SSH2 can now use Pageant to obtain keys from
[u/mdw/putty] / ssh.c
diff --git a/ssh.c b/ssh.c
index 7daae9f..f087bd9 100644 (file)
--- a/ssh.c
+++ b/ssh.c
@@ -20,7 +20,7 @@
                       fprintf(stderr, "%s\n", s); }
 
 #define bombout(msg) ( ssh_state = SSH_STATE_CLOSED, \
-                          (s ? sk_close(s), s = NULL : (void)0), \
+                          (s ? sk_close(s), s = NULL : 0), \
                           connection_fatal msg )
 
 #define SSH1_MSG_DISCONNECT                       1    /* 0x1 */
 #define SSH1_AUTH_TIS                             5    /* 0x5 */
 #define SSH1_AUTH_CCARD                           16   /* 0x10 */
 
-#define SSH_AGENTC_REQUEST_RSA_IDENTITIES         1    /* 0x1 */
-#define SSH_AGENT_RSA_IDENTITIES_ANSWER           2    /* 0x2 */
-#define SSH_AGENTC_RSA_CHALLENGE                  3    /* 0x3 */
-#define SSH_AGENT_RSA_RESPONSE                    4    /* 0x4 */
-#define SSH_AGENT_FAILURE                         5    /* 0x5 */
-#define SSH_AGENT_SUCCESS                         6    /* 0x6 */
-#define SSH_AGENTC_ADD_RSA_IDENTITY               7    /* 0x7 */
-#define SSH_AGENTC_REMOVE_RSA_IDENTITY            8    /* 0x8 */
-
 #define SSH2_MSG_DISCONNECT                       1    /* 0x1 */
 #define SSH2_MSG_IGNORE                           2    /* 0x2 */
 #define SSH2_MSG_UNIMPLEMENTED                    3    /* 0x3 */
 #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 */
@@ -160,12 +155,6 @@ enum { PKT_END, PKT_INT, PKT_CHAR, PKT_DATA, PKT_STR, PKT_BIGNUM };
 #define crWaitUntil(c) do { crReturn(0); } while (!(c))
 #define crWaitUntilV(c)        do { crReturnV; } while (!(c))
 
-extern const struct ssh_cipher ssh_3des;
-extern const struct ssh_cipher ssh_3des_ssh2;
-extern const struct ssh_cipher ssh_des;
-extern const struct ssh_cipher ssh_blowfish_ssh1;
-extern const struct ssh_cipher ssh_blowfish_ssh2;
-
 extern char *x11_init (Socket *, char *, void *);
 extern void x11_close (Socket);
 extern void x11_send  (Socket , char *, int);
@@ -177,15 +166,19 @@ extern void x11_invent_auth(char *, int, char *, int);
  * SSH1. (3DES uses outer chaining; Blowfish has the opposite
  * endianness and different-sized keys.)
  */
-const static struct ssh_cipher *ciphers[] = { &ssh_blowfish_ssh2, &ssh_3des_ssh2 };
-
-extern const struct ssh_kex ssh_diffiehellman;
-const static struct ssh_kex *kex_algs[] = { &ssh_diffiehellman };
+const static struct ssh2_ciphers *ciphers[] = {
+    &ssh2_aes,
+    &ssh2_blowfish,
+    &ssh2_3des,
+};
 
-extern const struct ssh_signkey ssh_dss;
-const static struct ssh_signkey *hostkey_algs[] = { &ssh_dss };
+const static struct ssh_kex *kex_algs[] = {
+#ifdef DO_DIFFIE_HELLMAN_GEX
+    &ssh_diffiehellman_gex,
+#endif
+    &ssh_diffiehellman };
 
-extern const struct ssh_mac ssh_md5, ssh_sha1, ssh_sha1_buggy;
+const static struct ssh_signkey *hostkey_algs[] = { &ssh_rsa, &ssh_dss };
 
 static void nullmac_key(unsigned char *key) { }
 static void nullmac_generate(unsigned char *blk, int len, unsigned long seq) { }
@@ -260,14 +253,15 @@ static int ssh1_compressing;
 static int ssh_agentfwd_enabled;
 static int ssh_X11_fwd_enabled;
 static const struct ssh_cipher *cipher = NULL;
-static const struct ssh_cipher *cscipher = NULL;
-static const struct ssh_cipher *sccipher = NULL;
+static const struct ssh2_cipher *cscipher = NULL;
+static const struct ssh2_cipher *sccipher = NULL;
 static const struct ssh_mac *csmac = NULL;
 static const struct ssh_mac *scmac = NULL;
 static const struct ssh_compress *cscomp = NULL;
 static const struct ssh_compress *sccomp = NULL;
 static const struct ssh_kex *kex = NULL;
 static const struct ssh_signkey *hostkey = NULL;
+static unsigned char ssh2_session_id[20];
 int (*ssh_get_password)(const char *prompt, char *str, int maxlen) = NULL;
 
 static char *savedhost;
@@ -290,6 +284,8 @@ static int size_needed = FALSE, eof_needed = FALSE;
 
 static struct Packet pktin = { 0, 0, NULL, NULL, 0 };
 static struct Packet pktout = { 0, 0, NULL, NULL, 0 };
+static unsigned char *deferred_send_data = NULL;
+static int deferred_len = 0, deferred_size = 0;
 
 static int ssh_version;
 static void (*ssh_protocol)(unsigned char *in, int inlen, int ispkt);
@@ -343,6 +339,10 @@ static void c_write (char *buf, int len) {
     from_backend(1, buf, len);
 }
 
+static void c_write_str (char *buf) {
+    c_write(buf, strlen(buf));
+}
+
 /*
  * Collect incoming data in the incoming packet buffer.
  * Decipher and verify the packet when it is completely read.
@@ -804,8 +804,8 @@ static int ssh_versioncmp(char *a, char *b) {
 
