) &&
        (GET_32BIT(pkblob) == 7 && !memcmp(pkblob+4, "ssh-rsa", 7))) {
        int pos, len, siglen;

        /*
         * Find the byte length of the modulus.
         */

        pos = 4+7;                     /* skip over "ssh-rsa" */
        pos += 4 + GET_32BIT(pkblob+pos);   /* skip over exponent */
        len = GET_32BIT(pkblob+pos);   /* find length of modulus */
        pos += 4;                      /* find modulus itself */
        while (len > 0 && pkblob[pos] == 0)
            len--, pos++;
        /* debug(("modulus length is %d\n", len)); */

        /*
         * Now find the signature integer.
         */
        pos = 4+7;                     /* skip over "ssh-rsa" */
        siglen = GET_32BIT(sigblob+pos);
        /* debug(("signature length is %d\n", siglen)); */

        if (len != siglen) {
            unsigned char newlen[4];
            ssh2_pkt_addstring_start(ssh);
            ssh2_pkt_addstring_data(ssh, sigblob, pos);
            /* dmemdump(sigblob, pos); */
            pos += 4;                  /* point to start of actual sig */
            PUT_32BIT(newlen, len);
            ssh2_pkt_addstring_data(ssh, newlen, 4);
            /* dmemdump(newlen, 4); */
            newlen[0] = 0;
            while (len-- > siglen) {
                ssh2_pkt_addstring_data(ssh, newlen, 1);
                /* dmemdump(newlen, 1); */
            }
            ssh2_pkt_addstring_data(ssh, sigblob+pos, siglen);
            /* dmemdump(sigblob+pos, siglen); */
            return;
        }

        /* Otherwise fall through and do it the easy way. */
    }

    ssh2_pkt_addstring_start(ssh);
    ssh2_pkt_addstring_data(ssh, sigblob, sigblob_len);
}

/*
 * Examine the remote side's version string and compare it against
 * a list of known buggy implementations.
 */
static void ssh_detect_bugs(Ssh ssh, char *vstring)
{
    char *imp;                         /* pointer to implementation part */
    imp = vstring;
    imp += strcspn(imp, "-");
    if (*imp) imp++;
    imp += strcspn(imp, "-");
    if (*imp) imp++;

    ssh->remote_bugs = 0;

    if (cfg.sshbug_ignore1 == BUG_ON ||
        (cfg.sshbug_ignore1 == BUG_AUTO &&
         (!strcmp(imp, "1.2.18") || !strcmp(imp, "1.2.19") ||
          !strcmp(imp, "1.2.20") || !strcmp(imp, "1.2.21") ||
          !strcmp(imp, "1.2.22") || !strcmp(imp, "Cisco-1.25")))) {
        /*
         * These versions don't support SSH1_MSG_IGNORE, so we have
         * to use a different defence against password length
         * sniffing.
         */
        ssh->remote_bugs |= BUG_CHOKES_ON_SSH1_IGNORE;
        logevent("We believe remote version has SSH1 ignore bug");
    }

    if (cfg.sshbug_plainpw1 == BUG_ON ||
        (cfg.sshbug_plainpw1 == BUG_AUTO &&
         (!strcmp(imp, "Cisco-1.25")))) {
        /*
         * These versions need a plain password sent; they can't
         * handle having a null and a random length of data after
         * the password.
         */
        ssh->remote_bugs |= BUG_NEEDS_SSH1_PLAIN_PASSWORD;
        logevent("We believe remote version needs a plain SSH1 password");
    }

    if (cfg.sshbug_rsa1 == BUG_ON ||
        (cfg.sshbug_rsa1 == BUG_AUTO &&
         (!strcmp(imp, "Cisco-1.25")))) {
        /*
         * These versions apparently have no clue whatever about
         * RSA authentication and will panic and die if they see
         * an AUTH_RSA message.
         */
        ssh->remote_bugs |= BUG_CHOKES_ON_RSA;
        logevent("We believe remote version can't handle RSA authentication");
    }

    if (cfg.sshbug_hmac2 == BUG_ON ||
        (cfg.sshbug_hmac2 == BUG_AUTO &&
         (!strncmp(imp, "2.1.0", 5) || !strncmp(imp, "2.0.", 4) ||
          !strncmp(imp, "2.2.0", 5) || !strncmp(imp, "2.3.0", 5) ||
          !strncmp(imp, "2.1 ", 4)))) {
        /*
         * These versions have the HMAC bug.
         */
        ssh->remote_bugs |= BUG_SSH2_HMAC;
        logevent("We believe remote version has SSH2 HMAC bug");
    }

    if (cfg.sshbug_derivekey2 == BUG_ON ||
        (cfg.sshbug_derivekey2 == BUG_AUTO &&
         (!strncmp(imp, "2.0.", 4)))) {
        /*
         * These versions have the key-derivation bug (failing to
         * include the literal shared secret in the hashes that
         * generate the keys).
         */
        ssh->remote_bugs |= BUG_SSH2_DERIVEKEY;
        logevent("We believe remote version has SSH2 key-derivation bug");
    }

    if (cfg.sshbug_rsapad2 == BUG_ON ||
        (cfg.sshbug_rsapad2 == BUG_AUTO &&
         ((!strncmp(imp, "OpenSSH_2.", 10) && imp[10]>='5' && imp[10]<='9') ||
          (!strncmp(imp, "OpenSSH_3.", 10) && imp[10]>='0' && imp[10]<='2')))){
        /*
         * These versions have the SSH2 RSA padding bug.
         */
        ssh->remote_bugs |= BUG_SSH2_RSA_PADDING;
        logevent("We believe remote version has SSH2 RSA padding bug");
    }

    if (cfg.sshbug_dhgex2 == BUG_ON) {
        /*
         * These versions have the SSH2 DH GEX bug.
         */
        ssh->remote_bugs |= BUG_SSH2_DH_GEX;
        logevent("We believe remote version has SSH2 DH group exchange bug");
    }
}

static int do_ssh_init(Ssh ssh, unsigned char c)
{
    struct do_ssh_init_state {
        int vslen;
        char version[10];
        char *vstring;
        int vstrsize;
        int i;
        int proto1, proto2;
    };
    crState(do_ssh_init_state);

    crBegin(ssh->do_ssh_init_crstate);

    /* Search for the string "SSH-" in the input. */
    s->i = 0;
    while (1) {
        static const int transS[] = { 1, 2, 2, 1 };
        static const int transH[] = { 0, 0, 3, 0 };
        static const int transminus[] = { 0, 0, 0, -1 };
        if (c == 'S')
            s->i = transS[s->i];
        else if (c == 'H')
            s->i = transH[s->i];
        else if (c == '-')
            s->i = transminus[s->i];
        else
            s->i = 0;
        if (s->i < 0)
            break;
        crReturn(1);                   /* get another character */
    }

    s->vstrsize = 16;
    s->vstring = smalloc(s->vstrsize);
    strcpy(s->vstring, "SSH-");
    s->vslen = 4;
    s->i = 0;
    while (1) {
        crReturn(1);                   /* get another char */
        if (s->vslen >= s->vstrsize - 1) {
            s->vstrsize += 16;
            s->vstring = srealloc(s->vstring, s->vstrsize);
        }
        s->vstring[s->vslen++] = c;
        if (s->i >= 0) {
            if (c == '-') {
                s->version[s->i] = '\0';
                s->i = -1;
            } else if (s->i < sizeof(s->version) - 1)
                s->version[s->i++] = c;
        } else if (c == '\n')
            break;
    }

    ssh->agentfwd_enabled = FALSE;
    ssh->rdpkt2_state.incoming_sequence = 0;

    s->vstring[s->vslen] = 0;
    s->vstring[strcspn(s->vstring, "\r\n")] = '\0';/* remove EOL chars */
    {
        char *vlog;
        vlog = smalloc(20 + s->vslen);
        sprintf(vlog, "Server version: %s", s->vstring);
        logevent(vlog);
        sfree(vlog);
    }
    ssh_detect_bugs(ssh, s->vstring);

    /*
     * Decide which SSH protocol version to support.
     */

    /* Anything strictly below "2.0" means protocol 1 is supported. */
    s->proto1 = ssh_versioncmp(s->version, "2.0") < 0;
    /* Anything greater or equal to "1.99" means protocol 2 is supported. */
    s->proto2 = ssh_versioncmp(s->version, "1.99") >= 0;

    if (cfg.sshprot == 0 && !s->proto1) {
        bombout(("SSH protocol version 1 required by user but not provided by server"));
        crReturn(0);
    }
    if (cfg.sshprot == 3 && !s->proto2) {
        bombout(("SSH protocol version 2 required by user but not provided by server"));
        crReturn(0);
    }

    if (s->proto2 && (cfg.sshprot >= 2 || !s->proto1)) {
        /*
         * Use v2 protocol.
         */
        char verstring[80], vlog[100];
        sprintf(verstring, "SSH-2.0-%s", sshver);
        SHA_Init(&ssh->exhashbase);
        /*
         * Hash our version string and their version string.
         */
        sha_string(&ssh->exhashbase, verstring, strlen(verstring));
        sha_string(&ssh->exhashbase, s->vstring, strcspn(s->vstring, "\r\n"));
        sprintf(vlog, "We claim version: %s", verstring);
        logevent(vlog);
        strcat(verstring, "\n");
        logevent("Using SSH protocol version 2");
        sk_write(ssh->s, verstring, strlen(verstring));
        ssh->protocol = ssh2_protocol;
        ssh->version = 2;
        ssh->s_rdpkt = ssh2_rdpkt;
    } else {
        /*
         * Use v1 protocol.
         */
        char verstring[80], vlog[100];
        sprintf(verstring, "SSH-%s-%s",
                (ssh_versioncmp(s->version, "1.5") <= 0 ? s->version : "1.5"),
                sshver);
        sprintf(vlog, "We claim version: %s", verstring);
        logevent(vlog);
        strcat(verstring, "\n");

        logevent("Using SSH protocol version 1");
        sk_write(ssh->s, verstring, strlen(verstring));
        ssh->protocol = ssh1_protocol;
        ssh->version = 1;
        ssh->s_rdpkt = ssh1_rdpkt;
    }
    ssh->state = SSH_STATE_BEFORE_SIZE;

    sfree(s->vstring);

    crFinish(0);
}

static void ssh_gotdata(Ssh ssh, unsigned char *data, int datalen)
{
    crBegin(ssh->ssh_gotdata_crstate);

    /*
     * To begin with, feed the characters one by one to the
     * protocol initialisation / selection function do_ssh_init().
     * When that returns 0, we're done with the initial greeting
     * exchange and can move on to packet discipline.
     */
    while (1) {
        int ret;                       /* need not be kept across crReturn */
        if (datalen == 0)
            crReturnV;                 /* more data please */
        ret = do_ssh_init(ssh, *data);
        data++;
        datalen--;
        if (ret == 0)
            break;
    }

    /*
     * We emerge from that loop when the initial negotiation is
     * over and we have selected an s_rdpkt function. Now pass
     * everything to s_rdpkt, and then pass the resulting packets
     * to the proper protocol handler.
     */
    if (datalen == 0)
        crReturnV;
    while (1) {
        while (datalen > 0) {
            if (ssh->s_rdpkt(ssh, &data, &datalen) == 0) {
                if (ssh->state == SSH_STATE_CLOSED) {
                    return;
                }
                ssh->protocol(ssh, NULL, 0, 1);
                if (ssh->state == SSH_STATE_CLOSED) {
                    return;
                }
            }
        }
        crReturnV;
    }
    crFinishV;
}

static int ssh_closing(Plug plug, char *error_msg, int error_code,
                       int calling_back)
{
    Ssh ssh = (Ssh) plug;
    ssh->state = SSH_STATE_CLOSED;
    if (ssh->s) {
        sk_close(ssh->s);
        ssh->s = NULL;
    }
    if (error_msg) {
        /* A socket error has occurred. */
        logevent(error_msg);
        connection_fatal(error_msg);
    } else {
        /* Otherwise, the remote side closed the connection normally. */
    }
    return 0;
}

static int ssh_receive(Plug plug, int urgent, char *data, int len)
{
    Ssh ssh = (Ssh) plug;
    ssh_gotdata(ssh, data, len);
    if (ssh->state == SSH_STATE_CLOSED) {
        if (ssh->s) {
            sk_close(ssh->s);
            ssh->s = NULL;
        }
        return 0;
    }
    return 1;
}

static void ssh_sent(Plug plug, int bufsize)
{
    Ssh ssh = (Ssh) plug;
    /*
     * If the send backlog on the SSH socket itself clears, we
     * should unthrottle the whole world if it was throttled.
     */
    if (bufsize < SSH_MAX_BACKLOG)
        ssh_throttle_all(ssh, 0, bufsize);
}

/*
 * Connect to specified host and port.
 * Returns an error message, or NULL on success.
 * Also places the canonical host name into `realhost'. It must be
 * freed by the caller.
 */
static char *connect_to_host(Ssh ssh, char *host, int port,
                             char **realhost, int nodelay)
{
    static const struct plug_function_table fn_table = {
        ssh_closing,
        ssh_receive,
        ssh_sent,
        NULL
    };

    SockAddr addr;
    char *err;

    ssh->savedhost = smalloc(1 + strlen(host));
    if (!ssh->savedhost)
        fatalbox("Out of memory");
    strcpy(ssh->savedhost, host);

    if (port < 0)
        port = 22;                     /* default ssh port */
    ssh->savedport = port;

    /*
     * Try to find host.
     */
    {
        char buf[200];
        sprintf(buf, "Looking up host \"%.170s\"", host);
        logevent(buf);
    }
    addr = sk_namelookup(host, realhost);
    if ((err = sk_addr_error(addr)))
        return err;

    /*
     * Open socket.
     */
    {
        char buf[200], addrbuf[100];
        sk_getaddr(addr, addrbuf, 100);
        sprintf(buf, "Connecting to %.100s port %d", addrbuf, port);
        logevent(buf);
    }
    ssh->fn = &fn_table;
    ssh->s = new_connection(addr, *realhost, port, 0, 1, nodelay, (Plug) ssh);
    if ((err = sk_socket_error(ssh->s))) {
        ssh->s = NULL;
        return err;
    }

    return NULL;
}

/*
 * Throttle or unthrottle the SSH connection.
 */
static void ssh1_throttle(Ssh ssh, int adjust)
{
    int old_count = ssh->v1_throttle_count;
    ssh->v1_throttle_count += adjust;
    assert(ssh->v1_throttle_count >= 0);
    if (ssh->v1_throttle_count && !old_count) {
        sk_set_frozen(ssh->s, 1);
    } else if (!ssh->v1_throttle_count && old_count) {
        sk_set_frozen(ssh->s, 0);
    }
}

/*
 * Throttle or unthrottle _all_ local data streams (for when sends
 * on the SSH connection itself back up).
 */
static void ssh_throttle_all(Ssh ssh, int enable, int bufsize)
{
    int i;
    struct ssh_channel *c;

    if (enable == ssh->throttled_all)
        return;
    ssh->throttled_all = enable;
    ssh->overall_bufsize = bufsize;
    if (!ssh->channels)
        return;
    for (i = 0; NULL != (c = index234(ssh->channels, i)); i++) {
        switch (c->type) {
          case CHAN_MAINSESSION:
            /*
             * This is treated separately, outside the switch.
             */
            break;
          case CHAN_X11:
            x11_override_throttle(c->u.x11.s, enable);
            break;
          case CHAN_AGENT:
            /* Agent channels require no buffer management. */
            break;
          case CHAN_SOCKDATA:
            pfd_override_throttle(c->u.x11.s, enable);
            break;
        }
    }
}

/*
 * Username and password input, abstracted off into routines
 * reusable in several places - even between SSH1 and SSH2.
 */

/* Set up a username or password input loop on a given buffer. */
void setup_userpass_input(Ssh ssh, char *buffer, int buflen, int echo)
{
    ssh->userpass_input_buffer = buffer;
    ssh->userpass_input_buflen = buflen;
    ssh->userpass_input_bufpos = 0;
    ssh->userpass_input_echo = echo;
}

/*
 * Process some terminal data in the course of username/password
 * input. Returns >0 for success (line of input returned in
 * buffer), <0 for failure (user hit ^C/^D, bomb out and exit), 0
 * for inconclusive (keep waiting for more input please).
 */
int process_userpass_input(Ssh ssh, unsigned char *in, int inlen)
{
    char c;

    while (inlen--) {
        switch (c = *in++) {
          case 10:
          case 13:
            ssh->userpass_input_buffer[ssh->userpass_input_bufpos] = 0;
            ssh->userpass_input_buffer[ssh->userpass_input_buflen-1] = 0;
            return +1;
            break;
          case 8:
          case 127:
            if (ssh->userpass_input_bufpos > 0) {
                if (ssh->userpass_input_echo)
                    c_write_str(ssh, "\b \b");
                ssh->userpass_input_bufpos--;
            }
            break;
          case 21:
          case 27:
            while (ssh->userpass_input_bufpos > 0) {
                if (ssh->userpass_input_echo)
                    c_write_str(ssh, "\b \b");
                ssh->userpass_input_bufpos--;
            }
            break;
          case 3:
          case 4:
            return -1;
            break;
          default:
            if (((c >= ' ' && c <= '~') ||
                 ((unsigned char) c >= 160))
                && ssh->userpass_input_bufpos < ssh->userpass_input_buflen-1) {
                ssh->userpass_input_buffer[ssh->userpass_input_bufpos++] = c;
                if (ssh->userpass_input_echo)
                    c_write(ssh, &c, 1);
            }
            break;
        }
    }
    return 0;
}

/*
 * Handle the key exchange and user authentication phases.
 */
static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen, int ispkt)
{
    int i, j;
    unsigned char cookie[8];
    struct RSAKey servkey, hostkey;
    struct MD5Context md5c;
    struct do_ssh1_login_state {
        int len;
        unsigned char *rsabuf, *keystr1, *keystr2;
        unsigned long supported_ciphers_mask, supported_auths_mask;
        int tried_publickey, tried_agent;
        int tis_auth_refused, ccard_auth_refused;
        unsigned char session_id[16];
        int cipher_type;
        char username[100];
        void *publickey_blob;
        int publickey_bloblen;
        char password[100];
        char prompt[200];
        int pos;
        char c;
        int pwpkt_type;
        unsigned char request[5], *response, *p;
        int responselen;
        int keyi, nkeys;
        int authed;
        struct RSAKey key;
        Bignum challenge;
        char *commentp;
        int commentlen;
    };
    crState(do_ssh1_login_state);

    crBegin(ssh->do_ssh1_login_crstate);

    if (!ispkt)
        crWaitUntil(ispkt);

    if (ssh->pktin.type != SSH1_SMSG_PUBLIC_KEY) {
        bombout(("Public key packet not received"));
        crReturn(0);
    }

    logevent("Received public keys");

    memcpy(cookie, ssh->pktin.body, 8);

    i = makekey(ssh->pktin.body + 8, &servkey, &s->keystr1, 0);
    j = makekey(ssh->pktin.body + 8 + i, &hostkey, &s->keystr2, 0);

    /*
     * Log the host key fingerprint.
     */
    {
        char logmsg[80];
        logevent("Host key fingerprint is:");
        strcpy(logmsg, "      ");
        hostkey.comment = NULL;
        rsa_fingerprint(logmsg + strlen(logmsg),
                        sizeof(logmsg) - strlen(logmsg), &hostkey);
        logevent(logmsg);
    }

    ssh->v1_remote_protoflags = GET_32BIT(ssh->pktin.body + 8 + i + j);
    s->supported_ciphers_mask = GET_32BIT(ssh->pktin.body + 12 + i + j);
    s->supported_auths_mask = GET_32BIT(ssh->pktin.body + 16 + i + j);

    ssh->v1_local_protoflags =
        ssh->v1_remote_protoflags & SSH1_PROTOFLAGS_SUPPORTED;
    ssh->v1_local_protoflags |= SSH1_PROTOFLAG_SCREEN_NUMBER;

    MD5Init(&md5c);
    MD5Update(&md5c, s->keystr2, hostkey.bytes);
    MD5Update(&md5c, s->keystr1, servkey.bytes);
    MD5Update(&md5c, ssh->pktin.body, 8);
    MD5Final(s->session_id, &md5c);

    for (i = 0; i < 32; i++)
        ssh->session_key[i] = random_byte();

    s->len = (hostkey.bytes > servkey.bytes ? hostkey.bytes : servkey.bytes);

    s->rsabuf = smalloc(s->len);
    if (!s->rsabuf)
        fatalbox("Out of memory");

