crypto/openssh/ssh-rsa.c

   1 /* $OpenBSD: ssh-rsa.c,v 1.59 2016/04/21 06:08:02 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
  37 static int openssh_RSA_verify(int, u_char *, size_t, u_char *, size_t, RSA *);
  38
  39 static const char *
  40 rsa_hash_alg_ident(int hash_alg)
  41 {
  42         switch (hash_alg) {
  43         case SSH_DIGEST_SHA1:
  44                 return "ssh-rsa";
  45         case SSH_DIGEST_SHA256:
  46                 return "rsa-sha2-256";
  47         case SSH_DIGEST_SHA512:
  48                 return "rsa-sha2-512";
  49         }
  50         return NULL;
  51 }
  52
  53 static int
  54 rsa_hash_alg_from_ident(const char *ident)
  55 {
  56         if (strcmp(ident, "ssh-rsa") == 0)
  57                 return SSH_DIGEST_SHA1;
  58         if (strcmp(ident, "rsa-sha2-256") == 0)
  59                 return SSH_DIGEST_SHA256;
  60         if (strcmp(ident, "rsa-sha2-512") == 0)
  61                 return SSH_DIGEST_SHA512;
  62         return -1;
  63 }
  64
  65 static int
  66 rsa_hash_alg_nid(int type)
  67 {
  68         switch (type) {
  69         case SSH_DIGEST_SHA1:
  70                 return NID_sha1;
  71         case SSH_DIGEST_SHA256:
  72                 return NID_sha256;
  73         case SSH_DIGEST_SHA512:
  74                 return NID_sha512;
  75         default:
  76                 return -1;
  77         }
  78 }
  79
  80 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
  81 int
  82 ssh_rsa_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
  83     const u_char *data, size_t datalen, const char *alg_ident)
  84 {
  85         u_char digest[SSH_DIGEST_MAX_LENGTH], *sig = NULL;
  86         size_t slen;
  87         u_int dlen, len;
  88         int nid, hash_alg, ret = SSH_ERR_INTERNAL_ERROR;
  89         struct sshbuf *b = NULL;
  90
  91         if (lenp != NULL)
  92                 *lenp = 0;
  93         if (sigp != NULL)
  94                 *sigp = NULL;
  95
  96         if (alg_ident == NULL || strlen(alg_ident) == 0 ||
  97             strncmp(alg_ident, "ssh-rsa-cert", strlen("ssh-rsa-cert")) == 0)
  98                 hash_alg = SSH_DIGEST_SHA1;
  99         else
 100                 hash_alg = rsa_hash_alg_from_ident(alg_ident);
 101         if (key == NULL || key->rsa == NULL || hash_alg == -1 ||
 102             sshkey_type_plain(key->type) != KEY_RSA ||
 103             BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE)
 104                 return SSH_ERR_INVALID_ARGUMENT;
 105         slen = RSA_size(key->rsa);
 106         if (slen <= 0 || slen > SSHBUF_MAX_BIGNUM)
 107                 return SSH_ERR_INVALID_ARGUMENT;
 108
 109         /* hash the data */
 110         nid = rsa_hash_alg_nid(hash_alg);
 111         if ((dlen = ssh_digest_bytes(hash_alg)) == 0)
 112                 return SSH_ERR_INTERNAL_ERROR;
 113         if ((ret = ssh_digest_memory(hash_alg, data, datalen,
 114             digest, sizeof(digest))) != 0)
 115                 goto out;
 116
 117         if ((sig = malloc(slen)) == NULL) {
 118                 ret = SSH_ERR_ALLOC_FAIL;
 119                 goto out;
 120         }
 121
 122         if (RSA_sign(nid, digest, dlen, sig, &len, key->rsa) != 1) {
 123                 ret = SSH_ERR_LIBCRYPTO_ERROR;
 124                 goto out;
 125         }
 126         if (len < slen) {
 127                 size_t diff = slen - len;
 128                 memmove(sig + diff, sig, len);
 129                 explicit_bzero(sig, diff);
 130         } else if (len > slen) {
 131                 ret = SSH_ERR_INTERNAL_ERROR;
 132                 goto out;
 133         }
 134         /* encode signature */
 135         if ((b = sshbuf_new()) == NULL) {
 136                 ret = SSH_ERR_ALLOC_FAIL;
 137                 goto out;
 138         }
 139         if ((ret = sshbuf_put_cstring(b, rsa_hash_alg_ident(hash_alg))) != 0 ||
 140             (ret = sshbuf_put_string(b, sig, slen)) != 0)
 141                 goto out;
 142         len = sshbuf_len(b);
 143         if (sigp != NULL) {
 144                 if ((*sigp = malloc(len)) == NULL) {
