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

   1 /*
   2  * RSA implementation just sufficient for ssh client-side
   3  * initialisation step
   4  *
   5  * Rewritten for more speed by Joris van Rantwijk, Jun 1999.
   6  */
   7
   8 #include <stdio.h>
   9 #include <stdlib.h>
  10 #include <string.h>
  11 #include <assert.h>
  12
  13 #include "ssh.h"
  14
  15
  16 int makekey(unsigned char *data, struct RSAKey *result,
  17             unsigned char **keystr, int order) {
  18     unsigned char *p = data;
  19     int i;
  20
  21     if (result) {
  22         result->bits = 0;
  23         for (i=0; i<4; i++)
  24             result->bits = (result->bits << 8) + *p++;
  25     } else
  26         p += 4;
  27
  28     /*
  29      * order=0 means exponent then modulus (the keys sent by the
  30      * server). order=1 means modulus then exponent (the keys
  31      * stored in a keyfile).
  32      */
  33
  34     if (order == 0)
  35         p += ssh1_read_bignum(p, result ? &result->exponent : NULL);
  36     if (result)
  37         result->bytes = (((p[0] << 8) + p[1]) + 7) / 8;
  38     if (keystr) *keystr = p+2;
  39     p += ssh1_read_bignum(p, result ? &result->modulus : NULL);
  40     if (order == 1)
  41         p += ssh1_read_bignum(p, result ? &result->exponent : NULL);
  42
  43     return p - data;
  44 }
  45
  46 int makeprivate(unsigned char *data, struct RSAKey *result) {
  47     return ssh1_read_bignum(data, &result->private_exponent);
  48 }
  49
  50 void rsaencrypt(unsigned char *data, int length, struct RSAKey *key) {
  51     Bignum b1, b2;
  52     int i;
  53     unsigned char *p;
  54
  55     memmove(data+key->bytes-length, data, length);
  56     data[0] = 0;
  57     data[1] = 2;
  58
  59     for (i = 2; i < key->bytes-length-1; i++) {
  60         do {
  61             data[i] = random_byte();
  62         } while (data[i] == 0);
  63     }
  64     data[key->bytes-length-1] = 0;
  65
  66     b1 = bignum_from_bytes(data, key->bytes);
  67
  68     b2 = modpow(b1, key->exponent, key->modulus);
  69
  70     p = data;
  71     for (i=key->bytes; i-- ;) {
  72         *p++ = bignum_byte(b2, i);
  73     }
  74
  75     freebn(b1);
  76     freebn(b2);
  77 }
  78
  79 Bignum rsadecrypt(Bignum input, struct RSAKey *key) {
  80     Bignum ret;
  81     ret = modpow(input, key->private_exponent, key->modulus);
  82     return ret;
  83 }
  84
  85 int rsastr_len(struct RSAKey *key) {
  86     Bignum md, ex;
  87     int mdlen, exlen;
  88
  89     md = key->modulus;
  90     ex = key->exponent;
  91     mdlen = (ssh1_bignum_bitcount(md)+15) / 16;
  92     exlen = (ssh1_bignum_bitcount(ex)+15) / 16;
  93     return 4 * (mdlen+exlen) + 20;
  94 }
  95
  96 void rsastr_fmt(char *str, struct RSAKey *key) {
  97     Bignum md, ex;
  98     int len = 0, i, nibbles;
  99     static const char hex[] = "0123456789abcdef";
 100
 101     md = key->modulus;
 102     ex = key->exponent;
 103
 104     len += sprintf(str+len, "0x");
 105
 106     nibbles = (3 + ssh1_bignum_bitcount(ex))/4; if (nibbles<1) nibbles=1;
 107     for (i=nibbles; i-- ;)
 108         str[len++] = hex[(bignum_byte(ex, i/2) >> (4*(i%2))) & 0xF];
 109
 110     len += sprintf(str+len, ",0x");
 111
 112     nibbles = (3 + ssh1_bignum_bitcount(md))/4; if (nibbles<1) nibbles=1;
 113     for (i=nibbles; i-- ;)
 114         str[len++] = hex[(bignum_byte(md, i/2) >> (4*(i%2))) & 0xF];
 115
 116     str[len] = '\0';
 117 }
 118
 119 /*
 120  * Generate a fingerprint string for the key. Compatible with the
 121  * OpenSSH fingerprint code.
