1 /* $OpenBSD: ssh-rsa.c,v 1.67 2018/07/03 11:39:54 djm Exp $ */ 2 /* 3 * Copyright (c) 2000, 2003 Markus Friedl <markus@openbsd.org> 4 * 5 * Permission to use, copy, modify, and distribute this software for any 6 * purpose with or without fee is hereby granted, provided that the above 7 * copyright notice and this permission notice appear in all copies. 8 * 9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16 */ 17 18 #include "includes.h" 19 20 #ifdef WITH_OPENSSL 21 22 #include <sys/types.h> 23 24 #include <openssl/evp.h> 25 #include <openssl/err.h> 26 27 #include <stdarg.h> 28 #include <string.h> 29 30 #include "sshbuf.h" 31 #include "compat.h" 32 #include "ssherr.h" 33 #define SSHKEY_INTERNAL 34 #include "sshkey.h" 35 #include "digest.h" 36 #include "log.h" 37 38 static int openssh_RSA_verify(int, u_char *, size_t, u_char *, size_t, RSA *); 39 40 static const char * 41 rsa_hash_alg_ident(int hash_alg) 42 { 43 switch (hash_alg) { 44 case SSH_DIGEST_SHA1: 45 return "ssh-rsa"; 46 case SSH_DIGEST_SHA256: 47 return "rsa-sha2-256"; 48 case SSH_DIGEST_SHA512: 49 return "rsa-sha2-512"; 50 } 51 return NULL; 52 } 53 54 /* 55 * Returns the hash algorithm ID for a given algorithm identifier as used 56 * inside the signature blob, 57 */ 58 static int 59 rsa_hash_id_from_ident(const char *ident) 60 { 61 if (strcmp(ident, "ssh-rsa") == 0) 62 return SSH_DIGEST_SHA1; 63 if (strcmp(ident, "rsa-sha2-256") == 0) 64 return SSH_DIGEST_SHA256; 65 if (strcmp(ident, "rsa-sha2-512") == 0) 66 return SSH_DIGEST_SHA512; 67 return -1; 68 } 69 70 /* 71 * Return the hash algorithm ID for the specified key name. This includes 72 * all the cases of rsa_hash_id_from_ident() but also the certificate key 73 * types. 74 */ 75 static int 76 rsa_hash_id_from_keyname(const char *alg) 77 { 78 int r; 79 80 if ((r = rsa_hash_id_from_ident(alg)) != -1) 81 return r; 82 if (strcmp(alg, "ssh-rsa-cert-v01@openssh.com") == 0) 83 return SSH_DIGEST_SHA1; 84 if (strcmp(alg, "rsa-sha2-256-cert-v01@openssh.com") == 0) 85 return SSH_DIGEST_SHA256; 86 if (strcmp(alg, "rsa-sha2-512-cert-v01@openssh.com") == 0) 87 return SSH_DIGEST_SHA512; 88 return -1; 89 } 90 91 static int 92 rsa_hash_alg_nid(int type) 93 { 94 switch (type) { 95 case SSH_DIGEST_SHA1: 96 return NID_sha1; 97 case SSH_DIGEST_SHA256: 98 return NID_sha256; 99 case SSH_DIGEST_SHA512: 100 return NID_sha512; 101 default: 102 return -1; 103 } 104 } 105 106 int 107 ssh_rsa_generate_additional_parameters(struct sshkey *key) 108 { 109 BIGNUM *aux = NULL; 110 BN_CTX *ctx = NULL; 111 BIGNUM d; 112 int r; 113 114 if (key == NULL || key->rsa == NULL || 115 sshkey_type_plain(key->type) != KEY_RSA) 116 return SSH_ERR_INVALID_ARGUMENT; 117 118 if ((ctx = BN_CTX_new()) == NULL) 119 return SSH_ERR_ALLOC_FAIL; 120 if ((aux = BN_new()) == NULL) { 121 r = SSH_ERR_ALLOC_FAIL; 122 goto out; 123 } 124 BN_set_flags(aux, BN_FLG_CONSTTIME); 125 126 BN_init(&d); 127 BN_with_flags(&d, key->rsa->d, BN_FLG_CONSTTIME); 128 129 if ((BN_sub(aux, key->rsa->q, BN_value_one()) == 0) || 130 (BN_mod(key->rsa->dmq1, &d, aux, ctx) == 0) || 131 (BN_sub(aux, key->rsa->p, BN_value_one()) == 0) || 132 (BN_mod(key->rsa->dmp1, &d, aux, ctx) == 0)) { 133 r = SSH_ERR_LIBCRYPTO_ERROR; 134 goto out; 135 } 136 r = 0; 137 out: 138 BN_clear_free(aux); 139 BN_CTX_free(ctx); 140 return r; 141 } 142 143 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */ 144 int 145 ssh_rsa_sign(const struct sshkey *key, u_char **sigp, size_t *lenp, 146 const u_char *data, size_t datalen, const char *alg_ident) 147 { 148 u_char digest[SSH_DIGEST_MAX_LENGTH], *sig = NULL; 149 size_t slen = 0; 150 u_int dlen, len; 151 int nid, hash_alg, ret = SSH_ERR_INTERNAL_ERROR; 152 struct sshbuf *b = NULL; 153 154 if (lenp != NULL) 155 *lenp = 0; 156 if (sigp != NULL) 157 *sigp = NULL; 158 159 if (alg_ident == NULL || strlen(alg_ident) == 0) 160 hash_alg = SSH_DIGEST_SHA1; 161 else 162 hash_alg = rsa_hash_id_from_keyname(alg_ident); 163 if (key == NULL || key->rsa == NULL || hash_alg == -1 || 164 sshkey_type_plain(key->type) != KEY_RSA) 165 return SSH_ERR_INVALID_ARGUMENT; 166 if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) 167 return SSH_ERR_KEY_LENGTH; 168 slen = RSA_size(key->rsa); 169 if (slen <= 0 || slen > SSHBUF_MAX_BIGNUM) 170 return SSH_ERR_INVALID_ARGUMENT; 171 172 /* hash the data */ 173 nid = rsa_hash_alg_nid(hash_alg); 174 if ((dlen = ssh_digest_bytes(hash_alg)) == 0) 175 return SSH_ERR_INTERNAL_ERROR; 176 if ((ret = ssh_digest_memory(hash_alg, data, datalen, 177 digest, sizeof(digest))) != 0) 178 goto out; 179 180 if ((sig = malloc(slen)) == NULL) { 181 ret = SSH_ERR_ALLOC_FAIL; 182 goto out; 183 } 184 185 if (RSA_sign(nid, digest, dlen, sig, &len, key->rsa) != 1) { 186 ret = SSH_ERR_LIBCRYPTO_ERROR; 187 goto out; 188 } 189 if (len < slen) { 190 size_t diff = slen - len; 191 memmove(sig + diff, sig, len); 192 explicit_bzero(sig, diff); 193 } else if (len > slen) { 194 ret = SSH_ERR_INTERNAL_ERROR; 195 goto out; 196 } 197 /* encode signature */ 198 if ((b = sshbuf_new()) == NULL) { 199 ret = SSH_ERR_ALLOC_FAIL; 200 goto out; 201 } 202 if ((ret = sshbuf_put_cstring(b, rsa_hash_alg_ident(hash_alg))) != 0 || 203 (ret = sshbuf_put_string(b, sig, slen)) != 0) 204 goto out; 205 len = sshbuf_len(b); 206 if (sigp != NULL) { 207 if ((*sigp = malloc(len)) == NULL) { 208 ret = SSH_ERR_ALLOC_FAIL; 209 goto out; 210 } 211 memcpy(*sigp, sshbuf_ptr(b), len); 212 } 213 if (lenp != NULL) 214 *lenp = len; 215 ret = 0; 216 out: 217 explicit_bzero(digest, sizeof(digest)); 218 freezero(sig, slen); 219 sshbuf_free(b); 220 return ret; 221 } 222 223 int 224 ssh_rsa_verify(const struct sshkey *key, 225 const u_char *sig, size_t siglen, const u_char *data, size_t datalen, 226 const char *alg) 227 { 228 char *sigtype = NULL; 229 int hash_alg, want_alg, ret = SSH_ERR_INTERNAL_ERROR; 230 size_t len = 0, diff, modlen, dlen; 231 struct sshbuf *b = NULL; 232 u_char digest[SSH_DIGEST_MAX_LENGTH], *osigblob, *sigblob = NULL; 233 234 if (key == NULL || key->rsa == NULL || 235 sshkey_type_plain(key->type) != KEY_RSA || 236 sig == NULL || siglen == 0) 237 return SSH_ERR_INVALID_ARGUMENT; 238 if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) 239 return SSH_ERR_KEY_LENGTH; 240 241 if ((b = sshbuf_from(sig, siglen)) == NULL) 242 return SSH_ERR_ALLOC_FAIL; 243 if (sshbuf_get_cstring(b, &sigtype, NULL) != 0) { 244 ret = SSH_ERR_INVALID_FORMAT; 245 goto out; 246 } 247 if ((hash_alg = rsa_hash_id_from_ident(sigtype)) == -1) { 248 ret = SSH_ERR_KEY_TYPE_MISMATCH; 249 goto out; 250 } 251 /* 252 * Allow ssh-rsa-cert-v01 certs to generate SHA2 signatures for 253 * legacy reasons, but otherwise the signature type should match. 254 */ 255 if (alg != NULL && strcmp(alg, "ssh-rsa-cert-v01@openssh.com") != 0) { 256 if ((want_alg = rsa_hash_id_from_keyname(alg)) == -1) { 257 ret = SSH_ERR_INVALID_ARGUMENT; 258 goto out; 259 } 260 if (hash_alg != want_alg) { 261 ret = SSH_ERR_SIGNATURE_INVALID; 262 goto out; 263 } 264 } 265 if (sshbuf_get_string(b, &sigblob, &len) != 0) { 266 ret = SSH_ERR_INVALID_FORMAT; 267 goto out; 268 } 269 if (sshbuf_len(b) != 0) { 270 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA; 271 goto out; 272 } 273 /* RSA_verify expects a signature of RSA_size */ 274 modlen = RSA_size(key->rsa); 275 if (len > modlen) { 276 ret = SSH_ERR_KEY_BITS_MISMATCH; 277 goto out; 278 } else if (len < modlen) { 279 diff = modlen - len; 280 osigblob = sigblob; 281 if ((sigblob = realloc(sigblob, modlen)) == NULL) { 282 sigblob = osigblob; /* put it back for clear/free */ 283 ret = SSH_ERR_ALLOC_FAIL; 284 goto out; 285 } 286 memmove(sigblob + diff, sigblob, len); 287 explicit_bzero(sigblob, diff); 288 len = modlen; 289 } 290 if ((dlen = ssh_digest_bytes(hash_alg)) == 0) { 291 ret = SSH_ERR_INTERNAL_ERROR; 292 goto out; 293 } 294 if ((ret = ssh_digest_memory(hash_alg, data, datalen, 295 digest, sizeof(digest))) != 0) 296 goto out; 297 298 ret = openssh_RSA_verify(hash_alg, digest, dlen, sigblob, len, 299 key->rsa); 300 out: 301 freezero(sigblob, len); 302 free(sigtype); 303 sshbuf_free(b); 304 explicit_bzero(digest, sizeof(digest)); 305 return ret; 306 } 307 308 /* 309 * See: 310 * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/ 311 * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn 312 */ 313 314 /* 315 * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) 316 * oiw(14) secsig(3) algorithms(2) 26 } 317 */ 318 static const u_char id_sha1[] = { 319 0x30, 0x21, /* type Sequence, length 0x21 (33) */ 320 0x30, 0x09, /* type Sequence, length 0x09 */ 321 0x06, 0x05, /* type OID, length 0x05 */ 322 0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */ 323 0x05, 0x00, /* NULL */ 324 0x04, 0x14 /* Octet string, length 0x14 (20), followed by sha1 hash */ 325 }; 326 327 /* 328 * See http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html 329 * id-sha256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) 330 * organization(1) gov(101) csor(3) nistAlgorithm(4) hashAlgs(2) 331 * id-sha256(1) } 332 */ 333 static const u_char id_sha256[] = { 334 0x30, 0x31, /* type Sequence, length 0x31 (49) */ 335 0x30, 0x0d, /* type Sequence, length 0x0d (13) */ 336 0x06, 0x09, /* type OID, length 0x09 */ 337 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, /* id-sha256 */ 338 0x05, 0x00, /* NULL */ 339 0x04, 0x20 /* Octet string, length 0x20 (32), followed by sha256 hash */ 340 }; 341 342 /* 343 * See http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html 344 * id-sha512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) 345 * organization(1) gov(101) csor(3) nistAlgorithm(4) hashAlgs(2) 346 * id-sha256(3) } 347 */ 348 static const u_char id_sha512[] = { 349 0x30, 0x51, /* type Sequence, length 0x51 (81) */ 350 0x30, 0x0d, /* type Sequence, length 0x0d (13) */ 351 0x06, 0x09, /* type OID, length 0x09 */ 352 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, /* id-sha512 */ 353 0x05, 0x00, /* NULL */ 354 0x04, 0x40 /* Octet string, length 0x40 (64), followed by sha512 hash */ 355 }; 356 357 static int 358 rsa_hash_alg_oid(int hash_alg, const u_char **oidp, size_t *oidlenp) 359 { 360 switch (hash_alg) { 361 case SSH_DIGEST_SHA1: 362 *oidp = id_sha1; 363 *oidlenp = sizeof(id_sha1); 364 break; 365 case SSH_DIGEST_SHA256: 366 *oidp = id_sha256; 367 *oidlenp = sizeof(id_sha256); 368 break; 369 case SSH_DIGEST_SHA512: 370 *oidp = id_sha512; 371 *oidlenp = sizeof(id_sha512); 372 break; 373 default: 374 return SSH_ERR_INVALID_ARGUMENT; 375 } 376 return 0; 377 } 378 379 static int 380 openssh_RSA_verify(int hash_alg, u_char *hash, size_t hashlen, 381 u_char *sigbuf, size_t siglen, RSA *rsa) 382 { 383 size_t rsasize = 0, oidlen = 0, hlen = 0; 384 int ret, len, oidmatch, hashmatch; 385 const u_char *oid = NULL; 386 u_char *decrypted = NULL; 387 388 if ((ret = rsa_hash_alg_oid(hash_alg, &oid, &oidlen)) != 0) 389 return ret; 390 ret = SSH_ERR_INTERNAL_ERROR; 391 hlen = ssh_digest_bytes(hash_alg); 392 if (hashlen != hlen) { 393 ret = SSH_ERR_INVALID_ARGUMENT; 394 goto done; 395 } 396 rsasize = RSA_size(rsa); 397 if (rsasize <= 0 || rsasize > SSHBUF_MAX_BIGNUM || 398 siglen == 0 || siglen > rsasize) { 399 ret = SSH_ERR_INVALID_ARGUMENT; 400 goto done; 401 } 402 if ((decrypted = malloc(rsasize)) == NULL) { 403 ret = SSH_ERR_ALLOC_FAIL; 404 goto done; 405 } 406 if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa, 407 RSA_PKCS1_PADDING)) < 0) { 408 ret = SSH_ERR_LIBCRYPTO_ERROR; 409 goto done; 410 } 411 if (len < 0 || (size_t)len != hlen + oidlen) { 412 ret = SSH_ERR_INVALID_FORMAT; 413 goto done; 414 } 415 oidmatch = timingsafe_bcmp(decrypted, oid, oidlen) == 0; 416 hashmatch = timingsafe_bcmp(decrypted + oidlen, hash, hlen) == 0; 417 if (!oidmatch || !hashmatch) { 418 ret = SSH_ERR_SIGNATURE_INVALID; 419 goto done; 420 } 421 ret = 0; 422 done: 423 freezero(decrypted, rsasize); 424 return ret; 425 } 426 #endif /* WITH_OPENSSL */ 427