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 /*
  20  * Condition this section in for debugging of DSS.
  21  */
  22 static void diagbn(char *prefix, Bignum md) {
  23     int i, nibbles, morenibbles;
  24     static const char hex[] = "0123456789ABCDEF";
  25
  26     printf("%s0x", prefix ? prefix : "");
  27
  28     nibbles = (3 + ssh1_bignum_bitcount(md))/4; if (nibbles<1) nibbles=1;
  29     morenibbles = 4*md[0] - nibbles;
  30     for (i=0; i<morenibbles; i++) putchar('-');
  31     for (i=nibbles; i-- ;)
  32         putchar(hex[(bignum_byte(md, i/2) >> (4*(i%2))) & 0xF]);
  33
  34     if (prefix) putchar('\n');
  35 }
  36 #define DEBUG_DSS
  37 #else
  38 #define diagbn(x,y)
  39 #endif
  40
  41 static void getstring(char **data, int *datalen, char **p, int *length) {
  42     *p = NULL;
  43     if (*datalen < 4)
  44         return;
  45     *length = GET_32BIT(*data);
  46     *datalen -= 4; *data += 4;
  47     if (*datalen < *length)
  48         return;
  49     *p = *data;
  50     *data += *length; *datalen -= *length;
  51 }
  52 static Bignum getmp(char **data, int *datalen) {
  53     char *p;
  54     int i, j, length;
  55     Bignum b;
  56
  57     getstring(data, datalen, &p, &length);
  58     if (!p)
  59         return NULL;
  60     if (p[0] & 0x80)
  61         return NULL;                   /* negative mp */
  62     b = newbn((length+1)/2);
  63     for (i = 0; i < length; i++) {
  64         j = length - 1 - i;
  65         if (j & 1)
  66             b[j/2+1] |= ((unsigned char)p[i]) << 8;
  67         else
  68             b[j/2+1] |= ((unsigned char)p[i]);
  69     }
  70     while (b[0] > 1 && b[b[0]] == 0) b[0]--;
  71     return b;
  72 }
  73
  74 static Bignum get160(char **data, int *datalen) {
  75     char *p;
  76     int i, j, length;
  77     Bignum b;
  78
  79     p = *data;
  80     *data += 20; *datalen -= 20;
  81
  82     length = 20;
  83     while (length > 0 && !p[0])
  84         p++, length--;
  85     b = newbn((length+1)/2);
  86     for (i = 0; i < length; i++) {
  87         j = length - 1 - i;
  88         if (j & 1)
  89             b[j/2+1] |= ((unsigned char)p[i]) << 8;
  90         else
  91             b[j/2+1] |= ((unsigned char)p[i]);
  92     }
  93     return b;
  94 }
  95
  96 struct dss_key {
  97     Bignum p, q, g, y;
  98 };
  99
 100 static void *dss_newkey(char *data, int len) {
 101     char *p;
 102     int slen;
 103     struct dss_key *dss;
 104
 105     dss = malloc(sizeof(struct dss_key));
 106     if (!dss) return NULL;
 107     getstring(&data, &len, &p, &slen);
 108
 109 #ifdef DEBUG_DSS
 110     {
 111         int i;
 112         printf("key:");
 113         for (i=0;i<len;i++)
 114             printf("  %02x", (unsigned char)(data[i]));
 115         printf("\n");
 116     }
 117 #endif
 118
 119     if (!p || memcmp(p, "ssh-dss", 7)) {
 120         free(dss);
 121         return NULL;
 122     }
 123     dss->p = getmp(&data, &len);
 124     dss->q = getmp(&data, &len);
 125     dss->g = getmp(&data, &len);
 126     dss->y = getmp(&data, &len);
 127
 128     return dss;
 129 }
 130
 131 static void dss_freekey(void *key) {
 132     struct dss_key *dss = (struct dss_key *)key;
 133     freebn(dss->p);
 134     freebn(dss->q);
 135     freebn(dss->g);
 136     freebn(dss->y);
 137     free(dss);
 138 }
 139
 140 static char *dss_fmtkey(void *key) {
 141     struct dss_key *dss = (struct dss_key *)key;
 142     char *p;
 143     int len, i, pos, nibbles;
 144     static const char hex[] = "0123456789abcdef";
 145     if (!dss->p)
