ssh-dss.c

   1 /* $OpenBSD: ssh-dss.c,v 1.25 2010/02/26 20:29:54 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 ||
  57             (key->type != KEY_DSA && key->type != KEY_DSA_CERT) ||
  58             key->dsa == NULL) {
  59                 error("ssh_dss_sign: no DSA key");
  60                 return -1;
  61         }
  62         EVP_DigestInit(&md, evp_md);
  63         EVP_DigestUpdate(&md, data, datalen);
  64         EVP_DigestFinal(&md, digest, &dlen);
  65
  66         sig = DSA_do_sign(digest, dlen, key->dsa);
  67         memset(digest, 'd', sizeof(digest));
  68
  69         if (sig == NULL) {
  70                 error("ssh_dss_sign: sign failed");
  71                 return -1;
  72         }
  73
  74         rlen = BN_num_bytes(sig->r);
  75         slen = BN_num_bytes(sig->s);
  76         if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
  77                 error("bad sig size %u %u", rlen, slen);
  78                 DSA_SIG_free(sig);
  79                 return -1;
  80         }
  81         memset(sigblob, 0, SIGBLOB_LEN);
  82         BN_bn2bin(sig->r, sigblob+ SIGBLOB_LEN - INTBLOB_LEN - rlen);
  83         BN_bn2bin(sig->s, sigblob+ SIGBLOB_LEN - slen);
  84         DSA_SIG_free(sig);
  85
  86         if (datafellows & SSH_BUG_SIGBLOB) {
  87                 if (lenp != NULL)
  88                         *lenp = SIGBLOB_LEN;
  89                 if (sigp != NULL) {
  90                         *sigp = xmalloc(SIGBLOB_LEN);
  91                         memcpy(*sigp, sigblob, SIGBLOB_LEN);
  92                 }
  93         } else {
  94                 /* ietf-drafts */
  95                 buffer_init(&b);
  96                 buffer_put_cstring(&b, "ssh-dss");
  97                 buffer_put_string(&b, sigblob, SIGBLOB_LEN);
  98                 len = buffer_len(&b);
  99                 if (lenp != NULL)
 100                         *lenp = len;
 101                 if (sigp != NULL) {
 102                         *sigp = xmalloc(len);
 103                         memcpy(*sigp, buffer_ptr(&b), len);
 104                 }
 105                 buffer_free(&b);
 106         }
 107         return 0;
 108 }
 109 int
 110 ssh_dss_verify(const Key *key, const u_char *signature, u_int signaturelen,
 111     const u_char *data, u_int datalen)
 112 {
 113         DSA_SIG *sig;
 114         const EVP_MD *evp_md = EVP_sha1();
 115         EVP_MD_CTX md;
 116         u_char digest[EVP_MAX_MD_SIZE], *sigblob;
 117         u_int len, dlen;
 118         int rlen, ret;
 119         Buffer b;
 120
 121         if (key == NULL ||
 122             (key->type != KEY_DSA && key->type != KEY_DSA_CERT) ||
 123             key->dsa == NULL) {
 124                 error("ssh_dss_verify: no DSA key");
 125                 return -1;
 126         }
 127
 128         /* fetch signature */
 129         if (datafellows & SSH_BUG_SIGBLOB) {
 130                 sigblob = xmalloc(signaturelen);
 131                 memcpy(sigblob, signature, signaturelen);
 132                 len = signaturelen;
 133         } else {
 134                 /* ietf-drafts */
 135                 char *ktype;
 136                 buffer_init(&b);
 137                 buffer_append(&b, signature, signaturelen);
 138                 ktype = buffer_get_string(&b, NULL);
 139                 if (strcmp("ssh-dss", ktype) != 0) {
 140                         error("ssh_dss_verify: cannot handle type %s", ktype);
 141                         buffer_free(&b);
 142                         xfree(ktype);
 143                         return -1;
 144                 }
 145                 xfree(ktype);
 146                 sigblob = buffer_get_string(&b, &len);
 147                 rlen = buffer_len(&b);
 148                 buffer_free(&b);
 149                 if (rlen != 0) {
 150                         error("ssh_dss_verify: "
 151                             "remaining bytes in signature %d", rlen);
 152                         xfree(sigblob);
 153                         return -1;
 154                 }
 155         }
 156
 157         if (len != SIGBLOB_LEN) {
 158                 fatal("bad sigbloblen %u != SIGBLOB_LEN", len);
 159         }
 160
 161         /* parse signature */
 162         if ((sig = DSA_SIG_new()) == NULL)
 163                 fatal("ssh_dss_verify: DSA_SIG_new failed");
 164         if ((sig->r = BN_new()) == NULL)
 165                 fatal("ssh_dss_verify: BN_new failed");
 166         if ((sig->s = BN_new()) == NULL)
 167                 fatal("ssh_dss_verify: BN_new failed");
 168         if ((BN_bin2bn(sigblob, INTBLOB_LEN, sig->r) == NULL) ||
 169             (BN_bin2bn(sigblob+ INTBLOB_LEN, INTBLOB_LEN, sig->s) == NULL))
 170                 fatal("ssh_dss_verify: BN_bin2bn failed");
 171
 172         /* clean up */
 173         memset(sigblob, 0, len);
 174         xfree(sigblob);
 175
 176         /* sha1 the data */
 177         EVP_DigestInit(&md, evp_md);
 178         EVP_DigestUpdate(&md, data, datalen);
 179         EVP_DigestFinal(&md, digest, &dlen);
 180
 181         ret = DSA_do_verify(digest, dlen, sig, key->dsa);
 182         memset(digest, 'd', sizeof(digest));
 183
 184         DSA_SIG_free(sig);
 185
 186         debug("ssh_dss_verify: signature %s",
 187             ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error");
 188         return ret;
 189 }