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