 122  */
 123 void rsa_fingerprint(char *str, int len, struct RSAKey *key) {
 124     struct MD5Context md5c;
 125     unsigned char digest[16];
 126     char buffer[16*3+40];
 127     int numlen, slen, i;
 128
 129     MD5Init(&md5c);
 130     numlen = ssh1_bignum_length(key->modulus) - 2;
 131     for (i = numlen; i-- ;) {
 132         unsigned char c = bignum_byte(key->modulus, i);
 133         MD5Update(&md5c, &c, 1);
 134     }
 135     numlen = ssh1_bignum_length(key->exponent) - 2;
 136     for (i = numlen; i-- ;) {
 137         unsigned char c = bignum_byte(key->exponent, i);
 138         MD5Update(&md5c, &c, 1);
 139     }
 140     MD5Final(digest, &md5c);
 141
 142     sprintf(buffer, "%d ", ssh1_bignum_bitcount(key->modulus));
 143     for (i = 0; i < 16; i++)
 144         sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
 145     strncpy(str, buffer, len); str[len-1] = '\0';
 146     slen = strlen(str);
 147     if (key->comment && slen < len-1) {
 148         str[slen] = ' ';
 149         strncpy(str+slen+1, key->comment, len-slen-1);
 150         str[len-1] = '\0';
 151     }
 152 }
 153
 154 /*
 155  * Verify that the public data in an RSA key matches the private
 156  * data.
 157  */
 158 int rsa_verify(struct RSAKey *key) {
 159     Bignum n, ed, pm1, qm1, pm1qm1;
 160     int cmp;
 161
 162     /* n must equal pq. */
 163     n = bigmul(key->p, key->q);
 164     cmp = bignum_cmp(n, key->modulus);
 165     freebn(n);
 166     if (cmp != 0)
 167         return 0;
 168
 169     /* e * d must be congruent to 1, modulo (p-1)(q-1). */
 170     pm1 = copybn(key->p);
 171     decbn(pm1);
 172     qm1 = copybn(key->q);
 173     decbn(qm1);
 174     pm1qm1 = bigmul(pm1, qm1);
 175     freebn(pm1);
 176     freebn(qm1);
 177     ed = modmul(key->exponent, key->private_exponent, pm1qm1);
 178     sfree(pm1qm1);
 179     cmp = bignum_cmp(ed, One);
 180     sfree(ed);
 181     if (cmp != 0)
 182         return 0;
 183 }
 184
 185 void freersakey(struct RSAKey *key) {
 186     if (key->modulus) freebn(key->modulus);
 187     if (key->exponent) freebn(key->exponent);
 188     if (key->private_exponent) freebn(key->private_exponent);
 189     if (key->comment) sfree(key->comment);
 190 }
 191
 192 /* ----------------------------------------------------------------------
 193  * Implementation of the ssh-rsa signing key type.
 194  */
 195
 196 #define GET_32BIT(cp) \
 197     (((unsigned long)(unsigned char)(cp)[0] << 24) | \
 198     ((unsigned long)(unsigned char)(cp)[1] << 16) | \
 199     ((unsigned long)(unsigned char)(cp)[2] << 8) | \
 200     ((unsigned long)(unsigned char)(cp)[3]))
 201
 202 #define PUT_32BIT(cp, value) { \
 203     (cp)[0] = (unsigned char)((value) >> 24); \
 204     (cp)[1] = (unsigned char)((value) >> 16); \
 205     (cp)[2] = (unsigned char)((value) >> 8); \
 206     (cp)[3] = (unsigned char)(value); }
 207
 208 static void getstring(char **data, int *datalen, char **p, int *length) {
 209     *p = NULL;