 146         return NULL;
 147     len = 8 + 4 + 1;                   /* 4 x "0x", punctuation, \0 */
 148     len += 4 * (dss->p[0] + dss->q[0] + dss->g[0] + dss->y[0]);   /* digits */
 149     p = malloc(len);
 150     if (!p) return NULL;
 151
 152     pos = 0;
 153     pos += sprintf(p+pos, "0x");
 154     nibbles = (3 + ssh1_bignum_bitcount(dss->p))/4; if (nibbles<1) nibbles=1;
 155     for (i=nibbles; i-- ;)
 156         p[pos++] = hex[(bignum_byte(dss->p, i/2) >> (4*(i%2))) & 0xF];
 157     pos += sprintf(p+pos, ",0x");
 158     nibbles = (3 + ssh1_bignum_bitcount(dss->q))/4; if (nibbles<1) nibbles=1;
 159     for (i=nibbles; i-- ;)
 160         p[pos++] = hex[(bignum_byte(dss->q, i/2) >> (4*(i%2))) & 0xF];
 161     pos += sprintf(p+pos, ",0x");
 162     nibbles = (3 + ssh1_bignum_bitcount(dss->g))/4; if (nibbles<1) nibbles=1;
 163     for (i=nibbles; i-- ;)
 164         p[pos++] = hex[(bignum_byte(dss->g, i/2) >> (4*(i%2))) & 0xF];
 165     pos += sprintf(p+pos, ",0x");
 166     nibbles = (3 + ssh1_bignum_bitcount(dss->y))/4; if (nibbles<1) nibbles=1;
 167     for (i=nibbles; i-- ;)
 168         p[pos++] = hex[(bignum_byte(dss->y, i/2) >> (4*(i%2))) & 0xF];
 169     p[pos] = '\0';
 170     return p;
 171 }
 172
 173 static char *dss_fingerprint(void *key) {
 174     struct dss_key *dss = (struct dss_key *)key;
 175     struct MD5Context md5c;
 176     unsigned char digest[16], lenbuf[4];
 177     char buffer[16*3+40];
 178     char *ret;
 179     int numlen, i;
 180
 181     MD5Init(&md5c);
 182     MD5Update(&md5c, "\0\0\0\7ssh-dss", 11);
 183
 184 #define ADD_BIGNUM(bignum) \
 185     numlen = (ssh1_bignum_bitcount(bignum)+8)/8; \
 186     PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \
 187     for (i = numlen; i-- ;) { \
 188         unsigned char c = bignum_byte(bignum, i); \
 189         MD5Update(&md5c, &c, 1); \
 190     }
 191     ADD_BIGNUM(dss->p);
 192     ADD_BIGNUM(dss->q);
 193     ADD_BIGNUM(dss->g);
 194     ADD_BIGNUM(dss->y);
 195 #undef ADD_BIGNUM
 196
 197     MD5Final(digest, &md5c);
 198
 199     sprintf(buffer, "%d ", ssh1_bignum_bitcount(dss->p));
 200     for (i = 0; i < 16; i++)
 201         sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
 202     ret = malloc(strlen(buffer)+1);
 203     if (ret)
 204         strcpy(ret, buffer);
 205     return ret;
 206 }
 207
 208 static int dss_verifysig(void *key, char *sig, int siglen,
 209                          char *data, int datalen) {
 210     struct dss_key *dss = (struct dss_key *)key;
 211     char *p;
 212     int slen;
 213     char hash[20];
 214     Bignum r, s, w, gu1p, yu2p, gu1yu2p, u1, u2, sha, v;
 215     int ret;
 216
 217     if (!dss->p)
 218         return 0;
 219
 220 #ifdef DEBUG_DSS
 221     {
 222         int i;
 223         printf("sig:");
 224         for (i=0;i<siglen;i++)
 225             printf("  %02xf", (unsigned char)(sig[i]));
 226         printf("\n");
 227     }
 228 #endif
 229     /*
 230      * Commercial SSH (2.0.13) and OpenSSH disagree over the format
 231      * of a DSA signature. OpenSSH is in line with the IETF drafts:
 232      * it uses a string "ssh-dss", followed by a 40-byte string
 233      * containing two 160-bit integers end-to-end. Commercial SSH
 234      * can't be bothered with the header bit, and considers a DSA
 235      * signature blob to be _just_ the 40-byte string containing
 236      * the two 160-bit integers. We tell them apart by measuring
 237      * the length: length 40 means the commercial-SSH bug, anything
 238      * else is assumed to be IETF-compliant.
