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 {
  19     unsigned char *p = data;
  20     int i;
  21
  22     if (result) {
  23         result->bits = 0;
  24         for (i = 0; i < 4; i++)
  25             result->bits = (result->bits << 8) + *p++;
  26     } else
  27         p += 4;
  28
  29     /*
  30      * order=0 means exponent then modulus (the keys sent by the
  31      * server). order=1 means modulus then exponent (the keys
  32      * stored in a keyfile).
  33      */
  34
  35     if (order == 0)
  36         p += ssh1_read_bignum(p, result ? &result->exponent : NULL);
  37     if (result)
  38         result->bytes = (((p[0] << 8) + p[1]) + 7) / 8;
  39     if (keystr)
  40         *keystr = p + 2;
  41     p += ssh1_read_bignum(p, result ? &result->modulus : NULL);
  42     if (order == 1)
  43         p += ssh1_read_bignum(p, result ? &result->exponent : NULL);
  44
  45     return p - data;
  46 }
  47
  48 int makeprivate(unsigned char *data, struct RSAKey *result)
  49 {
  50     return ssh1_read_bignum(data, &result->private_exponent);
  51 }
  52
  53 void rsaencrypt(unsigned char *data, int length, struct RSAKey *key)
  54 {
  55     Bignum b1, b2;
  56     int i;
  57     unsigned char *p;
  58
  59     memmove(data + key->bytes - length, data, length);
  60     data[0] = 0;
  61     data[1] = 2;
  62
  63     for (i = 2; i < key->bytes - length - 1; i++) {
  64         do {
  65             data[i] = random_byte();
  66         } while (data[i] == 0);
  67     }
  68     data[key->bytes - length - 1] = 0;
  69
  70     b1 = bignum_from_bytes(data, key->bytes);
  71
  72     b2 = modpow(b1, key->exponent, key->modulus);
  73
  74     p = data;
  75     for (i = key->bytes; i--;) {
  76         *p++ = bignum_byte(b2, i);
  77     }
  78
  79     freebn(b1);
  80     freebn(b2);
  81 }
  82
  83 Bignum rsadecrypt(Bignum input, struct RSAKey *key)
  84 {
  85     Bignum ret;
  86     ret = modpow(input, key->private_exponent, key->modulus);
  87     return ret;
  88 }
  89
  90 int rsastr_len(struct RSAKey *key)
  91 {
  92     Bignum md, ex;
  93     int mdlen, exlen;
  94
  95     md = key->modulus;
  96     ex = key->exponent;
  97     mdlen = (bignum_bitcount(md) + 15) / 16;
  98     exlen = (bignum_bitcount(ex) + 15) / 16;
  99     return 4 * (mdlen + exlen) + 20;
 100 }
 101
 102 void rsastr_fmt(char *str, struct RSAKey *key)
 103 {
 104     Bignum md, ex;
 105     int len = 0, i, nibbles;
 106     static const char hex[] = "0123456789abcdef";
 107
 108     md = key->modulus;
 109     ex = key->exponent;
 110
 111     len += sprintf(str + len, "0x");
 112
 113     nibbles = (3 + bignum_bitcount(ex)) / 4;
 114     if (nibbles < 1)
 115         nibbles = 1;
 116     for (i = nibbles; i--;)
 117         str[len++] = hex[(bignum_byte(ex, i / 2) >> (4 * (i % 2))) & 0xF];
 118
 119     len += sprintf(str + len, ",0x");
 120
 121     nibbles = (3 + bignum_bitcount(md)) / 4;
 122     if (nibbles < 1)
 123         nibbles = 1;
 124     for (i = nibbles; i--;)
 125         str[len++] = hex[(bignum_byte(md, i / 2) >> (4 * (i % 2))) & 0xF];
 126
 127     str[len] = '\0';
 128 }
 129
 130 /*
 131  * Generate a fingerprint string for the key. Compatible with the
 132  * OpenSSH fingerprint code.