 
 /*
- * Utility routine for putting an SSH-protocol `string' into a SHA
- * state.
+ * 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) {
@@ -815,6 +815,12 @@ static void sha_string(SHA_State *s, void *str, int len) {
     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.
  */
@@ -867,20 +873,18 @@ static void ssh2_pkt_addstring(char *data) {
 }
 static char *ssh2_mpint_fmt(Bignum b, int *len) {
     unsigned char *p;
-    int i, n = b[0];
-    p = smalloc(n * 2 + 1);
+    int i, n = (ssh1_bignum_bitcount(b)+7)/8;
+    p = smalloc(n + 1);
     if (!p)
         fatalbox("out of memory");
     p[0] = 0;
-    for (i = 0; i < n; i++) {
-        p[i*2+1] = (b[n-i] >> 8) & 0xFF;
-        p[i*2+2] = (b[n-i]     ) & 0xFF;
-    }
+    for (i = 1; i <= n; i++)
+        p[i] = bignum_byte(b, n-i);
     i = 0;
-    while (p[i] == 0 && (p[i+1] & 0x80) == 0)
+    while (i <= n && p[i] == 0 && (p[i+1] & 0x80) == 0)
         i++;
-    memmove(p, p+i, n*2+1-i);
-    *len = n*2+1-i;
+    memmove(p, p+i, n+1-i);
+    *len = n+1-i;
     return p;
 }
 static void ssh2_pkt_addmp(Bignum b) {
@@ -891,7 +895,13 @@ static void ssh2_pkt_addmp(Bignum b) {
     ssh2_pkt_addstring_data(p, len);
     sfree(p);
 }
-static void ssh2_pkt_send(void) {
+
+/*
+ * Construct an SSH2 final-form packet: compress it, encrypt it,
+ * put the MAC on it. Final packet, ready to be sent, is stored in
+ * pktout.data. Total length is returned.
+ */
+static int ssh2_pkt_construct(void) {
     int cipherblk, maclen, padding, i;
     static unsigned long outgoing_sequence = 0;
 
@@ -919,7 +929,7 @@ static void ssh2_pkt_send(void) {
      * Add padding. At least four bytes, and must also bring total
      * length (minus MAC) up to a multiple of the block size.
      */
-    cipherblk = cipher ? cipher->blksize : 8;   /* block size */
+    cipherblk = cscipher ? cscipher->blksize : 8;   /* block size */
     cipherblk = cipherblk < 8 ? 8 : cipherblk;   /* or 8 if blksize < 8 */
     padding = 4;
     padding += (cipherblk - (pktout.length + padding) % cipherblk) % cipherblk;
@@ -944,7 +954,48 @@ static void ssh2_pkt_send(void) {
     if (cscipher)
         cscipher->encrypt(pktout.data, pktout.length + padding);
 
-    sk_write(s, pktout.data, pktout.length + padding + maclen);
+    /* Ready-to-send packet starts at pktout.data. We return length. */
+    return pktout.length + padding + maclen;
+}
+
+/*
+ * Construct and send an SSH2 packet immediately.
+ */
+static void ssh2_pkt_send(void) {
+    int len = ssh2_pkt_construct();
+    sk_write(s, pktout.data, len);
+}
+
+/*
+ * 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(void) {
+    int len = ssh2_pkt_construct();
+    if (deferred_len + len > deferred_size) {
+        deferred_size = deferred_len + len + 128;
+        deferred_send_data = srealloc(deferred_send_data, deferred_size);
+    }
+    memcpy(deferred_send_data+deferred_len, pktout.data, len);
+    deferred_len += len;
+}
+
+/*
+ * Send the whole deferred data block constructed by
+ * ssh2_pkt_defer().
+ */
+static void ssh2_pkt_defersend(void) {
+    sk_write(s, deferred_send_data, deferred_len);
+    deferred_len = deferred_size = 0;
+    sfree(deferred_send_data);
+    deferred_send_data = NULL;
 }
 
 #if 0
@@ -979,6 +1030,14 @@ static unsigned long ssh2_pkt_getuint32(void) {
     pktin.savedpos += 4;
     return value;
 }
+static int ssh2_pkt_getbool(void) {
+    unsigned long value;
+    if (pktin.length - pktin.savedpos < 1)
+        return 0;                      /* arrgh, no way to decline (FIXME?) */
+    value = pktin.data[pktin.savedpos] != 0;
+    pktin.savedpos++;
+    return value;
+}
 static void ssh2_pkt_getstring(char **p, int *length) {
     *p = NULL;
     if (pktin.length - pktin.savedpos < 4)
@@ -992,7 +1051,7 @@ static void ssh2_pkt_getstring(char **p, int *length) {
 }
 static Bignum ssh2_pkt_getmp(void) {
     char *p;
-    int i, j, length;
+    int length;
     Bignum b;
 
     ssh2_pkt_getstring(&p, &length);
@@ -1002,15 +1061,7 @@ static Bignum ssh2_pkt_getmp(void) {
         bombout(("internal error: Can't handle negative mpints"));
         return NULL;
     }
-    b = newbn((length+1)/2);
-    for (i = 0; i < length; i++) {
-        j = length - 1 - i;
-        if (j & 1)
-            b[j/2+1] |= ((unsigned char)p[i]) << 8;
-        else
-            b[j/2+1] |= ((unsigned char)p[i]);
-    }
-    while (b[0] > 1 && b[b[0]] == 0) b[0]--;
+    b = bignum_from_bytes(p, length);
     return b;
 }
 
@@ -1333,11 +1384,17 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
 
     logevent("Encrypted session key");
 
-    cipher_type = cfg.cipher == CIPHER_BLOWFISH ? SSH_CIPHER_BLOWFISH :
-                  cfg.cipher == CIPHER_DES ? SSH_CIPHER_DES : 
-                  SSH_CIPHER_3DES;
+    switch (cfg.cipher) {
+      case CIPHER_BLOWFISH: cipher_type = SSH_CIPHER_BLOWFISH; break;
+      case CIPHER_DES:      cipher_type = SSH_CIPHER_DES;      break;
+      case CIPHER_3DES:     cipher_type = SSH_CIPHER_3DES;     break;
+      case CIPHER_AES:
+        c_write_str("AES not supported in SSH1, falling back to 3DES\r\n");
+        cipher_type = SSH_CIPHER_3DES;
+        break;
+    }
     if ((supported_ciphers_mask & (1 << cipher_type)) == 0) {
-       c_write("Selected cipher not supported, falling back to 3DES\r\n", 53);
+       c_write_str("Selected cipher not supported, falling back to 3DES\r\n");
        cipher_type = SSH_CIPHER_3DES;
     }
     switch (cipher_type) {
@@ -1377,7 +1434,7 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
        static int pos = 0;
        static char c;
        if ((flags & FLAG_INTERACTIVE) && !*cfg.username) {
-           c_write("login as: ", 10);
+           c_write_str("login as: ");
             ssh_send_ok = 1;
            while (pos >= 0) {
                crWaitUntil(!ispkt);
@@ -1388,13 +1445,13 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
                    break;
                  case 8: case 127:
                    if (pos > 0) {
-                       c_write("\b \b", 3);
+                       c_write_str("\b \b");
                        pos--;
                    }
                    break;
                  case 21: case 27:
                    while (pos > 0) {
-                       c_write("\b \b", 3);
+                       c_write_str("\b \b");
                        pos--;
                    }
                    break;
@@ -1411,7 +1468,7 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
                    break;
                }
            }
-           c_write("\r\n", 2);
+           c_write_str("\r\n");
            username[strcspn(username, "\n\r")] = '\0';
        } else {
            strncpy(username, cfg.username, 99);
@@ -1426,7 +1483,7 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
             if (flags & FLAG_INTERACTIVE &&
                 (!((flags & FLAG_STDERR) && (flags & FLAG_VERBOSE)))) {
                strcat(userlog, "\r\n");
-                c_write(userlog, strlen(userlog));
+                c_write_str(userlog);
            }
        }
     }
@@ -1461,7 +1518,7 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
 