 239      */
 240     if (siglen != 40) {                /* bug not present; read admin fields */
 241         getstring(&sig, &siglen, &p, &slen);
 242         if (!p || memcmp(p, "ssh-dss", 7)) {
 243             return 0;
 244         }
 245         sig += 4, siglen -= 4;             /* skip yet another length field */
 246     }
 247     diagbn("p=", dss->p);
 248     diagbn("q=", dss->q);
 249     diagbn("g=", dss->g);
 250     diagbn("y=", dss->y);
 251     r = get160(&sig, &siglen);
 252     diagbn("r=", r);
 253     s = get160(&sig, &siglen);
 254     diagbn("s=", s);
 255     if (!r || !s)
 256         return 0;
 257
 258     /*
 259      * Step 1. w <- s^-1 mod q.
 260      */
 261     w = modinv(s, dss->q);
 262     diagbn("w=", w);
 263
 264     /*
 265      * Step 2. u1 <- SHA(message) * w mod q.
 266      */
 267     SHA_Simple(data, datalen, hash);
 268     p = hash; slen = 20; sha = get160(&p, &slen);
 269     diagbn("sha=", sha);
 270     u1 = modmul(sha, w, dss->q);
 271     diagbn("u1=", u1);
 272
 273     /*
 274      * Step 3. u2 <- r * w mod q.
 275      */
 276     u2 = modmul(r, w, dss->q);
 277     diagbn("u2=", u2);
 278
 279     /*
 280      * Step 4. v <- (g^u1 * y^u2 mod p) mod q.
 281      */
 282     gu1p = modpow(dss->g, u1, dss->p);
 283     diagbn("gu1p=", gu1p);
 284     yu2p = modpow(dss->y, u2, dss->p);
 285     diagbn("yu2p=", yu2p);
 286     gu1yu2p = modmul(gu1p, yu2p, dss->p);
 287     diagbn("gu1yu2p=", gu1yu2p);
 288     v = modmul(gu1yu2p, One, dss->q);
 289     diagbn("gu1yu2q=v=", v);
 290     diagbn("r=", r);
 291
 292     /*
 293      * Step 5. v should now be equal to r.
 294      */
 295
 296     ret = !bignum_cmp(v, r);
 297
 298     freebn(w);
 299     freebn(sha);
 300     freebn(gu1p);
 301     freebn(yu2p);
 302     freebn(gu1yu2p);
 303     freebn(v);
 304     freebn(r);
 305     freebn(s);
 306
 307     return ret;
 308 }
 309
 310 int dss_sign(void *key, char *sig, int siglen,
 311              char *data, int datalen) {
 312     return 0;                          /* do nothing */
 313 }
 314
 315 struct ssh_signkey ssh_dss = {
 316     dss_newkey,
 317     dss_freekey,
 318     dss_fmtkey,
 319     dss_fingerprint,
 320     dss_verifysig,
 321     dss_sign,
 322     "ssh-dss",
 323     "dss"
 324 };