    /*
     * Verify the host key.
     */
    {
        /*
         * First format the key into a string.
         */
        int len = rsastr_len(&hostkey);
        char fingerprint[100];
        char *keystr = smalloc(len);
        if (!keystr)
            fatalbox("Out of memory");
        rsastr_fmt(keystr, &hostkey);
        rsa_fingerprint(fingerprint, sizeof(fingerprint), &hostkey);
        verify_ssh_host_key(ssh->savedhost, ssh->savedport, "rsa", keystr,
                            fingerprint);
        sfree(keystr);
    }

    for (i = 0; i < 32; i++) {
        s->rsabuf[i] = ssh->session_key[i];
        if (i < 16)
            s->rsabuf[i] ^= s->session_id[i];
    }

    if (hostkey.bytes > servkey.bytes) {
        rsaencrypt(s->rsabuf, 32, &servkey);
        rsaencrypt(s->rsabuf, servkey.bytes, &hostkey);
    } else {
        rsaencrypt(s->rsabuf, 32, &hostkey);
        rsaencrypt(s->rsabuf, hostkey.bytes, &servkey);
    }

    logevent("Encrypted session key");

    {
        int cipher_chosen = 0, warn = 0;
        char *cipher_string = NULL;
        int i;
        for (i = 0; !cipher_chosen && i < CIPHER_MAX; i++) {
            int next_cipher = cfg.ssh_cipherlist[i];
            if (next_cipher == CIPHER_WARN) {
                /* If/when we choose a cipher, warn about it */
                warn = 1;
            } else if (next_cipher == CIPHER_AES) {
                /* XXX Probably don't need to mention this. */
                logevent("AES not supported in SSH1, skipping");
            } else {
                switch (next_cipher) {
                  case CIPHER_3DES:     s->cipher_type = SSH_CIPHER_3DES;
                                        cipher_string = "3DES"; break;
                  case CIPHER_BLOWFISH: s->cipher_type = SSH_CIPHER_BLOWFISH;
                                        cipher_string = "Blowfish"; break;
                  case CIPHER_DES:      s->cipher_type = SSH_CIPHER_DES;
                                        cipher_string = "single-DES"; break;
                }
                if (s->supported_ciphers_mask & (1 << s->cipher_type))
                    cipher_chosen = 1;
            }
        }
        if (!cipher_chosen) {
            if ((s->supported_ciphers_mask & (1 << SSH_CIPHER_3DES)) == 0)
                bombout(("Server violates SSH 1 protocol by not "
                         "supporting 3DES encryption"));
            else
                /* shouldn't happen */
                bombout(("No supported ciphers found"));
            crReturn(0);
        }

        /* Warn about chosen cipher if necessary. */
        if (warn)
            askcipher(cipher_string, 0);
    }

    switch (s->cipher_type) {
      case SSH_CIPHER_3DES:
        logevent("Using 3DES encryption");
        break;
      case SSH_CIPHER_DES:
        logevent("Using single-DES encryption");
        break;
      case SSH_CIPHER_BLOWFISH:
        logevent("Using Blowfish encryption");
        break;
    }

    send_packet(ssh, SSH1_CMSG_SESSION_KEY,
                PKT_CHAR, s->cipher_type,
                PKT_DATA, cookie, 8,
                PKT_CHAR, (s->len * 8) >> 8, PKT_CHAR, (s->len * 8) & 0xFF,
                PKT_DATA, s->rsabuf, s->len,
                PKT_INT, ssh->v1_local_protoflags, PKT_END);

    logevent("Trying to enable encryption...");

    sfree(s->rsabuf);

    ssh->cipher = (s->cipher_type == SSH_CIPHER_BLOWFISH ? &ssh_blowfish_ssh1 :
                   s->cipher_type == SSH_CIPHER_DES ? &ssh_des :
                   &ssh_3des);
    ssh->v1_cipher_ctx = ssh->cipher->make_context();
    ssh->cipher->sesskey(ssh->v1_cipher_ctx, ssh->session_key);
    {
        char buf[256];
        sprintf(buf, "Initialised %.200s encryption", ssh->cipher->text_name);
        logevent(buf);
    }

    ssh->crcda_ctx = crcda_make_context();
    logevent("Installing CRC compensation attack detector");

    crWaitUntil(ispkt);

    if (ssh->pktin.type != SSH1_SMSG_SUCCESS) {
        bombout(("Encryption not successfully enabled"));
        crReturn(0);
    }

    logevent("Successfully started encryption");

    fflush(stdout);
    {
        if ((flags & FLAG_INTERACTIVE) && !*cfg.username) {
            if (ssh_get_line && !ssh_getline_pw_only) {
                if (!ssh_get_line("login as: ",
                                  s->username, sizeof(s->username), FALSE)) {
                    /*
                     * get_line failed to get a username.
                     * Terminate.
                     */
                    logevent("No username provided. Abandoning session.");
                    ssh->state = SSH_STATE_CLOSED;
                    crReturn(1);
                }
            } else {
                int ret;               /* need not be kept over crReturn */
                c_write_str(ssh, "login as: ");
                ssh->send_ok = 1;

                setup_userpass_input(ssh, s->username, sizeof(s->username), 1);
                do {
                    crWaitUntil(!ispkt);
                    ret = process_userpass_input(ssh, in, inlen);
                } while (ret == 0);
                if (ret < 0)
                    cleanup_exit(0);
                c_write_str(ssh, "\r\n");
            }
        } else {
            strncpy(s->username, cfg.username, sizeof(s->username));
            s->username[sizeof(s->username)-1] = '\0';
        }

        send_packet(ssh, SSH1_CMSG_USER, PKT_STR, s->username, PKT_END);
        {
            char userlog[22 + sizeof(s->username)];
            sprintf(userlog, "Sent username \"%s\"", s->username);
            logevent(userlog);
            if (flags & FLAG_INTERACTIVE &&
                (!((flags & FLAG_STDERR) && (flags & FLAG_VERBOSE)))) {
                strcat(userlog, "\r\n");
                c_write_str(ssh, userlog);
            }
        }
    }

    crWaitUntil(ispkt);

    if ((ssh->remote_bugs & BUG_CHOKES_ON_RSA)) {
        /* We must not attempt PK auth. Pretend we've already tried it. */
        s->tried_publickey = s->tried_agent = 1;
    } else {
        s->tried_publickey = s->tried_agent = 0;
    }
    s->tis_auth_refused = s->ccard_auth_refused = 0;
    /* Load the public half of cfg.keyfile so we notice if it's in Pageant */
    if (*cfg.keyfile) {
        if (!rsakey_pubblob(cfg.keyfile,
                            &s->publickey_blob, &s->publickey_bloblen))
            s->publickey_blob = NULL;
    } else
        s->publickey_blob = NULL;

    while (ssh->pktin.type == SSH1_SMSG_FAILURE) {
        s->pwpkt_type = SSH1_CMSG_AUTH_PASSWORD;

        if (agent_exists() && !s->tried_agent) {
            /*
             * Attempt RSA authentication using Pageant.
             */
            void *r;

            s->authed = FALSE;
            s->tried_agent = 1;
            logevent("Pageant is running. Requesting keys.");

            /* Request the keys held by the agent. */
            PUT_32BIT(s->request, 1);
            s->request[4] = SSH1_AGENTC_REQUEST_RSA_IDENTITIES;
            agent_query(s->request, 5, &r, &s->responselen);
            s->response = (unsigned char *) r;
            if (s->response && s->responselen >= 5 &&
                s->response[4] == SSH1_AGENT_RSA_IDENTITIES_ANSWER) {
                s->p = s->response + 5;
                s->nkeys = GET_32BIT(s->p);
                s->p += 4;
                {
                    char buf[64];
                    sprintf(buf, "Pageant has %d SSH1 keys", s->nkeys);
                    logevent(buf);
                }
                for (s->keyi = 0; s->keyi < s->nkeys; s->keyi++) {
                    {
                        char buf[64];
                        sprintf(buf, "Trying Pageant key #%d", s->keyi);
                        logevent(buf);
                    }
                    if (s->publickey_blob &&
                        !memcmp(s->p, s->publickey_blob,
                                s->publickey_bloblen)) {
                        logevent("This key matches configured key file");
                        s->tried_publickey = 1;
                    }
                    s->p += 4;
                    s->p += ssh1_read_bignum(s->p, &s->key.exponent);
                    s->p += ssh1_read_bignum(s->p, &s->key.modulus);
                    s->commentlen = GET_32BIT(s->p);
                    s->p += 4;
                    s->commentp = s->p;
                    s->p += s->commentlen;
                    send_packet(ssh, SSH1_CMSG_AUTH_RSA,
                                PKT_BIGNUM, s->key.modulus, PKT_END);
                    crWaitUntil(ispkt);
                    if (ssh->pktin.type != SSH1_SMSG_AUTH_RSA_CHALLENGE) {
                        logevent("Key refused");
                        continue;
                    }
                    logevent("Received RSA challenge");
                    ssh1_read_bignum(ssh->pktin.body, &s->challenge);
                    {
                        char *agentreq, *q, *ret;
                        void *vret;
                        int len, retlen;
                        len = 1 + 4;   /* message type, bit count */
                        len += ssh1_bignum_length(s->key.exponent);
                        len += ssh1_bignum_length(s->key.modulus);
                        len += ssh1_bignum_length(s->challenge);
                        len += 16;     /* session id */
                        len += 4;      /* response format */
                        agentreq = smalloc(4 + len);
                        PUT_32BIT(agentreq, len);
                        q = agentreq + 4;
                        *q++ = SSH1_AGENTC_RSA_CHALLENGE;
                        PUT_32BIT(q, bignum_bitcount(s->key.modulus));
                        q += 4;
                        q += ssh1_write_bignum(q, s->key.exponent);
                        q += ssh1_write_bignum(q, s->key.modulus);
                        q += ssh1_write_bignum(q, s->challenge);
                        memcpy(q, s->session_id, 16);
                        q += 16;
                        PUT_32BIT(q, 1);        /* response format */
                        agent_query(agentreq, len + 4, &vret, &retlen);
                        ret = vret;
                        sfree(agentreq);
                        if (ret) {
                            if (ret[4] == SSH1_AGENT_RSA_RESPONSE) {
                                logevent("Sending Pageant's response");
                                send_packet(ssh, SSH1_CMSG_AUTH_RSA_RESPONSE,
                                            PKT_DATA, ret + 5, 16,
                                            PKT_END);
                                sfree(ret);
                                crWaitUntil(ispkt);
                                if (ssh->pktin.type == SSH1_SMSG_SUCCESS) {
                                    logevent
                                        ("Pageant's response accepted");
                                    if (flags & FLAG_VERBOSE) {
                                        c_write_str(ssh, "Authenticated using"
                                                    " RSA key \"");
                                        c_write(ssh, s->commentp,
                                                s->commentlen);
                                        c_write_str(ssh, "\" from agent\r\n");
                                    }
                                    s->authed = TRUE;
                                } else
                                    logevent
                                        ("Pageant's response not accepted");
                            } else {
                                logevent
                                    ("Pageant failed to answer challenge");
                                sfree(ret);
                            }
                        } else {
                            logevent("No reply received from Pageant");
                        }
                    }
                    freebn(s->key.exponent);
                    freebn(s->key.modulus);
                    freebn(s->challenge);
                    if (s->authed)
                        break;
                }
            }
            if (s->authed)
                break;
        }
        if (*cfg.keyfile && !s->tried_publickey)
            s->pwpkt_type = SSH1_CMSG_AUTH_RSA;

        if (cfg.try_tis_auth &&
            (s->supported_auths_mask & (1 << SSH1_AUTH_TIS)) &&
            !s->tis_auth_refused) {
            s->pwpkt_type = SSH1_CMSG_AUTH_TIS_RESPONSE;
            logevent("Requested TIS authentication");
            send_packet(ssh, SSH1_CMSG_AUTH_TIS, PKT_END);
            crWaitUntil(ispkt);
            if (ssh->pktin.type != SSH1_SMSG_AUTH_TIS_CHALLENGE) {
                logevent("TIS authentication declined");
                if (flags & FLAG_INTERACTIVE)
                    c_write_str(ssh, "TIS authentication refused.\r\n");
                s->tis_auth_refused = 1;
                continue;
            } else {
                int challengelen = GET_32BIT(ssh->pktin.body);
                logevent("Received TIS challenge");
                if (challengelen > sizeof(s->prompt) - 1)
                    challengelen = sizeof(s->prompt) - 1;/* prevent overrun */
                memcpy(s->prompt, ssh->pktin.body + 4, challengelen);
                /* Prompt heuristic comes from OpenSSH */
                strncpy(s->prompt + challengelen,
                        memchr(s->prompt, '\n', challengelen) ?
                        "": "\r\nResponse: ",
                        (sizeof s->prompt) - challengelen);
                s->prompt[(sizeof s->prompt) - 1] = '\0';
            }
        }
        if (cfg.try_tis_auth &&
            (s->supported_auths_mask & (1 << SSH1_AUTH_CCARD)) &&
            !s->ccard_auth_refused) {
            s->pwpkt_type = SSH1_CMSG_AUTH_CCARD_RESPONSE;
            logevent("Requested CryptoCard authentication");
            send_packet(ssh, SSH1_CMSG_AUTH_CCARD, PKT_END);
            crWaitUntil(ispkt);
            if (ssh->pktin.type != SSH1_SMSG_AUTH_CCARD_CHALLENGE) {
                logevent("CryptoCard authentication declined");
                c_write_str(ssh, "CryptoCard authentication refused.\r\n");
                s->ccard_auth_refused = 1;
                continue;
            } else {
                int challengelen = GET_32BIT(ssh->pktin.body);
                logevent("Received CryptoCard challenge");
                if (challengelen > sizeof(s->prompt) - 1)
                    challengelen = sizeof(s->prompt) - 1;/* prevent overrun */
                memcpy(s->prompt, ssh->pktin.body + 4, challengelen);
                strncpy(s->prompt + challengelen,
                        memchr(s->prompt, '\n', challengelen) ?
                        "" : "\r\nResponse: ",
                        sizeof(s->prompt) - challengelen);
                s->prompt[sizeof(s->prompt) - 1] = '\0';
            }
        }
        if (s->pwpkt_type == SSH1_CMSG_AUTH_PASSWORD) {
            sprintf(s->prompt, "%.90s@%.90s's password: ",
                    s->username, ssh->savedhost);
        }
        if (s->pwpkt_type == SSH1_CMSG_AUTH_RSA) {
            char *comment = NULL;
            int type;
            char msgbuf[256];
            if (flags & FLAG_VERBOSE)
                c_write_str(ssh, "Trying public key authentication.\r\n");
            sprintf(msgbuf, "Trying public key \"%.200s\"", cfg.keyfile);
            logevent(msgbuf);
            type = key_type(cfg.keyfile);
            if (type != SSH_KEYTYPE_SSH1) {
                sprintf(msgbuf, "Key is of wrong type (%s)",
                        key_type_to_str(type));
                logevent(msgbuf);
                c_write_str(ssh, msgbuf);
                c_write_str(ssh, "\r\n");
                s->tried_publickey = 1;
                continue;
            }
            if (!rsakey_encrypted(cfg.keyfile, &comment)) {
                if (flags & FLAG_VERBOSE)
                    c_write_str(ssh, "No passphrase required.\r\n");
                goto tryauth;
            }
            sprintf(s->prompt, "Passphrase for key \"%.100s\": ", comment);
            sfree(comment);
        }

        /*
         * Show password prompt, having first obtained it via a TIS
         * or CryptoCard exchange if we're doing TIS or CryptoCard
         * authentication.
         */
        if (ssh_get_line) {
            if (!ssh_get_line(s->prompt, s->password,
                              sizeof(s->password), TRUE)) {
                /*
                 * get_line failed to get a password (for example
                 * because one was supplied on the command line
                 * which has already failed to work). Terminate.
                 */
                send_packet(ssh, SSH1_MSG_DISCONNECT,
                            PKT_STR, "No more passwords available to try",
                            PKT_END);
                logevent("Unable to authenticate");
                connection_fatal("Unable to authenticate");
                ssh->state = SSH_STATE_CLOSED;
                crReturn(1);
            }
        } else {
            /* Prompt may have come from server. We've munged it a bit, so
             * we know it to be zero-terminated at least once. */
            int ret;                   /* need not be saved over crReturn */
            c_write_untrusted(ssh, s->prompt, strlen(s->prompt));
            s->pos = 0;

            setup_userpass_input(ssh, s->password, sizeof(s->password), 0);
            do {
                crWaitUntil(!ispkt);
                ret = process_userpass_input(ssh, in, inlen);
            } while (ret == 0);
            if (ret < 0)
                cleanup_exit(0);
            c_write_str(ssh, "\r\n");
        }

      tryauth:
        if (s->pwpkt_type == SSH1_CMSG_AUTH_RSA) {
            /*
             * Try public key authentication with the specified
             * key file.
             */
            s->tried_publickey = 1;
            
            {
                int ret = loadrsakey(cfg.keyfile, &s->key, s->password);
                if (ret == 0) {
                    c_write_str(ssh, "Couldn't load private key from ");
                    c_write_str(ssh, cfg.keyfile);
                    c_write_str(ssh, ".\r\n");
                    continue;          /* go and try password */
                }
                if (ret == -1) {
                    c_write_str(ssh, "Wrong passphrase.\r\n");
                    s->tried_publickey = 0;
                    continue;          /* try again */
                }
            }

            /*
             * Send a public key attempt.
             */
            send_packet(ssh, SSH1_CMSG_AUTH_RSA,
                        PKT_BIGNUM, s->key.modulus, PKT_END);

            crWaitUntil(ispkt);
            if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
                c_write_str(ssh, "Server refused our public key.\r\n");
                continue;              /* go and try password */
            }
            if (ssh->pktin.type != SSH1_SMSG_AUTH_RSA_CHALLENGE) {
                bombout(("Bizarre response to offer of public key"));
                crReturn(0);
            }

            {
                int i;
                unsigned char buffer[32];
                Bignum challenge, response;

                ssh1_read_bignum(ssh->pktin.body, &challenge);
                response = rsadecrypt(challenge, &s->key);
                freebn(s->key.private_exponent);/* burn the evidence */

                for (i = 0; i < 32; i++) {
                    buffer[i] = bignum_byte(response, 31 - i);
                }

