ssh-rsa.c

   1 /* $OpenBSD: ssh-rsa.c,v 1.40 2010/02/26 20:29:54 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 #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 ||
  50             (key->type != KEY_RSA && key->type != KEY_RSA_CERT) ||
  51             key->rsa == NULL) {
  52                 error("ssh_rsa_sign: no RSA key");
  53                 return -1;
  54         }
  55         nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
  56         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
  57                 error("ssh_rsa_sign: EVP_get_digestbynid %d failed", nid);
  58                 return -1;
  59         }
  60         EVP_DigestInit(&md, evp_md);
  61         EVP_DigestUpdate(&md, data, datalen);
  62         EVP_DigestFinal(&md, digest, &dlen);
  63
  64         slen = RSA_size(key->rsa);
  65         sig = xmalloc(slen);
  66
  67         ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa);
  68         memset(digest, 'd', sizeof(digest));
  69
  70         if (ok != 1) {
  71                 int ecode = ERR_get_error();
  72
  73                 error("ssh_rsa_sign: RSA_sign failed: %s",
  74                     ERR_error_string(ecode, NULL));
  75                 xfree(sig);
  76                 return -1;
  77         }
  78         if (len < slen) {
  79                 u_int diff = slen - len;
  80                 debug("slen %u > len %u", slen, len);
  81                 memmove(sig + diff, sig, len);
  82                 memset(sig, 0, diff);
  83         } else if (len > slen) {
  84                 error("ssh_rsa_sign: slen %u slen2 %u", slen, len);
  85                 xfree(sig);
  86                 return -1;
  87         }
  88         /* encode signature */
  89         buffer_init(&b);
  90         buffer_put_cstring(&b, "ssh-rsa");
  91         buffer_put_string(&b, sig, slen);
  92         len = buffer_len(&b);
  93         if (lenp != NULL)
  94                 *lenp = len;
  95         if (sigp != NULL) {
  96                 *sigp = xmalloc(len);
  97                 memcpy(*sigp, buffer_ptr(&b), len);
  98         }
  99         buffer_free(&b);
 100         memset(sig, 's', slen);
 101         xfree(sig);
 102
 103         return 0;
 104 }
 105
 106 int
 107 ssh_rsa_verify(const Key *key, const u_char *signature, u_int signaturelen,
 108     const u_char *data, u_int datalen)
 109 {
 110         Buffer b;
 111         const EVP_MD *evp_md;
 112         EVP_MD_CTX md;
 113         char *ktype;
 114         u_char digest[EVP_MAX_MD_SIZE], *sigblob;
 115         u_int len, dlen, modlen;
 116         int rlen, ret, nid;
 117
 118         if (key == NULL ||
 119             (key->type != KEY_RSA && key->type != KEY_RSA_CERT) ||
 120             key->rsa == NULL) {
 121                 error("ssh_rsa_verify: no RSA key");
 122                 return -1;
 123         }
 124         if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
 125                 error("ssh_rsa_verify: RSA modulus too small: %d < minimum %d bits",
 126                     BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
 127                 return -1;
 128         }
 129         buffer_init(&b);
 130         buffer_append(&b, signature, signaturelen);
 131         ktype = buffer_get_string(&b, NULL);
 132         if (strcmp("ssh-rsa", ktype) != 0) {
 133                 error("ssh_rsa_verify: cannot handle type %s", ktype);
 134                 buffer_free(&b);
 135                 xfree(ktype);
 136                 return -1;
 137         }
 138         xfree(ktype);
 139         sigblob = buffer_get_string(&b, &len);
 140         rlen = buffer_len(&b);
 141         buffer_free(&b);
 142         if (rlen != 0) {
 143                 error("ssh_rsa_verify: remaining bytes in signature %d", rlen);
 144                 xfree(sigblob);
 145                 return -1;
 146         }
 147         /* RSA_verify expects a signature of RSA_size */
 148         modlen = RSA_size(key->rsa);
 149         if (len > modlen) {
 150                 error("ssh_rsa_verify: len %u > modlen %u", len, modlen);
 151                 xfree(sigblob);
 152                 return -1;
 153         } else if (len < modlen) {
 154                 u_int diff = modlen - len;
