ssh-dss.c

   1 /* $OpenBSD: ssh-dss.c,v 1.23 2006/08/03 03:34:42 deraadt 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 <string.h>
  34
  35 #include "xmalloc.h"
  36 #include "buffer.h"
  37 #include "compat.h"
  38 #include "log.h"
  39 #include "key.h"
  40
  41 #define INTBLOB_LEN     20
  42 #define SIGBLOB_LEN     (2*INTBLOB_LEN)
  43
  44 int
  45 ssh_dss_sign(const Key *key, u_char **sigp, u_int *lenp,
  46     const u_char *data, u_int datalen)
  47 {
  48         DSA_SIG *sig;
  49         const EVP_MD *evp_md = EVP_sha1();
  50         EVP_MD_CTX md;
  51         u_char digest[EVP_MAX_MD_SIZE], sigblob[SIGBLOB_LEN];
  52         u_int rlen, slen, len, dlen;
  53         Buffer b;
  54
  55         if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) {
  56                 error("ssh_dss_sign: no DSA key");
  57                 return -1;
  58         }
  59         EVP_DigestInit(&md, evp_md);
  60         EVP_DigestUpdate(&md, data, datalen);
  61         EVP_DigestFinal(&md, digest, &dlen);
  62
  63         sig = DSA_do_sign(digest, dlen, key->dsa);
  64         memset(digest, 'd', sizeof(digest));
  65
  66         if (sig == NULL) {
  67                 error("ssh_dss_sign: sign failed");
  68                 return -1;
  69         }
  70
  71         rlen = BN_num_bytes(sig->r);
  72         slen = BN_num_bytes(sig->s);
  73         if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
  74                 error("bad sig size %u %u", rlen, slen);
  75                 DSA_SIG_free(sig);
  76                 return -1;
  77         }
  78         memset(sigblob, 0, SIGBLOB_LEN);
  79         BN_bn2bin(sig->r, sigblob+ SIGBLOB_LEN - INTBLOB_LEN - rlen);
  80         BN_bn2bin(sig->s, sigblob+ SIGBLOB_LEN - slen);
  81         DSA_SIG_free(sig);
  82
  83         if (datafellows & SSH_BUG_SIGBLOB) {
  84                 if (lenp != NULL)
  85                         *lenp = SIGBLOB_LEN;
  86                 if (sigp != NULL) {
  87                         *sigp = xmalloc(SIGBLOB_LEN);
  88                         memcpy(*sigp, sigblob, SIGBLOB_LEN);
  89                 }
  90         } else {
  91                 /* ietf-drafts */
  92                 buffer_init(&b);
  93                 buffer_put_cstring(&b, "ssh-dss");
  94                 buffer_put_string(&b, sigblob, SIGBLOB_LEN);
  95                 len = buffer_len(&b);
  96                 if (lenp != NULL)
  97                         *lenp = len;
  98                 if (sigp != NULL) {
  99                         *sigp = xmalloc(len);
 100                         memcpy(*sigp, buffer_ptr(&b), len);
 101                 }
 102                 buffer_free(&b);
 103         }
 104         return 0;
 105 }
 106 int
 107 ssh_dss_verify(const Key *key, const u_char *signature, u_int signaturelen,
 108     const u_char *data, u_int datalen)
 109 {
 110         DSA_SIG *sig;
 111         const EVP_MD *evp_md = EVP_sha1();
 112         EVP_MD_CTX md;
 113         u_char digest[EVP_MAX_MD_SIZE], *sigblob;
 114         u_int len, dlen;
 115         int rlen, ret;
 116         Buffer b;
 117
 118         if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) {
 119                 error("ssh_dss_verify: no DSA key");
 120                 return -1;
 121         }
 122
 123         /* fetch signature */
 124         if (datafellows & SSH_BUG_SIGBLOB) {
 125                 sigblob = xmalloc(signaturelen);
 126                 memcpy(sigblob, signature, signaturelen);
 127                 len = signaturelen;
 128         } else {
 129                 /* ietf-drafts */
 130                 char *ktype;
 131                 buffer_init(&b);
 132                 buffer_append(&b, signature, signaturelen);
 133                 ktype = buffer_get_string(&b, NULL);
 134                 if (strcmp("ssh-dss", ktype) != 0) {
 135                         error("ssh_dss_verify: cannot handle type %s", ktype);
 136                         buffer_free(&b);
 137                         xfree(ktype);
 138                         return -1;
 139                 }
 140                 xfree(ktype);
 141                 sigblob = buffer_get_string(&b, &len);
 142                 rlen = buffer_len(&b);
 143                 buffer_free(&b);
 144                 if (rlen != 0) {
 145                         error("ssh_dss_verify: "
 146                             "remaining bytes in signature %d", rlen);
 147                         xfree(sigblob);
 148                         return -1;
 149                 }
 150         }
 151
 152         if (len != SIGBLOB_LEN) {
 153                 fatal("bad sigbloblen %u != SIGBLOB_LEN", len);
 154         }
 155
 156         /* parse signature */
 157         if ((sig = DSA_SIG_new()) == NULL)
 158                 fatal("ssh_dss_verify: DSA_SIG_new failed");
 159         if ((sig->r = BN_new()) == NULL)
 160                 fatal("ssh_dss_verify: BN_new failed");
 161         if ((sig->s = BN_new()) == NULL)
 162                 fatal("ssh_dss_verify: BN_new failed");
 163         BN_bin2bn(sigblob, INTBLOB_LEN, sig->r);
 164         BN_bin2bn(sigblob+ INTBLOB_LEN, INTBLOB_LEN, sig->s);
 165
 166         /* clean up */
 167         memset(sigblob, 0, len);
 168         xfree(sigblob);
 169
 170         /* sha1 the data */
 171         EVP_DigestInit(&md, evp_md);
 172         EVP_DigestUpdate(&md, data, datalen);
 173         EVP_DigestFinal(&md, digest, &dlen);
 174
 175         ret = DSA_do_verify(digest, dlen, sig, key->dsa);
 176         memset(digest, 'd', sizeof(digest));
 177
 178         DSA_SIG_free(sig);
 179
 180         debug("ssh_dss_verify: signature %s",
 181             ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error");
 182         return ret;
 183 }