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