 155                 debug("ssh_rsa_verify: add padding: modlen %u > len %u",
 156                     modlen, len);
 157                 sigblob = xrealloc(sigblob, 1, modlen);
 158                 memmove(sigblob + diff, sigblob, len);
 159                 memset(sigblob, 0, diff);
 160                 len = modlen;
 161         }
 162         nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
 163         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
 164                 error("ssh_rsa_verify: EVP_get_digestbynid %d failed", nid);
 165                 xfree(sigblob);
 166                 return -1;
 167         }
 168         EVP_DigestInit(&md, evp_md);
 169         EVP_DigestUpdate(&md, data, datalen);
 170         EVP_DigestFinal(&md, digest, &dlen);
 171
 172         ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa);
 173         memset(digest, 'd', sizeof(digest));
 174         memset(sigblob, 's', len);
 175         xfree(sigblob);
 176         debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : "");
 177         return ret;
 178 }
 179
 180 /*
 181  * See:
 182  * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
 183  * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
 184  */
 185 /*
 186  * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
 187  *      oiw(14) secsig(3) algorithms(2) 26 }
 188  */
 189 static const u_char id_sha1[] = {
 190         0x30, 0x21, /* type Sequence, length 0x21 (33) */
 191         0x30, 0x09, /* type Sequence, length 0x09 */
 192         0x06, 0x05, /* type OID, length 0x05 */
 193         0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
 194         0x05, 0x00, /* NULL */
 195         0x04, 0x14  /* Octet string, length 0x14 (20), followed by sha1 hash */
 196 };
 197 /*
 198  * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
 199  *      rsadsi(113549) digestAlgorithm(2) 5 }
 200  */
 201 static const u_char id_md5[] = {
 202         0x30, 0x20, /* type Sequence, length 0x20 (32) */
 203         0x30, 0x0c, /* type Sequence, length 0x09 */
 204         0x06, 0x08, /* type OID, length 0x05 */
 205         0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */
 206         0x05, 0x00, /* NULL */
 207         0x04, 0x10  /* Octet string, length 0x10 (16), followed by md5 hash */
 208 };
 209
 210 static int
 211 openssh_RSA_verify(int type, u_char *hash, u_int hashlen,
 212     u_char *sigbuf, u_int siglen, RSA *rsa)
 213 {
 214         u_int ret, rsasize, oidlen = 0, hlen = 0;
 215         int len;
 216         const u_char *oid = NULL;
 217         u_char *decrypted = NULL;
 218
 219         ret = 0;
 220         switch (type) {
 221         case NID_sha1:
 222                 oid = id_sha1;
 223                 oidlen = sizeof(id_sha1);
 224                 hlen = 20;
 225                 break;
 226         case NID_md5:
 227                 oid = id_md5;
 228                 oidlen = sizeof(id_md5);
 229                 hlen = 16;
 230                 break;
 231         default:
 232                 goto done;
 233         }
 234         if (hashlen != hlen) {
 235                 error("bad hashlen");
 236                 goto done;
 237         }
 238         rsasize = RSA_size(rsa);
 239         if (siglen == 0 || siglen > rsasize) {
 240                 error("bad siglen");
 241                 goto done;
 242         }
 243         decrypted = xmalloc(rsasize);
 244         if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
 245             RSA_PKCS1_PADDING)) < 0) {
 246                 error("RSA_public_decrypt failed: %s",
 247                     ERR_error_string(ERR_get_error(), NULL));
 248                 goto done;
 249         }
 250         if (len < 0 || (u_int)len != hlen + oidlen) {
 251                 error("bad decrypted len: %d != %d + %d", len, hlen, oidlen);
 252                 goto done;
 253         }
 254         if (memcmp(decrypted, oid, oidlen) != 0) {
 255                 error("oid mismatch");
 256                 goto done;
 257         }
 258         if (memcmp(decrypted + oidlen, hash, hlen) != 0) {
 259                 error("hash mismatch");
 260                 goto done;
 261         }
 262         ret = 1;
 263 done:
 264         if (decrypted)
 265                 xfree(decrypted);
 266         return ret;
 267 }