 210     if (*datalen < 4)
 211         return;
 212     *length = GET_32BIT(*data);
 213     *datalen -= 4; *data += 4;
 214     if (*datalen < *length)
 215         return;
 216     *p = *data;
 217     *data += *length; *datalen -= *length;
 218 }
 219 static Bignum getmp(char **data, int *datalen) {
 220     char *p;
 221     int length;
 222     Bignum b;
 223
 224     getstring(data, datalen, &p, &length);
 225     if (!p)
 226         return NULL;
 227     b = bignum_from_bytes(p, length);
 228     return b;
 229 }
 230
 231 static void *rsa2_newkey(char *data, int len) {
 232     char *p;
 233     int slen;
 234     struct RSAKey *rsa;
 235
 236     rsa = smalloc(sizeof(struct RSAKey));
 237     if (!rsa) return NULL;
 238     getstring(&data, &len, &p, &slen);
 239
 240     if (!p || slen != 7 || memcmp(p, "ssh-rsa", 7)) {
 241         sfree(rsa);
 242         return NULL;
 243     }
 244     rsa->exponent = getmp(&data, &len);
 245     rsa->modulus = getmp(&data, &len);
 246     rsa->private_exponent = NULL;
 247     rsa->comment = NULL;
 248
 249     return rsa;
 250 }
 251
 252 static void rsa2_freekey(void *key) {
 253     struct RSAKey *rsa = (struct RSAKey *)key;
 254     freersakey(rsa);
 255     sfree(rsa);
 256 }
 257
 258 static char *rsa2_fmtkey(void *key) {
 259     struct RSAKey *rsa = (struct RSAKey *)key;
 260     char *p;
 261     int len;
 262
 263     len = rsastr_len(rsa);
 264     p = smalloc(len);
 265      rsastr_fmt(p, rsa);
 266     return p;
 267 }
 268
 269 static unsigned char *rsa2_public_blob(void *key, int *len) {
 270     struct RSAKey *rsa = (struct RSAKey *)key;
 271     int elen, mlen, bloblen;
 272     int i;
 273     unsigned char *blob, *p;
 274
 275     elen = (ssh1_bignum_bitcount(rsa->exponent)+8)/8;
 276     mlen = (ssh1_bignum_bitcount(rsa->modulus)+8)/8;
 277
 278     /*
 279      * string "ssh-rsa", mpint exp, mpint mod. Total 19+elen+mlen.
 280      * (three length fields, 12+7=19).
 281      */
 282     bloblen = 19+elen+mlen;
 283     blob = smalloc(bloblen);
 284     p = blob;
 285     PUT_32BIT(p, 7); p += 4;
 286     memcpy(p, "ssh-rsa", 7); p += 7;
 287     PUT_32BIT(p, elen); p += 4;
 288     for (i = elen; i-- ;) *p++ = bignum_byte(rsa->exponent, i);
 289     PUT_32BIT(p, mlen); p += 4;
 290     for (i = mlen; i-- ;) *p++ = bignum_byte(rsa->modulus, i);
 291     assert(p == blob + bloblen);
 292     *len = bloblen;
 293     return blob;
 294 }
 295
 296 static unsigned char *rsa2_private_blob(void *key, int *len) {
 297     struct RSAKey *rsa = (struct RSAKey *)key;
 298     int dlen, plen, qlen, ulen, bloblen;
 299     int i;
 300     unsigned char *blob, *p;
 301
 302     dlen = (ssh1_bignum_bitcount(rsa->private_exponent)+8)/8;
 303     plen = (ssh1_bignum_bitcount(rsa->p)+8)/8;
 304     qlen = (ssh1_bignum_bitcount(rsa->q)+8)/8;
 305     ulen = (ssh1_bignum_bitcount(rsa->iqmp)+8)/8;
 306
 307     /*
 308      * mpint private_exp, mpint p, mpint q, mpint iqmp. Total 16 +
 309      * sum of lengths.