             /* Request the keys held by the agent. */
             PUT_32BIT(request, 1);
-            request[4] = SSH_AGENTC_REQUEST_RSA_IDENTITIES;
+            request[4] = SSH1_AGENTC_REQUEST_RSA_IDENTITIES;
             agent_query(request, 5, &r, &responselen);
             response = (unsigned char *)r;
             if (response) {
@@ -1503,7 +1560,7 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
                         agentreq = smalloc(4 + len);
                         PUT_32BIT(agentreq, len);
                         q = agentreq + 4;
-                        *q++ = SSH_AGENTC_RSA_CHALLENGE;
+                        *q++ = SSH1_AGENTC_RSA_CHALLENGE;
                         PUT_32BIT(q, ssh1_bignum_bitcount(key.modulus));
                         q += 4;
                         q += ssh1_write_bignum(q, key.exponent);
@@ -1514,7 +1571,7 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
                         agent_query(agentreq, len+4, &ret, &retlen);
                         sfree(agentreq);
                         if (ret) {
-                            if (ret[4] == SSH_AGENT_RSA_RESPONSE) {
+                            if (ret[4] == SSH1_AGENT_RSA_RESPONSE) {
                                 logevent("Sending Pageant's response");
                                 send_packet(SSH1_CMSG_AUTH_RSA_RESPONSE,
                                             PKT_DATA, ret+5, 16, PKT_END);
@@ -1523,10 +1580,9 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
                                 if (pktin.type == SSH1_SMSG_SUCCESS) {
                                     logevent("Pageant's response accepted");
                                     if (flags & FLAG_VERBOSE) {
-                                        c_write("Authenticated using RSA key \"",
-                                                29);
+                                        c_write_str("Authenticated using RSA key \"");
                                         c_write(commentp, commentlen);
-                                        c_write("\" from agent\r\n", 14);
+                                        c_write_str("\" from agent\r\n");
                                     }
                                     authed = TRUE;
                                 } else
@@ -1562,7 +1618,7 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
             if (pktin.type != SSH1_SMSG_AUTH_TIS_CHALLENGE) {
                 logevent("TIS authentication declined");
                 if (flags & FLAG_INTERACTIVE)
-                    c_write("TIS authentication refused.\r\n", 29);
+                    c_write_str("TIS authentication refused.\r\n");
             } else {
                 int challengelen = ((pktin.body[0] << 24) |
                                     (pktin.body[1] << 16) |
@@ -1584,7 +1640,7 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
             crWaitUntil(ispkt);
             if (pktin.type != SSH1_SMSG_AUTH_CCARD_CHALLENGE) {
                 logevent("CryptoCard authentication declined");
-                c_write("CryptoCard authentication refused.\r\n", 29);
+                c_write_str("CryptoCard authentication refused.\r\n");
             } else {
                 int challengelen = ((pktin.body[0] << 24) |
                                     (pktin.body[1] << 16) |
@@ -1606,10 +1662,10 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
         if (pwpkt_type == SSH1_CMSG_AUTH_RSA) {
             char *comment = NULL;
             if (flags & FLAG_VERBOSE)
-                c_write("Trying public key authentication.\r\n", 35);
+                c_write_str("Trying public key authentication.\r\n");
             if (!rsakey_encrypted(cfg.keyfile, &comment)) {
                 if (flags & FLAG_VERBOSE)
-                    c_write("No passphrase required.\r\n", 25);
+                    c_write_str("No passphrase required.\r\n");
                 goto tryauth;
             }
             sprintf(prompt, "Passphrase for key \"%.100s\": ", comment);
@@ -1629,7 +1685,7 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
                 crReturn(1);
             }
        } else {
-            c_write(prompt, strlen(prompt));
+            c_write_str(prompt);
             pos = 0;
             ssh_send_ok = 1;
             while (pos >= 0) {
@@ -1657,7 +1713,7 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
                     break;
                 }
             }
-            c_write("\r\n", 2);
+            c_write_str("\r\n");
         }
 
         tryauth:
@@ -1672,15 +1728,15 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
             static unsigned char buffer[32];
 
             tried_publickey = 1;
-            i = loadrsakey(cfg.keyfile, &pubkey, NULL, password);
+            i = loadrsakey(cfg.keyfile, &pubkey, password);
             if (i == 0) {
-                c_write("Couldn't load public key from ", 30);
-                c_write(cfg.keyfile, strlen(cfg.keyfile));
-                c_write(".\r\n", 3);
+                c_write_str("Couldn't load public key from ");
+                c_write_str(cfg.keyfile);
+                c_write_str(".\r\n");
                 continue;              /* go and try password */
             }
             if (i == -1) {
-                c_write("Wrong passphrase.\r\n", 19);
+                c_write_str("Wrong passphrase.\r\n");
                 tried_publickey = 0;
                 continue;              /* try again */
             }
@@ -1693,7 +1749,7 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
 
             crWaitUntil(ispkt);
             if (pktin.type == SSH1_SMSG_FAILURE) {
-                c_write("Server refused our public key.\r\n", 32);
+                c_write_str("Server refused our public key.\r\n");
                 continue;              /* go and try password */
             }
             if (pktin.type != SSH1_SMSG_AUTH_RSA_CHALLENGE) {
@@ -1704,9 +1760,8 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
             response = rsadecrypt(challenge, &pubkey);
             freebn(pubkey.private_exponent);   /* burn the evidence */
 
-            for (i = 0; i < 32; i += 2) {
-                buffer[i] = response[16-i/2] >> 8;
-                buffer[i+1] = response[16-i/2] & 0xFF;
+            for (i = 0; i < 32; i++) {
+                buffer[i] = bignum_byte(response, 31-i);
             }
 