 145                         ret = SSH_ERR_ALLOC_FAIL;
 146                         goto out;
 147                 }
 148                 memcpy(*sigp, sshbuf_ptr(b), len);
 149         }
 150         if (lenp != NULL)
 151                 *lenp = len;
 152         ret = 0;
 153  out:
 154         explicit_bzero(digest, sizeof(digest));
 155         if (sig != NULL) {
 156                 explicit_bzero(sig, slen);
 157                 free(sig);
 158         }
 159         sshbuf_free(b);
 160         return ret;
 161 }
 162
 163 int
 164 ssh_rsa_verify(const struct sshkey *key,
 165     const u_char *sig, size_t siglen, const u_char *data, size_t datalen)
 166 {
 167         char *ktype = NULL;
 168         int hash_alg, ret = SSH_ERR_INTERNAL_ERROR;
 169         size_t len, diff, modlen, dlen;
 170         struct sshbuf *b = NULL;
 171         u_char digest[SSH_DIGEST_MAX_LENGTH], *osigblob, *sigblob = NULL;
 172
 173         if (key == NULL || key->rsa == NULL ||
 174             sshkey_type_plain(key->type) != KEY_RSA ||
 175             BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE ||
 176             sig == NULL || siglen == 0)
 177                 return SSH_ERR_INVALID_ARGUMENT;
 178
 179         if ((b = sshbuf_from(sig, siglen)) == NULL)
 180                 return SSH_ERR_ALLOC_FAIL;
 181         if (sshbuf_get_cstring(b, &ktype, NULL) != 0) {
 182                 ret = SSH_ERR_INVALID_FORMAT;
 183                 goto out;
 184         }
 185         if ((hash_alg = rsa_hash_alg_from_ident(ktype)) == -1) {
 186                 ret = SSH_ERR_KEY_TYPE_MISMATCH;
 187                 goto out;
 188         }
 189         if (sshbuf_get_string(b, &sigblob, &len) != 0) {
 190                 ret = SSH_ERR_INVALID_FORMAT;
 191                 goto out;
 192         }
 193         if (sshbuf_len(b) != 0) {
 194                 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
 195                 goto out;
 196         }
 197         /* RSA_verify expects a signature of RSA_size */
 198         modlen = RSA_size(key->rsa);
 199         if (len > modlen) {
 200                 ret = SSH_ERR_KEY_BITS_MISMATCH;
 201                 goto out;
 202         } else if (len < modlen) {
 203                 diff = modlen - len;
 204                 osigblob = sigblob;
 205                 if ((sigblob = realloc(sigblob, modlen)) == NULL) {
 206                         sigblob = osigblob; /* put it back for clear/free */
 207                         ret = SSH_ERR_ALLOC_FAIL;
 208                         goto out;
 209                 }
 210                 memmove(sigblob + diff, sigblob, len);
 211                 explicit_bzero(sigblob, diff);
 212                 len = modlen;
 213         }
 214         if ((dlen = ssh_digest_bytes(hash_alg)) == 0) {
 215                 ret = SSH_ERR_INTERNAL_ERROR;
 216                 goto out;
 217         }
 218         if ((ret = ssh_digest_memory(hash_alg, data, datalen,
 219             digest, sizeof(digest))) != 0)
 220                 goto out;
 221
 222         ret = openssh_RSA_verify(hash_alg, digest, dlen, sigblob, len,
 223             key->rsa);
 224  out:
 225         if (sigblob != NULL) {
 226                 explicit_bzero(sigblob, len);
 227                 free(sigblob);
 228         }
 229         free(ktype);
 230         sshbuf_free(b);
 231         explicit_bzero(digest, sizeof(digest));
 232         return ret;
 233 }
 234
 235 /*
 236  * See:
 237  * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
 238  * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
 239  */
 240
 241 /*
 242  * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
 243  *      oiw(14) secsig(3) algorithms(2) 26 }
 244  */
 245 static const u_char id_sha1[] = {
 246         0x30, 0x21, /* type Sequence, length 0x21 (33) */
 247         0x30, 0x09, /* type Sequence, length 0x09 */
 248         0x06, 0x05, /* type OID, length 0x05 */
 249         0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
 250         0x05, 0x00, /* NULL */
 251         0x04, 0x14  /* Octet string, length 0x14 (20), followed by sha1 hash */
