Improve SSH2 host key abstraction into a generic `signing key'

abstraction, so as to be able to re-use the same abstraction for
user authentication keys and probably in the SSH2 agent (when that
happens) as well.

git-svn-id: svn://svn.tartarus.org/sgt/putty@815 cda61777-01e9-0310-a592-d414129be87e

diff --git a/ssh.c b/ssh.c
index e7518b6..92afd08 100644 (file)
--- a/ssh.c
+++ b/ssh.c
@@ -171,8 +171,8 @@ 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 };
 
-extern const struct ssh_hostkey ssh_dss;
-const static struct ssh_hostkey *hostkey_algs[] = { &ssh_dss };
+extern const struct ssh_signkey ssh_dss;
+const static struct ssh_signkey *hostkey_algs[] = { &ssh_dss };
 
 extern const struct ssh_mac ssh_md5, ssh_sha1, ssh_sha1_buggy;
 
@@ -246,7 +246,7 @@ 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_hostkey *hostkey = NULL;
+static const struct ssh_signkey *hostkey = NULL;
 int (*ssh_get_password)(const char *prompt, char *str, int maxlen) = NULL;
 
 static char *savedhost;
@@ -1987,6 +1987,7 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
     static const struct ssh_compress *sccomp_tobe = NULL;
     static char *hostkeydata, *sigdata, *keystr, *fingerprint;
     static int hostkeylen, siglen;
+    static void *hkey;                /* actual host key */
     static unsigned char exchange_hash[20];
     static unsigned char keyspace[40];
     static const struct ssh_cipher *preferred_cipher;
@@ -2216,8 +2217,8 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
     debug(("\r\n"));
 #endif
 
-    hostkey->setkey(hostkeydata, hostkeylen);
-    if (!hostkey->verifysig(sigdata, siglen, exchange_hash, 20)) {
+    hkey = hostkey->newkey(hostkeydata, hostkeylen);
+    if (!hostkey->verifysig(hkey, sigdata, siglen, exchange_hash, 20)) {
         bombout(("Server failed host key check"));
         crReturn(0);
     }
@@ -2235,14 +2236,15 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
      * Authenticate remote host: verify host key. (We've already
      * checked the signature of the exchange hash.)
      */
-    keystr = hostkey->fmtkey();
-    fingerprint = hostkey->fingerprint();
+    keystr = hostkey->fmtkey(hkey);
+    fingerprint = hostkey->fingerprint(hkey);
     verify_ssh_host_key(savedhost, savedport, hostkey->keytype,
                         keystr, fingerprint);
     logevent("Host key fingerprint is:");
     logevent(fingerprint);
     free(fingerprint);
     free(keystr);
+    hostkey->freekey(hkey);
 
     /*
      * Send SSH2_MSG_NEWKEYS.

diff --git a/ssh.h b/ssh.h
index 3d89dee..b999c66 100644 (file)
--- a/ssh.h
+++ b/ssh.h
@@ -126,11 +126,15 @@ struct ssh_kex {
     char *name;
 };
 
-struct ssh_hostkey {
-    void (*setkey)(char *data, int len);
-    char *(*fmtkey)(void);
-    char *(*fingerprint)(void);
-    int (*verifysig)(char *sig, int siglen, char *data, int datalen);
+struct ssh_signkey {
+    void *(*newkey)(char *data, int len);
+    void (*freekey)(void *key);
+    char *(*fmtkey)(void *key);
+    char *(*fingerprint)(void *key);
+    int (*verifysig)(void *key, char *sig, int siglen,
+                    char *data, int datalen);
+    int (*sign)(void *key, char *sig, int siglen,
+               char *data, int datalen);
     char *name;
     char *keytype;                     /* for host key cache */
 };

diff --git a/sshdss.c b/sshdss.c
index 15b97ba..656fa68 100644 (file)
--- a/sshdss.c
+++ b/sshdss.c
@@ -93,11 +93,17 @@ static Bignum get160(char **data, int *datalen) {
     return b;
 }
 
-static Bignum dss_p, dss_q, dss_g, dss_y;
+struct dss_key {
+    Bignum p, q, g, y;
+};
 
-static void dss_setkey(char *data, int len) {
+static void *dss_newkey(char *data, int len) {
     char *p;
     int slen;
+    struct dss_key *dss;
+
+    dss = malloc(sizeof(struct dss_key));
+    if (!dss) return NULL;
     getstring(&data, &len, &p, &slen);
 