             MD5Init(&md5c);
@@ -1720,8 +1775,7 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
             crWaitUntil(ispkt);
             if (pktin.type == SSH1_SMSG_FAILURE) {
                 if (flags & FLAG_VERBOSE)
-                    c_write("Failed to authenticate with our public key.\r\n",
-                            45);
+                    c_write_str("Failed to authenticate with our public key.\r\n");
                 continue;              /* go and try password */
             } else if (pktin.type != SSH1_SMSG_SUCCESS) {
                 bombout(("Bizarre response to RSA authentication response"));
@@ -1737,7 +1791,7 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt)
        crWaitUntil(ispkt);
        if (pktin.type == SSH1_SMSG_FAILURE) {
             if (flags & FLAG_VERBOSE)
-                c_write("Access denied\r\n", 15);
+                c_write_str("Access denied\r\n");
            logevent("Authentication refused");
        } else if (pktin.type == SSH1_MSG_DISCONNECT) {
            logevent("Received disconnect request");
@@ -1843,7 +1897,7 @@ static void ssh1_protocol(unsigned char *in, int inlen, int ispkt) {
             bombout(("Protocol confusion"));
             crReturnV;
         } else if (pktin.type == SSH1_SMSG_FAILURE) {
-            c_write("Server refused to allocate pty\r\n", 32);
+            c_write_str("Server refused to allocate pty\r\n");
             ssh_editing = ssh_echoing = 1;
         }
        logevent("Allocated pty");
@@ -1858,7 +1912,7 @@ static void ssh1_protocol(unsigned char *in, int inlen, int ispkt) {
             bombout(("Protocol confusion"));
             crReturnV;
         } else if (pktin.type == SSH1_SMSG_FAILURE) {
-            c_write("Server refused to compress\r\n", 32);
+            c_write_str("Server refused to compress\r\n");
         }
        logevent("Started compression");
        ssh1_compressing = TRUE;
@@ -2119,13 +2173,14 @@ static void ssh2_mkkey(Bignum K, char *H, char *sessid, char chr, char *keyspace
  */
 static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
 {
-    static int i, len;
+    static int i, j, len, nbits;
     static char *str;
-    static Bignum e, f, K;
+    static Bignum p, g, e, f, K;
+    static int kex_init_value, kex_reply_value;
     static const struct ssh_mac **maclist;
     static int nmacs;
-    static const struct ssh_cipher *cscipher_tobe = NULL;
-    static const struct ssh_cipher *sccipher_tobe = NULL;
+    static const struct ssh2_cipher *cscipher_tobe = NULL;
+    static const struct ssh2_cipher *sccipher_tobe = NULL;
     static const struct ssh_mac *csmac_tobe = NULL;
     static const struct ssh_mac *scmac_tobe = NULL;
     static const struct ssh_compress *cscomp_tobe = NULL;
@@ -2134,9 +2189,8 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
     static int hostkeylen, siglen;
     static void *hkey;                /* actual host key */
     static unsigned char exchange_hash[20];
-    static unsigned char first_exchange_hash[20];
     static unsigned char keyspace[40];
-    static const struct ssh_cipher *preferred_cipher;
+    static const struct ssh2_ciphers *preferred_cipher;
     static const struct ssh_compress *preferred_comp;
     static int first_kex;
 
@@ -2148,15 +2202,17 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
      * Set up the preferred cipher and compression.
      */
     if (cfg.cipher == CIPHER_BLOWFISH) {
-        preferred_cipher = &ssh_blowfish_ssh2;
+        preferred_cipher = &ssh2_blowfish;
     } else if (cfg.cipher == CIPHER_DES) {
         logevent("Single DES not supported in SSH2; using 3DES");
-        preferred_cipher = &ssh_3des_ssh2;
+        preferred_cipher = &ssh2_3des;
     } else if (cfg.cipher == CIPHER_3DES) {
-        preferred_cipher = &ssh_3des_ssh2;
+        preferred_cipher = &ssh2_3des;
+    } else if (cfg.cipher == CIPHER_AES) {
+        preferred_cipher = &ssh2_aes;
     } else {
         /* Shouldn't happen, but we do want to initialise to _something_. */
-        preferred_cipher = &ssh_3des_ssh2;
+        preferred_cipher = &ssh2_3des;
     }
     if (cfg.compression)
        preferred_comp = &ssh_zlib;
@@ -2195,18 +2251,22 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
     /* List client->server encryption algorithms. */
     ssh2_pkt_addstring_start();
     for (i = 0; i < lenof(ciphers)+1; i++) {
-        const struct ssh_cipher *c = i==0 ? preferred_cipher : ciphers[i-1];
-        ssh2_pkt_addstring_str(c->name);
-        if (i < lenof(ciphers))
-            ssh2_pkt_addstring_str(",");
+        const struct ssh2_ciphers *c = i==0 ? preferred_cipher : ciphers[i-1];
+        for (j = 0; j < c->nciphers; j++) {
+            ssh2_pkt_addstring_str(c->list[j]->name);
+            if (i < lenof(ciphers) || j < c->nciphers-1)
+                ssh2_pkt_addstring_str(",");
+        }
     }
     /* List server->client encryption algorithms. */
     ssh2_pkt_addstring_start();
     for (i = 0; i < lenof(ciphers)+1; i++) {
-        const struct ssh_cipher *c = i==0 ? preferred_cipher : ciphers[i-1];
-        ssh2_pkt_addstring_str(c->name);
-        if (i < lenof(ciphers))
-            ssh2_pkt_addstring_str(",");
+        const struct ssh2_ciphers *c = i==0 ? preferred_cipher : ciphers[i-1];
+        for (j = 0; j < c->nciphers; j++) {
+            ssh2_pkt_addstring_str(c->list[j]->name);
+            if (i < lenof(ciphers) || j < c->nciphers-1)
+                ssh2_pkt_addstring_str(",");
+        }
     }
     /* List client->server MAC algorithms. */
     ssh2_pkt_addstring_start();
@@ -2282,19 +2342,27 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
     }
     ssh2_pkt_getstring(&str, &len);    /* client->server cipher */
     for (i = 0; i < lenof(ciphers)+1; i++) {
-        const struct ssh_cipher *c = i==0 ? preferred_cipher : ciphers[i-1];
-        if (in_commasep_string(c->name, str, len)) {
-            cscipher_tobe = c;
-            break;
+        const struct ssh2_ciphers *c = i==0 ? preferred_cipher : ciphers[i-1];
+        for (j = 0; j < c->nciphers; j++) {
+            if (in_commasep_string(c->list[j]->name, str, len)) {
+                cscipher_tobe = c->list[j];
+                break;
+            }
         }
+        if (cscipher_tobe)
+            break;
     }
     ssh2_pkt_getstring(&str, &len);    /* server->client cipher */
     for (i = 0; i < lenof(ciphers)+1; i++) {
-        const struct ssh_cipher *c = i==0 ? preferred_cipher : ciphers[i-1];
-        if (in_commasep_string(c->name, str, len)) {
-            sccipher_tobe = c;
-            break;
+        const struct ssh2_ciphers *c = i==0 ? preferred_cipher : ciphers[i-1];
+        for (j = 0; j < c->nciphers; j++) {
+            if (in_commasep_string(c->list[j]->name, str, len)) {
+                sccipher_tobe = c->list[j];
+                break;
+            }
         }
+        if (sccipher_tobe)
+            break;
     }
     ssh2_pkt_getstring(&str, &len);    /* client->server mac */
     for (i = 0; i < nmacs; i++) {
@@ -2328,25 +2396,60 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
     }
 
