crypto/openssh/ssh-rsa.c

   1 /* $OpenBSD: ssh-rsa.c,v 1.52 2014/06/24 01:13:21 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 #include <sys/types.h>
  21
  22 #include <openssl/evp.h>
  23 #include <openssl/err.h>
  24
  25 #include <stdarg.h>
  26 #include <string.h>
  27
  28 #include "sshbuf.h"
  29 #include "compat.h"
  30 #include "ssherr.h"
  31 #define SSHKEY_INTERNAL
  32 #include "sshkey.h"
  33 #include "digest.h"
  34
  35 static int openssh_RSA_verify(int, u_char *, size_t, u_char *, size_t, RSA *);
  36
  37 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
  38 int
  39 ssh_rsa_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
  40     const u_char *data, size_t datalen, u_int compat)
  41 {
  42         int hash_alg;
  43         u_char digest[SSH_DIGEST_MAX_LENGTH], *sig = NULL;
  44         size_t slen;
  45         u_int dlen, len;
  46         int nid, ret = SSH_ERR_INTERNAL_ERROR;
  47         struct sshbuf *b = NULL;
  48
  49         if (lenp != NULL)
  50                 *lenp = 0;
  51         if (sigp != NULL)
  52                 *sigp = NULL;
  53
  54         if (key == NULL || key->rsa == NULL ||
  55             sshkey_type_plain(key->type) != KEY_RSA)
  56                 return SSH_ERR_INVALID_ARGUMENT;
  57         slen = RSA_size(key->rsa);
  58         if (slen <= 0 || slen > SSHBUF_MAX_BIGNUM)
  59                 return SSH_ERR_INVALID_ARGUMENT;
  60
  61         /* hash the data */
  62         hash_alg = SSH_DIGEST_SHA1;
  63         nid = NID_sha1;
  64         if ((dlen = ssh_digest_bytes(hash_alg)) == 0)
  65                 return SSH_ERR_INTERNAL_ERROR;
  66         if ((ret = ssh_digest_memory(hash_alg, data, datalen,
  67             digest, sizeof(digest))) != 0)
  68                 goto out;
  69
  70         if ((sig = malloc(slen)) == NULL) {
  71                 ret = SSH_ERR_ALLOC_FAIL;
  72                 goto out;
  73         }
  74
  75         if (RSA_sign(nid, digest, dlen, sig, &len, key->rsa) != 1) {
  76                 ret = SSH_ERR_LIBCRYPTO_ERROR;
  77                 goto out;
  78         }
  79         if (len < slen) {
  80                 size_t diff = slen - len;
  81                 memmove(sig + diff, sig, len);
  82                 explicit_bzero(sig, diff);
  83         } else if (len > slen) {
  84                 ret = SSH_ERR_INTERNAL_ERROR;
  85                 goto out;
  86         }
  87         /* encode signature */
  88         if ((b = sshbuf_new()) == NULL) {
  89                 ret = SSH_ERR_ALLOC_FAIL;
  90                 goto out;
  91         }
  92         if ((ret = sshbuf_put_cstring(b, "ssh-rsa")) != 0 ||
  93             (ret = sshbuf_put_string(b, sig, slen)) != 0)
  94                 goto out;
  95         len = sshbuf_len(b);
  96         if (sigp != NULL) {
  97                 if ((*sigp = malloc(len)) == NULL) {
  98                         ret = SSH_ERR_ALLOC_FAIL;
  99                         goto out;
 100                 }
 101                 memcpy(*sigp, sshbuf_ptr(b), len);
 102         }
 103         if (lenp != NULL)
 104                 *lenp = len;
 105         ret = 0;
 106  out:
 107         explicit_bzero(digest, sizeof(digest));
 108         if (sig != NULL) {
 109                 explicit_bzero(sig, slen);
 110                 free(sig);
 111         }
 112         if (b != NULL)
 113                 sshbuf_free(b);
 114         return 0;
 115 }
 116
 117 int
 118 ssh_rsa_verify(const struct sshkey *key,
 119     const u_char *signature, size_t signaturelen,
 120     const u_char *data, size_t datalen, u_int compat)
 121 {
 122         char *ktype = NULL;
 123         int hash_alg, ret = SSH_ERR_INTERNAL_ERROR;
 124         size_t len, diff, modlen, dlen;
 125         struct sshbuf *b = NULL;
 126         u_char digest[SSH_DIGEST_MAX_LENGTH], *osigblob, *sigblob = NULL;
 127
 128         if (key == NULL || key->rsa == NULL ||
 129             sshkey_type_plain(key->type) != KEY_RSA ||
 130             BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE)
 131                 return SSH_ERR_INVALID_ARGUMENT;
 132
 133         if ((b = sshbuf_from(signature, signaturelen)) == NULL)
 134                 return SSH_ERR_ALLOC_FAIL;
 135         if (sshbuf_get_cstring(b, &ktype, NULL) != 0) {
 136                 ret = SSH_ERR_INVALID_FORMAT;
 137                 goto out;
 138         }
 139         if (strcmp("ssh-rsa", ktype) != 0) {
 140                 ret = SSH_ERR_KEY_TYPE_MISMATCH;
 141                 goto out;
 142         }
 143         if (sshbuf_get_string(b, &sigblob, &len) != 0) {
