ssh-rsa.c

   1 /* $OpenBSD: ssh-rsa.c,v 1.39 2006/08/03 03:34:42 deraadt 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 "xmalloc.h"
  29 #include "log.h"
  30 #include "buffer.h"
  31 #include "key.h"
  32 #include "compat.h"
  33 #include "ssh.h"
  34
  35 static int openssh_RSA_verify(int, u_char *, u_int, u_char *, u_int, RSA *);
  36
  37 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
  38 int
  39 ssh_rsa_sign(const Key *key, u_char **sigp, u_int *lenp,
  40     const u_char *data, u_int datalen)
  41 {
  42         const EVP_MD *evp_md;
  43         EVP_MD_CTX md;
  44         u_char digest[EVP_MAX_MD_SIZE], *sig;
  45         u_int slen, dlen, len;
  46         int ok, nid;
  47         Buffer b;
  48
  49         if (key == NULL || key->type != KEY_RSA || key->rsa == NULL) {
  50                 error("ssh_rsa_sign: no RSA key");
  51                 return -1;
  52         }
  53         nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
  54         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
  55                 error("ssh_rsa_sign: EVP_get_digestbynid %d failed", nid);
  56                 return -1;
  57         }
  58         EVP_DigestInit(&md, evp_md);
  59         EVP_DigestUpdate(&md, data, datalen);
  60         EVP_DigestFinal(&md, digest, &dlen);
  61
  62         slen = RSA_size(key->rsa);
  63         sig = xmalloc(slen);
  64
  65         ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa);
  66         memset(digest, 'd', sizeof(digest));
  67
  68         if (ok != 1) {
  69                 int ecode = ERR_get_error();
  70
  71                 error("ssh_rsa_sign: RSA_sign failed: %s",
  72                     ERR_error_string(ecode, NULL));
  73                 xfree(sig);
  74                 return -1;
  75         }
  76         if (len < slen) {
  77                 u_int diff = slen - len;
  78                 debug("slen %u > len %u", slen, len);
  79                 memmove(sig + diff, sig, len);
  80                 memset(sig, 0, diff);
  81         } else if (len > slen) {
  82                 error("ssh_rsa_sign: slen %u slen2 %u", slen, len);
  83                 xfree(sig);
  84                 return -1;
  85         }
  86         /* encode signature */
  87         buffer_init(&b);
  88         buffer_put_cstring(&b, "ssh-rsa");
  89         buffer_put_string(&b, sig, slen);
  90         len = buffer_len(&b);
  91         if (lenp != NULL)
  92                 *lenp = len;
  93         if (sigp != NULL) {
  94                 *sigp = xmalloc(len);
  95                 memcpy(*sigp, buffer_ptr(&b), len);
  96         }
  97         buffer_free(&b);
  98         memset(sig, 's', slen);
  99         xfree(sig);
 100
 101         return 0;
 102 }
 103
 104 int
 105 ssh_rsa_verify(const Key *key, const u_char *signature, u_int signaturelen,
 106     const u_char *data, u_int datalen)
 107 {
 108         Buffer b;
 109         const EVP_MD *evp_md;
 110         EVP_MD_CTX md;
 111         char *ktype;
 112         u_char digest[EVP_MAX_MD_SIZE], *sigblob;
 113         u_int len, dlen, modlen;
 114         int rlen, ret, nid;
 115
 116         if (key == NULL || key->type != KEY_RSA || key->rsa == NULL) {
 117                 error("ssh_rsa_verify: no RSA key");
 118                 return -1;
 119         }
 120         if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
 121                 error("ssh_rsa_verify: RSA modulus too small: %d < minimum %d bits",
 122                     BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
 123                 return -1;
 124         }
 125         buffer_init(&b);
 126         buffer_append(&b, signature, signaturelen);
 127         ktype = buffer_get_string(&b, NULL);
 128         if (strcmp("ssh-rsa", ktype) != 0) {
 129                 error("ssh_rsa_verify: cannot handle type %s", ktype);
 130                 buffer_free(&b);
 131                 xfree(ktype);
 132                 return -1;
 133         }
 134         xfree(ktype);
 135         sigblob = buffer_get_string(&b, &len);
 136         rlen = buffer_len(&b);
 137         buffer_free(&b);
 138         if (rlen != 0) {
 139                 error("ssh_rsa_verify: remaining bytes in signature %d", rlen);
 140                 xfree(sigblob);
 141                 return -1;
 142         }
 143         /* RSA_verify expects a signature of RSA_size */
 144         modlen = RSA_size(key->rsa);
 145         if (len > modlen) {
 146                 error("ssh_rsa_verify: len %u > modlen %u", len, modlen);