     /*
-     * Currently we only support Diffie-Hellman and DSS, so let's
-     * bomb out if those aren't selected.
+     * If we're doing Diffie-Hellman group exchange, start by
+     * requesting a group.
      */
-    if (kex != &ssh_diffiehellman || hostkey != &ssh_dss) {
-        bombout(("internal fault: chaos in SSH 2 transport layer"));
-        crReturn(0);
+    if (kex == &ssh_diffiehellman_gex) {
+        int csbits, scbits;
+
+        logevent("Doing Diffie-Hellman group exchange");
+        /*
+         * Work out number of bits. We start with the maximum key
+         * length of either cipher...
+         */
+        csbits = cscipher_tobe->keylen;
+        scbits = sccipher_tobe->keylen;
+        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 (nbits > 160) nbits = 160;
+        /*
+         * ... and then work out how big a DH group we will need to
+         * allow that much data.
+         */
+        nbits = 512 << ((nbits-1) / 64);
+        ssh2_pkt_init(SSH2_MSG_KEX_DH_GEX_REQUEST);
+        ssh2_pkt_adduint32(nbits);
+        ssh2_pkt_send();
+
+        crWaitUntil(ispkt);
+        if (pktin.type != SSH2_MSG_KEX_DH_GEX_GROUP) {
+            bombout(("expected key exchange group packet from server"));
+            crReturn(0);
+        }
+        p = ssh2_pkt_getmp();
+        g = ssh2_pkt_getmp();
+        dh_setup_group(p, g);
+        kex_init_value = SSH2_MSG_KEX_DH_GEX_INIT;
+        kex_reply_value = SSH2_MSG_KEX_DH_GEX_REPLY;
+    } else {
+        dh_setup_group1();
+        kex_init_value = SSH2_MSG_KEXDH_INIT;
+        kex_reply_value = SSH2_MSG_KEXDH_REPLY;
     }
 
+    logevent("Doing Diffie-Hellman key exchange");
     /*
-     * Now we begin the fun. Generate and send e for Diffie-Hellman.
+     * Now generate and send e for Diffie-Hellman.
      */
     e = dh_create_e();
-    ssh2_pkt_init(SSH2_MSG_KEXDH_INIT);
+    ssh2_pkt_init(kex_init_value);
     ssh2_pkt_addmp(e);
     ssh2_pkt_send();
 
     crWaitUntil(ispkt);
-    if (pktin.type != SSH2_MSG_KEXDH_REPLY) {
-        bombout(("expected key exchange packet from server"));
+    if (pktin.type != kex_reply_value) {
+        bombout(("expected key exchange reply packet from server"));
         crReturn(0);
     }
     ssh2_pkt_getstring(&hostkeydata, &hostkeylen);
@@ -2356,11 +2459,18 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
     K = dh_find_K(f);
 
     sha_string(&exhash, hostkeydata, hostkeylen);
+    if (kex == &ssh_diffiehellman_gex) {
+        sha_uint32(&exhash, nbits);
+        sha_mpint(&exhash, p);
+        sha_mpint(&exhash, g);
+    }
     sha_mpint(&exhash, e);
     sha_mpint(&exhash, f);
     sha_mpint(&exhash, K);
     SHA_Final(&exhash, exchange_hash);
 
+    dh_cleanup();
+
 #if 0
     debug(("Exchange hash is:\r\n"));
     for (i = 0; i < 20; i++)
@@ -2391,7 +2501,7 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
     fingerprint = hostkey->fingerprint(hkey);
     verify_ssh_host_key(savedhost, savedport, hostkey->keytype,
                         keystr, fingerprint);
-    if (first_kex) {                  /* don't bother logging this in rekeys */
+    if (first_kex) {                /* don't bother logging this in rekeys */
        logevent("Host key fingerprint is:");
        logevent(fingerprint);
     }
@@ -2421,18 +2531,18 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
      * _first_ key exchange.
      */
     if (first_kex)
-       memcpy(first_exchange_hash, exchange_hash, sizeof(exchange_hash));
-    ssh2_mkkey(K, exchange_hash, first_exchange_hash, 'C', keyspace);
+       memcpy(ssh2_session_id, exchange_hash, sizeof(exchange_hash));
+    ssh2_mkkey(K, exchange_hash, ssh2_session_id, 'C', keyspace);
     cscipher->setcskey(keyspace);
-    ssh2_mkkey(K, exchange_hash, first_exchange_hash, 'D', keyspace);
+    ssh2_mkkey(K, exchange_hash, ssh2_session_id, 'D', keyspace);
     sccipher->setsckey(keyspace);
-    ssh2_mkkey(K, exchange_hash, first_exchange_hash, 'A', keyspace);
+    ssh2_mkkey(K, exchange_hash, ssh2_session_id, 'A', keyspace);
     cscipher->setcsiv(keyspace);
-    ssh2_mkkey(K, exchange_hash, first_exchange_hash, 'B', keyspace);
+    ssh2_mkkey(K, exchange_hash, ssh2_session_id, 'B', keyspace);
     sccipher->setsciv(keyspace);
-    ssh2_mkkey(K, exchange_hash, first_exchange_hash, 'E', keyspace);
+    ssh2_mkkey(K, exchange_hash, ssh2_session_id, 'E', keyspace);
     csmac->setcskey(keyspace);
-    ssh2_mkkey(K, exchange_hash, first_exchange_hash, 'F', keyspace);
+    ssh2_mkkey(K, exchange_hash, ssh2_session_id, 'F', keyspace);
     scmac->setsckey(keyspace);
 
     /*
@@ -2509,6 +2619,22 @@ static void do_ssh2_authconn(unsigned char *in, int inlen, int ispkt)
 {
     static unsigned long remote_winsize;
     static unsigned long remote_maxpkt;
+    static enum {
+       AUTH_INVALID, AUTH_PUBLICKEY_AGENT, AUTH_PUBLICKEY_FILE, AUTH_PASSWORD
+    } method;
+    static enum {
+        AUTH_TYPE_NONE,
+        AUTH_TYPE_PUBLICKEY,
+        AUTH_TYPE_PUBLICKEY_OFFER_LOUD,
+        AUTH_TYPE_PUBLICKEY_OFFER_QUIET,
+        AUTH_TYPE_PASSWORD
+    } type;
+    static int gotit, need_pw, can_pubkey, can_passwd;
+    static int tried_pubkey_config, tried_agent;
+    static int we_are_in;
+    static char username[100];
+    static char pwprompt[200];
+    static char password[100];
 
     crBegin;
 