 252 };
 253
 254 /*
 255  * See http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html
 256  * id-sha256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840)
 257  *      organization(1) gov(101) csor(3) nistAlgorithm(4) hashAlgs(2)
 258  *      id-sha256(1) }
 259  */
 260 static const u_char id_sha256[] = {
 261         0x30, 0x31, /* type Sequence, length 0x31 (49) */
 262         0x30, 0x0d, /* type Sequence, length 0x0d (13) */
 263         0x06, 0x09, /* type OID, length 0x09 */
 264         0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, /* id-sha256 */
 265         0x05, 0x00, /* NULL */
 266         0x04, 0x20  /* Octet string, length 0x20 (32), followed by sha256 hash */
 267 };
 268
 269 /*
 270  * See http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html
 271  * id-sha512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840)
 272  *      organization(1) gov(101) csor(3) nistAlgorithm(4) hashAlgs(2)
 273  *      id-sha256(3) }
 274  */
 275 static const u_char id_sha512[] = {
 276         0x30, 0x51, /* type Sequence, length 0x51 (81) */
 277         0x30, 0x0d, /* type Sequence, length 0x0d (13) */
 278         0x06, 0x09, /* type OID, length 0x09 */
 279         0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, /* id-sha512 */
 280         0x05, 0x00, /* NULL */
 281         0x04, 0x40  /* Octet string, length 0x40 (64), followed by sha512 hash */
 282 };
 283
 284 static int
 285 rsa_hash_alg_oid(int hash_alg, const u_char **oidp, size_t *oidlenp)
 286 {
 287         switch (hash_alg) {
 288         case SSH_DIGEST_SHA1:
 289                 *oidp = id_sha1;
 290                 *oidlenp = sizeof(id_sha1);
 291                 break;
 292         case SSH_DIGEST_SHA256:
 293                 *oidp = id_sha256;
 294                 *oidlenp = sizeof(id_sha256);
 295                 break;
 296         case SSH_DIGEST_SHA512:
 297                 *oidp = id_sha512;
 298                 *oidlenp = sizeof(id_sha512);
 299                 break;
 300         default:
 301                 return SSH_ERR_INVALID_ARGUMENT;
 302         }
 303         return 0;
 304 }
 305
 306 static int
 307 openssh_RSA_verify(int hash_alg, u_char *hash, size_t hashlen,
 308     u_char *sigbuf, size_t siglen, RSA *rsa)
 309 {
 310         size_t rsasize = 0, oidlen = 0, hlen = 0;
 311         int ret, len, oidmatch, hashmatch;
 312         const u_char *oid = NULL;
 313         u_char *decrypted = NULL;
 314
 315         if ((ret = rsa_hash_alg_oid(hash_alg, &oid, &oidlen)) != 0)
 316                 return ret;
 317         ret = SSH_ERR_INTERNAL_ERROR;
 318         hlen = ssh_digest_bytes(hash_alg);
 319         if (hashlen != hlen) {
 320                 ret = SSH_ERR_INVALID_ARGUMENT;
 321                 goto done;
 322         }
 323         rsasize = RSA_size(rsa);
 324         if (rsasize <= 0 || rsasize > SSHBUF_MAX_BIGNUM ||
 325             siglen == 0 || siglen > rsasize) {
 326                 ret = SSH_ERR_INVALID_ARGUMENT;
 327                 goto done;
 328         }
 329         if ((decrypted = malloc(rsasize)) == NULL) {
 330                 ret = SSH_ERR_ALLOC_FAIL;
 331                 goto done;
 332         }
 333         if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
 334             RSA_PKCS1_PADDING)) < 0) {
 335                 ret = SSH_ERR_LIBCRYPTO_ERROR;
 336                 goto done;
 337         }
 338         if (len < 0 || (size_t)len != hlen + oidlen) {
 339                 ret = SSH_ERR_INVALID_FORMAT;
 340                 goto done;
 341         }
 342         oidmatch = timingsafe_bcmp(decrypted, oid, oidlen) == 0;
 343         hashmatch = timingsafe_bcmp(decrypted + oidlen, hash, hlen) == 0;
 344         if (!oidmatch || !hashmatch) {
 345                 ret = SSH_ERR_SIGNATURE_INVALID;
 346                 goto done;
 347         }
 348         ret = 0;
 349 done:
 350         if (decrypted) {
 351                 explicit_bzero(decrypted, rsasize);
 352                 free(decrypted);
 353         }
 354         return ret;
 355 }
 356 #endif /* WITH_OPENSSL */