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. We also check the private data itself: we ensure that p >
 157  * q and that iqmp really is the inverse of q mod p.
 158  */
 159 int rsa_verify(struct RSAKey *key) {
 160     Bignum n, ed, pm1, qm1;
 161     int cmp;
 162
 163     /* n must equal pq. */
 164     n = bigmul(key->p, key->q);
 165     cmp = bignum_cmp(n, key->modulus);
 166     freebn(n);
 167     if (cmp != 0)
 168         return 0;
 169
 170     /* e * d must be congruent to 1, modulo (p-1) and modulo (q-1). */
 171     pm1 = copybn(key->p);
 172     decbn(pm1);
 173     ed = modmul(key->exponent, key->private_exponent, pm1);
 174     cmp = bignum_cmp(ed, One);
 175     sfree(ed);
 176     if (cmp != 0)
 177         return 0;
 178
 179     qm1 = copybn(key->q);
 180     decbn(qm1);
 181     ed = modmul(key->exponent, key->private_exponent, qm1);
 182     cmp = bignum_cmp(ed, One);
 183     sfree(ed);
 184     if (cmp != 0)
 185         return 0;
 186
 187     /*
 188      * Ensure p > q.
 189      */
 190     if (bignum_cmp(key->p, key->q) <= 0)
 191         return 0;
 192
 193     /*
 194      * Ensure iqmp * q is congruent to 1, modulo p.
 195      */
 196     n = modmul(key->iqmp, key->q, key->p);
 197     cmp = bignum_cmp(n, One);
 198     sfree(n);
 199     if (cmp != 0)
 200         return 0;
 201
 202     return 1;
 203 }
 204
 205 void freersakey(struct RSAKey *key) {
 206     if (key->modulus) freebn(key->modulus);
 207     if (key->exponent) freebn(key->exponent);
 208     if (key->private_exponent) freebn(key->private_exponent);
 209     if (key->comment) sfree(key->comment);
 210 }
 211
 212 /* ----------------------------------------------------------------------
 213  * Implementation of the ssh-rsa signing key type.
 214  */
 215
 216 #define GET_32BIT(cp) \
 217     (((unsigned long)(unsigned char)(cp)[0] << 24) | \
 218     ((unsigned long)(unsigned char)(cp)[1] << 16) | \
 219     ((unsigned long)(unsigned char)(cp)[2] << 8) | \
 220     ((unsigned long)(unsigned char)(cp)[3]))
 221
 222 #define PUT_32BIT(cp, value) { \
 223     (cp)[0] = (unsigned char)((value) >> 24); \
 224     (cp)[1] = (unsigned char)((value) >> 16); \
 225     (cp)[2] = (unsigned char)((value) >> 8); \
 226     (cp)[3] = (unsigned char)(value); }
 227
 228 static void getstring(char **data, int *datalen, char **p, int *length) {
 229     *p = NULL;
 230     if (*datalen < 4)
 231         return;
 232     *length = GET_32BIT(*data);
 233     *datalen -= 4; *data += 4;
 234     if (*datalen < *length)
 235         return;
 236     *p = *data;
 237     *data += *length; *datalen -= *length;
 238 }
 239 static Bignum getmp(char **data, int *datalen) {
 240     char *p;
 241     int length;
 242     Bignum b;
 243
 244     getstring(data, datalen, &p, &length);
 245     if (!p)
 246         return NULL;
 247     b = bignum_from_bytes(p, length);
 248     return b;
 249 }
 250
 251 static void *rsa2_newkey(char *data, int len) {
 252     char *p;
 253     int slen;
 254     struct RSAKey *rsa;
 255
 256     rsa = smalloc(sizeof(struct RSAKey));
 257     if (!rsa) return NULL;
 258     getstring(&data, &len, &p, &slen);
 259
 260     if (!p || slen != 7 || memcmp(p, "ssh-rsa", 7)) {
 261         sfree(rsa);
 262         return NULL;
 263     }
 264     rsa->exponent = getmp(&data, &len);
 265     rsa->modulus = getmp(&data, &len);
 266     rsa->private_exponent = NULL;
 267     rsa->comment = NULL;
 268
 269     return rsa;
 270 }
 271
 272 static void rsa2_freekey(void *key) {
 273     struct RSAKey *rsa = (struct RSAKey *)key;
 274     freersakey(rsa);
 275     sfree(rsa);
 276 }
 277
 278 static char *rsa2_fmtkey(void *key) {
 279     struct RSAKey *rsa = (struct RSAKey *)key;
 280     char *p;
 281     int len;
 282
 283     len = rsastr_len(rsa);
 284     p = smalloc(len);
 285      rsastr_fmt(p, rsa);
 286     return p;
 287 }
 288
 289 static unsigned char *rsa2_public_blob(void *key, int *len) {
 290     struct RSAKey *rsa = (struct RSAKey *)key;
 291     int elen, mlen, bloblen;
 292     int i;
 293     unsigned char *blob, *p;
 294
 295     elen = (ssh1_bignum_bitcount(rsa->exponent)+8)/8;
 296     mlen = (ssh1_bignum_bitcount(rsa->modulus)+8)/8;
 297
 298     /*
 299      * string "ssh-rsa", mpint exp, mpint mod. Total 19+elen+mlen.