@@ -2525,22 +2651,40 @@ static void do_ssh2_authconn(unsigned char *in, int inlen, int ispkt)
     }
 
     /*
-     * FIXME: currently we support only password authentication.
-     * (This places us technically in violation of the SSH2 spec.
-     * We must fix this.)
+     * We repeat this whole loop, including the username prompt,
+     * until we manage a successful authentication. If the user
+     * types the wrong _password_, they are sent back to the
+     * beginning to try another username. (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!
      */
-    while (1) {
-        /*
-         * Get a username and a password.
-         */
-       static char username[100];
-       static char password[100];
-       static int pos = 0;
+    do {
+       static int pos;
        static char c;
 
+       /*
+        * Get a username.
+        */
+       pos = 0;
        if ((flags & FLAG_INTERACTIVE) && !*cfg.username) {
-           c_write("login as: ", 10);
-            ssh_send_ok = 1;
+           c_write_str("login as: ");
+           ssh_send_ok = 1;
            while (pos >= 0) {
                crWaitUntilV(!ispkt);
                while (inlen--) switch (c = *in++) {
@@ -2550,13 +2694,13 @@ static void do_ssh2_authconn(unsigned char *in, int inlen, int ispkt)
                    break;
                  case 8: case 127:
                    if (pos > 0) {
-                       c_write("\b \b", 3);
+                       c_write_str("\b \b");
                        pos--;
                    }
                    break;
                  case 21: case 27:
                    while (pos > 0) {
-                       c_write("\b \b", 3);
+                       c_write_str("\b \b");
                        pos--;
                    }
                    break;
@@ -2566,87 +2710,463 @@ static void do_ssh2_authconn(unsigned char *in, int inlen, int ispkt)
                    break;
                  default:
                    if (((c >= ' ' && c <= '~') ||
-                         ((unsigned char)c >= 160)) && pos < 40) {
+                        ((unsigned char)c >= 160)) && pos < 40) {
                        username[pos++] = c;
                        c_write(&c, 1);
                    }
                    break;
                }
            }
-           c_write("\r\n", 2);
+           c_write_str("\r\n");
            username[strcspn(username, "\n\r")] = '\0';
        } else {
            char stuff[200];
            strncpy(username, cfg.username, 99);
            username[99] = '\0';
-            if ((flags & FLAG_VERBOSE) || (flags & FLAG_INTERACTIVE)) {
+           if ((flags & FLAG_VERBOSE) || (flags & FLAG_INTERACTIVE)) {
                sprintf(stuff, "Using username \"%s\".\r\n", username);
-               c_write(stuff, strlen(stuff));
+               c_write_str(stuff);
            }
        }
 
-       if (ssh_get_password) {
-           char prompt[200];
-           sprintf(prompt, "%.90s@%.90s's password: ", username, savedhost);
-           if (!ssh_get_password(prompt, password, sizeof(password))) {
-                /*
-                 * get_password failed to get a password (for
-                 * example because one was supplied on the command
-                 * line which has already failed to work).
-                 * Terminate.
-                 */
-                logevent("No more passwords to try");
-                ssh_state = SSH_STATE_CLOSED;
-                crReturnV;
-            }
-       } else {
-            c_write("password: ", 10);
-            ssh_send_ok = 1;
+       /*
+        * 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.
+        */
+       ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
+       ssh2_pkt_addstring(username);
+       ssh2_pkt_addstring("ssh-connection");   /* service requested */
+       ssh2_pkt_addstring("none");    /* method */
+       ssh2_pkt_send();
+       type = AUTH_TYPE_NONE;
+       gotit = FALSE;
+       we_are_in = FALSE;
+
+       tried_pubkey_config = FALSE;
+       tried_agent = FALSE;
+
+       while (1) {
+           /*
+            * Wait for the result of the last authentication request.
+            */
+           if (!gotit)
+               crWaitUntilV(ispkt);
+           while (pktin.type == SSH2_MSG_USERAUTH_BANNER) {
+               /* FIXME: should support this */
+               crWaitUntilV(ispkt);
+           }
+           if (pktin.type == SSH2_MSG_USERAUTH_SUCCESS) {
+               logevent("Access granted");
+               we_are_in = TRUE;
+               break;
+           }
 
-            pos = 0;
-            while (pos >= 0) {
-                crWaitUntilV(!ispkt);
-                while (inlen--) switch (c = *in++) {
-                  case 10: case 13:
-                    password[pos] = 0;
-                    pos = -1;
-                    break;
-                  case 8: case 127:
-                    if (pos > 0)
-                        pos--;
-                    break;
-                  case 21: case 27:
-                    pos = 0;
-                    break;
-                  case 3: case 4:
-                    random_save_seed();
-                    exit(0);
-                    break;
-                  default:
-                    if (((c >= ' ' && c <= '~') ||
-                         ((unsigned char)c >= 160)) && pos < 40)
-                        password[pos++] = c;
-                    break;
-                }
-            }
-            c_write("\r\n", 2);
-       }
+           if (pktin.type != SSH2_MSG_USERAUTH_FAILURE) {
+               bombout(("Strange packet received during authentication: type %d",
+                        pktin.type));
+           }
 
-        ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
-        ssh2_pkt_addstring(username);
-        ssh2_pkt_addstring("ssh-connection");   /* service requested */
-        ssh2_pkt_addstring("password");
-        ssh2_pkt_addbool(FALSE);
-        ssh2_pkt_addstring(password);
-        ssh2_pkt_send();
+           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.
+            */
+           {
+               char *methods;
+               int methlen;
+               ssh2_pkt_getstring(&methods, &methlen);
+               if (!ssh2_pkt_getbool()) {
+                   /*
+                    * 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 (type == AUTH_TYPE_NONE) {
+                       /* do nothing */
+                   } else if (type == AUTH_TYPE_PUBLICKEY_OFFER_LOUD ||
+                              type == AUTH_TYPE_PUBLICKEY_OFFER_QUIET) {
+                       if (type == AUTH_TYPE_PUBLICKEY_OFFER_LOUD)
+                           c_write_str("Server refused our key\r\n");
+                       logevent("Server refused public key");
+                   } else {
+                       c_write_str("Access denied\r\n");
+                       logevent("Access denied");
+                       if (type == AUTH_TYPE_PASSWORD) {
+                           we_are_in = FALSE;
+                           break;
+                       }
+                   }
+               } else {
+                   c_write_str("Further authentication required\r\n");
+                   logevent("Further authentication required");
+               }
 
