crypto/openssh/ssh-dss.c

   1 /* $OpenBSD: ssh-dss.c,v 1.39 2020/02/26 13:40:09 jsg 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 #ifdef WITH_OPENSSL
  29
  30 #include <sys/types.h>
  31
  32 #include <openssl/bn.h>
  33 #include <openssl/dsa.h>
  34 #include <openssl/evp.h>
  35
  36 #include <stdarg.h>
  37 #include <string.h>
  38
  39 #include "sshbuf.h"
  40 #include "compat.h"
  41 #include "ssherr.h"
  42 #include "digest.h"
  43 #define SSHKEY_INTERNAL
  44 #include "sshkey.h"
  45
  46 #include "openbsd-compat/openssl-compat.h"
  47
  48 #define INTBLOB_LEN     20
  49 #define SIGBLOB_LEN     (2*INTBLOB_LEN)
  50
  51 int
  52 ssh_dss_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
  53     const u_char *data, size_t datalen, u_int compat)
  54 {
  55         DSA_SIG *sig = NULL;
  56         const BIGNUM *sig_r, *sig_s;
  57         u_char digest[SSH_DIGEST_MAX_LENGTH], sigblob[SIGBLOB_LEN];
  58         size_t rlen, slen, len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1);
  59         struct sshbuf *b = NULL;
  60         int ret = SSH_ERR_INVALID_ARGUMENT;
  61
  62         if (lenp != NULL)
  63                 *lenp = 0;
  64         if (sigp != NULL)
  65                 *sigp = NULL;
  66
  67         if (key == NULL || key->dsa == NULL ||
  68             sshkey_type_plain(key->type) != KEY_DSA)
  69                 return SSH_ERR_INVALID_ARGUMENT;
  70         if (dlen == 0)
  71                 return SSH_ERR_INTERNAL_ERROR;
  72
  73         if ((ret = ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen,
  74             digest, sizeof(digest))) != 0)
  75                 goto out;
  76
  77         if ((sig = DSA_do_sign(digest, dlen, key->dsa)) == NULL) {
  78                 ret = SSH_ERR_LIBCRYPTO_ERROR;
  79                 goto out;
  80         }
  81
  82         DSA_SIG_get0(sig, &sig_r, &sig_s);
  83         rlen = BN_num_bytes(sig_r);
  84         slen = BN_num_bytes(sig_s);
  85         if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
  86                 ret = SSH_ERR_INTERNAL_ERROR;
  87                 goto out;
  88         }
  89         explicit_bzero(sigblob, SIGBLOB_LEN);
  90         BN_bn2bin(sig_r, sigblob + SIGBLOB_LEN - INTBLOB_LEN - rlen);
  91         BN_bn2bin(sig_s, sigblob + SIGBLOB_LEN - slen);
  92
  93         if ((b = sshbuf_new()) == NULL) {
  94                 ret = SSH_ERR_ALLOC_FAIL;
  95                 goto out;
  96         }
  97         if ((ret = sshbuf_put_cstring(b, "ssh-dss")) != 0 ||
  98             (ret = sshbuf_put_string(b, sigblob, SIGBLOB_LEN)) != 0)
  99                 goto out;
 100
 101         len = sshbuf_len(b);
 102         if (sigp != NULL) {
 103                 if ((*sigp = malloc(len)) == NULL) {
 104                         ret = SSH_ERR_ALLOC_FAIL;
 105                         goto out;
 106                 }
 107                 memcpy(*sigp, sshbuf_ptr(b), len);
 108         }
 109         if (lenp != NULL)
 110                 *lenp = len;
 111         ret = 0;
 112  out:
 113         explicit_bzero(digest, sizeof(digest));
 114         DSA_SIG_free(sig);
 115         sshbuf_free(b);
 116         return ret;
 117 }
 118
 119 int
 120 ssh_dss_verify(const struct sshkey *key,
 121     const u_char *signature, size_t signaturelen,
 122     const u_char *data, size_t datalen, u_int compat)
 123 {
 124         DSA_SIG *sig = NULL;
 125         BIGNUM *sig_r = NULL, *sig_s = NULL;
 126         u_char digest[SSH_DIGEST_MAX_LENGTH], *sigblob = NULL;
 127         size_t len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1);
 128         int ret = SSH_ERR_INTERNAL_ERROR;
 129         struct sshbuf *b = NULL;
 130         char *ktype = NULL;
 131
 132         if (key == NULL || key->dsa == NULL ||
 133             sshkey_type_plain(key->type) != KEY_DSA ||
 134             signature == NULL || signaturelen == 0)
 135                 return SSH_ERR_INVALID_ARGUMENT;
 136         if (dlen == 0)
 137                 return SSH_ERR_INTERNAL_ERROR;
 138
 139         /* fetch signature */
 140         if ((b = sshbuf_from(signature, signaturelen)) == NULL)
 141                 return SSH_ERR_ALLOC_FAIL;
 142         if (sshbuf_get_cstring(b, &ktype, NULL) != 0 ||
 143             sshbuf_get_string(b, &sigblob, &len) != 0) {
 144                 ret = SSH_ERR_INVALID_FORMAT;
 145                 goto out;
 146         }
 147         if (strcmp("ssh-dss", ktype) != 0) {
 148                 ret = SSH_ERR_KEY_TYPE_MISMATCH;
 149                 goto out;
 150         }
 151         if (sshbuf_len(b) != 0) {
 152                 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
 153                 goto out;
 154         }
 155
 156         if (len != SIGBLOB_LEN) {
 157                 ret = SSH_ERR_INVALID_FORMAT;
 158                 goto out;
 159         }
 160
 161         /* parse signature */
 162         if ((sig = DSA_SIG_new()) == NULL ||
 163             (sig_r = BN_new()) == NULL ||
 164             (sig_s = BN_new()) == NULL) {
 165                 ret = SSH_ERR_ALLOC_FAIL;
 166                 goto out;
 167         }
 168         if ((BN_bin2bn(sigblob, INTBLOB_LEN, sig_r) == NULL) ||
 169             (BN_bin2bn(sigblob + INTBLOB_LEN, INTBLOB_LEN, sig_s) == NULL)) {
 170                 ret = SSH_ERR_LIBCRYPTO_ERROR;
 171                 goto out;
 172         }
 173         if (!DSA_SIG_set0(sig, sig_r, sig_s)) {
 174                 ret = SSH_ERR_LIBCRYPTO_ERROR;
 175                 goto out;
 176         }
 177         sig_r = sig_s = NULL; /* transferred */
 178
 179         /* sha1 the data */
 180         if ((ret = ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen,
 181             digest, sizeof(digest))) != 0)
 182                 goto out;
 183
 184         switch (DSA_do_verify(digest, dlen, sig, key->dsa)) {
 185         case 1:
 186                 ret = 0;
 187                 break;
 188         case 0:
 189                 ret = SSH_ERR_SIGNATURE_INVALID;
 190                 goto out;
 191         default:
 192                 ret = SSH_ERR_LIBCRYPTO_ERROR;
 193                 goto out;
 194         }
 195
 196  out:
 197         explicit_bzero(digest, sizeof(digest));
 198         DSA_SIG_free(sig);
 199         BN_clear_free(sig_r);
 200         BN_clear_free(sig_s);
 201         sshbuf_free(b);
 202         free(ktype);
 203         if (sigblob != NULL)
 204                 freezero(sigblob, len);
 205         return ret;
 206 }
 207 #endif /* WITH_OPENSSL */