 133  */
 134 void rsa_fingerprint(char *str, int len, struct RSAKey *key)
 135 {
 136     struct MD5Context md5c;
 137     unsigned char digest[16];
 138     char buffer[16 * 3 + 40];
 139     int numlen, slen, i;
 140
 141     MD5Init(&md5c);
 142     numlen = ssh1_bignum_length(key->modulus) - 2;
 143     for (i = numlen; i--;) {
 144         unsigned char c = bignum_byte(key->modulus, i);
 145         MD5Update(&md5c, &c, 1);
 146     }
 147     numlen = ssh1_bignum_length(key->exponent) - 2;
 148     for (i = numlen; i--;) {
 149         unsigned char c = bignum_byte(key->exponent, i);
 150         MD5Update(&md5c, &c, 1);
 151     }
 152     MD5Final(digest, &md5c);
 153
 154     sprintf(buffer, "%d ", bignum_bitcount(key->modulus));
 155     for (i = 0; i < 16; i++)
 156         sprintf(buffer + strlen(buffer), "%s%02x", i ? ":" : "",
 157                 digest[i]);
 158     strncpy(str, buffer, len);
 159     str[len - 1] = '\0';
 160     slen = strlen(str);
 161     if (key->comment && slen < len - 1) {
 162         str[slen] = ' ';
 163         strncpy(str + slen + 1, key->comment, len - slen - 1);
 164         str[len - 1] = '\0';
 165     }
 166 }
 167
 168 /*
 169  * Verify that the public data in an RSA key matches the private
 170  * data. We also check the private data itself: we ensure that p >
 171  * q and that iqmp really is the inverse of q mod p.
 172  */
 173 int rsa_verify(struct RSAKey *key)
 174 {
 175     Bignum n, ed, pm1, qm1;
 176     int cmp;
 177
 178     /* n must equal pq. */
 179     n = bigmul(key->p, key->q);
 180     cmp = bignum_cmp(n, key->modulus);
 181     freebn(n);
 182     if (cmp != 0)
 183         return 0;
 184
 185     /* e * d must be congruent to 1, modulo (p-1) and modulo (q-1). */
 186     pm1 = copybn(key->p);
 187     decbn(pm1);
 188     ed = modmul(key->exponent, key->private_exponent, pm1);
 189     cmp = bignum_cmp(ed, One);
 190     sfree(ed);
 191     if (cmp != 0)
 192         return 0;
 193
 194     qm1 = copybn(key->q);
 195     decbn(qm1);
 196     ed = modmul(key->exponent, key->private_exponent, qm1);
 197     cmp = bignum_cmp(ed, One);
 198     sfree(ed);
 199     if (cmp != 0)
 200         return 0;
 201
 202     /*
 203      * Ensure p > q.
 204      */
 205     if (bignum_cmp(key->p, key->q) <= 0)
 206         return 0;
 207
 208     /*
 209      * Ensure iqmp * q is congruent to 1, modulo p.
 210      */
 211     n = modmul(key->iqmp, key->q, key->p);
 212     cmp = bignum_cmp(n, One);
 213     sfree(n);
 214     if (cmp != 0)
 215         return 0;
 216
 217     return 1;
 218 }
 219
 220 void freersakey(struct RSAKey *key)
 221 {
 222     if (key->modulus)
 223         freebn(key->modulus);
 224     if (key->exponent)
 225         freebn(key->exponent);
 226     if (key->private_exponent)
 227         freebn(key->private_exponent);
 228     if (key->comment)
 229         sfree(key->comment);
 230 }
 231
 232 /* ----------------------------------------------------------------------
 233  * Implementation of the ssh-rsa signing key type.
