ssh-dss.c

   1 /* $OpenBSD: ssh-dss.c,v 1.27 2010/08/31 09:58:37 djm Exp $ */
   2 /*
   3  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  15  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  16  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  17  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  18  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  19  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  20  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  21  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  23  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "includes.h"
  27
  28 #include <sys/types.h>
  29
  30 #include <openssl/bn.h>
  31 #include <openssl/evp.h>
  32
  33 #include <stdarg.h>
  34 #include <string.h>
  35
  36 #include "xmalloc.h"
  37 #include "buffer.h"
  38 #include "compat.h"
  39 #include "log.h"
  40 #include "key.h"
  41
  42 #define INTBLOB_LEN     20
  43 #define SIGBLOB_LEN     (2*INTBLOB_LEN)
  44
  45 int
  46 ssh_dss_sign(const Key *key, u_char **sigp, u_int *lenp,
  47     const u_char *data, u_int datalen)
  48 {
  49         DSA_SIG *sig;
  50         const EVP_MD *evp_md = EVP_sha1();
  51         EVP_MD_CTX md;
  52         u_char digest[EVP_MAX_MD_SIZE], sigblob[SIGBLOB_LEN];
  53         u_int rlen, slen, len, dlen;
  54         Buffer b;
  55
  56         if (key == NULL || key->dsa == NULL || (key->type != KEY_DSA &&
  57             key->type != KEY_DSA_CERT && key->type != KEY_DSA_CERT_V00)) {
  58                 error("ssh_dss_sign: no DSA key");
  59                 return -1;
  60         }
  61         EVP_DigestInit(&md, evp_md);
  62         EVP_DigestUpdate(&md, data, datalen);
  63         EVP_DigestFinal(&md, digest, &dlen);
  64
  65         sig = DSA_do_sign(digest, dlen, key->dsa);
  66         memset(digest, 'd', sizeof(digest));
  67
  68         if (sig == NULL) {
  69                 error("ssh_dss_sign: sign failed");
  70                 return -1;
  71         }
  72
  73         rlen = BN_num_bytes(sig->r);
  74         slen = BN_num_bytes(sig->s);
  75         if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
  76                 error("bad sig size %u %u", rlen, slen);
  77                 DSA_SIG_free(sig);
  78                 return -1;
  79         }
  80         memset(sigblob, 0, SIGBLOB_LEN);
  81         BN_bn2bin(sig->r, sigblob+ SIGBLOB_LEN - INTBLOB_LEN - rlen);
  82         BN_bn2bin(sig->s, sigblob+ SIGBLOB_LEN - slen);
  83         DSA_SIG_free(sig);
  84
  85         if (datafellows & SSH_BUG_SIGBLOB) {
  86                 if (lenp != NULL)
  87                         *lenp = SIGBLOB_LEN;
  88                 if (sigp != NULL) {
  89                         *sigp = xmalloc(SIGBLOB_LEN);
  90                         memcpy(*sigp, sigblob, SIGBLOB_LEN);
  91                 }
  92         } else {
  93                 /* ietf-drafts */
  94                 buffer_init(&b);
  95                 buffer_put_cstring(&b, "ssh-dss");
  96                 buffer_put_string(&b, sigblob, SIGBLOB_LEN);
  97                 len = buffer_len(&b);
  98                 if (lenp != NULL)
  99                         *lenp = len;
 100                 if (sigp != NULL) {
 101                         *sigp = xmalloc(len);
 102                         memcpy(*sigp, buffer_ptr(&b), len);
 103                 }
 104                 buffer_free(&b);
 105         }
 106         return 0;
 107 }
 108 int
 109 ssh_dss_verify(const Key *key, const u_char *signature, u_int signaturelen,
 110     const u_char *data, u_int datalen)
 111 {
 112         DSA_SIG *sig;
 113         const EVP_MD *evp_md = EVP_sha1();
 114         EVP_MD_CTX md;
 115         u_char digest[EVP_MAX_MD_SIZE], *sigblob;
 116         u_int len, dlen;
 117         int rlen, ret;
 118         Buffer b;
 119
 120         if (key == NULL || key->dsa == NULL || (key->type != KEY_DSA &&
 121             key->type != KEY_DSA_CERT && key->type != KEY_DSA_CERT_V00)) {
 122                 error("ssh_dss_verify: no DSA key");
 123                 return -1;
 124         }
 125
 126         /* fetch signature */
 127         if (datafellows & SSH_BUG_SIGBLOB) {
 128                 sigblob = xmalloc(signaturelen);
 129                 memcpy(sigblob, signature, signaturelen);
 130                 len = signaturelen;
 131         } else {
 132                 /* ietf-drafts */
 133                 char *ktype;
 134                 buffer_init(&b);
 135                 buffer_append(&b, signature, signaturelen);
 136                 ktype = buffer_get_cstring(&b, NULL);
 137                 if (strcmp("ssh-dss", ktype) != 0) {
 138                         error("ssh_dss_verify: cannot handle type %s", ktype);
 139                         buffer_free(&b);
 140                         xfree(ktype);
 141                         return -1;
 142                 }
 143                 xfree(ktype);
 144                 sigblob = buffer_get_string(&b, &len);
 145                 rlen = buffer_len(&b);
 146                 buffer_free(&b);
 147                 if (rlen != 0) {
 148                         error("ssh_dss_verify: "
 149                             "remaining bytes in signature %d", rlen);
 150                         xfree(sigblob);
 151                         return -1;
 152                 }
 153         }
 154
 155         if (len != SIGBLOB_LEN) {
 156                 fatal("bad sigbloblen %u != SIGBLOB_LEN", len);
 157         }
 158
 159         /* parse signature */
 160         if ((sig = DSA_SIG_new()) == NULL)
 161                 fatal("ssh_dss_verify: DSA_SIG_new failed");
 162         if ((sig->r = BN_new()) == NULL)
 163                 fatal("ssh_dss_verify: BN_new failed");
 164         if ((sig->s = BN_new()) == NULL)
 165                 fatal("ssh_dss_verify: BN_new failed");
 166         if ((BN_bin2bn(sigblob, INTBLOB_LEN, sig->r) == NULL) ||
 167             (BN_bin2bn(sigblob+ INTBLOB_LEN, INTBLOB_LEN, sig->s) == NULL))
 168                 fatal("ssh_dss_verify: BN_bin2bn failed");
 169
 170         /* clean up */
 171         memset(sigblob, 0, len);
 172         xfree(sigblob);
 173
 174         /* sha1 the data */
 175         EVP_DigestInit(&md, evp_md);
 176         EVP_DigestUpdate(&md, data, datalen);
 177         EVP_DigestFinal(&md, digest, &dlen);
 178
 179         ret = DSA_do_verify(digest, dlen, sig, key->dsa);
 180         memset(digest, 'd', sizeof(digest));
 181
 182         DSA_SIG_free(sig);
 183
 184         debug("ssh_dss_verify: signature %s",
 185             ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error");
 186         return ret;
 187 }