 300      * (three length fields, 12+7=19).
 301      */
 302     bloblen = 19+elen+mlen;
 303     blob = smalloc(bloblen);
 304     p = blob;
 305     PUT_32BIT(p, 7); p += 4;
 306     memcpy(p, "ssh-rsa", 7); p += 7;
 307     PUT_32BIT(p, elen); p += 4;
 308     for (i = elen; i-- ;) *p++ = bignum_byte(rsa->exponent, i);
 309     PUT_32BIT(p, mlen); p += 4;
 310     for (i = mlen; i-- ;) *p++ = bignum_byte(rsa->modulus, i);
 311     assert(p == blob + bloblen);
 312     *len = bloblen;
 313     return blob;
 314 }
 315
 316 static unsigned char *rsa2_private_blob(void *key, int *len) {
 317     struct RSAKey *rsa = (struct RSAKey *)key;
 318     int dlen, plen, qlen, ulen, bloblen;
 319     int i;
 320     unsigned char *blob, *p;
 321
 322     dlen = (ssh1_bignum_bitcount(rsa->private_exponent)+8)/8;
 323     plen = (ssh1_bignum_bitcount(rsa->p)+8)/8;
 324     qlen = (ssh1_bignum_bitcount(rsa->q)+8)/8;
 325     ulen = (ssh1_bignum_bitcount(rsa->iqmp)+8)/8;
 326
 327     /*
 328      * mpint private_exp, mpint p, mpint q, mpint iqmp. Total 16 +
 329      * sum of lengths.
 330      */
 331     bloblen = 16+dlen+plen+qlen+ulen;
 332     blob = smalloc(bloblen);
 333     p = blob;
 334     PUT_32BIT(p, dlen); p += 4;
 335     for (i = dlen; i-- ;) *p++ = bignum_byte(rsa->private_exponent, i);
 336     PUT_32BIT(p, plen); p += 4;
 337     for (i = plen; i-- ;) *p++ = bignum_byte(rsa->p, i);
 338     PUT_32BIT(p, qlen); p += 4;
 339     for (i = qlen; i-- ;) *p++ = bignum_byte(rsa->q, i);
 340     PUT_32BIT(p, ulen); p += 4;
 341     for (i = ulen; i-- ;) *p++ = bignum_byte(rsa->iqmp, i);
 342     assert(p == blob + bloblen);
 343     *len = bloblen;
 344     return blob;
 345 }
 346
 347 static void *rsa2_createkey(unsigned char *pub_blob, int pub_len,
 348                             unsigned char *priv_blob, int priv_len) {
 349     struct RSAKey *rsa;
 350     char *pb = (char *)priv_blob;
 351
 352     rsa = rsa2_newkey((char *)pub_blob, pub_len);
 353     rsa->private_exponent = getmp(&pb, &priv_len);
 354     rsa->p = getmp(&pb, &priv_len);
 355     rsa->q = getmp(&pb, &priv_len);
 356     rsa->iqmp = getmp(&pb, &priv_len);
 357
 358     if (!rsa_verify(rsa)) {
 359         rsa2_freekey(rsa);
 360         return NULL;
 361     }
 362
 363     return rsa;
 364 }
 365
 366 static void *rsa2_openssh_createkey(unsigned char **blob, int *len) {
 367     char **b = (char **)blob;
 368     struct RSAKey *rsa;
 369
 370     rsa = smalloc(sizeof(struct RSAKey));
 371     if (!rsa) return NULL;
 372     rsa->comment = NULL;
 373
 374     rsa->modulus = getmp(b, len);
 375     rsa->exponent = getmp(b, len);
 376     rsa->private_exponent = getmp(b, len);
 377     rsa->iqmp = getmp(b, len);
 378     rsa->p = getmp(b, len);
 379     rsa->q = getmp(b, len);
 380
 381     if (!rsa->modulus || !rsa->exponent || !rsa->private_exponent ||
 382         !rsa->iqmp || !rsa->p || !rsa->q) {