                MD5Init(&md5c);
                MD5Update(&md5c, buffer, 32);
                MD5Update(&md5c, s->session_id, 16);
                MD5Final(buffer, &md5c);

                send_packet(ssh, SSH1_CMSG_AUTH_RSA_RESPONSE,
                            PKT_DATA, buffer, 16, PKT_END);

                freebn(challenge);
                freebn(response);
            }

            crWaitUntil(ispkt);
            if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
                if (flags & FLAG_VERBOSE)
                    c_write_str(ssh, "Failed to authenticate with"
                                " our public key.\r\n");
                continue;              /* go and try password */
            } else if (ssh->pktin.type != SSH1_SMSG_SUCCESS) {
                bombout(("Bizarre response to RSA authentication response"));
                crReturn(0);
            }

            break;                     /* we're through! */
        } else {
            if (s->pwpkt_type == SSH1_CMSG_AUTH_PASSWORD) {
                /*
                 * Defence against traffic analysis: we send a
                 * whole bunch of packets containing strings of
                 * different lengths. One of these strings is the
                 * password, in a SSH1_CMSG_AUTH_PASSWORD packet.
                 * The others are all random data in
                 * SSH1_MSG_IGNORE packets. This way a passive
                 * listener can't tell which is the password, and
                 * hence can't deduce the password length.
                 * 
                 * Anybody with a password length greater than 16
                 * bytes is going to have enough entropy in their
                 * password that a listener won't find it _that_
                 * much help to know how long it is. So what we'll
                 * do is:
                 * 
                 *  - if password length < 16, we send 15 packets
                 *    containing string lengths 1 through 15
                 * 
                 *  - otherwise, we let N be the nearest multiple
                 *    of 8 below the password length, and send 8
                 *    packets containing string lengths N through
                 *    N+7. This won't obscure the order of
                 *    magnitude of the password length, but it will
                 *    introduce a bit of extra uncertainty.
                 * 
                 * A few servers (the old 1.2.18 through 1.2.22)
                 * can't deal with SSH1_MSG_IGNORE. For these
                 * servers, we need an alternative defence. We make
                 * use of the fact that the password is interpreted
                 * as a C string: so we can append a NUL, then some
                 * random data.
                 * 
                 * One server (a Cisco one) can deal with neither
                 * SSH1_MSG_IGNORE _nor_ a padded password string.
                 * For this server we are left with no defences
                 * against password length sniffing.
                 */
                if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH1_IGNORE)) {
                    /*
                     * The server can deal with SSH1_MSG_IGNORE, so
                     * we can use the primary defence.
                     */
                    int bottom, top, pwlen, i;
                    char *randomstr;

                    pwlen = strlen(s->password);
                    if (pwlen < 16) {
                        bottom = 0;    /* zero length passwords are OK! :-) */
                        top = 15;
                    } else {
                        bottom = pwlen & ~7;
                        top = bottom + 7;
                    }

                    assert(pwlen >= bottom && pwlen <= top);

                    randomstr = smalloc(top + 1);

                    for (i = bottom; i <= top; i++) {
                        if (i == pwlen)
                            defer_packet(ssh, s->pwpkt_type,
                                         PKT_STR, s->password, PKT_END);
                        else {
                            for (j = 0; j < i; j++) {
                                do {
                                    randomstr[j] = random_byte();
                                } while (randomstr[j] == '\0');
                            }
                            randomstr[i] = '\0';
                            defer_packet(ssh, SSH1_MSG_IGNORE,
                                         PKT_STR, randomstr, PKT_END);
                        }
                    }
                    logevent("Sending password with camouflage packets");
                    ssh_pkt_defersend(ssh);
                } 
                else if (!(ssh->remote_bugs & BUG_NEEDS_SSH1_PLAIN_PASSWORD)) {
                    /*
                     * The server can't deal with SSH1_MSG_IGNORE
                     * but can deal with padded passwords, so we
                     * can use the secondary defence.
                     */
                    char string[64];
                    char *ss;
                    int len;

                    len = strlen(s->password);
                    if (len < sizeof(string)) {
                        ss = string;
                        strcpy(string, s->password);
                        len++;         /* cover the zero byte */
                        while (len < sizeof(string)) {
                            string[len++] = (char) random_byte();
                        }
                    } else {
                        ss = s->password;
                    }
                    logevent("Sending length-padded password");
                    send_packet(ssh, s->pwpkt_type, PKT_INT, len,
                                PKT_DATA, ss, len, PKT_END);
                } else {
                    /*
                     * The server has _both_
                     * BUG_CHOKES_ON_SSH1_IGNORE and
                     * BUG_NEEDS_SSH1_PLAIN_PASSWORD. There is
                     * therefore nothing we can do.
                     */
                    int len;
                    len = strlen(s->password);
                    logevent("Sending unpadded password");
                    send_packet(ssh, s->pwpkt_type, PKT_INT, len,
                                PKT_DATA, s->password, len, PKT_END);
                }
            } else {
                send_packet(ssh, s->pwpkt_type, PKT_STR, s->password, PKT_END);
            }
        }
        logevent("Sent password");
        memset(s->password, 0, strlen(s->password));
        crWaitUntil(ispkt);
        if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
            if (flags & FLAG_VERBOSE)
                c_write_str(ssh, "Access denied\r\n");
            logevent("Authentication refused");
        } else if (ssh->pktin.type != SSH1_SMSG_SUCCESS) {
            bombout(("Strange packet received, type %d", ssh->pktin.type));
            crReturn(0);
        }
    }

    logevent("Authentication successful");

    crFinish(1);
}

void sshfwd_close(struct ssh_channel *c)
{
    Ssh ssh = c->ssh;

    if (c && !c->closes) {
        /*
         * If the channel's remoteid is -1, we have sent
         * CHANNEL_OPEN for this channel, but it hasn't even been
         * acknowledged by the server. So we must set a close flag
         * on it now, and then when the server acks the channel
         * open, we can close it then.
         */
        if (((int)c->remoteid) != -1) {
            if (ssh->version == 1) {
                send_packet(ssh, SSH1_MSG_CHANNEL_CLOSE, PKT_INT, c->remoteid,
                            PKT_END);
            } else {
                ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_CLOSE);
                ssh2_pkt_adduint32(ssh, c->remoteid);
                ssh2_pkt_send(ssh);
            }
        }
        c->closes = 1;                 /* sent MSG_CLOSE */
        if (c->type == CHAN_X11) {
            c->u.x11.s = NULL;
            logevent("Forwarded X11 connection terminated");
        } else if (c->type == CHAN_SOCKDATA ||
                   c->type == CHAN_SOCKDATA_DORMANT) {
            c->u.pfd.s = NULL;
            logevent("Forwarded port closed");
        }
    }
}

int sshfwd_write(struct ssh_channel *c, char *buf, int len)
{
    Ssh ssh = c->ssh;

    if (ssh->version == 1) {
        send_packet(ssh, SSH1_MSG_CHANNEL_DATA,
                    PKT_INT, c->remoteid,
                    PKT_INT, len, PKT_DATA, buf, len, PKT_END);
        /*
         * In SSH1 we can return 0 here - implying that forwarded
         * connections are never individually throttled - because
         * the only circumstance that can cause throttling will be
         * the whole SSH connection backing up, in which case
         * _everything_ will be throttled as a whole.
         */
        return 0;
    } else {
        ssh2_add_channel_data(c, buf, len);
        return ssh2_try_send(c);
    }
}

void sshfwd_unthrottle(struct ssh_channel *c, int bufsize)
{
    Ssh ssh = c->ssh;

    if (ssh->version == 1) {
        if (c->v.v1.throttling && bufsize < SSH1_BUFFER_LIMIT) {
            c->v.v1.throttling = 0;
            ssh1_throttle(ssh, -1);
        }
    } else {
        ssh2_set_window(c, OUR_V2_WINSIZE - bufsize);
    }
}

static void ssh1_protocol(Ssh ssh, unsigned char *in, int inlen, int ispkt)
{
    crBegin(ssh->ssh1_protocol_crstate);

    random_init();

    while (!do_ssh1_login(ssh, in, inlen, ispkt)) {
        crReturnV;
    }
    if (ssh->state == SSH_STATE_CLOSED)
        crReturnV;

    if (cfg.agentfwd && agent_exists()) {
        logevent("Requesting agent forwarding");
        send_packet(ssh, SSH1_CMSG_AGENT_REQUEST_FORWARDING, PKT_END);
        do {
            crReturnV;
        } while (!ispkt);
        if (ssh->pktin.type != SSH1_SMSG_SUCCESS
            && ssh->pktin.type != SSH1_SMSG_FAILURE) {
            bombout(("Protocol confusion"));
            crReturnV;
        } else if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
            logevent("Agent forwarding refused");
        } else {
            logevent("Agent forwarding enabled");
            ssh->agentfwd_enabled = TRUE;
        }
    }

    if (cfg.x11_forward) {
        char proto[20], data[64];
        logevent("Requesting X11 forwarding");
        x11_invent_auth(proto, sizeof(proto), data, sizeof(data));
        if (ssh->v1_local_protoflags & SSH1_PROTOFLAG_SCREEN_NUMBER) {
            send_packet(ssh, SSH1_CMSG_X11_REQUEST_FORWARDING,
                        PKT_STR, proto, PKT_STR, data,
                        PKT_INT, 0, PKT_END);
        } else {
            send_packet(ssh, SSH1_CMSG_X11_REQUEST_FORWARDING,
                        PKT_STR, proto, PKT_STR, data, PKT_END);
        }
        do {
            crReturnV;
        } while (!ispkt);
        if (ssh->pktin.type != SSH1_SMSG_SUCCESS
            && ssh->pktin.type != SSH1_SMSG_FAILURE) {
            bombout(("Protocol confusion"));
            crReturnV;
        } else if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
            logevent("X11 forwarding refused");
        } else {
            logevent("X11 forwarding enabled");
            ssh->X11_fwd_enabled = TRUE;
        }
    }

    {
        char type;
        int n;
        int sport,dport,sserv,dserv;
        char sports[256], dports[256], host[256];
        char buf[1024];
        struct servent *se;

        ssh->rportfwds = newtree234(ssh_rportcmp_ssh1);
        /* Add port forwardings. */
        ssh->portfwd_strptr = cfg.portfwd;
        while (*ssh->portfwd_strptr) {
            type = *ssh->portfwd_strptr++;
            n = 0;
            while (*ssh->portfwd_strptr && *ssh->portfwd_strptr != '\t')
                sports[n++] = *ssh->portfwd_strptr++;
            sports[n] = 0;
            if (*ssh->portfwd_strptr == '\t')
                ssh->portfwd_strptr++;
            n = 0;
            while (*ssh->portfwd_strptr && *ssh->portfwd_strptr != ':')
                host[n++] = *ssh->portfwd_strptr++;
            host[n] = 0;
            if (*ssh->portfwd_strptr == ':')
                ssh->portfwd_strptr++;
            n = 0;
            while (*ssh->portfwd_strptr)
                dports[n++] = *ssh->portfwd_strptr++;
            dports[n] = 0;
            ssh->portfwd_strptr++;
            dport = atoi(dports);
            dserv = 0;
            if (dport == 0) {
                dserv = 1;
                se = getservbyname(dports, NULL);
                if (se != NULL) {
                    dport = ntohs(se->s_port);
                } else {
                    sprintf(buf,
                            "Service lookup failed for destination port \"%s\"",
                            dports);
                    logevent(buf);
                }
            }
            sport = atoi(sports);
            sserv = 0;
            if (sport == 0) {
                sserv = 1;
                se = getservbyname(sports, NULL);
                if (se != NULL) {
                    sport = ntohs(se->s_port);
                } else {
                    sprintf(buf,
                            "Service lookup failed for source port \"%s\"",
                            sports);
                    logevent(buf);
                }
            }
            if (sport && dport) {
                if (type == 'L') {
                    pfd_addforward(host, dport, sport);
                    sprintf(buf, "Local port %.*s%.*s%d%.*s forwarding to"
                            " %s:%.*s%.*s%d%.*s",
                            sserv ? strlen(sports) : 0, sports,
                            sserv, "(", sport, sserv, ")",
                            host,
                            dserv ? strlen(dports) : 0, dports,
                            dserv, "(", dport, dserv, ")");
                    logevent(buf);
                } else {
                    struct ssh_rportfwd *pf;
                    pf = smalloc(sizeof(*pf));
                    strcpy(pf->dhost, host);
                    pf->dport = dport;
                    if (add234(ssh->rportfwds, pf) != pf) {
                        sprintf(buf, 
                                "Duplicate remote port forwarding to %s:%d",
                                host, dport);
                        logevent(buf);
                        sfree(pf);
                    } else {
                        sprintf(buf, "Requesting remote port %.*s%.*s%d%.*s"
                                " forward to %s:%.*s%.*s%d%.*s",
                            sserv ? strlen(sports) : 0, sports,
                            sserv, "(", sport, sserv, ")",
                            host,
                            dserv ? strlen(dports) : 0, dports,
                            dserv, "(", dport, dserv, ")");
                        logevent(buf);
                        send_packet(ssh, SSH1_CMSG_PORT_FORWARD_REQUEST,
                                    PKT_INT, sport,
                                    PKT_STR, host,
                                    PKT_INT, dport,
                                    PKT_END);
                        do {
                            crReturnV;
                        } while (!ispkt);
                        if (ssh->pktin.type != SSH1_SMSG_SUCCESS
                            && ssh->pktin.type != SSH1_SMSG_FAILURE) {
                            bombout(("Protocol confusion"));
                            crReturnV;
                        } else if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
                            c_write_str(ssh, "Server refused port"
                                        " forwarding\r\n");
                        }
                        logevent("Remote port forwarding enabled");
                    }
                }
            }
        }
    }

    if (!cfg.nopty) {
        send_packet(ssh, SSH1_CMSG_REQUEST_PTY,
                    PKT_STR, cfg.termtype,
                    PKT_INT, ssh->term_height,
                    PKT_INT, ssh->term_width,
                    PKT_INT, 0, PKT_INT, 0, PKT_CHAR, 0, PKT_END);
        ssh->state = SSH_STATE_INTERMED;
        do {
            crReturnV;
        } while (!ispkt);
        if (ssh->pktin.type != SSH1_SMSG_SUCCESS
            && ssh->pktin.type != SSH1_SMSG_FAILURE) {
            bombout(("Protocol confusion"));
            crReturnV;
        } else if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
            c_write_str(ssh, "Server refused to allocate pty\r\n");
            ssh->editing = ssh->echoing = 1;
        }
        logevent("Allocated pty");
    } else {
        ssh->editing = ssh->echoing = 1;
    }

    if (cfg.compression) {
        send_packet(ssh, SSH1_CMSG_REQUEST_COMPRESSION, PKT_INT, 6, PKT_END);
        do {
            crReturnV;
        } while (!ispkt);
        if (ssh->pktin.type != SSH1_SMSG_SUCCESS
            && ssh->pktin.type != SSH1_SMSG_FAILURE) {
            bombout(("Protocol confusion"));
            crReturnV;
        } else if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
            c_write_str(ssh, "Server refused to compress\r\n");
        }
        logevent("Started compression");
        ssh->v1_compressing = TRUE;
        zlib_compress_init();
        zlib_decompress_init();
    }

    /*
     * Start the shell or command.
     * 
     * Special case: if the first-choice command is an SSH2
     * subsystem (hence not usable here) and the second choice
     * exists, we fall straight back to that.
     */
    {
        char *cmd = cfg.remote_cmd_ptr;
        
        if (cfg.ssh_subsys && cfg.remote_cmd_ptr2) {
            cmd = cfg.remote_cmd_ptr2;
            ssh->fallback_cmd = TRUE;
        }
        if (*cmd)
            send_packet(ssh, SSH1_CMSG_EXEC_CMD, PKT_STR, cmd, PKT_END);
        else
            send_packet(ssh, SSH1_CMSG_EXEC_SHELL, PKT_END);
        logevent("Started session");
    }

    ssh->state = SSH_STATE_SESSION;
    if (ssh->size_needed)
        ssh_size(ssh, ssh->term_width, ssh->term_height);
    if (ssh->eof_needed)
        ssh_special(ssh, TS_EOF);

    ldisc_send(NULL, 0, 0);            /* cause ldisc to notice changes */
    ssh->send_ok = 1;
    ssh->channels = newtree234(ssh_channelcmp);
    while (1) {
        crReturnV;
        if (ispkt) {
            if (ssh->pktin.type == SSH1_SMSG_STDOUT_DATA ||
                ssh->pktin.type == SSH1_SMSG_STDERR_DATA) {
                long len = GET_32BIT(ssh->pktin.body);
                int bufsize =
                    from_backend(ssh->frontend,
                                 ssh->pktin.type == SSH1_SMSG_STDERR_DATA,
                                 ssh->pktin.body + 4, len);
                if (!ssh->v1_stdout_throttling && bufsize > SSH1_BUFFER_LIMIT) {
                    ssh->v1_stdout_throttling = 1;
                    ssh1_throttle(ssh, +1);
                }
            } else if (ssh->pktin.type == SSH1_MSG_DISCONNECT) {
                ssh->state = SSH_STATE_CLOSED;
                logevent("Received disconnect request");
                crReturnV;
            } else if (ssh->pktin.type == SSH1_SMSG_X11_OPEN) {
                /* Remote side is trying to open a channel to talk to our
                 * X-Server. Give them back a local channel number. */
                struct ssh_channel *c;

                logevent("Received X11 connect request");
                /* Refuse if X11 forwarding is disabled. */
                if (!ssh->X11_fwd_enabled) {
                    send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                                PKT_INT, GET_32BIT(ssh->pktin.body), PKT_END);
                    logevent("Rejected X11 connect request");
                } else {
                    c = smalloc(sizeof(struct ssh_channel));
                    c->ssh = ssh;

                    if (x11_init(&c->u.x11.s, cfg.x11_display, c) != NULL) {
                        logevent("opening X11 forward connection failed");
                        sfree(c);
                        send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                                    PKT_INT, GET_32BIT(ssh->pktin.body),
                                    PKT_END);
                    } else {
                        logevent
                            ("opening X11 forward connection succeeded");
                        c->remoteid = GET_32BIT(ssh->pktin.body);
                        c->localid = alloc_channel_id(ssh);
                        c->closes = 0;
                        c->v.v1.throttling = 0;
                        c->type = CHAN_X11;     /* identify channel type */
                        add234(ssh->channels, c);
                        send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_CONFIRMATION,
                                    PKT_INT, c->remoteid, PKT_INT,
                                    c->localid, PKT_END);
                        logevent("Opened X11 forward channel");
                    }
                }
            } else if (ssh->pktin.type == SSH1_SMSG_AGENT_OPEN) {
                /* Remote side is trying to open a channel to talk to our
                 * agent. Give them back a local channel number. */
                struct ssh_channel *c;

                /* Refuse if agent forwarding is disabled. */
                if (!ssh->agentfwd_enabled) {
                    send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                                PKT_INT, GET_32BIT(ssh->pktin.body), PKT_END);
                } else {
                    c = smalloc(sizeof(struct ssh_channel));
                    c->ssh = ssh;
                    c->remoteid = GET_32BIT(ssh->pktin.body);
                    c->localid = alloc_channel_id(ssh);
                    c->closes = 0;
                    c->v.v1.throttling = 0;
                    c->type = CHAN_AGENT;       /* identify channel type */
                    c->u.a.lensofar = 0;
                    add234(ssh->channels, c);
                    send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_CONFIRMATION,
                                PKT_INT, c->remoteid, PKT_INT, c->localid,
                                PKT_END);
                }
            } else if (ssh->pktin.type == SSH1_MSG_PORT_OPEN) {
                /* Remote side is trying to open a channel to talk to a
                 * forwarded port. Give them back a local channel number. */
                struct ssh_channel *c;
                struct ssh_rportfwd pf;
                int hostsize, port;
                char host[256], buf[1024];
                char *p, *h, *e;
                c = smalloc(sizeof(struct ssh_channel));
                c->ssh = ssh;

                hostsize = GET_32BIT(ssh->pktin.body+4);
                for(h = host, p = ssh->pktin.body+8; hostsize != 0; hostsize--) {
                    if (h+1 < host+sizeof(host))
                        *h++ = *p;
                    p++;
                }
                *h = 0;
                port = GET_32BIT(p);

                strcpy(pf.dhost, host);
                pf.dport = port;

                if (find234(ssh->rportfwds, &pf, NULL) == NULL) {
                    sprintf(buf, "Rejected remote port open request for %s:%d",
                            host, port);
                    logevent(buf);
                    send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                                PKT_INT, GET_32BIT(ssh->pktin.body), PKT_END);
                } else {
                    sprintf(buf, "Received remote port open request for %s:%d",
                            host, port);
                    logevent(buf);
                    e = pfd_newconnect(&c->u.pfd.s, host, port, c);
                    if (e != NULL) {
                        char buf[256];
                        sprintf(buf, "Port open failed: %s", e);
                        logevent(buf);
                        sfree(c);
                        send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                                    PKT_INT, GET_32BIT(ssh->pktin.body),
                                    PKT_END);
                    } else {
                        c->remoteid = GET_32BIT(ssh->pktin.body);
                        c->localid = alloc_channel_id(ssh);
                        c->closes = 0;
                        c->v.v1.throttling = 0;
                        c->type = CHAN_SOCKDATA;        /* identify channel type */
                        add234(ssh->channels, c);
                        send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_CONFIRMATION,
                                    PKT_INT, c->remoteid, PKT_INT,
                                    c->localid, PKT_END);
                        logevent("Forwarded port opened successfully");
                    }
                }