-        crWaitUntilV(ispkt);
-        if (pktin.type != SSH2_MSG_USERAUTH_SUCCESS) {
-           c_write("Access denied\r\n", 15);
-           logevent("Authentication refused");
-        } else
-            break;
-    }
+               can_pubkey = in_commasep_string("publickey", methods, methlen);
+               can_passwd = in_commasep_string("password", methods, methlen);
+           }
+
+           method = 0;
+
+           if (!method && can_pubkey && agent_exists && !tried_agent) {
+               /*
+                * Attempt public-key authentication using Pageant.
+                */
+               static unsigned char request[5], *response, *p;
+               static int responselen;
+               static int i, nkeys;
+               static int authed = FALSE;
+               void *r;
+
+               tried_agent = TRUE;
+
+               logevent("Pageant is running. Requesting keys.");
+
+               /* Request the keys held by the agent. */
+               PUT_32BIT(request, 1);
+               request[4] = SSH2_AGENTC_REQUEST_IDENTITIES;
+               agent_query(request, 5, &r, &responselen);
+               response = (unsigned char *)r;
+               if (response) {
+                   p = response + 5;
+                   nkeys = GET_32BIT(p); p += 4;
+                   { char buf[64]; sprintf(buf, "Pageant has %d keys", nkeys);
+                       logevent(buf); }
+                   for (i = 0; i < nkeys; i++) {
+                       static char *pkblob, *alg, *commentp;
+                       static int pklen, alglen, commentlen;
+                       static int siglen, retlen, len;
+                       static char *q, *agentreq, *ret;
+
+                       { char buf[64]; sprintf(buf, "Trying Pageant key #%d", i);
+                           logevent(buf); }
+                       pklen = GET_32BIT(p); p += 4;
+                       pkblob = p; p += pklen;
+                       alglen = GET_32BIT(pkblob);
+                       alg = pkblob + 4;
+                       commentlen = GET_32BIT(p); p += 4;
+                       commentp = p; p += commentlen;
+                       ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
+                       ssh2_pkt_addstring(username);
+                       ssh2_pkt_addstring("ssh-connection");/* service requested */
+                       ssh2_pkt_addstring("publickey");/* method */
+                       ssh2_pkt_addbool(FALSE);   /* no signature included */
+                       ssh2_pkt_addstring_start();
+                       ssh2_pkt_addstring_data(alg, alglen);
+                       ssh2_pkt_addstring_start();
+                       ssh2_pkt_addstring_data(pkblob, pklen);
+                       ssh2_pkt_send();
+
+                       crWaitUntilV(ispkt);
+                       if (pktin.type != SSH2_MSG_USERAUTH_PK_OK) {
+                           logevent("Key refused");
+                           continue;
+                       }
+
+                       c_write_str("Authenticating with public key \"");
+                       c_write(commentp, commentlen);
+                       c_write_str("\" from agent\r\n");
+
+                       /*
+                        * Server is willing to accept the key.
+                        * Construct a SIGN_REQUEST.
+                        */
+                       ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
+                       ssh2_pkt_addstring(username);
+                       ssh2_pkt_addstring("ssh-connection");   /* service requested */
+                       ssh2_pkt_addstring("publickey");    /* method */
+                       ssh2_pkt_addbool(TRUE);
+                       ssh2_pkt_addstring_start();
+                       ssh2_pkt_addstring_data(alg, alglen);
+                       ssh2_pkt_addstring_start();
+                       ssh2_pkt_addstring_data(pkblob, pklen);
+
+                       siglen = pktout.length - 5 + 4 + 20;
+                       len = 1;   /* message type */
+                       len += 4 + pklen;   /* key blob */
+                       len += 4 + siglen;   /* data to sign */
+                       len += 4;  /* flags */
+                       agentreq = smalloc(4 + len);
+                       PUT_32BIT(agentreq, len);
+                       q = agentreq + 4;
+                       *q++ = SSH2_AGENTC_SIGN_REQUEST;
+                       PUT_32BIT(q, pklen); q += 4;
+                       memcpy(q, pkblob, pklen); q += pklen;
+                       PUT_32BIT(q, siglen); q += 4;
+                       /* Now the data to be signed... */
+                       PUT_32BIT(q, 20); q += 4;
+                       memcpy(q, ssh2_session_id, 20); q += 20;
+                       memcpy(q, pktout.data+5, pktout.length-5);
+                       q += pktout.length-5;
+                       /* And finally the (zero) flags word. */
+                       PUT_32BIT(q, 0);
+                       agent_query(agentreq, len+4, &ret, &retlen);
+                       sfree(agentreq);
+                       if (ret) {
+                           if (ret[4] == SSH2_AGENT_SIGN_RESPONSE) {
+                               logevent("Sending Pageant's response");
+                               ssh2_pkt_addstring_start();
+                               ssh2_pkt_addstring_data(ret+9, GET_32BIT(ret+5));
+                               ssh2_pkt_send();
+                               authed = TRUE;
+                               break;
+                           } else {
+                               logevent("Pageant failed to answer challenge");
+                               sfree(ret);
+                           }
+                       }
+                   }
+                   if (authed)
+                       continue;
+               }
+           }
+
+           if (!method && can_pubkey && *cfg.keyfile && !tried_pubkey_config) {
+               unsigned char *pub_blob;
+               char *algorithm, *comment;
+               int pub_blob_len;
+
+               tried_pubkey_config = TRUE;
+
+               /*
+                * 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(SSH2_MSG_USERAUTH_REQUEST);
+                   ssh2_pkt_addstring(username);
+                   ssh2_pkt_addstring("ssh-connection");   /* service requested */
+                   ssh2_pkt_addstring("publickey");/* method */
+                   ssh2_pkt_addbool(FALSE);   /* no signature included */
+                   ssh2_pkt_addstring(algorithm);
+                   ssh2_pkt_addstring_start();
+                   ssh2_pkt_addstring_data(pub_blob, pub_blob_len);
+                   ssh2_pkt_send();
+                   logevent("Offered public key"); /* FIXME */
+
+                   crWaitUntilV(ispkt);
+                   if (pktin.type != SSH2_MSG_USERAUTH_PK_OK) {
+                       gotit = TRUE;
+                       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(pwprompt, "Passphrase for key \"%.100s\": ", comment);
+                       need_pw = TRUE;
+                   } else {
+                       need_pw = FALSE;
+                   }
+                   c_write_str("Authenticating with public key \"");
+                   c_write_str(comment);
+                   c_write_str("\"\r\n");
+                   method = AUTH_PUBLICKEY_FILE;
+               }
+           }
+
+           if (!method && can_passwd) {
+               method = AUTH_PASSWORD;
+               sprintf(pwprompt, "%.90s@%.90s's password: ", username, savedhost);
+               need_pw = TRUE;
+           }
+
+           if (need_pw) {
+               if (ssh_get_password) {
+                   if (!ssh_get_password(pwprompt, password, sizeof(password))) {
+                       /*
+                        * get_password failed to get a password (for
+                        * example because one was supplied on the command
+                        * line which has already failed to work).
+                        * Terminate.
+                        */
+                       logevent("No more passwords to try");
+                       ssh_state = SSH_STATE_CLOSED;
+                       crReturnV;
+                   }
+               } else {
+                   static int pos = 0;
+                   static char c;
+
+                   c_write_str(pwprompt);
+                   ssh_send_ok = 1;
+
+                   pos = 0;
+                   while (pos >= 0) {
+                       crWaitUntilV(!ispkt);
+                       while (inlen--) switch (c = *in++) {
+                         case 10: case 13:
+                           password[pos] = 0;
+                           pos = -1;
+                           break;
+                         case 8: case 127:
+                           if (pos > 0)
+                               pos--;
+                           break;
+                         case 21: case 27:
+                           pos = 0;
+                           break;
+                         case 3: case 4:
+                           random_save_seed();
+                           exit(0);
+                           break;
+                         default:
+                           if (((c >= ' ' && c <= '~') ||
+                                ((unsigned char)c >= 160)) && pos < 40)
+                               password[pos++] = c;
+                           break;
+                       }
+                   }
+                   c_write_str("\r\n");
+               }
+           }
+
+           if (method == AUTH_PUBLICKEY_FILE) {
+               /*
+                * We have our passphrase. Now try the actual authentication.
+                */
+               struct ssh2_userkey *key;
+
+               key = ssh2_load_userkey(cfg.keyfile, password);
+               if (key == SSH2_WRONG_PASSPHRASE || key == NULL) {
+                   if (key == SSH2_WRONG_PASSPHRASE) {
+                       c_write_str("Wrong passphrase\r\n");
+                       tried_pubkey_config = FALSE;
+                   } else {
+                       c_write_str("Unable to load private key\r\n");
+                       tried_pubkey_config = TRUE;
+                   }
+                   /* Send a spurious AUTH_NONE to return to the top. */
+                   ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
+                   ssh2_pkt_addstring(username);
+                   ssh2_pkt_addstring("ssh-connection");   /* service requested */
+                   ssh2_pkt_addstring("none");    /* method */
+                   ssh2_pkt_send();
+                   type = AUTH_TYPE_NONE;
+               } else {
+                   unsigned char *blob, *sigdata;
+                   int blob_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(SSH2_MSG_USERAUTH_REQUEST);
+                   ssh2_pkt_addstring(username);
+                   ssh2_pkt_addstring("ssh-connection");   /* service requested */
+                   ssh2_pkt_addstring("publickey");    /* method */
+                   ssh2_pkt_addbool(TRUE);
+                   ssh2_pkt_addstring(key->alg->name);
+                   blob = key->alg->public_blob(key->data, &blob_len);
+                   ssh2_pkt_addstring_start();
+                   ssh2_pkt_addstring_data(blob, blob_len);
+                   sfree(blob);
+
+                   /*
+                    * The data to be signed is:
+                    *
+                    *   string  session-id
+                    *
+                    * followed by everything so far placed in the
+                    * outgoing packet.
+                    */
+                   sigdata_len = pktout.length - 5 + 4 + 20;
+                   sigdata = smalloc(sigdata_len);
+                   PUT_32BIT(sigdata, 20);
+                   memcpy(sigdata+4, ssh2_session_id, 20);
+                   memcpy(sigdata+24, pktout.data+5, pktout.length-5);
+                   blob = key->alg->sign(key->data, sigdata, sigdata_len, &blob_len);
+                   ssh2_pkt_addstring_start();
+                   ssh2_pkt_addstring_data(blob, blob_len);
+                   sfree(blob);
+                   sfree(sigdata);
+
+                   ssh2_pkt_send();
+                   type = AUTH_TYPE_PUBLICKEY;
+               }
+           } else if (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(SSH2_MSG_USERAUTH_REQUEST);
+               ssh2_pkt_addstring(username);
+               ssh2_pkt_addstring("ssh-connection");   /* service requested */
+               ssh2_pkt_addstring("password");
+               ssh2_pkt_addbool(FALSE);
+               ssh2_pkt_addstring(password);
+               ssh2_pkt_defer();
+               /*
+                * 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 (cscipher) {
+                   int i, j;
+                   ssh2_pkt_init(SSH2_MSG_IGNORE);
+                   ssh2_pkt_addstring_start();
+                   for (i = deferred_len; i <= 256; i += cscipher->blksize) {
+                       for (j = 0; j < cscipher->blksize; j++) {
+                           char c = (char)random_byte();
+                           ssh2_pkt_addstring_data(&c, 1);
+                       }
+                   }
+                   ssh2_pkt_defer();
+               }
+               ssh2_pkt_defersend();
+               logevent("Sent password\r\n");
+               type = AUTH_TYPE_PASSWORD;
+           } else {
+               c_write_str("No supported authentication methods left to try!\r\n");
+               logevent("No supported authentications offered. Disconnecting");
+               ssh2_pkt_init(SSH2_MSG_DISCONNECT);
+               ssh2_pkt_adduint32(SSH2_DISCONNECT_BY_APPLICATION);
+               ssh2_pkt_addstring("No supported authentication methods available");
+               ssh2_pkt_addstring("en");   /* language tag */
+               ssh2_pkt_send();
+               ssh_state = SSH_STATE_CLOSED;
+               crReturnV;
+           }
+       }
+    } while (!we_are_in);
 
