ssh-dss.c

   1 /* $OpenBSD: ssh-dss.c,v 1.21 2006/03/25 13:17:02 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 <openssl/bn.h>
  29 #include <openssl/evp.h>
  30
  31 #include "xmalloc.h"
  32 #include "buffer.h"
  33 #include "bufaux.h"
  34 #include "compat.h"
  35 #include "log.h"
  36 #include "key.h"
  37
  38 #define INTBLOB_LEN     20
  39 #define SIGBLOB_LEN     (2*INTBLOB_LEN)
  40
  41 int
  42 ssh_dss_sign(const Key *key, u_char **sigp, u_int *lenp,
  43     const u_char *data, u_int datalen)
  44 {
  45         DSA_SIG *sig;
  46         const EVP_MD *evp_md = EVP_sha1();
  47         EVP_MD_CTX md;
  48         u_char digest[EVP_MAX_MD_SIZE], sigblob[SIGBLOB_LEN];
  49         u_int rlen, slen, len, dlen;
  50         Buffer b;
  51
  52         if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) {
  53                 error("ssh_dss_sign: no DSA key");
  54                 return -1;
  55         }
  56         EVP_DigestInit(&md, evp_md);
  57         EVP_DigestUpdate(&md, data, datalen);
  58         EVP_DigestFinal(&md, digest, &dlen);
  59
  60         sig = DSA_do_sign(digest, dlen, key->dsa);
  61         memset(digest, 'd', sizeof(digest));
  62
  63         if (sig == NULL) {
  64                 error("ssh_dss_sign: sign failed");
  65                 return -1;
  66         }
  67
  68         rlen = BN_num_bytes(sig->r);
  69         slen = BN_num_bytes(sig->s);
  70         if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
  71                 error("bad sig size %u %u", rlen, slen);
  72                 DSA_SIG_free(sig);
  73                 return -1;
  74         }
  75         memset(sigblob, 0, SIGBLOB_LEN);
  76         BN_bn2bin(sig->r, sigblob+ SIGBLOB_LEN - INTBLOB_LEN - rlen);
  77         BN_bn2bin(sig->s, sigblob+ SIGBLOB_LEN - slen);
  78         DSA_SIG_free(sig);
  79
  80         if (datafellows & SSH_BUG_SIGBLOB) {
  81                 if (lenp != NULL)
  82                         *lenp = SIGBLOB_LEN;
  83                 if (sigp != NULL) {
  84                         *sigp = xmalloc(SIGBLOB_LEN);
  85                         memcpy(*sigp, sigblob, SIGBLOB_LEN);
  86                 }
  87         } else {
  88                 /* ietf-drafts */
  89                 buffer_init(&b);
  90                 buffer_put_cstring(&b, "ssh-dss");
  91                 buffer_put_string(&b, sigblob, SIGBLOB_LEN);
  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         }
 101         return 0;
 102 }
 103 int
 104 ssh_dss_verify(const Key *key, const u_char *signature, u_int signaturelen,
 105     const u_char *data, u_int datalen)
 106 {
 107         DSA_SIG *sig;
 108         const EVP_MD *evp_md = EVP_sha1();
 109         EVP_MD_CTX md;
 110         u_char digest[EVP_MAX_MD_SIZE], *sigblob;
 111         u_int len, dlen;
 112         int rlen, ret;
 113         Buffer b;
 114
 115         if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) {
 116                 error("ssh_dss_verify: no DSA key");
 117                 return -1;
 118         }
 119
 120         /* fetch signature */
 121         if (datafellows & SSH_BUG_SIGBLOB) {
 122                 sigblob = xmalloc(signaturelen);
 123                 memcpy(sigblob, signature, signaturelen);
 124                 len = signaturelen;
 125         } else {
 126                 /* ietf-drafts */
 127                 char *ktype;
 128                 buffer_init(&b);
 129                 buffer_append(&b, signature, signaturelen);
 130                 ktype = buffer_get_string(&b, NULL);
 131                 if (strcmp("ssh-dss", ktype) != 0) {
 132                         error("ssh_dss_verify: cannot handle type %s", ktype);
 133                         buffer_free(&b);
 134                         xfree(ktype);
 135                         return -1;
 136                 }
 137                 xfree(ktype);
 138                 sigblob = buffer_get_string(&b, &len);
 139                 rlen = buffer_len(&b);
 140                 buffer_free(&b);
 141                 if (rlen != 0) {
 142                         error("ssh_dss_verify: "
 143                             "remaining bytes in signature %d", rlen);
 144                         xfree(sigblob);
 145                         return -1;
 146                 }
 147         }
 148
 149         if (len != SIGBLOB_LEN) {
 150                 fatal("bad sigbloblen %u != SIGBLOB_LEN", len);
 151         }
 152
 153         /* parse signature */
 154         if ((sig = DSA_SIG_new()) == NULL)
 155                 fatal("ssh_dss_verify: DSA_SIG_new failed");
 156         if ((sig->r = BN_new()) == NULL)
 157                 fatal("ssh_dss_verify: BN_new failed");
 158         if ((sig->s = BN_new()) == NULL)
 159                 fatal("ssh_dss_verify: BN_new failed");
 160         BN_bin2bn(sigblob, INTBLOB_LEN, sig->r);
 161         BN_bin2bn(sigblob+ INTBLOB_LEN, INTBLOB_LEN, sig->s);
 162
 163         /* clean up */
 164         memset(sigblob, 0, len);
 165         xfree(sigblob);
 166
 167         /* sha1 the data */
 168         EVP_DigestInit(&md, evp_md);
 169         EVP_DigestUpdate(&md, data, datalen);
 170         EVP_DigestFinal(&md, digest, &dlen);
 171
 172         ret = DSA_do_verify(digest, dlen, sig, key->dsa);
 173         memset(digest, 'd', sizeof(digest));
 174
 175         DSA_SIG_free(sig);
 176
 177         debug("ssh_dss_verify: signature %s",
 178             ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error");
 179         return ret;
 180 }