 383         sfree(rsa->modulus);
 384         sfree(rsa->exponent);
 385         sfree(rsa->private_exponent);
 386         sfree(rsa->iqmp);
 387         sfree(rsa->p);
 388         sfree(rsa->q);
 389         sfree(rsa);
 390         return NULL;
 391     }
 392
 393     return rsa;
 394 }
 395
 396 static char *rsa2_fingerprint(void *key) {
 397     struct RSAKey *rsa = (struct RSAKey *)key;
 398     struct MD5Context md5c;
 399     unsigned char digest[16], lenbuf[4];
 400     char buffer[16*3+40];
 401     char *ret;
 402     int numlen, i;
 403
 404     MD5Init(&md5c);
 405     MD5Update(&md5c, "\0\0\0\7ssh-rsa", 11);
 406
 407 #define ADD_BIGNUM(bignum) \
 408     numlen = (ssh1_bignum_bitcount(bignum)+8)/8; \
 409     PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \
 410     for (i = numlen; i-- ;) { \
 411         unsigned char c = bignum_byte(bignum, i); \
 412         MD5Update(&md5c, &c, 1); \
 413     }
 414     ADD_BIGNUM(rsa->exponent);
 415     ADD_BIGNUM(rsa->modulus);
 416 #undef ADD_BIGNUM
 417
 418     MD5Final(digest, &md5c);
 419
 420     sprintf(buffer, "ssh-rsa %d ", ssh1_bignum_bitcount(rsa->modulus));
 421     for (i = 0; i < 16; i++)
 422         sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
 423     ret = smalloc(strlen(buffer)+1);
 424     if (ret)
 425         strcpy(ret, buffer);
 426     return ret;
 427 }
 428
 429 /*
 430  * This is the magic ASN.1/DER prefix that goes in the decoded
 431  * signature, between the string of FFs and the actual SHA hash
 432  * value. The meaning of it is:
 433  *
 434  * 00 -- this marks the end of the FFs; not part of the ASN.1 bit itself
 435  *
 436  * 30 21 -- a constructed SEQUENCE of length 0x21
 437  *    30 09 -- a constructed sub-SEQUENCE of length 9
 438  *       06 05 -- an object identifier, length 5
 439  *          2B 0E 03 02 1A -- object id { 1 3 14 3 2 26 }
 440  *                            (the 1,3 comes from 0x2B = 43 = 40*1+3)
 441  *       05 00 -- NULL
 442  *    04 14 -- a primitive OCTET STRING of length 0x14
 443  *       [0x14 bytes of hash data follows]
 444  *
 445  * The object id in the middle there is listed as `id-sha1' in
 446  * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1d2.asn (the
 447  * ASN module for PKCS #1) and its expanded form is as follows:
 448  *
 449  * id-sha1                OBJECT IDENTIFIER ::= {
 450  *    iso(1) identified-organization(3) oiw(14) secsig(3)
 451  *    algorithms(2) 26 }
 452  */
 453 static unsigned char asn1_weird_stuff[] = {
 454     0x00,0x30,0x21,0x30,0x09,0x06,0x05,0x2B,
 455     0x0E,0x03,0x02,0x1A,0x05,0x00,0x04,0x14,
 456 };
 457
 458 #define ASN1_LEN ( (int) sizeof(asn1_weird_stuff) )
 459
 460 static int rsa2_verifysig(void *key, char *sig, int siglen,
 461                          char *data, int datalen) {
 462     struct RSAKey *rsa = (struct RSAKey *)key;
 463     Bignum in, out;
 464     char *p;
 465     int slen;