            } else if (ssh->pktin.type == SSH1_MSG_CHANNEL_OPEN_CONFIRMATION) {
                unsigned int remoteid = GET_32BIT(ssh->pktin.body);
                unsigned int localid = GET_32BIT(ssh->pktin.body+4);
                struct ssh_channel *c;

                c = find234(ssh->channels, &remoteid, ssh_channelfind);
                if (c && c->type == CHAN_SOCKDATA_DORMANT) {
                    c->remoteid = localid;
                    c->type = CHAN_SOCKDATA;
                    c->v.v1.throttling = 0;
                    pfd_confirm(c->u.pfd.s);
                }

                if (c && c->closes) {
                    /*
                     * We have a pending close on this channel,
                     * which we decided on before the server acked
                     * the channel open. So now we know the
                     * remoteid, we can close it again.
                     */
                    send_packet(ssh, SSH1_MSG_CHANNEL_CLOSE,
                                PKT_INT, c->remoteid, PKT_END);
                }

            } else if (ssh->pktin.type == SSH1_MSG_CHANNEL_OPEN_FAILURE) {
                unsigned int remoteid = GET_32BIT(ssh->pktin.body);
                unsigned int localid = GET_32BIT(ssh->pktin.body+4);
                struct ssh_channel *c;

                c = find234(ssh->channels, &remoteid, ssh_channelfind);
                if (c && c->type == CHAN_SOCKDATA_DORMANT) {
                    logevent("Forwarded connection refused by server");
                    pfd_close(c->u.pfd.s);
                    del234(ssh->channels, c);
                    sfree(c);
                }

            } else if (ssh->pktin.type == SSH1_MSG_CHANNEL_CLOSE ||
                       ssh->pktin.type == SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION) {
                /* Remote side closes a channel. */
                unsigned i = GET_32BIT(ssh->pktin.body);
                struct ssh_channel *c;
                c = find234(ssh->channels, &i, ssh_channelfind);
                if (c && ((int)c->remoteid) != -1) {
                    int closetype;
                    closetype =
                        (ssh->pktin.type == SSH1_MSG_CHANNEL_CLOSE ? 1 : 2);

                    if ((c->closes == 0) && (c->type == CHAN_X11)) {
                        logevent("Forwarded X11 connection terminated");
                        assert(c->u.x11.s != NULL);
                        x11_close(c->u.x11.s);
                        c->u.x11.s = NULL;
                    }
                    if ((c->closes == 0) && (c->type == CHAN_SOCKDATA)) {
                        logevent("Forwarded port closed");
                        assert(c->u.pfd.s != NULL);
                        pfd_close(c->u.pfd.s);
                        c->u.pfd.s = NULL;
                    }

                    c->closes |= (closetype << 2);   /* seen this message */
                    if (!(c->closes & closetype)) {
                        send_packet(ssh, ssh->pktin.type, PKT_INT, c->remoteid,
                                    PKT_END);
                        c->closes |= closetype;      /* sent it too */
                    }

                    if (c->closes == 15) {
                        del234(ssh->channels, c);
                        sfree(c);
                    }
                } else {
                    bombout(("Received CHANNEL_CLOSE%s for %s channel %d\n",
                             ssh->pktin.type == SSH1_MSG_CHANNEL_CLOSE ? "" :
                             "_CONFIRMATION", c ? "half-open" : "nonexistent",
                             i));
                }
            } else if (ssh->pktin.type == SSH1_MSG_CHANNEL_DATA) {
                /* Data sent down one of our channels. */
                int i = GET_32BIT(ssh->pktin.body);
                int len = GET_32BIT(ssh->pktin.body + 4);
                unsigned char *p = ssh->pktin.body + 8;
                struct ssh_channel *c;
                c = find234(ssh->channels, &i, ssh_channelfind);
                if (c) {
                    int bufsize;
                    switch (c->type) {
                      case CHAN_X11:
                        bufsize = x11_send(c->u.x11.s, p, len);
                        break;
                      case CHAN_SOCKDATA:
                        bufsize = pfd_send(c->u.pfd.s, p, len);
                        break;
                      case CHAN_AGENT:
                        /* Data for an agent message. Buffer it. */
                        while (len > 0) {
                            if (c->u.a.lensofar < 4) {
                                int l = min(4 - c->u.a.lensofar, len);
                                memcpy(c->u.a.msglen + c->u.a.lensofar, p,
                                       l);
                                p += l;
                                len -= l;
                                c->u.a.lensofar += l;
                            }
                            if (c->u.a.lensofar == 4) {
                                c->u.a.totallen =
                                    4 + GET_32BIT(c->u.a.msglen);
                                c->u.a.message = smalloc(c->u.a.totallen);
                                memcpy(c->u.a.message, c->u.a.msglen, 4);
                            }
                            if (c->u.a.lensofar >= 4 && len > 0) {
                                int l =
                                    min(c->u.a.totallen - c->u.a.lensofar,
                                        len);
                                memcpy(c->u.a.message + c->u.a.lensofar, p,
                                       l);
                                p += l;
                                len -= l;
                                c->u.a.lensofar += l;
                            }
                            if (c->u.a.lensofar == c->u.a.totallen) {
                                void *reply, *sentreply;
                                int replylen;
                                agent_query(c->u.a.message,
                                            c->u.a.totallen, &reply,
                                            &replylen);
                                if (reply)
                                    sentreply = reply;
                                else {
                                    /* Fake SSH_AGENT_FAILURE. */
                                    sentreply = "\0\0\0\1\5";
                                    replylen = 5;
                                }
                                send_packet(ssh, SSH1_MSG_CHANNEL_DATA,
                                            PKT_INT, c->remoteid,
                                            PKT_INT, replylen,
                                            PKT_DATA, sentreply, replylen,
                                            PKT_END);
                                if (reply)
                                    sfree(reply);
                                sfree(c->u.a.message);
                                c->u.a.lensofar = 0;
                            }
                        }
                        bufsize = 0;   /* agent channels never back up */
                        break;
                    }
                    if (!c->v.v1.throttling && bufsize > SSH1_BUFFER_LIMIT) {
                        c->v.v1.throttling = 1;
                        ssh1_throttle(ssh, +1);
                    }
                }
            } else if (ssh->pktin.type == SSH1_SMSG_SUCCESS) {
                /* may be from EXEC_SHELL on some servers */
            } else if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
                /* may be from EXEC_SHELL on some servers
                 * if no pty is available or in other odd cases. Ignore */
            } else if (ssh->pktin.type == SSH1_SMSG_EXIT_STATUS) {
                char buf[100];
                ssh->exitcode = GET_32BIT(ssh->pktin.body);
                sprintf(buf, "Server sent command exit status %d",
                        ssh->exitcode);
                logevent(buf);
                send_packet(ssh, SSH1_CMSG_EXIT_CONFIRMATION, PKT_END);
                /*
                 * In case `helpful' firewalls or proxies tack
                 * extra human-readable text on the end of the
                 * session which we might mistake for another
                 * encrypted packet, we close the session once
                 * we've sent EXIT_CONFIRMATION.
                 */
                ssh->state = SSH_STATE_CLOSED;
                crReturnV;
            } else {
                bombout(("Strange packet received: type %d", ssh->pktin.type));
                crReturnV;
            }
        } else {
            while (inlen > 0) {
                int len = min(inlen, 512);
                send_packet(ssh, SSH1_CMSG_STDIN_DATA,
                            PKT_INT, len, PKT_DATA, in, len, PKT_END);
                in += len;
                inlen -= len;
            }
        }
    }

    crFinishV;
}

/*
 * Utility routine for decoding comma-separated strings in KEXINIT.
 */
static int in_commasep_string(char *needle, char *haystack, int haylen)
{
    int needlen = strlen(needle);
    while (1) {
        /*
         * Is it at the start of the string?
         */
        if (haylen >= needlen &&       /* haystack is long enough */
            !memcmp(needle, haystack, needlen) &&       /* initial match */
            (haylen == needlen || haystack[needlen] == ',')
            /* either , or EOS follows */
            )
            return 1;
        /*
         * If not, search for the next comma and resume after that.
         * If no comma found, terminate.
         */
        while (haylen > 0 && *haystack != ',')
            haylen--, haystack++;
        if (haylen == 0)
            return 0;
        haylen--, haystack++;          /* skip over comma itself */
    }
}

/*
 * SSH2 key creation method.
 */
static void ssh2_mkkey(Ssh ssh, Bignum K, char *H, char *sessid, char chr,
                       char *keyspace)
{
    SHA_State s;
    /* First 20 bytes. */
    SHA_Init(&s);
    if (!(ssh->remote_bugs & BUG_SSH2_DERIVEKEY))
        sha_mpint(&s, K);
    SHA_Bytes(&s, H, 20);
    SHA_Bytes(&s, &chr, 1);
    SHA_Bytes(&s, sessid, 20);
    SHA_Final(&s, keyspace);
    /* Next 20 bytes. */
    SHA_Init(&s);
    if (!(ssh->remote_bugs & BUG_SSH2_DERIVEKEY))
        sha_mpint(&s, K);
    SHA_Bytes(&s, H, 20);
    SHA_Bytes(&s, keyspace, 20);
    SHA_Final(&s, keyspace + 20);
}

/*
 * Handle the SSH2 transport layer.
 */
static int do_ssh2_transport(Ssh ssh, unsigned char *in, int inlen, int ispkt)
{
    struct do_ssh2_transport_state {
        int nbits, pbits, warn;
        Bignum p, g, e, f, K;
        int kex_init_value, kex_reply_value;
        const struct ssh_mac **maclist;
        int nmacs;
        const struct ssh2_cipher *cscipher_tobe;
        const struct ssh2_cipher *sccipher_tobe;
        const struct ssh_mac *csmac_tobe;
        const struct ssh_mac *scmac_tobe;
        const struct ssh_compress *cscomp_tobe;
        const struct ssh_compress *sccomp_tobe;
        char *hostkeydata, *sigdata, *keystr, *fingerprint;
        int hostkeylen, siglen;
        void *hkey;                    /* actual host key */
        unsigned char exchange_hash[20];
        int n_preferred_ciphers;
        const struct ssh2_ciphers *preferred_ciphers[CIPHER_MAX];
        const struct ssh_compress *preferred_comp;
        int first_kex;
    };
    crState(do_ssh2_transport_state);

    crBegin(ssh->do_ssh2_transport_crstate);

    s->cscipher_tobe = s->sccipher_tobe = NULL;
    s->csmac_tobe = s->scmac_tobe = NULL;
    s->cscomp_tobe = s->sccomp_tobe = NULL;

    random_init();
    s->first_kex = 1;

    {
        int i;
        /*
         * Set up the preferred ciphers. (NULL => warn below here)
         */
        s->n_preferred_ciphers = 0;
        for (i = 0; i < CIPHER_MAX; i++) {
            switch (cfg.ssh_cipherlist[i]) {
              case CIPHER_BLOWFISH:
                s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_blowfish;
                break;
              case CIPHER_DES:
                if (cfg.ssh2_des_cbc) {
                    s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_des;
                }
                break;
              case CIPHER_3DES:
                s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_3des;
                break;
              case CIPHER_AES:
                s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_aes;
                break;
              case CIPHER_WARN:
                /* Flag for later. Don't bother if it's the last in
                 * the list. */
                if (i < CIPHER_MAX - 1) {
                    s->preferred_ciphers[s->n_preferred_ciphers++] = NULL;
                }
                break;
            }
        }
    }

    /*
     * Set up preferred compression.
     */
    if (cfg.compression)
        s->preferred_comp = &ssh_zlib;
    else
        s->preferred_comp = &ssh_comp_none;

    /*
     * Be prepared to work around the buggy MAC problem.
     */
    if (ssh->remote_bugs & BUG_SSH2_HMAC)
        s->maclist = buggymacs, s->nmacs = lenof(buggymacs);
    else
        s->maclist = macs, s->nmacs = lenof(macs);

  begin_key_exchange:
    {
        int i, j, cipherstr_started;

        /*
         * Construct and send our key exchange packet.
         */
        ssh2_pkt_init(ssh, SSH2_MSG_KEXINIT);
        for (i = 0; i < 16; i++)
            ssh2_pkt_addbyte(ssh, (unsigned char) random_byte());
        /* List key exchange algorithms. */
        ssh2_pkt_addstring_start(ssh);
        for (i = 0; i < lenof(kex_algs); i++) {
            if (kex_algs[i] == &ssh_diffiehellman_gex &&
                (ssh->remote_bugs & BUG_SSH2_DH_GEX))
                continue;
            ssh2_pkt_addstring_str(ssh, kex_algs[i]->name);
            if (i < lenof(kex_algs) - 1)
                ssh2_pkt_addstring_str(ssh, ",");
        }
        /* List server host key algorithms. */
        ssh2_pkt_addstring_start(ssh);
        for (i = 0; i < lenof(hostkey_algs); i++) {
            ssh2_pkt_addstring_str(ssh, hostkey_algs[i]->name);
            if (i < lenof(hostkey_algs) - 1)
                ssh2_pkt_addstring_str(ssh, ",");
        }
        /* List client->server encryption algorithms. */
        ssh2_pkt_addstring_start(ssh);
        cipherstr_started = 0;
        for (i = 0; i < s->n_preferred_ciphers; i++) {
            const struct ssh2_ciphers *c = s->preferred_ciphers[i];
            if (!c) continue;          /* warning flag */
            for (j = 0; j < c->nciphers; j++) {
                if (cipherstr_started)
                    ssh2_pkt_addstring_str(ssh, ",");
                ssh2_pkt_addstring_str(ssh, c->list[j]->name);
                cipherstr_started = 1;
            }
        }
        /* List server->client encryption algorithms. */
        ssh2_pkt_addstring_start(ssh);
        cipherstr_started = 0;
        for (i = 0; i < s->n_preferred_ciphers; i++) {
            const struct ssh2_ciphers *c = s->preferred_ciphers[i];
            if (!c) continue; /* warning flag */
            for (j = 0; j < c->nciphers; j++) {
                if (cipherstr_started)
                    ssh2_pkt_addstring_str(ssh, ",");
                ssh2_pkt_addstring_str(ssh, c->list[j]->name);
                cipherstr_started = 1;
            }
        }
        /* List client->server MAC algorithms. */
        ssh2_pkt_addstring_start(ssh);
        for (i = 0; i < s->nmacs; i++) {
            ssh2_pkt_addstring_str(ssh, s->maclist[i]->name);
            if (i < s->nmacs - 1)
                ssh2_pkt_addstring_str(ssh, ",");
        }
        /* List server->client MAC algorithms. */
        ssh2_pkt_addstring_start(ssh);
        for (i = 0; i < s->nmacs; i++) {
            ssh2_pkt_addstring_str(ssh, s->maclist[i]->name);
            if (i < s->nmacs - 1)
                ssh2_pkt_addstring_str(ssh, ",");
        }
        /* List client->server compression algorithms. */
        ssh2_pkt_addstring_start(ssh);
        for (i = 0; i < lenof(compressions) + 1; i++) {
            const struct ssh_compress *c =
                i == 0 ? s->preferred_comp : compressions[i - 1];
            ssh2_pkt_addstring_str(ssh, c->name);
            if (i < lenof(compressions))
                ssh2_pkt_addstring_str(ssh, ",");
        }
        /* List server->client compression algorithms. */
        ssh2_pkt_addstring_start(ssh);
        for (i = 0; i < lenof(compressions) + 1; i++) {
            const struct ssh_compress *c =
                i == 0 ? s->preferred_comp : compressions[i - 1];
            ssh2_pkt_addstring_str(ssh, c->name);
            if (i < lenof(compressions))
                ssh2_pkt_addstring_str(ssh, ",");
        }
        /* List client->server languages. Empty list. */
        ssh2_pkt_addstring_start(ssh);
        /* List server->client languages. Empty list. */
        ssh2_pkt_addstring_start(ssh);
        /* First KEX packet does _not_ follow, because we're not that brave. */
        ssh2_pkt_addbool(ssh, FALSE);
        /* Reserved. */
        ssh2_pkt_adduint32(ssh, 0);
    }

    ssh->exhash = ssh->exhashbase;
    sha_string(&ssh->exhash, ssh->pktout.data + 5, ssh->pktout.length - 5);

    ssh2_pkt_send(ssh);

    if (!ispkt)
        crWaitUntil(ispkt);
    sha_string(&ssh->exhash, ssh->pktin.data + 5, ssh->pktin.length - 5);

    /*
     * Now examine the other side's KEXINIT to see what we're up
     * to.
     */
    {
        char *str;
        int i, j, len;

        if (ssh->pktin.type != SSH2_MSG_KEXINIT) {
            bombout(("expected key exchange packet from server"));
            crReturn(0);
        }
        ssh->kex = NULL;
        ssh->hostkey = NULL;
        s->cscipher_tobe = NULL;
        s->sccipher_tobe = NULL;
        s->csmac_tobe = NULL;
        s->scmac_tobe = NULL;
        s->cscomp_tobe = NULL;
        s->sccomp_tobe = NULL;
        ssh->pktin.savedpos += 16;              /* skip garbage cookie */
        ssh2_pkt_getstring(ssh, &str, &len);    /* key exchange algorithms */
        for (i = 0; i < lenof(kex_algs); i++) {
            if (kex_algs[i] == &ssh_diffiehellman_gex &&
                (ssh->remote_bugs & BUG_SSH2_DH_GEX))
                continue;
            if (in_commasep_string(kex_algs[i]->name, str, len)) {
                ssh->kex = kex_algs[i];
                break;
            }
        }
        ssh2_pkt_getstring(ssh, &str, &len);    /* host key algorithms */
        for (i = 0; i < lenof(hostkey_algs); i++) {
            if (in_commasep_string(hostkey_algs[i]->name, str, len)) {
                ssh->hostkey = hostkey_algs[i];
                break;
            }
        }
        ssh2_pkt_getstring(ssh, &str, &len);    /* client->server cipher */
        s->warn = 0;
        for (i = 0; i < s->n_preferred_ciphers; i++) {
            const struct ssh2_ciphers *c = s->preferred_ciphers[i];
            if (!c) {
                s->warn = 1;
            } else {
                for (j = 0; j < c->nciphers; j++) {
                    if (in_commasep_string(c->list[j]->name, str, len)) {
                        s->cscipher_tobe = c->list[j];
                        break;
                    }
                }
            }
            if (s->cscipher_tobe) {
                if (s->warn)
                    askcipher(s->cscipher_tobe->name, 1);
                break;
            }
        }
        if (!s->cscipher_tobe) {
            bombout(("Couldn't agree a client-to-server cipher (available: %s)", str));
            crReturn(0);
        }

        ssh2_pkt_getstring(ssh, &str, &len);    /* server->client cipher */
        s->warn = 0;
        for (i = 0; i < s->n_preferred_ciphers; i++) {
            const struct ssh2_ciphers *c = s->preferred_ciphers[i];
            if (!c) {
                s->warn = 1;
            } else {
                for (j = 0; j < c->nciphers; j++) {
                    if (in_commasep_string(c->list[j]->name, str, len)) {
                        s->sccipher_tobe = c->list[j];
                        break;
                    }
                }
            }
            if (s->sccipher_tobe) {
                if (s->warn)
                    askcipher(s->sccipher_tobe->name, 2);
                break;
            }
        }
        if (!s->sccipher_tobe) {
            bombout(("Couldn't agree a server-to-client cipher (available: %s)", str));
            crReturn(0);
        }

        ssh2_pkt_getstring(ssh, &str, &len);    /* client->server mac */
        for (i = 0; i < s->nmacs; i++) {
            if (in_commasep_string(s->maclist[i]->name, str, len)) {
                s->csmac_tobe = s->maclist[i];
                break;
            }
        }
        ssh2_pkt_getstring(ssh, &str, &len);    /* server->client mac */
        for (i = 0; i < s->nmacs; i++) {
            if (in_commasep_string(s->maclist[i]->name, str, len)) {
                s->scmac_tobe = s->maclist[i];
                break;
            }
        }
        ssh2_pkt_getstring(ssh, &str, &len);  /* client->server compression */
        for (i = 0; i < lenof(compressions) + 1; i++) {
            const struct ssh_compress *c =
                i == 0 ? s->preferred_comp : compressions[i - 1];
            if (in_commasep_string(c->name, str, len)) {
                s->cscomp_tobe = c;
                break;
            }
        }
        ssh2_pkt_getstring(ssh, &str, &len);  /* server->client compression */
        for (i = 0; i < lenof(compressions) + 1; i++) {
            const struct ssh_compress *c =
                i == 0 ? s->preferred_comp : compressions[i - 1];
            if (in_commasep_string(c->name, str, len)) {
                s->sccomp_tobe = c;
                break;
            }
        }
    }

