git.distorted.org.uk Git - u/mdw/putty/blob - sshdss.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3
   4 #include "ssh.h"
   5
   6 #define GET_32BIT(cp) \
   7     (((unsigned long)(unsigned char)(cp)[0] << 24) | \
   8     ((unsigned long)(unsigned char)(cp)[1] << 16) | \
   9     ((unsigned long)(unsigned char)(cp)[2] << 8) | \
  10     ((unsigned long)(unsigned char)(cp)[3]))
  11
  12 #define PUT_32BIT(cp, value) { \
  13     (cp)[0] = (unsigned char)((value) >> 24); \
  14     (cp)[1] = (unsigned char)((value) >> 16); \
  15     (cp)[2] = (unsigned char)((value) >> 8); \
  16     (cp)[3] = (unsigned char)(value); }
  17
  18 #if 0
  19 #define DEBUG_DSS
  20 #else
  21 #define diagbn(x,y)
  22 #endif
  23
  24 static void getstring(char **data, int *datalen, char **p, int *length) {
  25     *p = NULL;
  26     if (*datalen < 4)
  27         return;
  28     *length = GET_32BIT(*data);
  29     *datalen -= 4; *data += 4;
  30     if (*datalen < *length)
  31         return;
  32     *p = *data;
  33     *data += *length; *datalen -= *length;
  34 }
  35 static Bignum getmp(char **data, int *datalen) {
  36     char *p;
  37     int length;
  38     Bignum b;
  39
  40     getstring(data, datalen, &p, &length);
  41     if (!p)
  42         return NULL;
  43     if (p[0] & 0x80)
  44         return NULL;                   /* negative mp */
  45     b = bignum_from_bytes(p, length);
  46     return b;
  47 }
  48
  49 static Bignum get160(char **data, int *datalen) {
  50     Bignum b;
  51
  52     b = bignum_from_bytes(*data, 20);
  53     *data += 20; *datalen -= 20;
  54
  55     return b;
  56 }
  57
  58 struct dss_key {
  59     Bignum p, q, g, y;
  60 };
  61
  62 static void *dss_newkey(char *data, int len) {
  63     char *p;
  64     int slen;
  65     struct dss_key *dss;
  66
  67     dss = smalloc(sizeof(struct dss_key));
  68     if (!dss) return NULL;
  69     getstring(&data, &len, &p, &slen);
  70
  71 #ifdef DEBUG_DSS
  72     {
  73         int i;
  74         printf("key:");
  75         for (i=0;i<len;i++)
  76             printf("  %02x", (unsigned char)(data[i]));
  77         printf("\n");
  78     }
  79 #endif
  80
  81     if (!p || memcmp(p, "ssh-dss", 7)) {
  82         sfree(dss);
  83         return NULL;
  84     }
  85     dss->p = getmp(&data, &len);
  86     dss->q = getmp(&data, &len);
  87     dss->g = getmp(&data, &len);
  88     dss->y = getmp(&data, &len);
  89
  90     return dss;
  91 }
  92
  93 static void dss_freekey(void *key) {
  94     struct dss_key *dss = (struct dss_key *)key;
  95     freebn(dss->p);
  96     freebn(dss->q);
  97     freebn(dss->g);
  98     freebn(dss->y);
  99     sfree(dss);
 100 }
 101
 102 static char *dss_fmtkey(void *key) {
 103     struct dss_key *dss = (struct dss_key *)key;
 104     char *p;
 105     int len, i, pos, nibbles;
 106     static const char hex[] = "0123456789abcdef";
 107     if (!dss->p)
 108         return NULL;
 109     len = 8 + 4 + 1;                   /* 4 x "0x", punctuation, \0 */
 110     len += 4 * (ssh1_bignum_bitcount(dss->p)+15)/16;
 111     len += 4 * (ssh1_bignum_bitcount(dss->q)+15)/16;
 112     len += 4 * (ssh1_bignum_bitcount(dss->g)+15)/16;
 113     len += 4 * (ssh1_bignum_bitcount(dss->y)+15)/16;
 114     p = smalloc(len);
 115     if (!p) return NULL;
 116
 117     pos = 0;
 118     pos += sprintf(p+pos, "0x");
 119     nibbles = (3 + ssh1_bignum_bitcount(dss->p))/4; if (nibbles<1) nibbles=1;
 120     for (i=nibbles; i-- ;)
 121         p[pos++] = hex[(bignum_byte(dss->p, i/2) >> (4*(i%2))) & 0xF];
 122     pos += sprintf(p+pos, ",0x");
 123     nibbles = (3 + ssh1_bignum_bitcount(dss->q))/4; if (nibbles<1) nibbles=1;
 124     for (i=nibbles; i-- ;)
 125         p[pos++] = hex[(bignum_byte(dss->q, i/2) >> (4*(i%2))) & 0xF];
 126     pos += sprintf(p+pos, ",0x");
 127     nibbles = (3 + ssh1_bignum_bitcount(dss->g))/4; if (nibbles<1) nibbles=1;
 128     for (i=nibbles; i-- ;)
 129         p[pos++] = hex[(bignum_byte(dss->g, i/2) >> (4*(i%2))) & 0xF];
 130     pos += sprintf(p+pos, ",0x");
 131     nibbles = (3 + ssh1_bignum_bitcount(dss->y))/4; if (nibbles<1) nibbles=1;
 132     for (i=nibbles; i-- ;)
 133         p[pos++] = hex[(bignum_byte(dss->y, i/2) >> (4*(i%2))) & 0xF];
 134     p[pos] = '\0';
 135     return p;
 136 }
 137
 138 static char *dss_fingerprint(void *key) {
 139     struct dss_key *dss = (struct dss_key *)key;
 140     struct MD5Context md5c;
 141     unsigned char digest[16], lenbuf[4];