 234  */
 235
 236 #define GET_32BIT(cp) \
 237     (((unsigned long)(unsigned char)(cp)[0] << 24) | \
 238     ((unsigned long)(unsigned char)(cp)[1] << 16) | \
 239     ((unsigned long)(unsigned char)(cp)[2] << 8) | \
 240     ((unsigned long)(unsigned char)(cp)[3]))
 241
 242 #define PUT_32BIT(cp, value) { \
 243     (cp)[0] = (unsigned char)((value) >> 24); \
 244     (cp)[1] = (unsigned char)((value) >> 16); \
 245     (cp)[2] = (unsigned char)((value) >> 8); \
 246     (cp)[3] = (unsigned char)(value); }
 247
 248 static void getstring(char **data, int *datalen, char **p, int *length)
 249 {
 250     *p = NULL;
 251     if (*datalen < 4)
 252         return;
 253     *length = GET_32BIT(*data);
 254     *datalen -= 4;
 255     *data += 4;
 256     if (*datalen < *length)
 257         return;
 258     *p = *data;
 259     *data += *length;
 260     *datalen -= *length;
 261 }
 262 static Bignum getmp(char **data, int *datalen)
 263 {
 264     char *p;
 265     int length;
 266     Bignum b;
 267
 268     getstring(data, datalen, &p, &length);
 269     if (!p)
 270         return NULL;
 271     b = bignum_from_bytes(p, length);
 272     return b;
 273 }
 274
 275 static void *rsa2_newkey(char *data, int len)
 276 {
 277     char *p;
 278     int slen;
 279     struct RSAKey *rsa;
 280
 281     rsa = smalloc(sizeof(struct RSAKey));
 282     if (!rsa)
 283         return NULL;
 284     getstring(&data, &len, &p, &slen);
 285
 286     if (!p || slen != 7 || memcmp(p, "ssh-rsa", 7)) {
 287         sfree(rsa);
 288         return NULL;
 289     }
 290     rsa->exponent = getmp(&data, &len);
 291     rsa->modulus = getmp(&data, &len);
 292     rsa->private_exponent = NULL;
 293     rsa->comment = NULL;
 294
 295     return rsa;
 296 }
 297
 298 static void rsa2_freekey(void *key)
 299 {
 300     struct RSAKey *rsa = (struct RSAKey *) key;
 301     freersakey(rsa);
 302     sfree(rsa);
 303 }
 304
 305 static char *rsa2_fmtkey(void *key)
 306 {
 307     struct RSAKey *rsa = (struct RSAKey *) key;
 308     char *p;
 309     int len;
 310
 311     len = rsastr_len(rsa);
 312     p = smalloc(len);
 313     rsastr_fmt(p, rsa);
 314     return p;
 315 }
 316
 317 static unsigned char *rsa2_public_blob(void *key, int *len)
 318 {
 319     struct RSAKey *rsa = (struct RSAKey *) key;
 320     int elen, mlen, bloblen;
 321     int i;
 322     unsigned char *blob, *p;
 323
 324     elen = (bignum_bitcount(rsa->exponent) + 8) / 8;
 325     mlen = (bignum_bitcount(rsa->modulus) + 8) / 8;
 326
 327     /*
 328      * string "ssh-rsa", mpint exp, mpint mod. Total 19+elen+mlen.
 329      * (three length fields, 12+7=19).
 330      */
 331     bloblen = 19 + elen + mlen;
 332     blob = smalloc(bloblen);
 333     p = blob;
 334     PUT_32BIT(p, 7);
 335     p += 4;
 336     memcpy(p, "ssh-rsa", 7);
 337     p += 7;
 338     PUT_32BIT(p, elen);
 339     p += 4;
 340     for (i = elen; i--;)
 341         *p++ = bignum_byte(rsa->exponent, i);
 342     PUT_32BIT(p, mlen);
 343     p += 4;
 344     for (i = mlen; i--;)
 345         *p++ = bignum_byte(rsa->modulus, i);
 346     assert(p == blob + bloblen);
 347     *len = bloblen;
 348     return blob;
 349 }
 350
 351 static unsigned char *rsa2_private_blob(void *key, int *len)
 352 {
 353     struct RSAKey *rsa = (struct RSAKey *) key;
 354     int dlen, plen, qlen, ulen, bloblen;
 355     int i;
 356     unsigned char *blob, *p;
 357
 358     dlen = (bignum_bitcount(rsa->private_exponent) + 8) / 8;
 359     plen = (bignum_bitcount(rsa->p) + 8) / 8;
 360     qlen = (bignum_bitcount(rsa->q) + 8) / 8;
 361     ulen = (bignum_bitcount(rsa->iqmp) + 8) / 8;
 362
 363     /*
 364      * mpint private_exp, mpint p, mpint q, mpint iqmp. Total 16 +
 365      * sum of lengths.