    /*
     * Work out the number of bits of key we will need from the key
     * exchange. We start with the maximum key length of either
     * cipher...
     */
    {
        int csbits, scbits;

        csbits = s->cscipher_tobe->keylen;
        scbits = s->sccipher_tobe->keylen;
        s->nbits = (csbits > scbits ? csbits : scbits);
    }
    /* The keys only have 160-bit entropy, since they're based on
     * a SHA-1 hash. So cap the key size at 160 bits. */
    if (s->nbits > 160)
        s->nbits = 160;

    /*
     * If we're doing Diffie-Hellman group exchange, start by
     * requesting a group.
     */
    if (ssh->kex == &ssh_diffiehellman_gex) {
        logevent("Doing Diffie-Hellman group exchange");
        ssh->pkt_ctx |= SSH2_PKTCTX_DHGEX;
        /*
         * Work out how big a DH group we will need to allow that
         * much data.
         */
        s->pbits = 512 << ((s->nbits - 1) / 64);
        ssh2_pkt_init(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST);
        ssh2_pkt_adduint32(ssh, s->pbits);
        ssh2_pkt_send(ssh);

        crWaitUntil(ispkt);
        if (ssh->pktin.type != SSH2_MSG_KEX_DH_GEX_GROUP) {
            bombout(("expected key exchange group packet from server"));
            crReturn(0);
        }
        s->p = ssh2_pkt_getmp(ssh);
        s->g = ssh2_pkt_getmp(ssh);
        dh_setup_group(s->p, s->g);
        s->kex_init_value = SSH2_MSG_KEX_DH_GEX_INIT;
        s->kex_reply_value = SSH2_MSG_KEX_DH_GEX_REPLY;
    } else {
        ssh->pkt_ctx |= SSH2_PKTCTX_DHGROUP1;
        dh_setup_group1();
        s->kex_init_value = SSH2_MSG_KEXDH_INIT;
        s->kex_reply_value = SSH2_MSG_KEXDH_REPLY;
    }

    logevent("Doing Diffie-Hellman key exchange");
    /*
     * Now generate and send e for Diffie-Hellman.
     */
    s->e = dh_create_e(s->nbits * 2);
    ssh2_pkt_init(ssh, s->kex_init_value);
    ssh2_pkt_addmp(ssh, s->e);
    ssh2_pkt_send(ssh);

    crWaitUntil(ispkt);
    if (ssh->pktin.type != s->kex_reply_value) {
        bombout(("expected key exchange reply packet from server"));
        crReturn(0);
    }
    ssh2_pkt_getstring(ssh, &s->hostkeydata, &s->hostkeylen);
    s->f = ssh2_pkt_getmp(ssh);
    ssh2_pkt_getstring(ssh, &s->sigdata, &s->siglen);

    s->K = dh_find_K(s->f);

    sha_string(&ssh->exhash, s->hostkeydata, s->hostkeylen);
    if (ssh->kex == &ssh_diffiehellman_gex) {
        sha_uint32(&ssh->exhash, s->pbits);
        sha_mpint(&ssh->exhash, s->p);
        sha_mpint(&ssh->exhash, s->g);
    }
    sha_mpint(&ssh->exhash, s->e);
    sha_mpint(&ssh->exhash, s->f);
    sha_mpint(&ssh->exhash, s->K);
    SHA_Final(&ssh->exhash, s->exchange_hash);

    dh_cleanup();

#if 0
    debug(("Exchange hash is:\n"));
    dmemdump(s->exchange_hash, 20);
#endif

    s->hkey = ssh->hostkey->newkey(s->hostkeydata, s->hostkeylen);
    if (!s->hkey ||
        !ssh->hostkey->verifysig(s->hkey, s->sigdata, s->siglen,
                                 s->exchange_hash, 20)) {
        bombout(("Server's host key did not match the signature supplied"));
        crReturn(0);
    }

    /*
     * Authenticate remote host: verify host key. (We've already
     * checked the signature of the exchange hash.)
     */
    s->keystr = ssh->hostkey->fmtkey(s->hkey);
    s->fingerprint = ssh->hostkey->fingerprint(s->hkey);
    verify_ssh_host_key(ssh->savedhost, ssh->savedport, ssh->hostkey->keytype,
                        s->keystr, s->fingerprint);
    if (s->first_kex) {                /* don't bother logging this in rekeys */
        logevent("Host key fingerprint is:");
        logevent(s->fingerprint);
    }
    sfree(s->fingerprint);
    sfree(s->keystr);
    ssh->hostkey->freekey(s->hkey);

    /*
     * Send SSH2_MSG_NEWKEYS.
     */
    ssh2_pkt_init(ssh, SSH2_MSG_NEWKEYS);
    ssh2_pkt_send(ssh);

    /*
     * Expect SSH2_MSG_NEWKEYS from server.
     */
    crWaitUntil(ispkt);
    if (ssh->pktin.type != SSH2_MSG_NEWKEYS) {
        bombout(("expected new-keys packet from server"));
        crReturn(0);
    }

    /*
     * Create and initialise session keys.
     */
    if (ssh->cs_cipher_ctx)
        ssh->cscipher->free_context(ssh->cs_cipher_ctx);
    ssh->cscipher = s->cscipher_tobe;
    ssh->cs_cipher_ctx = ssh->cscipher->make_context();

    if (ssh->sc_cipher_ctx)
        ssh->sccipher->free_context(ssh->sc_cipher_ctx);
    ssh->sccipher = s->sccipher_tobe;
    ssh->sc_cipher_ctx = ssh->sccipher->make_context();

    if (ssh->cs_mac_ctx)
        ssh->csmac->free_context(ssh->cs_mac_ctx);
    ssh->csmac = s->csmac_tobe;
    ssh->cs_mac_ctx = ssh->csmac->make_context();

    if (ssh->sc_mac_ctx)
        ssh->scmac->free_context(ssh->sc_mac_ctx);
    ssh->scmac = s->scmac_tobe;
    ssh->sc_mac_ctx = ssh->scmac->make_context();

    ssh->cscomp = s->cscomp_tobe;
    ssh->sccomp = s->sccomp_tobe;
    ssh->cscomp->compress_init();
    ssh->sccomp->decompress_init();
    /*
     * Set IVs after keys. Here we use the exchange hash from the
     * _first_ key exchange.
     */
    {
        unsigned char keyspace[40];
        if (s->first_kex)
            memcpy(ssh->v2_session_id, s->exchange_hash,
                   sizeof(s->exchange_hash));
        ssh2_mkkey(ssh,s->K,s->exchange_hash,ssh->v2_session_id,'C',keyspace);
        ssh->cscipher->setkey(ssh->cs_cipher_ctx, keyspace);
        ssh2_mkkey(ssh,s->K,s->exchange_hash,ssh->v2_session_id,'D',keyspace);
        ssh->sccipher->setkey(ssh->sc_cipher_ctx, keyspace);
        ssh2_mkkey(ssh,s->K,s->exchange_hash,ssh->v2_session_id,'A',keyspace);
        ssh->cscipher->setiv(ssh->cs_cipher_ctx, keyspace);
        ssh2_mkkey(ssh,s->K,s->exchange_hash,ssh->v2_session_id,'B',keyspace);
        ssh->sccipher->setiv(ssh->sc_cipher_ctx, keyspace);
        ssh2_mkkey(ssh,s->K,s->exchange_hash,ssh->v2_session_id,'E',keyspace);
        ssh->csmac->setkey(ssh->cs_mac_ctx, keyspace);
        ssh2_mkkey(ssh,s->K,s->exchange_hash,ssh->v2_session_id,'F',keyspace);
        ssh->scmac->setkey(ssh->sc_mac_ctx, keyspace);
    }
    {
        char buf[256];
        sprintf(buf, "Initialised %.200s client->server encryption",
                ssh->cscipher->text_name);
        logevent(buf);
        sprintf(buf, "Initialised %.200s server->client encryption",
                ssh->sccipher->text_name);
        logevent(buf);
    }


    /*
     * If this is the first key exchange phase, we must pass the
     * SSH2_MSG_NEWKEYS packet to the next layer, not because it
     * wants to see it but because it will need time to initialise
     * itself before it sees an actual packet. In subsequent key
     * exchange phases, we don't pass SSH2_MSG_NEWKEYS on, because
     * it would only confuse the layer above.
     */
    if (!s->first_kex) {
        crReturn(0);
    }
    s->first_kex = 0;

    /*
     * Now we're encrypting. Begin returning 1 to the protocol main
     * function so that other things can run on top of the
     * transport. If we ever see a KEXINIT, we must go back to the
     * start.
     */
    while (!(ispkt && ssh->pktin.type == SSH2_MSG_KEXINIT)) {
        crReturn(1);
    }
    logevent("Server initiated key re-exchange");
    goto begin_key_exchange;

    crFinish(1);
}

/*
 * Add data to an SSH2 channel output buffer.
 */
static void ssh2_add_channel_data(struct ssh_channel *c, char *buf,
                                  int len)
{
    bufchain_add(&c->v.v2.outbuffer, buf, len);
}

/*
 * Attempt to send data on an SSH2 channel.
 */
static int ssh2_try_send(struct ssh_channel *c)
{
    Ssh ssh = c->ssh;

    while (c->v.v2.remwindow > 0 && bufchain_size(&c->v.v2.outbuffer) > 0) {
        int len;
        void *data;
        bufchain_prefix(&c->v.v2.outbuffer, &data, &len);
        if ((unsigned)len > c->v.v2.remwindow)
            len = c->v.v2.remwindow;
        if ((unsigned)len > c->v.v2.remmaxpkt)
            len = c->v.v2.remmaxpkt;
        ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_DATA);
        ssh2_pkt_adduint32(ssh, c->remoteid);
        ssh2_pkt_addstring_start(ssh);
        ssh2_pkt_addstring_data(ssh, data, len);
        ssh2_pkt_send(ssh);
        bufchain_consume(&c->v.v2.outbuffer, len);
        c->v.v2.remwindow -= len;
    }

    /*
     * After having sent as much data as we can, return the amount
     * still buffered.
     */
    return bufchain_size(&c->v.v2.outbuffer);
}

/*
 * Potentially enlarge the window on an SSH2 channel.
 */
static void ssh2_set_window(struct ssh_channel *c, unsigned newwin)
{
    Ssh ssh = c->ssh;

    /*
     * Never send WINDOW_ADJUST for a channel that the remote side
     * already thinks it's closed; there's no point, since it won't
     * be sending any more data anyway.
     */
    if (c->closes != 0)
        return;

    if (newwin > c->v.v2.locwindow) {
        ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_WINDOW_ADJUST);
        ssh2_pkt_adduint32(ssh, c->remoteid);
        ssh2_pkt_adduint32(ssh, newwin - c->v.v2.locwindow);
        ssh2_pkt_send(ssh);
        c->v.v2.locwindow = newwin;
    }
}

/*
 * Handle the SSH2 userauth and connection layers.
 */
static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
{
    struct do_ssh2_authconn_state {
        enum {
            AUTH_INVALID, AUTH_PUBLICKEY_AGENT, AUTH_PUBLICKEY_FILE,
                AUTH_PASSWORD,
                AUTH_KEYBOARD_INTERACTIVE
        } method;
        enum {
            AUTH_TYPE_NONE,
                AUTH_TYPE_PUBLICKEY,
                AUTH_TYPE_PUBLICKEY_OFFER_LOUD,
                AUTH_TYPE_PUBLICKEY_OFFER_QUIET,
                AUTH_TYPE_PASSWORD,
                AUTH_TYPE_KEYBOARD_INTERACTIVE,
                AUTH_TYPE_KEYBOARD_INTERACTIVE_QUIET
        } type;
        int gotit, need_pw, can_pubkey, can_passwd, can_keyb_inter;
        int tried_pubkey_config, tried_agent, tried_keyb_inter;
        int kbd_inter_running;
        int we_are_in;
        int num_prompts, curr_prompt, echo;
        char username[100];
        int got_username;
        char pwprompt[200];
        char password[100];
        void *publickey_blob;
        int publickey_bloblen;
        unsigned char request[5], *response, *p;
        int responselen;
        int keyi, nkeys;
        int authed;
        char *pkblob, *alg, *commentp;
        int pklen, alglen, commentlen;
        int siglen, retlen, len;
        char *q, *agentreq, *ret;
        int try_send;
    };
    crState(do_ssh2_authconn_state);

    crBegin(ssh->do_ssh2_authconn_crstate);

    /*
     * Request userauth protocol, and await a response to it.
     */
    ssh2_pkt_init(ssh, SSH2_MSG_SERVICE_REQUEST);
    ssh2_pkt_addstring(ssh, "ssh-userauth");
    ssh2_pkt_send(ssh);
    crWaitUntilV(ispkt);
    if (ssh->pktin.type != SSH2_MSG_SERVICE_ACCEPT) {
        bombout(("Server refused user authentication protocol"));
        crReturnV;
    }

    /*
     * We repeat this whole loop, including the username prompt,
     * until we manage a successful authentication. If the user
     * types the wrong _password_, they can be sent back to the
     * beginning to try another username, if this is configured on.
     * (If they specify a username in the config, they are never
     * asked, even if they do give a wrong password.)
     * 
     * I think this best serves the needs of
     * 
     *  - the people who have no configuration, no keys, and just
     *    want to try repeated (username,password) pairs until they
     *    type both correctly
     * 
     *  - people who have keys and configuration but occasionally
     *    need to fall back to passwords
     * 
     *  - people with a key held in Pageant, who might not have
     *    logged in to a particular machine before; so they want to
     *    type a username, and then _either_ their key will be
     *    accepted, _or_ they will type a password. If they mistype
     *    the username they will want to be able to get back and
     *    retype it!
     */
    s->username[0] = '\0';
    s->got_username = FALSE;
    do {
        /*
         * Get a username.
         */
        if (s->got_username && !cfg.change_username) {
            /*
             * We got a username last time round this loop, and
             * with change_username turned off we don't try to get
             * it again.
             */
        } else if ((flags & FLAG_INTERACTIVE) && !*cfg.username) {
            if (ssh_get_line && !ssh_getline_pw_only) {
                if (!ssh_get_line("login as: ",
                                  s->username, sizeof(s->username), FALSE)) {
                    /*
                     * get_line failed to get a username.
                     * Terminate.
                     */
                    logevent("No username provided. Abandoning session.");
                    ssh->state = SSH_STATE_CLOSED;
                    crReturnV;
                }
            } else {
                int ret;               /* need not be saved across crReturn */
                c_write_str(ssh, "login as: ");
                ssh->send_ok = 1;
                setup_userpass_input(ssh, s->username, sizeof(s->username), 1);
                do {
                    crWaitUntilV(!ispkt);
                    ret = process_userpass_input(ssh, in, inlen);
                } while (ret == 0);
                if (ret < 0)
                    cleanup_exit(0);
            }
            c_write_str(ssh, "\r\n");
            s->username[strcspn(s->username, "\n\r")] = '\0';
        } else {
            char stuff[200];
            strncpy(s->username, cfg.username, sizeof(s->username));
            s->username[sizeof(s->username)-1] = '\0';
            if ((flags & FLAG_VERBOSE) || (flags & FLAG_INTERACTIVE)) {
                sprintf(stuff, "Using username \"%s\".\r\n", s->username);
                c_write_str(ssh, stuff);
            }
        }
        s->got_username = TRUE;

        /*
         * Send an authentication request using method "none": (a)
         * just in case it succeeds, and (b) so that we know what
         * authentication methods we can usefully try next.
         */
        ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;

        ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
        ssh2_pkt_addstring(ssh, s->username);
        ssh2_pkt_addstring(ssh, "ssh-connection");/* service requested */
        ssh2_pkt_addstring(ssh, "none");    /* method */
        ssh2_pkt_send(ssh);
        s->type = AUTH_TYPE_NONE;
        s->gotit = FALSE;
        s->we_are_in = FALSE;

        s->tried_pubkey_config = FALSE;
        s->tried_agent = FALSE;
        s->tried_keyb_inter = FALSE;
        s->kbd_inter_running = FALSE;
        /* Load the pub half of cfg.keyfile so we notice if it's in Pageant */
        if (*cfg.keyfile) {
            int keytype;
            logeventf("Reading private key file \"%.150s\"", cfg.keyfile);
            keytype = key_type(cfg.keyfile);
            if (keytype == SSH_KEYTYPE_SSH2) {
                s->publickey_blob =
                    ssh2_userkey_loadpub(cfg.keyfile, NULL,
                                         &s->publickey_bloblen);
            } else {
                char msgbuf[256];
                logeventf("Unable to use this key file (%s)",
                        key_type_to_str(keytype));
                sprintf(msgbuf, "Unable to use key file \"%.150s\" (%s)\r\n",
                        cfg.keyfile, key_type_to_str(keytype));
                c_write_str(ssh, msgbuf);
                s->publickey_blob = NULL;
            }
        } else
            s->publickey_blob = NULL;

        while (1) {
            /*
             * Wait for the result of the last authentication request.
             */
            if (!s->gotit)
                crWaitUntilV(ispkt);
            while (ssh->pktin.type == SSH2_MSG_USERAUTH_BANNER) {
                char *banner;
                int size;
                /*
                 * Don't show the banner if we're operating in
                 * non-verbose non-interactive mode. (It's probably
                 * a script, which means nobody will read the
                 * banner _anyway_, and moreover the printing of
                 * the banner will screw up processing on the
                 * output of (say) plink.)
                 */
                if (flags & (FLAG_VERBOSE | FLAG_INTERACTIVE)) {
                    ssh2_pkt_getstring(ssh, &banner, &size);
                    if (banner)
                        c_write_untrusted(ssh, banner, size);
                }
                crWaitUntilV(ispkt);
            }
            if (ssh->pktin.type == SSH2_MSG_USERAUTH_SUCCESS) {
                logevent("Access granted");
                s->we_are_in = TRUE;
                break;
            }

            if (s->kbd_inter_running &&
                ssh->pktin.type == SSH2_MSG_USERAUTH_INFO_REQUEST) {
                /*
                 * This is either a further set-of-prompts packet
                 * in keyboard-interactive authentication, or it's
                 * the same one and we came back here with `gotit'
                 * set. In the former case, we must reset the
                 * curr_prompt variable.
                 */
                if (!s->gotit)
                    s->curr_prompt = 0;
            } else if (ssh->pktin.type != SSH2_MSG_USERAUTH_FAILURE) {
                bombout(("Strange packet received during authentication: type %d",
                         ssh->pktin.type));
                crReturnV;
            }

            s->gotit = FALSE;

            /*
             * OK, we're now sitting on a USERAUTH_FAILURE message, so
             * we can look at the string in it and know what we can
             * helpfully try next.
             */
            if (ssh->pktin.type == SSH2_MSG_USERAUTH_FAILURE) {
                char *methods;
                int methlen;
                ssh2_pkt_getstring(ssh, &methods, &methlen);
                s->kbd_inter_running = FALSE;
                if (!ssh2_pkt_getbool(ssh)) {
                    /*
                     * We have received an unequivocal Access
                     * Denied. This can translate to a variety of
                     * messages:
                     * 
                     *  - if we'd just tried "none" authentication,
                     *    it's not worth printing anything at all
                     * 
                     *  - if we'd just tried a public key _offer_,
                     *    the message should be "Server refused our
                     *    key" (or no message at all if the key
                     *    came from Pageant)
                     * 
                     *  - if we'd just tried anything else, the
                     *    message really should be "Access denied".
                     * 
                     * Additionally, if we'd just tried password
                     * authentication, we should break out of this
                     * whole loop so as to go back to the username
                     * prompt.
                     */
                    if (s->type == AUTH_TYPE_NONE) {
                        /* do nothing */
                    } else if (s->type == AUTH_TYPE_PUBLICKEY_OFFER_LOUD ||
                               s->type == AUTH_TYPE_PUBLICKEY_OFFER_QUIET) {
                        if (s->type == AUTH_TYPE_PUBLICKEY_OFFER_LOUD)
                            c_write_str(ssh, "Server refused our key\r\n");
                        logevent("Server refused public key");
                    } else if (s->type==AUTH_TYPE_KEYBOARD_INTERACTIVE_QUIET) {
                        /* server declined keyboard-interactive; ignore */
                    } else {
                        c_write_str(ssh, "Access denied\r\n");
                        logevent("Access denied");
                        if (s->type == AUTH_TYPE_PASSWORD) {
                            s->we_are_in = FALSE;
                            break;
                        }
                    }
                } else {
                    c_write_str(ssh, "Further authentication required\r\n");
                    logevent("Further authentication required");
                }

                s->can_pubkey =
                    in_commasep_string("publickey", methods, methlen);
                s->can_passwd =
                    in_commasep_string("password", methods, methlen);
                s->can_keyb_inter = cfg.try_ki_auth &&
                    in_commasep_string("keyboard-interactive", methods, methlen);
            }

            s->method = 0;
            ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;

