ssh-rsa.c

   1 /* $OpenBSD: ssh-rsa.c,v 1.38 2006/07/22 20:48:23 stevesk 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 #include "includes.h"
  18
  19 #include <openssl/evp.h>
  20 #include <openssl/err.h>
  21
  22 #include <string.h>
  23
  24 #include "xmalloc.h"
  25 #include "log.h"
  26 #include "buffer.h"
  27 #include "bufaux.h"
  28 #include "key.h"
  29 #include "compat.h"
  30 #include "ssh.h"
  31
  32 static int openssh_RSA_verify(int, u_char *, u_int, u_char *, u_int, RSA *);
  33
  34 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
  35 int
  36 ssh_rsa_sign(const Key *key, u_char **sigp, u_int *lenp,
  37     const u_char *data, u_int datalen)
  38 {
  39         const EVP_MD *evp_md;
  40         EVP_MD_CTX md;
  41         u_char digest[EVP_MAX_MD_SIZE], *sig;
  42         u_int slen, dlen, len;
  43         int ok, nid;
  44         Buffer b;
  45
  46         if (key == NULL || key->type != KEY_RSA || key->rsa == NULL) {
  47                 error("ssh_rsa_sign: no RSA key");
  48                 return -1;
  49         }
  50         nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
  51         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
  52                 error("ssh_rsa_sign: EVP_get_digestbynid %d failed", nid);
  53                 return -1;
  54         }
  55         EVP_DigestInit(&md, evp_md);
  56         EVP_DigestUpdate(&md, data, datalen);
  57         EVP_DigestFinal(&md, digest, &dlen);
  58
  59         slen = RSA_size(key->rsa);
  60         sig = xmalloc(slen);
  61
  62         ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa);
  63         memset(digest, 'd', sizeof(digest));
  64
  65         if (ok != 1) {
  66                 int ecode = ERR_get_error();
  67
  68                 error("ssh_rsa_sign: RSA_sign failed: %s",
  69                     ERR_error_string(ecode, NULL));
  70                 xfree(sig);
  71                 return -1;
  72         }
  73         if (len < slen) {
  74                 u_int diff = slen - len;
  75                 debug("slen %u > len %u", slen, len);
  76                 memmove(sig + diff, sig, len);
  77                 memset(sig, 0, diff);
  78         } else if (len > slen) {
  79                 error("ssh_rsa_sign: slen %u slen2 %u", slen, len);
  80                 xfree(sig);
  81                 return -1;
  82         }
  83         /* encode signature */
  84         buffer_init(&b);
  85         buffer_put_cstring(&b, "ssh-rsa");
  86         buffer_put_string(&b, sig, slen);
  87         len = buffer_len(&b);
  88         if (lenp != NULL)
  89                 *lenp = len;
  90         if (sigp != NULL) {
  91                 *sigp = xmalloc(len);
  92                 memcpy(*sigp, buffer_ptr(&b), len);
  93         }
  94         buffer_free(&b);
  95         memset(sig, 's', slen);
  96         xfree(sig);
  97
  98         return 0;
  99 }
 100
 101 int
 102 ssh_rsa_verify(const Key *key, const u_char *signature, u_int signaturelen,
 103     const u_char *data, u_int datalen)
 104 {
 105         Buffer b;
 106         const EVP_MD *evp_md;
 107         EVP_MD_CTX md;
 108         char *ktype;
 109         u_char digest[EVP_MAX_MD_SIZE], *sigblob;
 110         u_int len, dlen, modlen;
 111         int rlen, ret, nid;
 112
 113         if (key == NULL || key->type != KEY_RSA || key->rsa == NULL) {
 114                 error("ssh_rsa_verify: no RSA key");
 115                 return -1;
 116         }
 117         if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
 118                 error("ssh_rsa_verify: RSA modulus too small: %d < minimum %d bits",
 119                     BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
 120                 return -1;
 121         }
 122         buffer_init(&b);
 123         buffer_append(&b, signature, signaturelen);
 124         ktype = buffer_get_string(&b, NULL);
 125         if (strcmp("ssh-rsa", ktype) != 0) {
 126                 error("ssh_rsa_verify: cannot handle type %s", ktype);
 127                 buffer_free(&b);
 128                 xfree(ktype);
 129                 return -1;
 130         }
 131         xfree(ktype);
 132         sigblob = buffer_get_string(&b, &len);
 133         rlen = buffer_len(&b);
 134         buffer_free(&b);
 135         if (rlen != 0) {
 136                 error("ssh_rsa_verify: remaining bytes in signature %d", rlen);
 137                 xfree(sigblob);
 138                 return -1;
 139         }
 140         /* RSA_verify expects a signature of RSA_size */
 141         modlen = RSA_size(key->rsa);