 #ifdef DEBUG_DSS
@@ -111,48 +117,61 @@ static void dss_setkey(char *data, int len) {
 #endif
 
     if (!p || memcmp(p, "ssh-dss", 7)) {
-        dss_p = NULL;
-        return;
+       free(dss);
+       return NULL;
     }
-    dss_p = getmp(&data, &len);
-    dss_q = getmp(&data, &len);
-    dss_g = getmp(&data, &len);
-    dss_y = getmp(&data, &len);
+    dss->p = getmp(&data, &len);
+    dss->q = getmp(&data, &len);
+    dss->g = getmp(&data, &len);
+    dss->y = getmp(&data, &len);
+
+    return dss;
 }
 
-static char *dss_fmtkey(void) {
+static void dss_freekey(void *key) {
+    struct dss_key *dss = (struct dss_key *)key;
+    freebn(dss->p);
+    freebn(dss->q);
+    freebn(dss->g);
+    freebn(dss->y);
+    free(dss);
+}
+
+static char *dss_fmtkey(void *key) {
+    struct dss_key *dss = (struct dss_key *)key;
     char *p;
     int len, i, pos, nibbles;
     static const char hex[] = "0123456789abcdef";
-    if (!dss_p)
+    if (!dss->p)
         return NULL;
     len = 8 + 4 + 1;                   /* 4 x "0x", punctuation, \0 */
-    len += 4 * (dss_p[0] + dss_q[0] + dss_g[0] + dss_y[0]);   /* digits */
+    len += 4 * (dss->p[0] + dss->q[0] + dss->g[0] + dss->y[0]);   /* digits */
     p = malloc(len);
     if (!p) return NULL;
 
     pos = 0;
     pos += sprintf(p+pos, "0x");
-    nibbles = (3 + ssh1_bignum_bitcount(dss_p))/4; if (nibbles<1) nibbles=1;
+    nibbles = (3 + ssh1_bignum_bitcount(dss->p))/4; if (nibbles<1) nibbles=1;
     for (i=nibbles; i-- ;)
-        p[pos++] = hex[(bignum_byte(dss_p, i/2) >> (4*(i%2))) & 0xF];
+        p[pos++] = hex[(bignum_byte(dss->p, i/2) >> (4*(i%2))) & 0xF];
     pos += sprintf(p+pos, ",0x");
-    nibbles = (3 + ssh1_bignum_bitcount(dss_q))/4; if (nibbles<1) nibbles=1;
+    nibbles = (3 + ssh1_bignum_bitcount(dss->q))/4; if (nibbles<1) nibbles=1;
     for (i=nibbles; i-- ;)
-        p[pos++] = hex[(bignum_byte(dss_q, i/2) >> (4*(i%2))) & 0xF];
+        p[pos++] = hex[(bignum_byte(dss->q, i/2) >> (4*(i%2))) & 0xF];
     pos += sprintf(p+pos, ",0x");
-    nibbles = (3 + ssh1_bignum_bitcount(dss_g))/4; if (nibbles<1) nibbles=1;
+    nibbles = (3 + ssh1_bignum_bitcount(dss->g))/4; if (nibbles<1) nibbles=1;
     for (i=nibbles; i-- ;)
-        p[pos++] = hex[(bignum_byte(dss_g, i/2) >> (4*(i%2))) & 0xF];
+        p[pos++] = hex[(bignum_byte(dss->g, i/2) >> (4*(i%2))) & 0xF];
     pos += sprintf(p+pos, ",0x");
-    nibbles = (3 + ssh1_bignum_bitcount(dss_y))/4; if (nibbles<1) nibbles=1;
+    nibbles = (3 + ssh1_bignum_bitcount(dss->y))/4; if (nibbles<1) nibbles=1;
     for (i=nibbles; i-- ;)
-        p[pos++] = hex[(bignum_byte(dss_y, i/2) >> (4*(i%2))) & 0xF];
+        p[pos++] = hex[(bignum_byte(dss->y, i/2) >> (4*(i%2))) & 0xF];
     p[pos] = '\0';
     return p;
 }
 
