X-Git-Url: https://git.distorted.org.uk/u/mdw/putty/blobdiff_plain/d5859615f641e5bbd853cd42aafd4fa577da17eb..0d694692c59504838ec2043ddfe670b3a9247faf:/sshdss.c

diff --git a/sshdss.c b/sshdss.c
index 86a16176..bacf68d4 100644
--- a/sshdss.c
+++ b/sshdss.c
@@ -15,6 +15,29 @@
     (cp)[2] = (unsigned char)((value) >> 8); \
     (cp)[3] = (unsigned char)(value); }
 
+#if 0
+/*
+ * Condition this section in for debugging of DSS.
+ */
+static void diagbn(char *prefix, Bignum md) {
+    int i, nibbles, morenibbles;
+    static const char hex[] = "0123456789ABCDEF";
+
+    printf("%s0x", prefix ? prefix : "");
+
+    nibbles = (3 + ssh1_bignum_bitcount(md))/4; if (nibbles<1) nibbles=1;
+    morenibbles = 4*md[0] - nibbles;
+    for (i=0; i<morenibbles; i++) putchar('-');
+    for (i=nibbles; i-- ;)
+        putchar(hex[(bignum_byte(md, i/2) >> (4*(i%2))) & 0xF]);
+
+    if (prefix) putchar('\n');
+}
+#define DEBUG_DSS
+#else
+#define diagbn(x,y)
+#endif
+
 static void getstring(char **data, int *datalen, char **p, int *length) {
     *p = NULL;
     if (*datalen < 4)
@@ -44,6 +67,7 @@ static Bignum getmp(char **data, int *datalen) {
         else
             b[j/2+1] |= ((unsigned char)p[i]);
     }
+    while (b[0] > 1 && b[b[0]] == 0) b[0]--;
     return b;
 }
 
@@ -69,55 +93,85 @@ 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 = smalloc(sizeof(struct dss_key));
+    if (!dss) return NULL;
     getstring(&data, &len, &p, &slen);
+
+#ifdef DEBUG_DSS
+    {
+        int i;
+        printf("key:");
+        for (i=0;i<len;i++)
+            printf("  %02x", (unsigned char)(data[i]));
+        printf("\n");
+    }
+#endif
+
     if (!p || memcmp(p, "ssh-dss", 7)) {
-        dss_p = NULL;
-        return;
+	sfree(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);
+    sfree(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 */
-    p = malloc(len);
+    len += 4 * (dss->p[0] + dss->q[0] + dss->g[0] + dss->y[0]);   /* digits */
+    p = smalloc(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];
-    pos += sprintf(p+pos, "0x");
-    nibbles = (3 + ssh1_bignum_bitcount(dss_q))/4; if (nibbles<1) nibbles=1;
+        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;
     for (i=nibbles; i-- ;)
-        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;
+        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;
     for (i=nibbles; i-- ;)
-        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;
+        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;
     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];
@@ -134,97 +188,118 @@ 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);
+    ret = smalloc(strlen(buffer)+1);
     if (ret)
         strcpy(ret, buffer);
     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 i, slen;
+    int slen;
     char hash[20];
-    Bignum qm2, r, s, w, i1, i2, i3, u1, u2, sha, v;
+    Bignum r, s, w, gu1p, yu2p, gu1yu2p, u1, u2, sha, v;
     int ret;
 
-    if (!dss_p)
+    if (!dss->p)
         return 0;
 
