ssh-dss.c

   1 /* $OpenBSD: ssh-dss.c,v 1.22 2006/07/22 20:48:23 stevesk 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 <string.h>
  32
  33 #include "xmalloc.h"
  34 #include "buffer.h"
  35 #include "bufaux.h"
  36 #include "compat.h"
  37 #include "log.h"
  38 #include "key.h"
  39
  40 #define INTBLOB_LEN     20
  41 #define SIGBLOB_LEN     (2*INTBLOB_LEN)
  42
  43 int
  44 ssh_dss_sign(const Key *key, u_char **sigp, u_int *lenp,
  45     const u_char *data, u_int datalen)
  46 {
  47         DSA_SIG *sig;
  48         const EVP_MD *evp_md = EVP_sha1();
  49         EVP_MD_CTX md;
  50         u_char digest[EVP_MAX_MD_SIZE], sigblob[SIGBLOB_LEN];
  51         u_int rlen, slen, len, dlen;
  52         Buffer b;
  53
  54         if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) {
  55                 error("ssh_dss_sign: no DSA key");
  56                 return -1;
  57         }
  58         EVP_DigestInit(&md, evp_md);
  59         EVP_DigestUpdate(&md, data, datalen);
  60         EVP_DigestFinal(&md, digest, &dlen);
  61
  62         sig = DSA_do_sign(digest, dlen, key->dsa);
  63         memset(digest, 'd', sizeof(digest));
  64
  65         if (sig == NULL) {
  66                 error("ssh_dss_sign: sign failed");
  67                 return -1;
  68         }
  69
  70         rlen = BN_num_bytes(sig->r);
  71         slen = BN_num_bytes(sig->s);
  72         if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
  73                 error("bad sig size %u %u", rlen, slen);
  74                 DSA_SIG_free(sig);
  75                 return -1;
  76         }
  77         memset(sigblob, 0, SIGBLOB_LEN);
  78         BN_bn2bin(sig->r, sigblob+ SIGBLOB_LEN - INTBLOB_LEN - rlen);
  79         BN_bn2bin(sig->s, sigblob+ SIGBLOB_LEN - slen);
  80         DSA_SIG_free(sig);
  81
  82         if (datafellows & SSH_BUG_SIGBLOB) {
  83                 if (lenp != NULL)
  84                         *lenp = SIGBLOB_LEN;
  85                 if (sigp != NULL) {
  86                         *sigp = xmalloc(SIGBLOB_LEN);
  87                         memcpy(*sigp, sigblob, SIGBLOB_LEN);
  88                 }
  89         } else {
  90                 /* ietf-drafts */
  91                 buffer_init(&b);
  92                 buffer_put_cstring(&b, "ssh-dss");
  93                 buffer_put_string(&b, sigblob, SIGBLOB_LEN);
  94                 len = buffer_len(&b);
  95                 if (lenp != NULL)
  96                         *lenp = len;
  97                 if (sigp != NULL) {
  98                         *sigp = xmalloc(len);
  99                         memcpy(*sigp, buffer_ptr(&b), len);
 100                 }
 101                 buffer_free(&b);
 102         }
 103         return 0;
 104 }
 105 int
 106 ssh_dss_verify(const Key *key, const u_char *signature, u_int signaturelen,
 107     const u_char *data, u_int datalen)
 108 {
 109         DSA_SIG *sig;
 110         const EVP_MD *evp_md = EVP_sha1();
 111         EVP_MD_CTX md;
 112         u_char digest[EVP_MAX_MD_SIZE], *sigblob;
 113         u_int len, dlen;
 114         int rlen, ret;
 115         Buffer b;
 116
 117         if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) {
 118                 error("ssh_dss_verify: no DSA key");
 119                 return -1;
 120         }
 121
 122         /* fetch signature */
 123         if (datafellows & SSH_BUG_SIGBLOB) {
 124                 sigblob = xmalloc(signaturelen);
 125                 memcpy(sigblob, signature, signaturelen);
 126                 len = signaturelen;
 127         } else {
 128                 /* ietf-drafts */
 129                 char *ktype;
 130                 buffer_init(&b);
 131                 buffer_append(&b, signature, signaturelen);
 132                 ktype = buffer_get_string(&b, NULL);
 133                 if (strcmp("ssh-dss", ktype) != 0) {
 134                         error("ssh_dss_verify: cannot handle type %s", ktype);
 135                         buffer_free(&b);
 136                         xfree(ktype);
 137                         return -1;
 138                 }
 139                 xfree(ktype);
 140                 sigblob = buffer_get_string(&b, &len);
 141                 rlen = buffer_len(&b);
 142                 buffer_free(&b);
 143                 if (rlen != 0) {
 144                         error("ssh_dss_verify: "
 145                             "remaining bytes in signature %d", rlen);
 146                         xfree(sigblob);
 147                         return -1;
 148                 }
 149         }
 150
 151         if (len != SIGBLOB_LEN) {
 152                 fatal("bad sigbloblen %u != SIGBLOB_LEN", len);
 153         }
 154
 155         /* parse signature */
 156         if ((sig = DSA_SIG_new()) == NULL)
 157                 fatal("ssh_dss_verify: DSA_SIG_new failed");
 158         if ((sig->r = BN_new()) == NULL)
 159                 fatal("ssh_dss_verify: BN_new failed");
 160         if ((sig->s = BN_new()) == NULL)
 161                 fatal("ssh_dss_verify: BN_new failed");
 162         BN_bin2bn(sigblob, INTBLOB_LEN, sig->r);
 163         BN_bin2bn(sigblob+ INTBLOB_LEN, INTBLOB_LEN, sig->s);
 164
 165         /* clean up */
 166         memset(sigblob, 0, len);
 167         xfree(sigblob);
 168
 169         /* sha1 the data */
 170         EVP_DigestInit(&md, evp_md);
 171         EVP_DigestUpdate(&md, data, datalen);
 172         EVP_DigestFinal(&md, digest, &dlen);
 173
 174         ret = DSA_do_verify(digest, dlen, sig, key->dsa);
 175         memset(digest, 'd', sizeof(digest));
 176
 177         DSA_SIG_free(sig);
 178
 179         debug("ssh_dss_verify: signature %s",
 180             ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error");
 181         return ret;
 182 }