-static char *dss_fingerprint(void) {
+static char *dss_fingerprint(void *key) {
+    struct dss_key *dss = (struct dss_key *)key;
     struct MD5Context md5c;
     unsigned char digest[16], lenbuf[4];
     char buffer[16*3+40];
@@ -169,15 +188,15 @@ static char *dss_fingerprint(void) {
         unsigned char c = bignum_byte(bignum, i); \
         MD5Update(&md5c, &c, 1); \
     }
-    ADD_BIGNUM(dss_p);
-    ADD_BIGNUM(dss_q);
-    ADD_BIGNUM(dss_g);
-    ADD_BIGNUM(dss_y);
+    ADD_BIGNUM(dss->p);
+    ADD_BIGNUM(dss->q);
+    ADD_BIGNUM(dss->g);
+    ADD_BIGNUM(dss->y);
 #undef ADD_BIGNUM
 
     MD5Final(digest, &md5c);
 
-    sprintf(buffer, "%d ", ssh1_bignum_bitcount(dss_p));
+    sprintf(buffer, "%d ", ssh1_bignum_bitcount(dss->p));
     for (i = 0; i < 16; i++)
         sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
     ret = malloc(strlen(buffer)+1);
@@ -186,14 +205,16 @@ static char *dss_fingerprint(void) {
     return ret;
 }
 
-static int dss_verifysig(char *sig, int siglen, char *data, int datalen) {
+static int dss_verifysig(void *key, char *sig, int siglen,
+                        char *data, int datalen) {
+    struct dss_key *dss = (struct dss_key *)key;
     char *p;
     int slen;
     char hash[20];
     Bignum r, s, w, gu1p, yu2p, gu1yu2p, u1, u2, sha, v;
     int ret;
 
-    if (!dss_p)
+    if (!dss->p)
         return 0;
 
 #ifdef DEBUG_DSS
@@ -223,10 +244,10 @@ static int dss_verifysig(char *sig, int siglen, char *data, int datalen) {
         }
         sig += 4, siglen -= 4;             /* skip yet another length field */
     }
-    diagbn("p=", dss_p);
-    diagbn("q=", dss_q);
-    diagbn("g=", dss_g);
-    diagbn("y=", dss_y);
+    diagbn("p=", dss->p);
+    diagbn("q=", dss->q);
+    diagbn("g=", dss->g);
+    diagbn("y=", dss->y);
     r = get160(&sig, &siglen);
     diagbn("r=", r);
     s = get160(&sig, &siglen);
@@ -237,7 +258,7 @@ static int dss_verifysig(char *sig, int siglen, char *data, int datalen) {
     /*
      * Step 1. w <- s^-1 mod q.
      */
-    w = modinv(s, dss_q);
+    w = modinv(s, dss->q);
     diagbn("w=", w);
 
     /*
@@ -246,25 +267,25 @@ static int dss_verifysig(char *sig, int siglen, char *data, int datalen) {
     SHA_Simple(data, datalen, hash);
     p = hash; slen = 20; sha = get160(&p, &slen);
     diagbn("sha=", sha);
-    u1 = modmul(sha, w, dss_q);
+    u1 = modmul(sha, w, dss->q);
     diagbn("u1=", u1);
 
     /*
      * Step 3. u2 <- r * w mod q.
      */
-    u2 = modmul(r, w, dss_q);
+    u2 = modmul(r, w, dss->q);
     diagbn("u2=", u2);
 
     /*
      * Step 4. v <- (g^u1 * y^u2 mod p) mod q.
      */
-    gu1p = modpow(dss_g, u1, dss_p);
+    gu1p = modpow(dss->g, u1, dss->p);
     diagbn("gu1p=", gu1p);
-    yu2p = modpow(dss_y, u2, dss_p);
+    yu2p = modpow(dss->y, u2, dss->p);
     diagbn("yu2p=", yu2p);
-    gu1yu2p = modmul(gu1p, yu2p, dss_p);
+    gu1yu2p = modmul(gu1p, yu2p, dss->p);
     diagbn("gu1yu2p=", gu1yu2p);
-    v = modmul(gu1yu2p, One, dss_q);
+    v = modmul(gu1yu2p, One, dss->q);
     diagbn("gu1yu2q=v=", v);
     diagbn("r=", r);
 
@@ -286,11 +307,18 @@ static int dss_verifysig(char *sig, int siglen, char *data, int datalen) {
     return ret;
 }
 
-struct ssh_hostkey ssh_dss = {
-    dss_setkey,
+int dss_sign(void *key, char *sig, int siglen,
+            char *data, int datalen) {
+    return 0;                         /* do nothing */
+}
+
+struct ssh_signkey ssh_dss = {
+    dss_newkey,
+    dss_freekey,
     dss_fmtkey,
     dss_fingerprint,
     dss_verifysig,
+    dss_sign,
     "ssh-dss",
     "dss"
 };