     /*
      * Now we're authenticated for the connection protocol. The
@@ -2762,7 +3282,7 @@ static void do_ssh2_authconn(unsigned char *in, int inlen, int ispkt)
                 bombout(("Server got confused by pty request"));
                 crReturnV;
             }
-            c_write("Server refused to allocate pty\r\n", 32);
+            c_write_str("Server refused to allocate pty\r\n");
             ssh_editing = ssh_echoing = 1;
         } else {
             logevent("Allocated pty");
@@ -2776,7 +3296,11 @@ static void do_ssh2_authconn(unsigned char *in, int inlen, int ispkt)
      */
     ssh2_pkt_init(SSH2_MSG_CHANNEL_REQUEST);
     ssh2_pkt_adduint32(mainchan->remoteid); /* recipient channel */
-    if (*cfg.remote_cmd) {
+    if (cfg.ssh_subsys) {
+        ssh2_pkt_addstring("subsystem");
+        ssh2_pkt_addbool(1);           /* want reply */
+        ssh2_pkt_addstring(cfg.remote_cmd);
+    } else if (*cfg.remote_cmd) {
         ssh2_pkt_addstring("exec");
         ssh2_pkt_addbool(1);           /* want reply */
         ssh2_pkt_addstring(cfg.remote_cmd);