 366      */
 367     bloblen = 16 + dlen + plen + qlen + ulen;
 368     blob = smalloc(bloblen);
 369     p = blob;
 370     PUT_32BIT(p, dlen);
 371     p += 4;
 372     for (i = dlen; i--;)
 373         *p++ = bignum_byte(rsa->private_exponent, i);
 374     PUT_32BIT(p, plen);
 375     p += 4;
 376     for (i = plen; i--;)
 377         *p++ = bignum_byte(rsa->p, i);
 378     PUT_32BIT(p, qlen);
 379     p += 4;
 380     for (i = qlen; i--;)
 381         *p++ = bignum_byte(rsa->q, i);
 382     PUT_32BIT(p, ulen);
 383     p += 4;
 384     for (i = ulen; i--;)
 385         *p++ = bignum_byte(rsa->iqmp, i);
 386     assert(p == blob + bloblen);
 387     *len = bloblen;
 388     return blob;
 389 }
 390
 391 static void *rsa2_createkey(unsigned char *pub_blob, int pub_len,
 392                             unsigned char *priv_blob, int priv_len)
 393 {
 394     struct RSAKey *rsa;
 395     char *pb = (char *) priv_blob;
 396
 397     rsa = rsa2_newkey((char *) pub_blob, pub_len);
 398     rsa->private_exponent = getmp(&pb, &priv_len);
 399     rsa->p = getmp(&pb, &priv_len);
 400     rsa->q = getmp(&pb, &priv_len);
 401     rsa->iqmp = getmp(&pb, &priv_len);
 402
 403     if (!rsa_verify(rsa)) {
 404         rsa2_freekey(rsa);
 405         return NULL;
 406     }
 407
 408     return rsa;
 409 }
 410
 411 static void *rsa2_openssh_createkey(unsigned char **blob, int *len)
 412 {
 413     char **b = (char **) blob;
 414     struct RSAKey *rsa;
 415
 416     rsa = smalloc(sizeof(struct RSAKey));
 417     if (!rsa)
 418         return NULL;
 419     rsa->comment = NULL;
 420
 421     rsa->modulus = getmp(b, len);
 422     rsa->exponent = getmp(b, len);
 423     rsa->private_exponent = getmp(b, len);
 424     rsa->iqmp = getmp(b, len);
 425     rsa->p = getmp(b, len);
 426     rsa->q = getmp(b, len);
 427
 428     if (!rsa->modulus || !rsa->exponent || !rsa->private_exponent ||
 429         !rsa->iqmp || !rsa->p || !rsa->q) {
 430         sfree(rsa->modulus);
 431         sfree(rsa->exponent);
 432         sfree(rsa->private_exponent);
 433         sfree(rsa->iqmp);
 434         sfree(rsa->p);
 435         sfree(rsa->q);
 436         sfree(rsa);
 437         return NULL;
 438     }
 439
 440     return rsa;
 441 }
 442
 443 static int rsa2_openssh_fmtkey(void *key, unsigned char *blob, int len)
 444 {
 445     struct RSAKey *rsa = (struct RSAKey *) key;
 446     int bloblen, i;
 447
 448     bloblen =
 449         ssh2_bignum_length(rsa->modulus) +
 450         ssh2_bignum_length(rsa->exponent) +
 451         ssh2_bignum_length(rsa->private_exponent) +
 452         ssh2_bignum_length(rsa->iqmp) +
 453         ssh2_bignum_length(rsa->p) + ssh2_bignum_length(rsa->q);
 454
 455     if (bloblen > len)
 456         return bloblen;
 457
 458     bloblen = 0;
 459 #define ENC(x) \
 460     PUT_32BIT(blob+bloblen, ssh2_bignum_length((x))-4); bloblen += 4; \
 461     for (i = ssh2_bignum_length((x))-4; i-- ;) blob[bloblen++]=bignum_byte((x),i);