 142     char buffer[16*3+40];
 143     char *ret;
 144     int numlen, i;
 145
 146     MD5Init(&md5c);
 147     MD5Update(&md5c, "\0\0\0\7ssh-dss", 11);
 148
 149 #define ADD_BIGNUM(bignum) \
 150     numlen = (ssh1_bignum_bitcount(bignum)+8)/8; \
 151     PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \
 152     for (i = numlen; i-- ;) { \
 153         unsigned char c = bignum_byte(bignum, i); \
 154         MD5Update(&md5c, &c, 1); \
 155     }
 156     ADD_BIGNUM(dss->p);
 157     ADD_BIGNUM(dss->q);
 158     ADD_BIGNUM(dss->g);
 159     ADD_BIGNUM(dss->y);
 160 #undef ADD_BIGNUM
 161
 162     MD5Final(digest, &md5c);
 163
 164     sprintf(buffer, "%d ", ssh1_bignum_bitcount(dss->p));
 165     for (i = 0; i < 16; i++)
 166         sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
 167     ret = smalloc(strlen(buffer)+1);
 168     if (ret)
 169         strcpy(ret, buffer);
 170     return ret;
 171 }
 172
 173 static int dss_verifysig(void *key, char *sig, int siglen,
 174                          char *data, int datalen) {
 175     struct dss_key *dss = (struct dss_key *)key;
 176     char *p;
 177     int slen;
 178     char hash[20];
 179     Bignum r, s, w, gu1p, yu2p, gu1yu2p, u1, u2, sha, v;
 180     int ret;
 181
 182     if (!dss->p)
 183         return 0;
 184
 185 #ifdef DEBUG_DSS
 186     {
 187         int i;
 188         printf("sig:");
 189         for (i=0;i<siglen;i++)
 190             printf("  %02x", (unsigned char)(sig[i]));
 191         printf("\n");
 192     }
 193 #endif
 194     /*
 195      * Commercial SSH (2.0.13) and OpenSSH disagree over the format
 196      * of a DSA signature. OpenSSH is in line with the IETF drafts:
 197      * it uses a string "ssh-dss", followed by a 40-byte string
 198      * containing two 160-bit integers end-to-end. Commercial SSH
 199      * can't be bothered with the header bit, and considers a DSA
 200      * signature blob to be _just_ the 40-byte string containing
 201      * the two 160-bit integers. We tell them apart by measuring
 202      * the length: length 40 means the commercial-SSH bug, anything
 203      * else is assumed to be IETF-compliant.
 204      */
 205     if (siglen != 40) {                /* bug not present; read admin fields */
 206         getstring(&sig, &siglen, &p, &slen);
 207         if (!p || slen != 7 || memcmp(p, "ssh-dss", 7)) {
 208             return 0;
 209         }
 210         sig += 4, siglen -= 4;             /* skip yet another length field */
 211     }
 212     diagbn("p=", dss->p);
 213     diagbn("q=", dss->q);
 214     diagbn("g=", dss->g);
 215     diagbn("y=", dss->y);
 216     r = get160(&sig, &siglen);
 217     diagbn("r=", r);
 218     s = get160(&sig, &siglen);
 219     diagbn("s=", s);
 220     if (!r || !s)
 221         return 0;
 222
 223     /*
 224      * Step 1. w <- s^-1 mod q.
 225      */
 226     w = modinv(s, dss->q);
 227     diagbn("w=", w);
 228
 229     /*
 230      * Step 2. u1 <- SHA(message) * w mod q.
 231      */
 232     SHA_Simple(data, datalen, hash);
 233     p = hash; slen = 20; sha = get160(&p, &slen);
 234     diagbn("sha=", sha);
 235     u1 = modmul(sha, w, dss->q);
 236     diagbn("u1=", u1);
 237
 238     /*
 239      * Step 3. u2 <- r * w mod q.
 240      */
 241     u2 = modmul(r, w, dss->q);
 242     diagbn("u2=", u2);
 243
 244     /*
 245      * Step 4. v <- (g^u1 * y^u2 mod p) mod q.
 246      */
 247     gu1p = modpow(dss->g, u1, dss->p);
 248     diagbn("gu1p=", gu1p);
 249     yu2p = modpow(dss->y, u2, dss->p);
 250     diagbn("yu2p=", yu2p);
 251     gu1yu2p = modmul(gu1p, yu2p, dss->p);
 252     diagbn("gu1yu2p=", gu1yu2p);
 253     v = modmul(gu1yu2p, One, dss->q);
 254     diagbn("gu1yu2q=v=", v);
 255     diagbn("r=", r);
 256
 257     /*
 258      * Step 5. v should now be equal to r.
 259      */
 260
 261     ret = !bignum_cmp(v, r);
 262
 263     freebn(w);
 264     freebn(sha);
 265     freebn(gu1p);
 266     freebn(yu2p);
 267     freebn(gu1yu2p);
 268     freebn(v);
 269     freebn(r);
 270     freebn(s);
 271
 272     return ret;
 273 }
 274
 275 int dss_sign(void *key, char *sig, int siglen,
 276              char *data, int datalen) {
 277     return 0;                          /* do nothing */
 278 }
 279
 280 struct ssh_signkey ssh_dss = {
 281     dss_newkey,
 282     dss_freekey,
 283     dss_fmtkey,
 284     dss_fingerprint,
 285     dss_verifysig,
 286     dss_sign,
 287     "ssh-dss",
 288     "dss"
 289 };