 310      */
 311     bloblen = 16+dlen+plen+qlen+ulen;
 312     blob = smalloc(bloblen);
 313     p = blob;
 314     PUT_32BIT(p, dlen); p += 4;
 315     for (i = dlen; i-- ;) *p++ = bignum_byte(rsa->private_exponent, i);
 316     PUT_32BIT(p, plen); p += 4;
 317     for (i = plen; i-- ;) *p++ = bignum_byte(rsa->p, i);
 318     PUT_32BIT(p, qlen); p += 4;
 319     for (i = qlen; i-- ;) *p++ = bignum_byte(rsa->q, i);
 320     PUT_32BIT(p, ulen); p += 4;
 321     for (i = ulen; i-- ;) *p++ = bignum_byte(rsa->iqmp, i);
 322     assert(p == blob + bloblen);
 323     *len = bloblen;
 324     return blob;
 325 }
 326
 327 static void *rsa2_createkey(unsigned char *pub_blob, int pub_len,
 328                             unsigned char *priv_blob, int priv_len) {
 329     struct RSAKey *rsa;
 330     char *pb = (char *)priv_blob;
 331
 332     rsa = rsa2_newkey((char *)pub_blob, pub_len);
 333     rsa->private_exponent = getmp(&pb, &priv_len);
 334     rsa->p = getmp(&pb, &priv_len);
 335     rsa->q = getmp(&pb, &priv_len);
 336     rsa->iqmp = getmp(&pb, &priv_len);
 337
 338     if (!rsa_verify(rsa)) {
 339         rsa2_freekey(rsa);
 340         return NULL;
 341     }
 342
 343     return rsa;
 344 }
 345
 346 static void *rsa2_openssh_createkey(unsigned char **blob, int *len) {
 347     char **b = (char **)blob;
 348     struct RSAKey *rsa;
 349
 350     rsa = smalloc(sizeof(struct RSAKey));
 351     if (!rsa) return NULL;
 352     rsa->comment = NULL;
 353
 354     rsa->modulus = getmp(b, len);
 355     rsa->exponent = getmp(b, len);
 356     rsa->private_exponent = getmp(b, len);
 357     rsa->iqmp = getmp(b, len);
 358     rsa->p = getmp(b, len);
 359     rsa->q = getmp(b, len);
 360
 361     if (!rsa->modulus || !rsa->exponent || !rsa->private_exponent ||
 362         !rsa->iqmp || !rsa->p || !rsa->q) {
 363         sfree(rsa->modulus);
 364         sfree(rsa->exponent);
 365         sfree(rsa->private_exponent);
 366         sfree(rsa->iqmp);
 367         sfree(rsa->p);
 368         sfree(rsa->q);
 369         sfree(rsa);
 370         return NULL;
 371     }
 372
 373     return rsa;
 374 }
 375
 376 static char *rsa2_fingerprint(void *key) {
 377     struct RSAKey *rsa = (struct RSAKey *)key;
 378     struct MD5Context md5c;
 379     unsigned char digest[16], lenbuf[4];
 380     char buffer[16*3+40];
 381     char *ret;
 382     int numlen, i;
 383
 384     MD5Init(&md5c);
 385     MD5Update(&md5c, "\0\0\0\7ssh-rsa", 11);
 386
 387 #define ADD_BIGNUM(bignum) \
 388     numlen = (ssh1_bignum_bitcount(bignum)+8)/8; \
 389     PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \
 390     for (i = numlen; i-- ;) { \
 391         unsigned char c = bignum_byte(bignum, i); \
 392         MD5Update(&md5c, &c, 1); \
 393     }
 394     ADD_BIGNUM(rsa->exponent);
 395     ADD_BIGNUM(rsa->modulus);
 396 #undef ADD_BIGNUM
 397
 398     MD5Final(digest, &md5c);
 399
 400     sprintf(buffer, "ssh-rsa %d ", ssh1_bignum_bitcount(rsa->modulus));
 401     for (i = 0; i < 16; i++)
 402         sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
 403     ret = smalloc(strlen(buffer)+1);
 404     if (ret)
 405         strcpy(ret, buffer);
 406     return ret;
 407 }
 408
 409 /*
 410  * This is the magic ASN.1/DER prefix that goes in the decoded
 411  * signature, between the string of FFs and the actual SHA hash
 412  * value. The meaning of it is:
 413  *
 414  * 00 -- this marks the end of the FFs; not part of the ASN.1 bit itself
 415  *
 416  * 30 21 -- a constructed SEQUENCE of length 0x21
 417  *    30 09 -- a constructed sub-SEQUENCE of length 9
 418  *       06 05 -- an object identifier, length 5
 419  *          2B 0E 03 02 1A -- object id { 1 3 14 3 2 26 }
 420  *                            (the 1,3 comes from 0x2B = 43 = 40*1+3)
 421  *       05 00 -- NULL
 422  *    04 14 -- a primitive OCTET STRING of length 0x14