            /*
             * Most password/passphrase prompts will be
             * non-echoing, so we set this to 0 by default.
             * Exception is that some keyboard-interactive prompts
             * can be echoing, in which case we'll set this to 1.
             */
            s->echo = 0;

            if (!s->method && s->can_pubkey &&
                agent_exists() && !s->tried_agent) {
                /*
                 * Attempt public-key authentication using Pageant.
                 */
                void *r;
                s->authed = FALSE;

                ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;
                ssh->pkt_ctx |= SSH2_PKTCTX_PUBLICKEY;

                s->tried_agent = TRUE;

                logevent("Pageant is running. Requesting keys.");

                /* Request the keys held by the agent. */
                PUT_32BIT(s->request, 1);
                s->request[4] = SSH2_AGENTC_REQUEST_IDENTITIES;
                agent_query(s->request, 5, &r, &s->responselen);
                s->response = (unsigned char *) r;
                if (s->response && s->responselen >= 5 &&
                    s->response[4] == SSH2_AGENT_IDENTITIES_ANSWER) {
                    s->p = s->response + 5;
                    s->nkeys = GET_32BIT(s->p);
                    s->p += 4;
                    {
                        char buf[64];
                        sprintf(buf, "Pageant has %d SSH2 keys", s->nkeys);
                        logevent(buf);
                    }
                    for (s->keyi = 0; s->keyi < s->nkeys; s->keyi++) {
                        void *vret;

                        {
                            char buf[64];
                            sprintf(buf, "Trying Pageant key #%d", s->keyi);
                            logevent(buf);
                        }
                        s->pklen = GET_32BIT(s->p);
                        s->p += 4;
                        if (s->publickey_blob &&
                            s->pklen == s->publickey_bloblen &&
                            !memcmp(s->p, s->publickey_blob,
                                    s->publickey_bloblen)) {
                            logevent("This key matches configured key file");
                            s->tried_pubkey_config = 1;
                        }
                        s->pkblob = s->p;
                        s->p += s->pklen;
                        s->alglen = GET_32BIT(s->pkblob);
                        s->alg = s->pkblob + 4;
                        s->commentlen = GET_32BIT(s->p);
                        s->p += 4;
                        s->commentp = s->p;
                        s->p += s->commentlen;
                        ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
                        ssh2_pkt_addstring(ssh, s->username);
                        ssh2_pkt_addstring(ssh, "ssh-connection");      /* service requested */
                        ssh2_pkt_addstring(ssh, "publickey");   /* method */
                        ssh2_pkt_addbool(ssh, FALSE);   /* no signature included */
                        ssh2_pkt_addstring_start(ssh);
                        ssh2_pkt_addstring_data(ssh, s->alg, s->alglen);
                        ssh2_pkt_addstring_start(ssh);
                        ssh2_pkt_addstring_data(ssh, s->pkblob, s->pklen);
                        ssh2_pkt_send(ssh);

                        crWaitUntilV(ispkt);
                        if (ssh->pktin.type != SSH2_MSG_USERAUTH_PK_OK) {
                            logevent("Key refused");
                            continue;
                        }

                        if (flags & FLAG_VERBOSE) {
                            c_write_str(ssh, "Authenticating with "
                                        "public key \"");
                            c_write(ssh, s->commentp, s->commentlen);
                            c_write_str(ssh, "\" from agent\r\n");
                        }

                        /*
                         * Server is willing to accept the key.
                         * Construct a SIGN_REQUEST.
                         */
                        ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
                        ssh2_pkt_addstring(ssh, s->username);
                        ssh2_pkt_addstring(ssh, "ssh-connection");      /* service requested */
                        ssh2_pkt_addstring(ssh, "publickey");   /* method */
                        ssh2_pkt_addbool(ssh, TRUE);
                        ssh2_pkt_addstring_start(ssh);
                        ssh2_pkt_addstring_data(ssh, s->alg, s->alglen);
                        ssh2_pkt_addstring_start(ssh);
                        ssh2_pkt_addstring_data(ssh, s->pkblob, s->pklen);

                        s->siglen = ssh->pktout.length - 5 + 4 + 20;
                        s->len = 1;       /* message type */
                        s->len += 4 + s->pklen; /* key blob */
                        s->len += 4 + s->siglen;        /* data to sign */
                        s->len += 4;      /* flags */
                        s->agentreq = smalloc(4 + s->len);
                        PUT_32BIT(s->agentreq, s->len);
                        s->q = s->agentreq + 4;
                        *s->q++ = SSH2_AGENTC_SIGN_REQUEST;
                        PUT_32BIT(s->q, s->pklen);
                        s->q += 4;
                        memcpy(s->q, s->pkblob, s->pklen);
                        s->q += s->pklen;
                        PUT_32BIT(s->q, s->siglen);
                        s->q += 4;
                        /* Now the data to be signed... */
                        PUT_32BIT(s->q, 20);
                        s->q += 4;
                        memcpy(s->q, ssh->v2_session_id, 20);
                        s->q += 20;
                        memcpy(s->q, ssh->pktout.data + 5,
                               ssh->pktout.length - 5);
                        s->q += ssh->pktout.length - 5;
                        /* And finally the (zero) flags word. */
                        PUT_32BIT(s->q, 0);
                        agent_query(s->agentreq, s->len + 4, &vret, &s->retlen);
                        s->ret = vret;
                        sfree(s->agentreq);
                        if (s->ret) {
                            if (s->ret[4] == SSH2_AGENT_SIGN_RESPONSE) {
                                logevent("Sending Pageant's response");
                                ssh2_add_sigblob(ssh, s->pkblob, s->pklen,
                                                 s->ret + 9,
                                                 GET_32BIT(s->ret + 5));
                                ssh2_pkt_send(ssh);
                                s->authed = TRUE;
                                break;
                            } else {
                                logevent
                                    ("Pageant failed to answer challenge");
                                sfree(s->ret);
                            }
                        }
                    }
                    if (s->authed)
                        continue;
                }
            }

            if (!s->method && s->can_pubkey && s->publickey_blob
                && !s->tried_pubkey_config) {
                unsigned char *pub_blob;
                char *algorithm, *comment;
                int pub_blob_len;

                s->tried_pubkey_config = TRUE;

                ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;
                ssh->pkt_ctx |= SSH2_PKTCTX_PUBLICKEY;

                /*
                 * Try the public key supplied in the configuration.
                 *
                 * First, offer the public blob to see if the server is
                 * willing to accept it.
                 */
                pub_blob = ssh2_userkey_loadpub(cfg.keyfile, &algorithm,
                                                &pub_blob_len);
                if (pub_blob) {
                    ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
                    ssh2_pkt_addstring(ssh, s->username);
                    ssh2_pkt_addstring(ssh, "ssh-connection");  /* service requested */
                    ssh2_pkt_addstring(ssh, "publickey");       /* method */
                    ssh2_pkt_addbool(ssh, FALSE);       /* no signature included */
                    ssh2_pkt_addstring(ssh, algorithm);
                    ssh2_pkt_addstring_start(ssh);
                    ssh2_pkt_addstring_data(ssh, pub_blob, pub_blob_len);
                    ssh2_pkt_send(ssh);
                    logevent("Offered public key");     /* FIXME */

                    crWaitUntilV(ispkt);
                    if (ssh->pktin.type != SSH2_MSG_USERAUTH_PK_OK) {
                        s->gotit = TRUE;
                        s->type = AUTH_TYPE_PUBLICKEY_OFFER_LOUD;
                        continue;      /* key refused; give up on it */
                    }

                    logevent("Offer of public key accepted");
                    /*
                     * Actually attempt a serious authentication using
                     * the key.
                     */
                    if (ssh2_userkey_encrypted(cfg.keyfile, &comment)) {
                        sprintf(s->pwprompt,
                                "Passphrase for key \"%.100s\": ",
                                comment);
                        s->need_pw = TRUE;
                    } else {
                        s->need_pw = FALSE;
                    }
                    c_write_str(ssh, "Authenticating with public key \"");
                    c_write_str(ssh, comment);
                    c_write_str(ssh, "\"\r\n");
                    s->method = AUTH_PUBLICKEY_FILE;
                }
            }

            if (!s->method && s->can_keyb_inter && !s->tried_keyb_inter) {
                s->method = AUTH_KEYBOARD_INTERACTIVE;
                s->type = AUTH_TYPE_KEYBOARD_INTERACTIVE;
                s->tried_keyb_inter = TRUE;

                ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;
                ssh->pkt_ctx |= SSH2_PKTCTX_KBDINTER;

                ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
                ssh2_pkt_addstring(ssh, s->username);
                ssh2_pkt_addstring(ssh, "ssh-connection");      /* service requested */
                ssh2_pkt_addstring(ssh, "keyboard-interactive");        /* method */
                ssh2_pkt_addstring(ssh, ""); /* lang */
                ssh2_pkt_addstring(ssh, "");
                ssh2_pkt_send(ssh);

                crWaitUntilV(ispkt);
                if (ssh->pktin.type != SSH2_MSG_USERAUTH_INFO_REQUEST) {
                    if (ssh->pktin.type == SSH2_MSG_USERAUTH_FAILURE)
                        s->gotit = TRUE;
                    logevent("Keyboard-interactive authentication refused");
                    s->type = AUTH_TYPE_KEYBOARD_INTERACTIVE_QUIET;
                    continue;
                }

                s->kbd_inter_running = TRUE;
                s->curr_prompt = 0;
            }

            if (s->kbd_inter_running) {
                s->method = AUTH_KEYBOARD_INTERACTIVE;
                s->type = AUTH_TYPE_KEYBOARD_INTERACTIVE;
                s->tried_keyb_inter = TRUE;

                ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;
                ssh->pkt_ctx |= SSH2_PKTCTX_KBDINTER;

                if (s->curr_prompt == 0) {
                    /*
                     * We've got a fresh USERAUTH_INFO_REQUEST.
                     * Display header data, and start going through
                     * the prompts.
                     */
                    char *name, *inst, *lang;
                    int name_len, inst_len, lang_len;

                    ssh2_pkt_getstring(ssh, &name, &name_len);
                    ssh2_pkt_getstring(ssh, &inst, &inst_len);
                    ssh2_pkt_getstring(ssh, &lang, &lang_len);
                    if (name_len > 0) {
                        c_write_untrusted(ssh, name, name_len);
                        c_write_str(ssh, "\r\n");
                    }
                    if (inst_len > 0) {
                        c_write_untrusted(ssh, inst, inst_len);
                        c_write_str(ssh, "\r\n");
                    }
                    s->num_prompts = ssh2_pkt_getuint32(ssh);
                }

                /*
                 * If there are prompts remaining in the packet,
                 * display one and get a response.
                 */
                if (s->curr_prompt < s->num_prompts) {
                    char *prompt;
                    int prompt_len;

                    ssh2_pkt_getstring(ssh, &prompt, &prompt_len);
                    if (prompt_len > 0) {
                        strncpy(s->pwprompt, prompt, sizeof(s->pwprompt));
                        s->pwprompt[prompt_len < sizeof(s->pwprompt) ?
                                    prompt_len : sizeof(s->pwprompt)-1] = '\0';
                    } else {
                        strcpy(s->pwprompt,
                               "<server failed to send prompt>: ");
                    }
                    s->echo = ssh2_pkt_getbool(ssh);
                    s->need_pw = TRUE;
                } else
                    s->need_pw = FALSE;
            }

            if (!s->method && s->can_passwd) {
                s->method = AUTH_PASSWORD;
                ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;
                ssh->pkt_ctx |= SSH2_PKTCTX_PASSWORD;
                sprintf(s->pwprompt, "%.90s@%.90s's password: ", s->username,
                        ssh->savedhost);
                s->need_pw = TRUE;
            }

            if (s->need_pw) {
                if (ssh_get_line) {
                    if (!ssh_get_line(s->pwprompt, s->password,
                                      sizeof(s->password), TRUE)) {
                        /*
                         * get_line failed to get a password (for
                         * example because one was supplied on the
                         * command line which has already failed to
                         * work). Terminate.
                         */
                        ssh2_pkt_init(ssh, SSH2_MSG_DISCONNECT);
                        ssh2_pkt_adduint32(ssh,SSH2_DISCONNECT_BY_APPLICATION);
                        ssh2_pkt_addstring(ssh, "No more passwords available"
                                           " to try");
                        ssh2_pkt_addstring(ssh, "en");  /* language tag */
                        ssh2_pkt_send(ssh);
                        logevent("Unable to authenticate");
                        connection_fatal("Unable to authenticate");
                        ssh->state = SSH_STATE_CLOSED;
                        crReturnV;
                    }
                } else {
                    int ret;           /* need not be saved across crReturn */
                    c_write_untrusted(ssh, s->pwprompt, strlen(s->pwprompt));
                    ssh->send_ok = 1;

                    setup_userpass_input(ssh, s->password,
                                         sizeof(s->password), s->echo);
                    do {
                        crWaitUntilV(!ispkt);
                        ret = process_userpass_input(ssh, in, inlen);
                    } while (ret == 0);
                    if (ret < 0)
                        cleanup_exit(0);
                    c_write_str(ssh, "\r\n");
                }
            }

            if (s->method == AUTH_PUBLICKEY_FILE) {
                /*
                 * We have our passphrase. Now try the actual authentication.
                 */
                struct ssh2_userkey *key;

                key = ssh2_load_userkey(cfg.keyfile, s->password);
                if (key == SSH2_WRONG_PASSPHRASE || key == NULL) {
                    if (key == SSH2_WRONG_PASSPHRASE) {
                        c_write_str(ssh, "Wrong passphrase\r\n");
                        s->tried_pubkey_config = FALSE;
                    } else {
                        c_write_str(ssh, "Unable to load private key\r\n");
                        s->tried_pubkey_config = TRUE;
                    }
                    /* Send a spurious AUTH_NONE to return to the top. */
                    ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
                    ssh2_pkt_addstring(ssh, s->username);
                    ssh2_pkt_addstring(ssh, "ssh-connection");  /* service requested */
                    ssh2_pkt_addstring(ssh, "none");    /* method */
                    ssh2_pkt_send(ssh);
                    s->type = AUTH_TYPE_NONE;
                } else {
                    unsigned char *pkblob, *sigblob, *sigdata;
                    int pkblob_len, sigblob_len, sigdata_len;

                    /*
                     * We have loaded the private key and the server
                     * has announced that it's willing to accept it.
                     * Hallelujah. Generate a signature and send it.
                     */
                    ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
                    ssh2_pkt_addstring(ssh, s->username);
                    ssh2_pkt_addstring(ssh, "ssh-connection");  /* service requested */
                    ssh2_pkt_addstring(ssh, "publickey");       /* method */
                    ssh2_pkt_addbool(ssh, TRUE);
                    ssh2_pkt_addstring(ssh, key->alg->name);
                    pkblob = key->alg->public_blob(key->data, &pkblob_len);
                    ssh2_pkt_addstring_start(ssh);
                    ssh2_pkt_addstring_data(ssh, pkblob, pkblob_len);

                    /*
                     * The data to be signed is:
                     *
                     *   string  session-id
                     *
                     * followed by everything so far placed in the
                     * outgoing packet.
                     */
                    sigdata_len = ssh->pktout.length - 5 + 4 + 20;
                    sigdata = smalloc(sigdata_len);
                    PUT_32BIT(sigdata, 20);
                    memcpy(sigdata + 4, ssh->v2_session_id, 20);
                    memcpy(sigdata + 24, ssh->pktout.data + 5,
                           ssh->pktout.length - 5);
                    sigblob = key->alg->sign(key->data, sigdata,
                                             sigdata_len, &sigblob_len);
                    ssh2_add_sigblob(ssh, pkblob, pkblob_len,
                                     sigblob, sigblob_len);
                    sfree(pkblob);
                    sfree(sigblob);
                    sfree(sigdata);

                    ssh2_pkt_send(ssh);
                    s->type = AUTH_TYPE_PUBLICKEY;
                }
            } else if (s->method == AUTH_PASSWORD) {
                /*
                 * We send the password packet lumped tightly together with
                 * an SSH_MSG_IGNORE packet. The IGNORE packet contains a
                 * string long enough to make the total length of the two
                 * packets constant. This should ensure that a passive
                 * listener doing traffic analyis can't work out the length
                 * of the password.
                 *
                 * For this to work, we need an assumption about the
                 * maximum length of the password packet. I think 256 is
                 * pretty conservative. Anyone using a password longer than
                 * that probably doesn't have much to worry about from
                 * people who find out how long their password is!
                 */
                ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
                ssh2_pkt_addstring(ssh, s->username);
                ssh2_pkt_addstring(ssh, "ssh-connection");      /* service requested */
                ssh2_pkt_addstring(ssh, "password");
                ssh2_pkt_addbool(ssh, FALSE);
                ssh2_pkt_addstring(ssh, s->password);
                ssh2_pkt_defer(ssh);
                /*
                 * We'll include a string that's an exact multiple of the
                 * cipher block size. If the cipher is NULL for some
                 * reason, we don't do this trick at all because we gain
                 * nothing by it.
                 */
                if (ssh->cscipher) {
                    int stringlen, i;

                    stringlen = (256 - ssh->deferred_len);
                    stringlen += ssh->cscipher->blksize - 1;
                    stringlen -= (stringlen % ssh->cscipher->blksize);
                    if (ssh->cscomp) {
                        /*
                         * Temporarily disable actual compression,
                         * so we can guarantee to get this string
                         * exactly the length we want it. The
                         * compression-disabling routine should
                         * return an integer indicating how many
                         * bytes we should adjust our string length
                         * by.
                         */
                        stringlen -= ssh->cscomp->disable_compression();
                    }
                    ssh2_pkt_init(ssh, SSH2_MSG_IGNORE);
                    ssh2_pkt_addstring_start(ssh);
                    for (i = 0; i < stringlen; i++) {
                        char c = (char) random_byte();
                        ssh2_pkt_addstring_data(ssh, &c, 1);
                    }
                    ssh2_pkt_defer(ssh);
                }
                ssh_pkt_defersend(ssh);
                logevent("Sent password");
                s->type = AUTH_TYPE_PASSWORD;
            } else if (s->method == AUTH_KEYBOARD_INTERACTIVE) {
                if (s->curr_prompt == 0) {
                    ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_INFO_RESPONSE);
                    ssh2_pkt_adduint32(ssh, s->num_prompts);
                }
                if (s->need_pw) {      /* only add pw if we just got one! */
                    ssh2_pkt_addstring(ssh, s->password);
                    memset(s->password, 0, sizeof(s->password));
                    s->curr_prompt++;
                }
                if (s->curr_prompt >= s->num_prompts) {
                    ssh2_pkt_send(ssh);
                } else {
                    /*
                     * If there are prompts remaining, we set
                     * `gotit' so that we won't attempt to get
                     * another packet. Then we go back round the
                     * loop and will end up retrieving another
                     * prompt out of the existing packet. Funky or
                     * what?
                     */
                    s->gotit = TRUE;
                }
                s->type = AUTH_TYPE_KEYBOARD_INTERACTIVE;
            } else {
                c_write_str(ssh, "No supported authentication methods"
                            " left to try!\r\n");
                logevent("No supported authentications offered."
                         " Disconnecting");
                ssh2_pkt_init(ssh, SSH2_MSG_DISCONNECT);
                ssh2_pkt_adduint32(ssh, SSH2_DISCONNECT_BY_APPLICATION);
                ssh2_pkt_addstring(ssh, "No supported authentication"
                                   " methods available");
                ssh2_pkt_addstring(ssh, "en");  /* language tag */
                ssh2_pkt_send(ssh);
                ssh->state = SSH_STATE_CLOSED;
                crReturnV;
            }
        }
    } while (!s->we_are_in);