-    getstring(&sig, &siglen, &p, &slen);
-    if (!p || memcmp(p, "ssh-dss", 7)) {
-        return 0;
+#ifdef DEBUG_DSS
+    {
+        int i;
+        printf("sig:");
+        for (i=0;i<siglen;i++)
+            printf("  %02xf", (unsigned char)(sig[i]));
+        printf("\n");
     }
-    sig += 4, siglen -= 4;             /* skip yet another length field */
+#endif
+    /*
+     * Commercial SSH (2.0.13) and OpenSSH disagree over the format
+     * of a DSA signature. OpenSSH is in line with the IETF drafts:
+     * it uses a string "ssh-dss", followed by a 40-byte string
+     * containing two 160-bit integers end-to-end. Commercial SSH
+     * can't be bothered with the header bit, and considers a DSA
+     * signature blob to be _just_ the 40-byte string containing
+     * the two 160-bit integers. We tell them apart by measuring
+     * the length: length 40 means the commercial-SSH bug, anything
+     * else is assumed to be IETF-compliant.
+     */
+    if (siglen != 40) {                /* bug not present; read admin fields */
+        getstring(&sig, &siglen, &p, &slen);
+        if (!p || memcmp(p, "ssh-dss", 7)) {
+            return 0;
+        }
+        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);
     r = get160(&sig, &siglen);
+    diagbn("r=", r);
     s = get160(&sig, &siglen);
+    diagbn("s=", s);
     if (!r || !s)
         return 0;
 
     /*
      * Step 1. w <- s^-1 mod q.
      */
-    w = newbn(dss_q[0]);
-    qm2 = copybn(dss_q);
-    decbn(qm2); decbn(qm2);
-    /* Now qm2 is q-2, and by Fermat's Little Theorem, s^qm2 == s^-1 (mod q).
-     * This is a silly way to do it; may fix it later. */
-    modpow(s, qm2, dss_q, w);
+    w = modinv(s, dss->q);
+    diagbn("w=", w);
 
     /*
      * Step 2. u1 <- SHA(message) * w mod q.
      */
-    u1 = newbn(dss_q[0]);
     SHA_Simple(data, datalen, hash);
     p = hash; slen = 20; sha = get160(&p, &slen);
-    modmul(sha, w, dss_q, u1);
+    diagbn("sha=", sha);
+    u1 = modmul(sha, w, dss->q);
+    diagbn("u1=", u1);
 
     /*
      * Step 3. u2 <- r * w mod q.
      */
-    u2 = newbn(dss_q[0]);
-    modmul(r, w, dss_q, u2);
+    u2 = modmul(r, w, dss->q);
+    diagbn("u2=", u2);
 
     /*
      * Step 4. v <- (g^u1 * y^u2 mod p) mod q.
      */
-    i1 = newbn(dss_p[0]);
-    i2 = newbn(dss_p[0]);
-    i3 = newbn(dss_p[0]);
-    v = newbn(dss_q[0]);
-    modpow(dss_g, u1, dss_p, i1);
-    modpow(dss_y, u2, dss_p, i2);
-    modmul(i1, i2, dss_p, i3);
-    modmul(i3, One, dss_q, v);
+    gu1p = modpow(dss->g, u1, dss->p);
+    diagbn("gu1p=", gu1p);
+    yu2p = modpow(dss->y, u2, dss->p);
+    diagbn("yu2p=", yu2p);
+    gu1yu2p = modmul(gu1p, yu2p, dss->p);
+    diagbn("gu1yu2p=", gu1yu2p);
+    v = modmul(gu1yu2p, One, dss->q);
+    diagbn("gu1yu2q=v=", v);
+    diagbn("r=", r);
 
     /*
      * Step 5. v should now be equal to r.
      */
 
-    ret = 1;
-    for (i = 1; i <= v[0] || i <= r[0]; i++) {
-        if ((i > v[0] && r[i] != 0) ||
-            (i > r[0] && v[i] != 0) ||
-            (i <= v[0] && i <= r[0] && r[i] != v[i]))
-            ret = 0;
-    }
+    ret = !bignum_cmp(v, r);
 
     freebn(w);
-    freebn(qm2);
     freebn(sha);
-    freebn(i1);
-    freebn(i2);
-    freebn(i3);
+    freebn(gu1p);
+    freebn(yu2p);
+    freebn(gu1yu2p);
     freebn(v);
     freebn(r);
     freebn(s);
@@ -232,11 +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"
 };