 144                 ret = SSH_ERR_INVALID_FORMAT;
 145                 goto out;
 146         }
 147         if (sshbuf_len(b) != 0) {
 148                 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
 149                 goto out;
 150         }
 151         /* RSA_verify expects a signature of RSA_size */
 152         modlen = RSA_size(key->rsa);
 153         if (len > modlen) {
 154                 ret = SSH_ERR_KEY_BITS_MISMATCH;
 155                 goto out;
 156         } else if (len < modlen) {
 157                 diff = modlen - len;
 158                 osigblob = sigblob;
 159                 if ((sigblob = realloc(sigblob, modlen)) == NULL) {
 160                         sigblob = osigblob; /* put it back for clear/free */
 161                         ret = SSH_ERR_ALLOC_FAIL;
 162                         goto out;
 163                 }
 164                 memmove(sigblob + diff, sigblob, len);
 165                 explicit_bzero(sigblob, diff);
 166                 len = modlen;
 167         }
 168         hash_alg = SSH_DIGEST_SHA1;
 169         if ((dlen = ssh_digest_bytes(hash_alg)) == 0) {
 170                 ret = SSH_ERR_INTERNAL_ERROR;
 171                 goto out;
 172         }
 173         if ((ret = ssh_digest_memory(hash_alg, data, datalen,
 174             digest, sizeof(digest))) != 0)
 175                 goto out;
 176
 177         ret = openssh_RSA_verify(hash_alg, digest, dlen, sigblob, len,
 178             key->rsa);
 179  out:
 180         if (sigblob != NULL) {
 181                 explicit_bzero(sigblob, len);
 182                 free(sigblob);
 183         }
 184         if (ktype != NULL)
 185                 free(ktype);
 186         if (b != NULL)
 187                 sshbuf_free(b);
 188         explicit_bzero(digest, sizeof(digest));
 189         return ret;
 190 }
 191
 192 /*
 193  * See:
 194  * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
 195  * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
 196  */
 197 /*
 198  * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
 199  *      oiw(14) secsig(3) algorithms(2) 26 }
 200  */
 201 static const u_char id_sha1[] = {
 202         0x30, 0x21, /* type Sequence, length 0x21 (33) */
 203         0x30, 0x09, /* type Sequence, length 0x09 */
 204         0x06, 0x05, /* type OID, length 0x05 */
 205         0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
 206         0x05, 0x00, /* NULL */
 207         0x04, 0x14  /* Octet string, length 0x14 (20), followed by sha1 hash */
 208 };
 209
 210 static int
 211 openssh_RSA_verify(int hash_alg, u_char *hash, size_t hashlen,
 212     u_char *sigbuf, size_t siglen, RSA *rsa)
 213 {
 214         size_t ret, rsasize = 0, oidlen = 0, hlen = 0;
 215         int len, oidmatch, hashmatch;
 216         const u_char *oid = NULL;
 217         u_char *decrypted = NULL;
 218
 219         ret = SSH_ERR_INTERNAL_ERROR;
 220         switch (hash_alg) {
 221         case SSH_DIGEST_SHA1:
 222                 oid = id_sha1;
 223                 oidlen = sizeof(id_sha1);
 224                 hlen = 20;
 225                 break;
 226         default:
 227                 goto done;
 228         }
 229         if (hashlen != hlen) {
 230                 ret = SSH_ERR_INVALID_ARGUMENT;
 231                 goto done;
 232         }
 233         rsasize = RSA_size(rsa);
 234         if (rsasize <= 0 || rsasize > SSHBUF_MAX_BIGNUM ||
 235             siglen == 0 || siglen > rsasize) {
 236                 ret = SSH_ERR_INVALID_ARGUMENT;
 237                 goto done;
 238         }
 239         if ((decrypted = malloc(rsasize)) == NULL) {
 240                 ret = SSH_ERR_ALLOC_FAIL;
 241                 goto done;
 242         }
 243         if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
 244             RSA_PKCS1_PADDING)) < 0) {
 245                 ret = SSH_ERR_LIBCRYPTO_ERROR;
 246                 goto done;
 247         }
 248         if (len < 0 || (size_t)len != hlen + oidlen) {
 249                 ret = SSH_ERR_INVALID_FORMAT;
 250                 goto done;
 251         }
 252         oidmatch = timingsafe_bcmp(decrypted, oid, oidlen) == 0;
 253         hashmatch = timingsafe_bcmp(decrypted + oidlen, hash, hlen) == 0;
 254         if (!oidmatch || !hashmatch) {
 255                 ret = SSH_ERR_SIGNATURE_INVALID;
 256                 goto done;
 257         }
 258         ret = 0;
 259 done:
 260         if (decrypted) {
 261                 explicit_bzero(decrypted, rsasize);
 262                 free(decrypted);
 263         }
 264         return ret;
 265 }