    /*
     * Now we're authenticated for the connection protocol. The
     * connection protocol will automatically have started at this
     * point; there's no need to send SERVICE_REQUEST.
     */

    /*
     * So now create a channel with a session in it.
     */
    ssh->channels = newtree234(ssh_channelcmp);
    ssh->mainchan = smalloc(sizeof(struct ssh_channel));
    ssh->mainchan->ssh = ssh;
    ssh->mainchan->localid = alloc_channel_id(ssh);
    ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_OPEN);
    ssh2_pkt_addstring(ssh, "session");
    ssh2_pkt_adduint32(ssh, ssh->mainchan->localid);
    ssh->mainchan->v.v2.locwindow = OUR_V2_WINSIZE;
    ssh2_pkt_adduint32(ssh, ssh->mainchan->v.v2.locwindow);/* our window size */
    ssh2_pkt_adduint32(ssh, 0x4000UL);      /* our max pkt size */
    ssh2_pkt_send(ssh);
    crWaitUntilV(ispkt);
    if (ssh->pktin.type != SSH2_MSG_CHANNEL_OPEN_CONFIRMATION) {
        bombout(("Server refused to open a session"));
        crReturnV;
        /* FIXME: error data comes back in FAILURE packet */
    }
    if (ssh2_pkt_getuint32(ssh) != ssh->mainchan->localid) {
        bombout(("Server's channel confirmation cited wrong channel"));
        crReturnV;
    }
    ssh->mainchan->remoteid = ssh2_pkt_getuint32(ssh);
    ssh->mainchan->type = CHAN_MAINSESSION;
    ssh->mainchan->closes = 0;
    ssh->mainchan->v.v2.remwindow = ssh2_pkt_getuint32(ssh);
    ssh->mainchan->v.v2.remmaxpkt = ssh2_pkt_getuint32(ssh);
    bufchain_init(&ssh->mainchan->v.v2.outbuffer);
    add234(ssh->channels, ssh->mainchan);
    logevent("Opened channel for session");

    /*
     * Potentially enable X11 forwarding.
     */
    if (cfg.x11_forward) {
        char proto[20], data[64];
        logevent("Requesting X11 forwarding");
        x11_invent_auth(proto, sizeof(proto), data, sizeof(data));
        ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
        ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);
        ssh2_pkt_addstring(ssh, "x11-req");
        ssh2_pkt_addbool(ssh, 1);              /* want reply */
        ssh2_pkt_addbool(ssh, 0);              /* many connections */
        ssh2_pkt_addstring(ssh, proto);
        ssh2_pkt_addstring(ssh, data);
        ssh2_pkt_adduint32(ssh, 0);            /* screen number */
        ssh2_pkt_send(ssh);

        do {
            crWaitUntilV(ispkt);
            if (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST) {
                unsigned i = ssh2_pkt_getuint32(ssh);
                struct ssh_channel *c;
                c = find234(ssh->channels, &i, ssh_channelfind);
                if (!c)
                    continue;          /* nonexistent channel */
                c->v.v2.remwindow += ssh2_pkt_getuint32(ssh);
            }
        } while (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST);

        if (ssh->pktin.type != SSH2_MSG_CHANNEL_SUCCESS) {
            if (ssh->pktin.type != SSH2_MSG_CHANNEL_FAILURE) {
                bombout(("Unexpected response to X11 forwarding request:"
                         " packet type %d", ssh->pktin.type));
                crReturnV;
            }
            logevent("X11 forwarding refused");
        } else {
            logevent("X11 forwarding enabled");
            ssh->X11_fwd_enabled = TRUE;
        }
    }

    /*
     * Enable port forwardings.
     */
    {
        char type;
        int n;
        int sport,dport,sserv,dserv;
        char sports[256], dports[256], host[256];
        char buf[1024];
        struct servent *se;

        ssh->rportfwds = newtree234(ssh_rportcmp_ssh2);
        /* Add port forwardings. */
        ssh->portfwd_strptr = cfg.portfwd;
        while (*ssh->portfwd_strptr) {
            type = *ssh->portfwd_strptr++;
            n = 0;
            while (*ssh->portfwd_strptr && *ssh->portfwd_strptr != '\t')
                sports[n++] = *ssh->portfwd_strptr++;
            sports[n] = 0;
            if (*ssh->portfwd_strptr == '\t')
                ssh->portfwd_strptr++;
            n = 0;
            while (*ssh->portfwd_strptr && *ssh->portfwd_strptr != ':')
                host[n++] = *ssh->portfwd_strptr++;
            host[n] = 0;
            if (*ssh->portfwd_strptr == ':')
                ssh->portfwd_strptr++;
            n = 0;
            while (*ssh->portfwd_strptr)
                dports[n++] = *ssh->portfwd_strptr++;
            dports[n] = 0;
            ssh->portfwd_strptr++;
            dport = atoi(dports);
            dserv = 0;
            if (dport == 0) {
                dserv = 1;
                se = getservbyname(dports, NULL);
                if (se != NULL) {
                    dport = ntohs(se->s_port);
                } else {
                    sprintf(buf,
                            "Service lookup failed for destination port \"%s\"",
                            dports);
                    logevent(buf);
                }
            }
            sport = atoi(sports);
            sserv = 0;
            if (sport == 0) {
                sserv = 1;
                se = getservbyname(sports, NULL);
                if (se != NULL) {
                    sport = ntohs(se->s_port);
                } else {
                    sprintf(buf,
                            "Service lookup failed for source port \"%s\"",
                            sports);
                    logevent(buf);
                }
            }
            if (sport && dport) {
                if (type == 'L') {
                    pfd_addforward(host, dport, sport);
                    sprintf(buf, "Local port %.*s%.*s%d%.*s forwarding to"
                            " %s:%.*s%.*s%d%.*s",
                            sserv ? strlen(sports) : 0, sports,
                            sserv, "(", sport, sserv, ")",
                            host,
                            dserv ? strlen(dports) : 0, dports,
                            dserv, "(", dport, dserv, ")");
                    logevent(buf);
                } else {
                    struct ssh_rportfwd *pf;
                    pf = smalloc(sizeof(*pf));
                    strcpy(pf->dhost, host);
                    pf->dport = dport;
                    pf->sport = sport;
                    if (add234(ssh->rportfwds, pf) != pf) {
                        sprintf(buf, 
                                "Duplicate remote port forwarding to %s:%d",
                                host, dport);
                        logevent(buf);
                        sfree(pf);
                    } else {
                        sprintf(buf, "Requesting remote port %.*s%.*s%d%.*s"
                                " forward to %s:%.*s%.*s%d%.*s",
                            sserv ? strlen(sports) : 0, sports,
                            sserv, "(", sport, sserv, ")",
                            host,
                            dserv ? strlen(dports) : 0, dports,
                            dserv, "(", dport, dserv, ")");
                        logevent(buf);
                        ssh2_pkt_init(ssh, SSH2_MSG_GLOBAL_REQUEST);
                        ssh2_pkt_addstring(ssh, "tcpip-forward");
                        ssh2_pkt_addbool(ssh, 1);/* want reply */
                        if (cfg.rport_acceptall)
                            ssh2_pkt_addstring(ssh, "0.0.0.0");
                        else
                            ssh2_pkt_addstring(ssh, "127.0.0.1");
                        ssh2_pkt_adduint32(ssh, sport);
                        ssh2_pkt_send(ssh);

                        do {
                            crWaitUntilV(ispkt);
                            if (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST) {
                                unsigned i = ssh2_pkt_getuint32(ssh);
                                struct ssh_channel *c;
                                c = find234(ssh->channels, &i, ssh_channelfind);
                                if (!c)
                                    continue;/* nonexistent channel */
                                c->v.v2.remwindow += ssh2_pkt_getuint32(ssh);
                            }
                        } while (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST);

                        if (ssh->pktin.type != SSH2_MSG_REQUEST_SUCCESS) {
                            if (ssh->pktin.type != SSH2_MSG_REQUEST_FAILURE) {
                                bombout(("Unexpected response to port "
                                         "forwarding request: packet type %d",
                                         ssh->pktin.type));
                                crReturnV;
                            }
                            logevent("Server refused this port forwarding");
                        } else {
                            logevent("Remote port forwarding enabled");
                        }
                    }
                }
            }
        }
    }

    /*
     * Potentially enable agent forwarding.
     */
    if (cfg.agentfwd && agent_exists()) {
        logevent("Requesting OpenSSH-style agent forwarding");
        ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
        ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);
        ssh2_pkt_addstring(ssh, "auth-agent-req@openssh.com");
        ssh2_pkt_addbool(ssh, 1);              /* want reply */
        ssh2_pkt_send(ssh);

        do {
            crWaitUntilV(ispkt);
            if (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST) {
                unsigned i = ssh2_pkt_getuint32(ssh);
                struct ssh_channel *c;
                c = find234(ssh->channels, &i, ssh_channelfind);
                if (!c)
                    continue;          /* nonexistent channel */
                c->v.v2.remwindow += ssh2_pkt_getuint32(ssh);
            }
        } while (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST);

        if (ssh->pktin.type != SSH2_MSG_CHANNEL_SUCCESS) {
            if (ssh->pktin.type != SSH2_MSG_CHANNEL_FAILURE) {
                bombout(("Unexpected response to agent forwarding request:"
                         " packet type %d", ssh->pktin.type));
                crReturnV;
            }
            logevent("Agent forwarding refused");
        } else {
            logevent("Agent forwarding enabled");
            ssh->agentfwd_enabled = TRUE;
        }
    }

    /*
     * Now allocate a pty for the session.
     */
    if (!cfg.nopty) {
        ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
        ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);       /* recipient channel */
        ssh2_pkt_addstring(ssh, "pty-req");
        ssh2_pkt_addbool(ssh, 1);              /* want reply */
        ssh2_pkt_addstring(ssh, cfg.termtype);
        ssh2_pkt_adduint32(ssh, ssh->term_width);
        ssh2_pkt_adduint32(ssh, ssh->term_height);
        ssh2_pkt_adduint32(ssh, 0);            /* pixel width */
        ssh2_pkt_adduint32(ssh, 0);            /* pixel height */
        ssh2_pkt_addstring_start(ssh);
        ssh2_pkt_addstring_data(ssh, "\0", 1);  /* TTY_OP_END, no special options */
        ssh2_pkt_send(ssh);
        ssh->state = SSH_STATE_INTERMED;

        do {
            crWaitUntilV(ispkt);
            if (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST) {
                unsigned i = ssh2_pkt_getuint32(ssh);
                struct ssh_channel *c;
                c = find234(ssh->channels, &i, ssh_channelfind);
                if (!c)
                    continue;          /* nonexistent channel */
                c->v.v2.remwindow += ssh2_pkt_getuint32(ssh);
            }
        } while (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST);

        if (ssh->pktin.type != SSH2_MSG_CHANNEL_SUCCESS) {
            if (ssh->pktin.type != SSH2_MSG_CHANNEL_FAILURE) {
                bombout(("Unexpected response to pty request:"
                         " packet type %d", ssh->pktin.type));
                crReturnV;
            }
            c_write_str(ssh, "Server refused to allocate pty\r\n");
            ssh->editing = ssh->echoing = 1;
        } else {
            logevent("Allocated pty");
        }
    } else {
        ssh->editing = ssh->echoing = 1;
    }

    /*
     * Start a shell or a remote command. We may have to attempt
     * this twice if the config data has provided a second choice
     * of command.
     */
    while (1) {
        int subsys;
        char *cmd;

        if (ssh->fallback_cmd) {
            subsys = cfg.ssh_subsys2;
            cmd = cfg.remote_cmd_ptr2;
        } else {
            subsys = cfg.ssh_subsys;
            cmd = cfg.remote_cmd_ptr;
        }

        ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
        ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);       /* recipient channel */
        if (subsys) {
            ssh2_pkt_addstring(ssh, "subsystem");
            ssh2_pkt_addbool(ssh, 1);          /* want reply */
            ssh2_pkt_addstring(ssh, cmd);
        } else if (*cmd) {
            ssh2_pkt_addstring(ssh, "exec");
            ssh2_pkt_addbool(ssh, 1);          /* want reply */
            ssh2_pkt_addstring(ssh, cmd);
        } else {
            ssh2_pkt_addstring(ssh, "shell");
            ssh2_pkt_addbool(ssh, 1);          /* want reply */
        }
        ssh2_pkt_send(ssh);
        do {
            crWaitUntilV(ispkt);
            if (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST) {
                unsigned i = ssh2_pkt_getuint32(ssh);
                struct ssh_channel *c;
                c = find234(ssh->channels, &i, ssh_channelfind);
                if (!c)
                    continue;          /* nonexistent channel */
                c->v.v2.remwindow += ssh2_pkt_getuint32(ssh);
            }
        } while (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST);
        if (ssh->pktin.type != SSH2_MSG_CHANNEL_SUCCESS) {
            if (ssh->pktin.type != SSH2_MSG_CHANNEL_FAILURE) {
                bombout(("Unexpected response to shell/command request:"
                         " packet type %d", ssh->pktin.type));
                crReturnV;
            }
            /*
             * We failed to start the command. If this is the
             * fallback command, we really are finished; if it's
             * not, and if the fallback command exists, try falling
             * back to it before complaining.
             */
            if (!ssh->fallback_cmd && cfg.remote_cmd_ptr2 != NULL) {
                logevent("Primary command failed; attempting fallback");
                ssh->fallback_cmd = TRUE;
                continue;
            }
            bombout(("Server refused to start a shell/command"));
            crReturnV;
        } else {
            logevent("Started a shell/command");
        }
        break;
    }

    ssh->state = SSH_STATE_SESSION;
    if (ssh->size_needed)
        ssh_size(ssh, ssh->term_width, ssh->term_height);
    if (ssh->eof_needed)
        ssh_special(ssh, TS_EOF);

    /*
     * Transfer data!
     */
    ldisc_send(NULL, 0, 0);            /* cause ldisc to notice changes */
    ssh->send_ok = 1;
    while (1) {
        crReturnV;
        s->try_send = FALSE;
        if (ispkt) {
            if (ssh->pktin.type == SSH2_MSG_CHANNEL_DATA ||
                ssh->pktin.type == SSH2_MSG_CHANNEL_EXTENDED_DATA) {
                char *data;
                int length;
                unsigned i = ssh2_pkt_getuint32(ssh);
                struct ssh_channel *c;
                c = find234(ssh->channels, &i, ssh_channelfind);
                if (!c)
                    continue;          /* nonexistent channel */
                if (ssh->pktin.type == SSH2_MSG_CHANNEL_EXTENDED_DATA &&
                    ssh2_pkt_getuint32(ssh) != SSH2_EXTENDED_DATA_STDERR)
                    continue;          /* extended but not stderr */
                ssh2_pkt_getstring(ssh, &data, &length);
                if (data) {
                    int bufsize;
                    c->v.v2.locwindow -= length;
                    switch (c->type) {
                      case CHAN_MAINSESSION:
                        bufsize =
                            from_backend(ssh->frontend, ssh->pktin.type ==
                                         SSH2_MSG_CHANNEL_EXTENDED_DATA,
                                         data, length);
                        break;
                      case CHAN_X11:
                        bufsize = x11_send(c->u.x11.s, data, length);
                        break;
                      case CHAN_SOCKDATA:
                        bufsize = pfd_send(c->u.pfd.s, data, length);
                        break;
                      case CHAN_AGENT:
                        while (length > 0) {
                            if (c->u.a.lensofar < 4) {
                                int l = min(4 - c->u.a.lensofar, length);
                                memcpy(c->u.a.msglen + c->u.a.lensofar,
                                       data, l);
                                data += l;
                                length -= l;
                                c->u.a.lensofar += l;
                            }
                            if (c->u.a.lensofar == 4) {
                                c->u.a.totallen =
                                    4 + GET_32BIT(c->u.a.msglen);
                                c->u.a.message = smalloc(c->u.a.totallen);
                                memcpy(c->u.a.message, c->u.a.msglen, 4);
                            }
                            if (c->u.a.lensofar >= 4 && length > 0) {
                                int l =
                                    min(c->u.a.totallen - c->u.a.lensofar,
                                        length);
                                memcpy(c->u.a.message + c->u.a.lensofar,
                                       data, l);
                                data += l;
                                length -= l;
                                c->u.a.lensofar += l;
                            }
                            if (c->u.a.lensofar == c->u.a.totallen) {
                                void *reply, *sentreply;
                                int replylen;
                                agent_query(c->u.a.message,
                                            c->u.a.totallen, &reply,
                                            &replylen);
                                if (reply)
                                    sentreply = reply;
                                else {
                                    /* Fake SSH_AGENT_FAILURE. */
                                    sentreply = "\0\0\0\1\5";
                                    replylen = 5;
                                }
                                ssh2_add_channel_data(c, sentreply, replylen);
                                s->try_send = TRUE;
                                if (reply)
                                    sfree(reply);
                                sfree(c->u.a.message);
                                c->u.a.lensofar = 0;
                            }
                        }
                        bufsize = 0;
                        break;
                    }
                    /*
                     * If we are not buffering too much data,
                     * enlarge the window again at the remote side.
                     */
                    if (bufsize < OUR_V2_WINSIZE)
                        ssh2_set_window(c, OUR_V2_WINSIZE - bufsize);
                }
            } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_EOF) {
                unsigned i = ssh2_pkt_getuint32(ssh);
                struct ssh_channel *c;

                c = find234(ssh->channels, &i, ssh_channelfind);
                if (!c)
                    continue;          /* nonexistent channel */

                if (c->type == CHAN_X11) {
                    /*
                     * Remote EOF on an X11 channel means we should
                     * wrap up and close the channel ourselves.
                     */
                    x11_close(c->u.x11.s);
                    sshfwd_close(c);
                } else if (c->type == CHAN_AGENT) {
                    sshfwd_close(c);
                } else if (c->type == CHAN_SOCKDATA) {
                    pfd_close(c->u.pfd.s);
                    sshfwd_close(c);
                }
            } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_CLOSE) {
                unsigned i = ssh2_pkt_getuint32(ssh);
                struct ssh_channel *c;

                c = find234(ssh->channels, &i, ssh_channelfind);
                if (!c || ((int)c->remoteid) == -1) {
                    bombout(("Received CHANNEL_CLOSE for %s channel %d\n",
                             c ? "half-open" : "nonexistent", i));
                }
                /* Do pre-close processing on the channel. */
                switch (c->type) {
                  case CHAN_MAINSESSION:
                    break;             /* nothing to see here, move along */
                  case CHAN_X11:
                    if (c->u.x11.s != NULL)
                        x11_close(c->u.x11.s);
                    sshfwd_close(c);
                    break;
                  case CHAN_AGENT:
                    sshfwd_close(c);
                    break;
                  case CHAN_SOCKDATA:
                    if (c->u.pfd.s != NULL)
                        pfd_close(c->u.pfd.s);
                    sshfwd_close(c);
                    break;
                }
                if (c->closes == 0) {
                    ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_CLOSE);
                    ssh2_pkt_adduint32(ssh, c->remoteid);
                    ssh2_pkt_send(ssh);
                }
                del234(ssh->channels, c);
                bufchain_clear(&c->v.v2.outbuffer);
                sfree(c);

