ssh-dss.c

   1 /* $OpenBSD: ssh-dss.c,v 1.24 2006/11/06 21:25:28 markus 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->type != KEY_DSA || key->dsa == NULL) {
  57                 error("ssh_dss_sign: no DSA key");
  58                 return -1;
  59         }
  60         EVP_DigestInit(&md, evp_md);
  61         EVP_DigestUpdate(&md, data, datalen);
  62         EVP_DigestFinal(&md, digest, &dlen);
  63
  64         sig = DSA_do_sign(digest, dlen, key->dsa);
  65         memset(digest, 'd', sizeof(digest));
  66
  67         if (sig == NULL) {
  68                 error("ssh_dss_sign: sign failed");
  69                 return -1;
  70         }
  71
  72         rlen = BN_num_bytes(sig->r);
  73         slen = BN_num_bytes(sig->s);
  74         if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
  75                 error("bad sig size %u %u", rlen, slen);
  76                 DSA_SIG_free(sig);
  77                 return -1;
  78         }
  79         memset(sigblob, 0, SIGBLOB_LEN);
  80         BN_bn2bin(sig->r, sigblob+ SIGBLOB_LEN - INTBLOB_LEN - rlen);
  81         BN_bn2bin(sig->s, sigblob+ SIGBLOB_LEN - slen);
  82         DSA_SIG_free(sig);
  83
  84         if (datafellows & SSH_BUG_SIGBLOB) {
  85                 if (lenp != NULL)
  86                         *lenp = SIGBLOB_LEN;
  87                 if (sigp != NULL) {
  88                         *sigp = xmalloc(SIGBLOB_LEN);
  89                         memcpy(*sigp, sigblob, SIGBLOB_LEN);
  90                 }
  91         } else {
  92                 /* ietf-drafts */
  93                 buffer_init(&b);
  94                 buffer_put_cstring(&b, "ssh-dss");
  95                 buffer_put_string(&b, sigblob, SIGBLOB_LEN);
  96                 len = buffer_len(&b);
  97                 if (lenp != NULL)
  98                         *lenp = len;
  99                 if (sigp != NULL) {
 100                         *sigp = xmalloc(len);
 101                         memcpy(*sigp, buffer_ptr(&b), len);
 102                 }
 103                 buffer_free(&b);
 104         }
 105         return 0;
 106 }
 107 int
 108 ssh_dss_verify(const Key *key, const u_char *signature, u_int signaturelen,
 109     const u_char *data, u_int datalen)
 110 {
 111         DSA_SIG *sig;
 112         const EVP_MD *evp_md = EVP_sha1();
 113         EVP_MD_CTX md;
 114         u_char digest[EVP_MAX_MD_SIZE], *sigblob;
 115         u_int len, dlen;
 116         int rlen, ret;
 117         Buffer b;
 118
 119         if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) {
 120                 error("ssh_dss_verify: no DSA key");
 121                 return -1;
 122         }
 123
 124         /* fetch signature */
 125         if (datafellows & SSH_BUG_SIGBLOB) {
 126                 sigblob = xmalloc(signaturelen);
 127                 memcpy(sigblob, signature, signaturelen);
 128                 len = signaturelen;
 129         } else {
 130                 /* ietf-drafts */
 131                 char *ktype;
 132                 buffer_init(&b);
 133                 buffer_append(&b, signature, signaturelen);
 134                 ktype = buffer_get_string(&b, NULL);
 135                 if (strcmp("ssh-dss", ktype) != 0) {
 136                         error("ssh_dss_verify: cannot handle type %s", ktype);
 137                         buffer_free(&b);
 138                         xfree(ktype);
 139                         return -1;
 140                 }
 141                 xfree(ktype);
 142                 sigblob = buffer_get_string(&b, &len);
 143                 rlen = buffer_len(&b);
 144                 buffer_free(&b);
 145                 if (rlen != 0) {
 146                         error("ssh_dss_verify: "
 147                             "remaining bytes in signature %d", rlen);
 148                         xfree(sigblob);
 149                         return -1;
 150                 }
 151         }
 152
 153         if (len != SIGBLOB_LEN) {
 154                 fatal("bad sigbloblen %u != SIGBLOB_LEN", len);
 155         }
 156
 157         /* parse signature */
 158         if ((sig = DSA_SIG_new()) == NULL)
 159                 fatal("ssh_dss_verify: DSA_SIG_new failed");
 160         if ((sig->r = BN_new()) == NULL)
 161                 fatal("ssh_dss_verify: BN_new failed");
 162         if ((sig->s = BN_new()) == NULL)
 163                 fatal("ssh_dss_verify: BN_new failed");
 164         if ((BN_bin2bn(sigblob, INTBLOB_LEN, sig->r) == NULL) ||
 165             (BN_bin2bn(sigblob+ INTBLOB_LEN, INTBLOB_LEN, sig->s) == NULL))
 166                 fatal("ssh_dss_verify: BN_bin2bn failed");
 167
 168         /* clean up */
 169         memset(sigblob, 0, len);
 170         xfree(sigblob);
 171
 172         /* sha1 the data */
 173         EVP_DigestInit(&md, evp_md);
 174         EVP_DigestUpdate(&md, data, datalen);
 175         EVP_DigestFinal(&md, digest, &dlen);
 176
 177         ret = DSA_do_verify(digest, dlen, sig, key->dsa);
 178         memset(digest, 'd', sizeof(digest));
 179
 180         DSA_SIG_free(sig);
 181
 182         debug("ssh_dss_verify: signature %s",
 183             ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error");
 184         return ret;
 185 }