 147                 xfree(sigblob);
 148                 return -1;
 149         } else if (len < modlen) {
 150                 u_int diff = modlen - len;
 151                 debug("ssh_rsa_verify: add padding: modlen %u > len %u",
 152                     modlen, len);
 153                 sigblob = xrealloc(sigblob, 1, modlen);
 154                 memmove(sigblob + diff, sigblob, len);
 155                 memset(sigblob, 0, diff);
 156                 len = modlen;
 157         }
 158         nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
 159         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
 160                 error("ssh_rsa_verify: EVP_get_digestbynid %d failed", nid);
 161                 xfree(sigblob);
 162                 return -1;
 163         }
 164         EVP_DigestInit(&md, evp_md);
 165         EVP_DigestUpdate(&md, data, datalen);
 166         EVP_DigestFinal(&md, digest, &dlen);
 167
 168         ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa);
 169         memset(digest, 'd', sizeof(digest));
 170         memset(sigblob, 's', len);
 171         xfree(sigblob);
 172         debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : "");
 173         return ret;
 174 }
 175
 176 /*
 177  * See:
 178  * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
 179  * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
 180  */
 181 /*
 182  * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
 183  *      oiw(14) secsig(3) algorithms(2) 26 }
 184  */
 185 static const u_char id_sha1[] = {
 186         0x30, 0x21, /* type Sequence, length 0x21 (33) */
 187         0x30, 0x09, /* type Sequence, length 0x09 */
 188         0x06, 0x05, /* type OID, length 0x05 */
 189         0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
 190         0x05, 0x00, /* NULL */
 191         0x04, 0x14  /* Octet string, length 0x14 (20), followed by sha1 hash */
 192 };
 193 /*
 194  * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
 195  *      rsadsi(113549) digestAlgorithm(2) 5 }
 196  */
 197 static const u_char id_md5[] = {
 198         0x30, 0x20, /* type Sequence, length 0x20 (32) */
 199         0x30, 0x0c, /* type Sequence, length 0x09 */
 200         0x06, 0x08, /* type OID, length 0x05 */
 201         0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */
 202         0x05, 0x00, /* NULL */
 203         0x04, 0x10  /* Octet string, length 0x10 (16), followed by md5 hash */
 204 };
 205
 206 static int
 207 openssh_RSA_verify(int type, u_char *hash, u_int hashlen,
 208     u_char *sigbuf, u_int siglen, RSA *rsa)
 209 {
 210         u_int ret, rsasize, oidlen = 0, hlen = 0;
 211         int len;
 212         const u_char *oid = NULL;
 213         u_char *decrypted = NULL;
 214
 215         ret = 0;
 216         switch (type) {
 217         case NID_sha1:
 218                 oid = id_sha1;
 219                 oidlen = sizeof(id_sha1);
 220                 hlen = 20;
 221                 break;
 222         case NID_md5:
 223                 oid = id_md5;
 224                 oidlen = sizeof(id_md5);
 225                 hlen = 16;
 226                 break;
 227         default:
 228                 goto done;
 229         }
 230         if (hashlen != hlen) {
 231                 error("bad hashlen");
 232                 goto done;
 233         }
 234         rsasize = RSA_size(rsa);
 235         if (siglen == 0 || siglen > rsasize) {
 236                 error("bad siglen");
 237                 goto done;
 238         }
 239         decrypted = xmalloc(rsasize);
 240         if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
 241             RSA_PKCS1_PADDING)) < 0) {
 242                 error("RSA_public_decrypt failed: %s",
 243                     ERR_error_string(ERR_get_error(), NULL));
 244                 goto done;
 245         }
 246         if (len < 0 || (u_int)len != hlen + oidlen) {
 247                 error("bad decrypted len: %d != %d + %d", len, hlen, oidlen);
 248                 goto done;
 249         }
 250         if (memcmp(decrypted, oid, oidlen) != 0) {
 251                 error("oid mismatch");
 252                 goto done;
 253         }
 254         if (memcmp(decrypted + oidlen, hash, hlen) != 0) {
 255                 error("hash mismatch");
 256                 goto done;
 257         }
 258         ret = 1;
 259 done:
 260         if (decrypted)
 261                 xfree(decrypted);
 262         return ret;
 263 }