                /*
                 * See if that was the last channel left open.
                 */
                if (count234(ssh->channels) == 0) {
#if 0
                    /*
                     * We used to send SSH_MSG_DISCONNECT here,
                     * because I'd believed that _every_ conforming
                     * SSH2 connection had to end with a disconnect
                     * being sent by at least one side; apparently
                     * I was wrong and it's perfectly OK to
                     * unceremoniously slam the connection shut
                     * when you're done, and indeed OpenSSH feels
                     * this is more polite than sending a
                     * DISCONNECT. So now we don't.
                     */
                    logevent("All channels closed. Disconnecting");
                    ssh2_pkt_init(ssh, SSH2_MSG_DISCONNECT);
                    ssh2_pkt_adduint32(ssh, SSH2_DISCONNECT_BY_APPLICATION);
                    ssh2_pkt_addstring(ssh, "All open channels closed");
                    ssh2_pkt_addstring(ssh, "en");      /* language tag */
                    ssh2_pkt_send(ssh);
#endif
                    ssh->state = SSH_STATE_CLOSED;
                    crReturnV;
                }
                continue;              /* remote sends close; ignore (FIXME) */
            } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST) {
                unsigned i = ssh2_pkt_getuint32(ssh);
                struct ssh_channel *c;
                c = find234(ssh->channels, &i, ssh_channelfind);
                if (!c)
                    continue;          /* nonexistent channel */
                c->v.v2.remwindow += ssh2_pkt_getuint32(ssh);
                s->try_send = TRUE;
            } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_OPEN_CONFIRMATION) {
                unsigned i = ssh2_pkt_getuint32(ssh);
                struct ssh_channel *c;
                c = find234(ssh->channels, &i, ssh_channelfind);
                if (!c)
                    continue;          /* nonexistent channel */
                if (c->type != CHAN_SOCKDATA_DORMANT)
                    continue;          /* dunno why they're confirming this */
                c->remoteid = ssh2_pkt_getuint32(ssh);
                c->type = CHAN_SOCKDATA;
                c->v.v2.remwindow = ssh2_pkt_getuint32(ssh);
                c->v.v2.remmaxpkt = ssh2_pkt_getuint32(ssh);
                if (c->u.pfd.s)
                    pfd_confirm(c->u.pfd.s);
                if (c->closes) {
                    /*
                     * We have a pending close on this channel,
                     * which we decided on before the server acked
                     * the channel open. So now we know the
                     * remoteid, we can close it again.
                     */
                    ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_CLOSE);
                    ssh2_pkt_adduint32(ssh, c->remoteid);
                    ssh2_pkt_send(ssh);
                }
            } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_OPEN_FAILURE) {
                unsigned i = ssh2_pkt_getuint32(ssh);
                struct ssh_channel *c;
                c = find234(ssh->channels, &i, ssh_channelfind);
                if (!c)
                    continue;          /* nonexistent channel */
                if (c->type != CHAN_SOCKDATA_DORMANT)
                    continue;          /* dunno why they're failing this */

                logevent("Forwarded connection refused by server");

                pfd_close(c->u.pfd.s);

                del234(ssh->channels, c);
                sfree(c);
            } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_REQUEST) {
                unsigned localid;
                char *type;
                int typelen, want_reply;
                struct ssh_channel *c;

                localid = ssh2_pkt_getuint32(ssh);
                ssh2_pkt_getstring(ssh, &type, &typelen);
                want_reply = ssh2_pkt_getbool(ssh);

                /*
                 * First, check that the channel exists. Otherwise,
                 * we can instantly disconnect with a rude message.
                 */
                c = find234(ssh->channels, &localid, ssh_channelfind);
                if (!c) {
                    char buf[80];
                    sprintf(buf, "Received channel request for nonexistent"
                            " channel %d", localid);
                    logevent(buf);
                    ssh2_pkt_init(ssh, SSH2_MSG_DISCONNECT);
                    ssh2_pkt_adduint32(ssh, SSH2_DISCONNECT_BY_APPLICATION);
                    ssh2_pkt_addstring(ssh, buf);
                    ssh2_pkt_addstring(ssh, "en");      /* language tag */
                    ssh2_pkt_send(ssh);
                    connection_fatal("%s", buf);
                    ssh->state = SSH_STATE_CLOSED;
                    crReturnV;
                }

                /*
                 * Having got the channel number, we now look at
                 * the request type string to see if it's something
                 * we recognise.
                 */
                if (typelen == 11 && !memcmp(type, "exit-status", 11) &&
                    c == ssh->mainchan) {
                    /* We recognise "exit-status" on the primary channel. */
                    char buf[100];
                    ssh->exitcode = ssh2_pkt_getuint32(ssh);
                    sprintf(buf, "Server sent command exit status %d",
                            ssh->exitcode);
                    logevent(buf);
                    if (want_reply) {
                        ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_SUCCESS);
                        ssh2_pkt_adduint32(ssh, c->remoteid);
                        ssh2_pkt_send(ssh);
                    }
                } else {
                    /*
                     * This is a channel request we don't know
                     * about, so we now either ignore the request
                     * or respond with CHANNEL_FAILURE, depending
                     * on want_reply.
                     */
                    if (want_reply) {
                        ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_FAILURE);
                        ssh2_pkt_adduint32(ssh, c->remoteid);
                        ssh2_pkt_send(ssh);
                    }
                }
            } else if (ssh->pktin.type == SSH2_MSG_GLOBAL_REQUEST) {
                char *type;
                int typelen, want_reply;

                ssh2_pkt_getstring(ssh, &type, &typelen);
                want_reply = ssh2_pkt_getbool(ssh);

                /*
                 * We currently don't support any global requests
                 * at all, so we either ignore the request or
                 * respond with REQUEST_FAILURE, depending on
                 * want_reply.
                 */
                if (want_reply) {
                    ssh2_pkt_init(ssh, SSH2_MSG_REQUEST_FAILURE);
                    ssh2_pkt_send(ssh);
                }
            } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_OPEN) {
                char *type;
                int typelen;
                char *error = NULL;
                struct ssh_channel *c;
                unsigned remid, winsize, pktsize;
                ssh2_pkt_getstring(ssh, &type, &typelen);
                c = smalloc(sizeof(struct ssh_channel));
                c->ssh = ssh;

                remid = ssh2_pkt_getuint32(ssh);
                winsize = ssh2_pkt_getuint32(ssh);
                pktsize = ssh2_pkt_getuint32(ssh);

                if (typelen == 3 && !memcmp(type, "x11", 3)) {
                    if (!ssh->X11_fwd_enabled)
                        error = "X11 forwarding is not enabled";
                    else if (x11_init(&c->u.x11.s, cfg.x11_display, c) !=
                             NULL) {
                        error = "Unable to open an X11 connection";
                    } else {
                        c->type = CHAN_X11;
                    }
                } else if (typelen == 15 &&
                           !memcmp(type, "forwarded-tcpip", 15)) {
                    struct ssh_rportfwd pf, *realpf;
                    char *dummy;
                    int dummylen;
                    ssh2_pkt_getstring(ssh, &dummy, &dummylen);/* skip address */
                    pf.sport = ssh2_pkt_getuint32(ssh);
                    realpf = find234(ssh->rportfwds, &pf, NULL);
                    if (realpf == NULL) {
                        error = "Remote port is not recognised";
                    } else {
                        char *e = pfd_newconnect(&c->u.pfd.s, realpf->dhost,
                                                 realpf->dport, c);
                        char buf[1024];
                        sprintf(buf, "Received remote port open request for %s:%d",
                                realpf->dhost, realpf->dport);
                        logevent(buf);
                        if (e != NULL) {
                            sprintf(buf, "Port open failed: %s", e);
                            logevent(buf);
                            error = "Port open failed";
                        } else {
                            logevent("Forwarded port opened successfully");
                            c->type = CHAN_SOCKDATA;
                        }
                    }
                } else if (typelen == 22 &&
                           !memcmp(type, "auth-agent@openssh.com", 3)) {
                    if (!ssh->agentfwd_enabled)
                        error = "Agent forwarding is not enabled";
                    else {
                        c->type = CHAN_AGENT;   /* identify channel type */
                        c->u.a.lensofar = 0;
                    }
                } else {
                    error = "Unsupported channel type requested";
                }

                c->remoteid = remid;
                if (error) {
                    ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_OPEN_FAILURE);
                    ssh2_pkt_adduint32(ssh, c->remoteid);
                    ssh2_pkt_adduint32(ssh, SSH2_OPEN_CONNECT_FAILED);
                    ssh2_pkt_addstring(ssh, error);
                    ssh2_pkt_addstring(ssh, "en");      /* language tag */
                    ssh2_pkt_send(ssh);
                    sfree(c);
                } else {
                    c->localid = alloc_channel_id(ssh);
                    c->closes = 0;
                    c->v.v2.locwindow = OUR_V2_WINSIZE;
                    c->v.v2.remwindow = winsize;
                    c->v.v2.remmaxpkt = pktsize;
                    bufchain_init(&c->v.v2.outbuffer);
                    add234(ssh->channels, c);
                    ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_OPEN_CONFIRMATION);
                    ssh2_pkt_adduint32(ssh, c->remoteid);
                    ssh2_pkt_adduint32(ssh, c->localid);
                    ssh2_pkt_adduint32(ssh, c->v.v2.locwindow);
                    ssh2_pkt_adduint32(ssh, 0x4000UL);  /* our max pkt size */
                    ssh2_pkt_send(ssh);
                }
            } else {
                bombout(("Strange packet received: type %d", ssh->pktin.type));
                crReturnV;
            }
        } else {
            /*
             * We have spare data. Add it to the channel buffer.
             */
            ssh2_add_channel_data(ssh->mainchan, in, inlen);
            s->try_send = TRUE;
        }
        if (s->try_send) {
            int i;
            struct ssh_channel *c;
            /*
             * Try to send data on all channels if we can.
             */
            for (i = 0; NULL != (c = index234(ssh->channels, i)); i++) {
                int bufsize = ssh2_try_send(c);
                if (bufsize == 0) {
                    switch (c->type) {
                      case CHAN_MAINSESSION:
                        /* stdin need not receive an unthrottle
                         * notification since it will be polled */
                        break;
                      case CHAN_X11:
                        x11_unthrottle(c->u.x11.s);
                        break;
                      case CHAN_AGENT:
                        /* agent sockets are request/response and need no
                         * buffer management */
                        break;
                      case CHAN_SOCKDATA:
                        pfd_unthrottle(c->u.pfd.s);
                        break;
                    }
                }
            }
        }
    }

    crFinishV;
}

/*
 * Handle the top-level SSH2 protocol.
 */
static void ssh2_protocol(Ssh ssh, unsigned char *in, int inlen, int ispkt)
{
    if (do_ssh2_transport(ssh, in, inlen, ispkt) == 0)
        return;
    do_ssh2_authconn(ssh, in, inlen, ispkt);
}

/*
 * Called to set up the connection.
 *
 * Returns an error message, or NULL on success.
 */
static char *ssh_init(void *frontend_handle, void **backend_handle,
                      char *host, int port, char **realhost, int nodelay)
{
    char *p;
    Ssh ssh;

    ssh = smalloc(sizeof(*ssh));
    ssh->s = NULL;
    ssh->cipher = NULL;
    ssh->v1_cipher_ctx = NULL;
    ssh->crcda_ctx = NULL;
    ssh->cscipher = NULL;
    ssh->cs_cipher_ctx = NULL;
    ssh->sccipher = NULL;
    ssh->sc_cipher_ctx = NULL;
    ssh->csmac = NULL;
    ssh->sc_mac_ctx = NULL;
    ssh->scmac = NULL;
    ssh->sc_mac_ctx = NULL;
    ssh->cscomp = NULL;
    ssh->sccomp = NULL;
    ssh->kex = NULL;
    ssh->hostkey = NULL;
    ssh->exitcode = -1;
    ssh->state = SSH_STATE_PREPACKET;
    ssh->size_needed = FALSE;
    ssh->eof_needed = FALSE;
    {
        static const struct Packet empty = { 0, 0, NULL, NULL, 0 };
        ssh->pktin = ssh->pktout = empty;
    }
    ssh->deferred_send_data = NULL;
    ssh->deferred_len = 0;
    ssh->deferred_size = 0;
    ssh->fallback_cmd = 0;
    ssh->pkt_ctx = 0;
    ssh->v2_outgoing_sequence = 0;
    ssh->ssh1_rdpkt_crstate = 0;
    ssh->ssh2_rdpkt_crstate = 0;
    ssh->do_ssh_init_crstate = 0;
    ssh->ssh_gotdata_crstate = 0;
    ssh->ssh1_protocol_crstate = 0;
    ssh->do_ssh1_login_crstate = 0;
    ssh->do_ssh2_transport_crstate = 0;
    ssh->do_ssh2_authconn_crstate = 0;
    ssh->do_ssh_init_state = NULL;
    ssh->do_ssh1_login_state = NULL;
    ssh->do_ssh2_transport_state = NULL;
    ssh->do_ssh2_authconn_state = NULL;

    *backend_handle = ssh;

#ifdef MSCRYPTOAPI
    if (crypto_startup() == 0)
        return "Microsoft high encryption pack not installed!";
#endif

    ssh->frontend = frontend_handle;
    ssh->term_width = cfg.width;
    ssh->term_height = cfg.height;

    ssh->send_ok = 0;
    ssh->editing = 0;
    ssh->echoing = 0;
    ssh->v1_throttle_count = 0;
    ssh->overall_bufsize = 0;
    ssh->fallback_cmd = 0;

    p = connect_to_host(ssh, host, port, realhost, nodelay);
    if (p != NULL)
        return p;

    return NULL;
}

/*
 * Called to send data down the Telnet connection.
 */
static int ssh_send(void *handle, char *buf, int len)
{
    Ssh ssh = (Ssh) handle;

    if (ssh == NULL || ssh->s == NULL || ssh->protocol == NULL)
        return 0;

    ssh->protocol(ssh, buf, len, 0);

    return ssh_sendbuffer(ssh);
}

/*
 * Called to query the current amount of buffered stdin data.
 */
static int ssh_sendbuffer(void *handle)
{
    Ssh ssh = (Ssh) handle;
    int override_value;

    if (ssh == NULL || ssh->s == NULL || ssh->protocol == NULL)
        return 0;

    /*
     * If the SSH socket itself has backed up, add the total backup
     * size on that to any individual buffer on the stdin channel.
     */
    override_value = 0;
    if (ssh->throttled_all)
        override_value = ssh->overall_bufsize;

    if (ssh->version == 1) {
        return override_value;
    } else if (ssh->version == 2) {
        if (!ssh->mainchan || ssh->mainchan->closes > 0)
            return override_value;
        else
            return (override_value +
                    bufchain_size(&ssh->mainchan->v.v2.outbuffer));
    }

    return 0;
}

/*
 * Called to set the size of the window from SSH's POV.
 */
static void ssh_size(void *handle, int width, int height)
{
    Ssh ssh = (Ssh) handle;

    ssh->term_width = width;
    ssh->term_height = height;

    switch (ssh->state) {
      case SSH_STATE_BEFORE_SIZE:
      case SSH_STATE_PREPACKET:
      case SSH_STATE_CLOSED:
        break;                         /* do nothing */
      case SSH_STATE_INTERMED:
        ssh->size_needed = TRUE;       /* buffer for later */
        break;
      case SSH_STATE_SESSION:
        if (!cfg.nopty) {
            if (!term)
                return;
            if (ssh->version == 1) {
                send_packet(ssh, SSH1_CMSG_WINDOW_SIZE,
                            PKT_INT, ssh->term_height,
                            PKT_INT, ssh->term_width,
                            PKT_INT, 0, PKT_INT, 0, PKT_END);
            } else {
                ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
                ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);
                ssh2_pkt_addstring(ssh, "window-change");
                ssh2_pkt_addbool(ssh, 0);
                ssh2_pkt_adduint32(ssh, ssh->term_width);
                ssh2_pkt_adduint32(ssh, ssh->term_height);
                ssh2_pkt_adduint32(ssh, 0);
                ssh2_pkt_adduint32(ssh, 0);
                ssh2_pkt_send(ssh);
            }
        }
        break;
    }
}

/*
 * Send Telnet special codes. TS_EOF is useful for `plink', so you
 * can send an EOF and collect resulting output (e.g. `plink
 * hostname sort').
 */
static void ssh_special(void *handle, Telnet_Special code)
{
    Ssh ssh = (Ssh) handle;

    if (code == TS_EOF) {
        if (ssh->state != SSH_STATE_SESSION) {
            /*
             * Buffer the EOF in case we are pre-SESSION, so we can
             * send it as soon as we reach SESSION.
             */
            if (code == TS_EOF)
                ssh->eof_needed = TRUE;
            return;
        }
        if (ssh->version == 1) {
            send_packet(ssh, SSH1_CMSG_EOF, PKT_END);
        } else {
            ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_EOF);
            ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);
            ssh2_pkt_send(ssh);
        }
        logevent("Sent EOF message");
    } else if (code == TS_PING) {
        if (ssh->state == SSH_STATE_CLOSED
            || ssh->state == SSH_STATE_PREPACKET) return;
        if (ssh->version == 1) {
            if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH1_IGNORE))
                send_packet(ssh, SSH1_MSG_IGNORE, PKT_STR, "", PKT_END);
        } else {
            ssh2_pkt_init(ssh, SSH2_MSG_IGNORE);
            ssh2_pkt_addstring_start(ssh);
            ssh2_pkt_send(ssh);
        }
    } else {
        /* do nothing */
    }
}

void *new_sock_channel(void *handle, Socket s)
{
    Ssh ssh = (Ssh) handle;
    struct ssh_channel *c;
    c = smalloc(sizeof(struct ssh_channel));
    c->ssh = ssh;

    if (c) {
        c->remoteid = -1;              /* to be set when open confirmed */
        c->localid = alloc_channel_id(ssh);
        c->closes = 0;
        c->type = CHAN_SOCKDATA_DORMANT;/* identify channel type */
        c->u.pfd.s = s;
        bufchain_init(&c->v.v2.outbuffer);
        add234(ssh->channels, c);
    }
    return c;
}

/*
 * This is called when stdout/stderr (the entity to which
 * from_backend sends data) manages to clear some backlog.
 */
void ssh_unthrottle(void *handle, int bufsize)
{
    Ssh ssh = (Ssh) handle;
    if (ssh->version == 1) {
        if (ssh->v1_stdout_throttling && bufsize < SSH1_BUFFER_LIMIT) {
            ssh->v1_stdout_throttling = 0;
            ssh1_throttle(ssh, -1);
        }
    } else {
        if (ssh->mainchan && ssh->mainchan->closes == 0)
            ssh2_set_window(ssh->mainchan, OUR_V2_WINSIZE - bufsize);
    }
}

void ssh_send_port_open(void *handle, void *channel, char *hostname,
                        int port, char *org)
{
    Ssh ssh = (Ssh) handle;
    struct ssh_channel *c = (struct ssh_channel *)channel;
    char buf[1024];

    sprintf(buf, "Opening forwarded connection to %.512s:%d", hostname, port);
    logevent(buf);

    if (ssh->version == 1) {
        send_packet(ssh, SSH1_MSG_PORT_OPEN,
                    PKT_INT, c->localid,
                    PKT_STR, hostname,
                    PKT_INT, port,
                    //PKT_STR, <org:orgport>,
                    PKT_END);
    } else {
        ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_OPEN);
        ssh2_pkt_addstring(ssh, "direct-tcpip");
        ssh2_pkt_adduint32(ssh, c->localid);
        c->v.v2.locwindow = OUR_V2_WINSIZE;
        ssh2_pkt_adduint32(ssh, c->v.v2.locwindow);/* our window size */
        ssh2_pkt_adduint32(ssh, 0x4000UL);      /* our max pkt size */
        ssh2_pkt_addstring(ssh, hostname);
        ssh2_pkt_adduint32(ssh, port);
        /*
         * We make up values for the originator data; partly it's
         * too much hassle to keep track, and partly I'm not
         * convinced the server should be told details like that
         * about my local network configuration.
         */
        ssh2_pkt_addstring(ssh, "client-side-connection");
        ssh2_pkt_adduint32(ssh, 0);
        ssh2_pkt_send(ssh);
    }
}


static Socket ssh_socket(void *handle)
{
    Ssh ssh = (Ssh) handle;
    return ssh->s;
}

static int ssh_sendok(void *handle)
{
    Ssh ssh = (Ssh) handle;
    return ssh->send_ok;
}

static int ssh_ldisc(void *handle, int option)
{
    Ssh ssh = (Ssh) handle;
    if (option == LD_ECHO)
        return ssh->echoing;
    if (option == LD_EDIT)
        return ssh->editing;
    return FALSE;
}

static int ssh_return_exitcode(void *handle)
{
    Ssh ssh = (Ssh) handle;
    return ssh->exitcode;
}

/*
 * Gross hack: pscp will try to start SFTP but fall back to scp1 if
 * that fails. This variable is the means by which scp.c can reach
 * into the SSH code and find out which one it got.
 */
extern int ssh_fallback_cmd(void *handle)
{
    Ssh ssh = (Ssh) handle;
    return ssh->fallback_cmd;
}

Backend ssh_backend = {
    ssh_init,
    ssh_send,
    ssh_sendbuffer,
    ssh_size,
    ssh_special,
    ssh_socket,
    ssh_return_exitcode,
    ssh_sendok,
    ssh_ldisc,
    ssh_unthrottle,
    22
};