 466     int bytes, i, j, ret;
 467     unsigned char hash[20];
 468
 469     getstring(&sig, &siglen, &p, &slen);
 470     if (!p || slen != 7 || memcmp(p, "ssh-rsa", 7)) {
 471         return 0;
 472     }
 473     in = getmp(&sig, &siglen);
 474     out = modpow(in, rsa->exponent, rsa->modulus);
 475     freebn(in);
 476
 477     ret = 1;
 478
 479     bytes = ssh1_bignum_bitcount(rsa->modulus) / 8;
 480     /* Top (partial) byte should be zero. */
 481     if (bignum_byte(out, bytes-1) != 0)
 482         ret = 0;
 483     /* First whole byte should be 1. */
 484     if (bignum_byte(out, bytes-2) != 1)
 485         ret = 0;
 486     /* Most of the rest should be FF. */
 487     for (i = bytes-3; i >= 20 + ASN1_LEN; i--) {
 488         if (bignum_byte(out, i) != 0xFF)
 489             ret = 0;
 490     }
 491     /* Then we expect to see the asn1_weird_stuff. */
 492     for (i = 20 + ASN1_LEN - 1, j=0; i >= 20; i--,j++) {
 493         if (bignum_byte(out, i) != asn1_weird_stuff[j])
 494             ret = 0;
 495     }
 496     /* Finally, we expect to see the SHA-1 hash of the signed data. */
 497     SHA_Simple(data, datalen, hash);
 498     for (i = 19, j=0; i >= 0; i--,j++) {
 499         if (bignum_byte(out, i) != hash[j])
 500             ret = 0;
 501     }
 502
 503     return ret;
 504 }
 505
 506 unsigned char *rsa2_sign(void *key, char *data, int datalen, int *siglen) {
 507     struct RSAKey *rsa = (struct RSAKey *)key;
 508     unsigned char *bytes;
 509     int nbytes;
 510     unsigned char hash[20];
 511     Bignum in, out;
 512     int i, j;
 513
 514     SHA_Simple(data, datalen, hash);
 515
 516     nbytes = (ssh1_bignum_bitcount(rsa->modulus)-1) / 8;
 517     bytes = smalloc(nbytes);
 518
 519     bytes[0] = 1;
 520     for (i = 1; i < nbytes-20-ASN1_LEN; i++)
 521         bytes[i] = 0xFF;
 522     for (i = nbytes-20-ASN1_LEN, j=0; i < nbytes-20; i++,j++)
 523         bytes[i] = asn1_weird_stuff[j];
 524     for (i = nbytes-20, j=0; i < nbytes; i++,j++)
 525         bytes[i] = hash[j];
 526
 527     in = bignum_from_bytes(bytes, nbytes);
 528     sfree(bytes);
 529
 530     out = modpow(in, rsa->private_exponent, rsa->modulus);
 531     freebn(in);
 532
 533     nbytes = (ssh1_bignum_bitcount(out)+7)/8;
 534     bytes = smalloc(4+7+4+nbytes);
 535     PUT_32BIT(bytes, 7);
 536     memcpy(bytes+4, "ssh-rsa", 7);
 537     PUT_32BIT(bytes+4+7, nbytes);
 538     for (i = 0; i < nbytes; i++)
 539         bytes[4+7+4+i] = bignum_byte(out, nbytes-1-i);
 540     freebn(out);
 541
 542     *siglen = 4+7+4+nbytes;
 543     return bytes;
 544 }
 545
 546 const struct ssh_signkey ssh_rsa = {
 547     rsa2_newkey,
 548     rsa2_freekey,
 549     rsa2_fmtkey,
 550     rsa2_public_blob,
 551     rsa2_private_blob,
 552     rsa2_createkey,
 553     rsa2_openssh_createkey,
 554     rsa2_fingerprint,
 555     rsa2_verifysig,
 556     rsa2_sign,
 557     "ssh-rsa",
 558     "rsa2"
 559 };