 142         if (len > modlen) {
 143                 error("ssh_rsa_verify: len %u > modlen %u", len, modlen);
 144                 xfree(sigblob);
 145                 return -1;
 146         } else if (len < modlen) {
 147                 u_int diff = modlen - len;
 148                 debug("ssh_rsa_verify: add padding: modlen %u > len %u",
 149                     modlen, len);
 150                 sigblob = xrealloc(sigblob, 1, modlen);
 151                 memmove(sigblob + diff, sigblob, len);
 152                 memset(sigblob, 0, diff);
 153                 len = modlen;
 154         }
 155         nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
 156         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
 157                 error("ssh_rsa_verify: EVP_get_digestbynid %d failed", nid);
 158                 xfree(sigblob);
 159                 return -1;
 160         }
 161         EVP_DigestInit(&md, evp_md);
 162         EVP_DigestUpdate(&md, data, datalen);
 163         EVP_DigestFinal(&md, digest, &dlen);
 164
 165         ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa);
 166         memset(digest, 'd', sizeof(digest));
 167         memset(sigblob, 's', len);
 168         xfree(sigblob);
 169         debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : "");
 170         return ret;
 171 }
 172
 173 /*
 174  * See:
 175  * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
 176  * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
 177  */
 178 /*
 179  * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
 180  *      oiw(14) secsig(3) algorithms(2) 26 }
 181  */
 182 static const u_char id_sha1[] = {
 183         0x30, 0x21, /* type Sequence, length 0x21 (33) */
 184         0x30, 0x09, /* type Sequence, length 0x09 */
 185         0x06, 0x05, /* type OID, length 0x05 */
 186         0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
 187         0x05, 0x00, /* NULL */
 188         0x04, 0x14  /* Octet string, length 0x14 (20), followed by sha1 hash */
 189 };
 190 /*
 191  * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
 192  *      rsadsi(113549) digestAlgorithm(2) 5 }
 193  */
 194 static const u_char id_md5[] = {
 195         0x30, 0x20, /* type Sequence, length 0x20 (32) */
 196         0x30, 0x0c, /* type Sequence, length 0x09 */
 197         0x06, 0x08, /* type OID, length 0x05 */
 198         0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */
 199         0x05, 0x00, /* NULL */
 200         0x04, 0x10  /* Octet string, length 0x10 (16), followed by md5 hash */
 201 };
 202
 203 static int
 204 openssh_RSA_verify(int type, u_char *hash, u_int hashlen,
 205     u_char *sigbuf, u_int siglen, RSA *rsa)
 206 {
 207         u_int ret, rsasize, oidlen = 0, hlen = 0;
 208         int len;
 209         const u_char *oid = NULL;
 210         u_char *decrypted = NULL;
 211
 212         ret = 0;
 213         switch (type) {
 214         case NID_sha1:
 215                 oid = id_sha1;
 216                 oidlen = sizeof(id_sha1);
 217                 hlen = 20;
 218                 break;
 219         case NID_md5:
 220                 oid = id_md5;
 221                 oidlen = sizeof(id_md5);
 222                 hlen = 16;
 223                 break;
 224         default:
 225                 goto done;
 226         }
 227         if (hashlen != hlen) {
 228                 error("bad hashlen");
 229                 goto done;
 230         }
 231         rsasize = RSA_size(rsa);
 232         if (siglen == 0 || siglen > rsasize) {
 233                 error("bad siglen");
 234                 goto done;
 235         }
 236         decrypted = xmalloc(rsasize);
 237         if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
 238             RSA_PKCS1_PADDING)) < 0) {
 239                 error("RSA_public_decrypt failed: %s",
 240                     ERR_error_string(ERR_get_error(), NULL));
 241                 goto done;
 242         }
 243         if (len < 0 || (u_int)len != hlen + oidlen) {
 244                 error("bad decrypted len: %d != %d + %d", len, hlen, oidlen);
 245                 goto done;
 246         }
 247         if (memcmp(decrypted, oid, oidlen) != 0) {
 248                 error("oid mismatch");
 249                 goto done;
 250         }
 251         if (memcmp(decrypted + oidlen, hash, hlen) != 0) {
 252                 error("hash mismatch");
 253                 goto done;
 254         }
 255         ret = 1;
 256 done:
 257         if (decrypted)
 258                 xfree(decrypted);
 259         return ret;
 260 }