 462     ENC(rsa->modulus);
 463     ENC(rsa->exponent);
 464     ENC(rsa->private_exponent);
 465     ENC(rsa->iqmp);
 466     ENC(rsa->p);
 467     ENC(rsa->q);
 468
 469     return bloblen;
 470 }
 471
 472 static char *rsa2_fingerprint(void *key)
 473 {
 474     struct RSAKey *rsa = (struct RSAKey *) key;
 475     struct MD5Context md5c;
 476     unsigned char digest[16], lenbuf[4];
 477     char buffer[16 * 3 + 40];
 478     char *ret;
 479     int numlen, i;
 480
 481     MD5Init(&md5c);
 482     MD5Update(&md5c, "\0\0\0\7ssh-rsa", 11);
 483
 484 #define ADD_BIGNUM(bignum) \
 485     numlen = (bignum_bitcount(bignum)+8)/8; \
 486     PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \
 487     for (i = numlen; i-- ;) { \
 488         unsigned char c = bignum_byte(bignum, i); \
 489         MD5Update(&md5c, &c, 1); \
 490     }
 491     ADD_BIGNUM(rsa->exponent);
 492     ADD_BIGNUM(rsa->modulus);
 493 #undef ADD_BIGNUM
 494
 495     MD5Final(digest, &md5c);
 496
 497     sprintf(buffer, "ssh-rsa %d ", bignum_bitcount(rsa->modulus));
 498     for (i = 0; i < 16; i++)
 499         sprintf(buffer + strlen(buffer), "%s%02x", i ? ":" : "",
 500                 digest[i]);
 501     ret = smalloc(strlen(buffer) + 1);
 502     if (ret)
 503         strcpy(ret, buffer);
 504     return ret;
 505 }
 506
 507 /*
 508  * This is the magic ASN.1/DER prefix that goes in the decoded
 509  * signature, between the string of FFs and the actual SHA hash
 510  * value. The meaning of it is:
 511  *
 512  * 00 -- this marks the end of the FFs; not part of the ASN.1 bit itself
 513  *
 514  * 30 21 -- a constructed SEQUENCE of length 0x21
 515  *    30 09 -- a constructed sub-SEQUENCE of length 9
 516  *       06 05 -- an object identifier, length 5
 517  *          2B 0E 03 02 1A -- object id { 1 3 14 3 2 26 }
 518  *                            (the 1,3 comes from 0x2B = 43 = 40*1+3)
 519  *       05 00 -- NULL
 520  *    04 14 -- a primitive OCTET STRING of length 0x14
 521  *       [0x14 bytes of hash data follows]
 522  *
 523  * The object id in the middle there is listed as `id-sha1' in
 524  * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1d2.asn (the
 525  * ASN module for PKCS #1) and its expanded form is as follows:
 526  *
 527  * id-sha1                OBJECT IDENTIFIER ::= {
 528  *    iso(1) identified-organization(3) oiw(14) secsig(3)
 529  *    algorithms(2) 26 }
 530  */
 531 static unsigned char asn1_weird_stuff[] = {
 532     0x00, 0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2B,
 533     0x0E, 0x03, 0x02, 0x1A, 0x05, 0x00, 0x04, 0x14,
 534 };
 535
 536 #define ASN1_LEN ( (int) sizeof(asn1_weird_stuff) )
 537
 538 static int rsa2_verifysig(void *key, char *sig, int siglen,
 539                           char *data, int datalen)
 540 {
 541     struct RSAKey *rsa = (struct RSAKey *) key;
 542     Bignum in, out;
 543     char *p;
 544     int slen;
 545     int bytes, i, j, ret;
 546     unsigned char hash[20];