 423  *       [0x14 bytes of hash data follows]
 424  *
 425  * The object id in the middle there is listed as `id-sha1' in
 426  * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1d2.asn (the
 427  * ASN module for PKCS #1) and its expanded form is as follows:
 428  *
 429  * id-sha1                OBJECT IDENTIFIER ::= {
 430  *    iso(1) identified-organization(3) oiw(14) secsig(3)
 431  *    algorithms(2) 26 }
 432  */
 433 static unsigned char asn1_weird_stuff[] = {
 434     0x00,0x30,0x21,0x30,0x09,0x06,0x05,0x2B,
 435     0x0E,0x03,0x02,0x1A,0x05,0x00,0x04,0x14,
 436 };
 437
 438 #define ASN1_LEN ( (int) sizeof(asn1_weird_stuff) )
 439
 440 static int rsa2_verifysig(void *key, char *sig, int siglen,
 441                          char *data, int datalen) {
 442     struct RSAKey *rsa = (struct RSAKey *)key;
 443     Bignum in, out;
 444     char *p;
 445     int slen;
 446     int bytes, i, j, ret;
 447     unsigned char hash[20];
 448
 449     getstring(&sig, &siglen, &p, &slen);
 450     if (!p || slen != 7 || memcmp(p, "ssh-rsa", 7)) {
 451         return 0;
 452     }
 453     in = getmp(&sig, &siglen);
 454     out = modpow(in, rsa->exponent, rsa->modulus);
 455     freebn(in);
 456
 457     ret = 1;
 458
 459     bytes = ssh1_bignum_bitcount(rsa->modulus) / 8;
 460     /* Top (partial) byte should be zero. */
 461     if (bignum_byte(out, bytes-1) != 0)
 462         ret = 0;
 463     /* First whole byte should be 1. */
 464     if (bignum_byte(out, bytes-2) != 1)
 465         ret = 0;
 466     /* Most of the rest should be FF. */
 467     for (i = bytes-3; i >= 20 + ASN1_LEN; i--) {
 468         if (bignum_byte(out, i) != 0xFF)
 469             ret = 0;
 470     }
 471     /* Then we expect to see the asn1_weird_stuff. */
 472     for (i = 20 + ASN1_LEN - 1, j=0; i >= 20; i--,j++) {
 473         if (bignum_byte(out, i) != asn1_weird_stuff[j])
 474             ret = 0;
 475     }
 476     /* Finally, we expect to see the SHA-1 hash of the signed data. */
 477     SHA_Simple(data, datalen, hash);
 478     for (i = 19, j=0; i >= 0; i--,j++) {
 479         if (bignum_byte(out, i) != hash[j])
 480             ret = 0;
 481     }
 482
 483     return ret;
 484 }
 485
 486 unsigned char *rsa2_sign(void *key, char *data, int datalen, int *siglen) {
 487     struct RSAKey *rsa = (struct RSAKey *)key;
 488     unsigned char *bytes;
 489     int nbytes;
 490     unsigned char hash[20];
 491     Bignum in, out;
 492     int i, j;
 493
 494     SHA_Simple(data, datalen, hash);
 495
 496     nbytes = (ssh1_bignum_bitcount(rsa->modulus)-1) / 8;
 497     bytes = smalloc(nbytes);
 498
 499     bytes[0] = 1;
 500     for (i = 1; i < nbytes-20-ASN1_LEN; i++)
 501         bytes[i] = 0xFF;
 502     for (i = nbytes-20-ASN1_LEN, j=0; i < nbytes-20; i++,j++)
 503         bytes[i] = asn1_weird_stuff[j];
 504     for (i = nbytes-20, j=0; i < nbytes; i++,j++)
 505         bytes[i] = hash[j];
 506
 507     in = bignum_from_bytes(bytes, nbytes);
 508     sfree(bytes);
 509
 510     out = modpow(in, rsa->private_exponent, rsa->modulus);
 511     freebn(in);
 512
 513     nbytes = (ssh1_bignum_bitcount(out)+7)/8;
 514     bytes = smalloc(4+7+4+nbytes);
 515     PUT_32BIT(bytes, 7);
 516     memcpy(bytes+4, "ssh-rsa", 7);
 517     PUT_32BIT(bytes+4+7, nbytes);
 518     for (i = 0; i < nbytes; i++)
 519         bytes[4+7+4+i] = bignum_byte(out, nbytes-1-i);
 520     freebn(out);
 521
 522     *siglen = 4+7+4+nbytes;
 523     return bytes;
 524 }
 525
 526 const struct ssh_signkey ssh_rsa = {
 527     rsa2_newkey,
 528     rsa2_freekey,
 529     rsa2_fmtkey,
 530     rsa2_public_blob,
 531     rsa2_private_blob,
 532     rsa2_createkey,
 533     rsa2_openssh_createkey,
 534     rsa2_fingerprint,
 535     rsa2_verifysig,
 536     rsa2_sign,
 537     "ssh-rsa",
 538     "rsa2"
 539 };