 547
 548     getstring(&sig, &siglen, &p, &slen);
 549     if (!p || slen != 7 || memcmp(p, "ssh-rsa", 7)) {
 550         return 0;
 551     }
 552     in = getmp(&sig, &siglen);
 553     out = modpow(in, rsa->exponent, rsa->modulus);
 554     freebn(in);
 555
 556     ret = 1;
 557
 558     bytes = bignum_bitcount(rsa->modulus) / 8;
 559     /* Top (partial) byte should be zero. */
 560     if (bignum_byte(out, bytes - 1) != 0)
 561         ret = 0;
 562     /* First whole byte should be 1. */
 563     if (bignum_byte(out, bytes - 2) != 1)
 564         ret = 0;
 565     /* Most of the rest should be FF. */
 566     for (i = bytes - 3; i >= 20 + ASN1_LEN; i--) {
 567         if (bignum_byte(out, i) != 0xFF)
 568             ret = 0;
 569     }
 570     /* Then we expect to see the asn1_weird_stuff. */
 571     for (i = 20 + ASN1_LEN - 1, j = 0; i >= 20; i--, j++) {
 572         if (bignum_byte(out, i) != asn1_weird_stuff[j])
 573             ret = 0;
 574     }
 575     /* Finally, we expect to see the SHA-1 hash of the signed data. */
 576     SHA_Simple(data, datalen, hash);
 577     for (i = 19, j = 0; i >= 0; i--, j++) {
 578         if (bignum_byte(out, i) != hash[j])
 579             ret = 0;
 580     }
 581
 582     return ret;
 583 }
 584
 585 unsigned char *rsa2_sign(void *key, char *data, int datalen, int *siglen)
 586 {
 587     struct RSAKey *rsa = (struct RSAKey *) key;
 588     unsigned char *bytes;
 589     int nbytes;
 590     unsigned char hash[20];
 591     Bignum in, out;
 592     int i, j;
 593
 594     SHA_Simple(data, datalen, hash);
 595
 596     nbytes = (bignum_bitcount(rsa->modulus) - 1) / 8;
 597     bytes = smalloc(nbytes);
 598
 599     bytes[0] = 1;
 600     for (i = 1; i < nbytes - 20 - ASN1_LEN; i++)
 601         bytes[i] = 0xFF;
 602     for (i = nbytes - 20 - ASN1_LEN, j = 0; i < nbytes - 20; i++, j++)
 603         bytes[i] = asn1_weird_stuff[j];
 604     for (i = nbytes - 20, j = 0; i < nbytes; i++, j++)
 605         bytes[i] = hash[j];
 606
 607     in = bignum_from_bytes(bytes, nbytes);
 608     sfree(bytes);
 609
 610     out = modpow(in, rsa->private_exponent, rsa->modulus);
 611     freebn(in);
 612
 613     nbytes = (bignum_bitcount(out) + 7) / 8;
 614     bytes = smalloc(4 + 7 + 4 + nbytes);
 615     PUT_32BIT(bytes, 7);
 616     memcpy(bytes + 4, "ssh-rsa", 7);
 617     PUT_32BIT(bytes + 4 + 7, nbytes);
 618     for (i = 0; i < nbytes; i++)
 619         bytes[4 + 7 + 4 + i] = bignum_byte(out, nbytes - 1 - i);
 620     freebn(out);
 621
 622     *siglen = 4 + 7 + 4 + nbytes;
 623     return bytes;
 624 }
 625
 626 const struct ssh_signkey ssh_rsa = {
 627     rsa2_newkey,
 628     rsa2_freekey,
 629     rsa2_fmtkey,
 630     rsa2_public_blob,
 631     rsa2_private_blob,
 632     rsa2_createkey,
 633     rsa2_openssh_createkey,
 634     rsa2_openssh_fmtkey,
 635     rsa2_fingerprint,
 636     rsa2_verifysig,
 637     rsa2_sign,
 638     "ssh-rsa",
 639     "rsa2"
 640 };