1 /* $NetBSD: ssh-dss.c,v 1.17 2020/05/28 17:05:49 christos Exp $ */ 2 /* $OpenBSD: ssh-dss.c,v 1.39 2020/02/26 13:40:09 jsg Exp $ */ 3 /* 4 * Copyright (c) 2000 Markus Friedl. All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25 */ 26 27 #include "includes.h" 28 __RCSID("$NetBSD: ssh-dss.c,v 1.17 2020/05/28 17:05:49 christos Exp $"); 29 #include <sys/types.h> 30 31 #include <openssl/bn.h> 32 #include <openssl/evp.h> 33 34 #include <string.h> 35 36 #include "sshbuf.h" 37 #include "compat.h" 38 #include "ssherr.h" 39 #include "digest.h" 40 #define SSHKEY_INTERNAL 41 #include "sshkey.h" 42 43 #define INTBLOB_LEN 20 44 #define SIGBLOB_LEN (2*INTBLOB_LEN) 45 46 int 47 ssh_dss_sign(const struct sshkey *key, u_char **sigp, size_t *lenp, 48 const u_char *data, size_t datalen, u_int compat) 49 { 50 DSA_SIG *sig = NULL; 51 const BIGNUM *sig_r, *sig_s; 52 u_char digest[SSH_DIGEST_MAX_LENGTH], sigblob[SIGBLOB_LEN]; 53 size_t rlen, slen, len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1); 54 struct sshbuf *b = NULL; 55 int ret = SSH_ERR_INVALID_ARGUMENT; 56 57 if (lenp != NULL) 58 *lenp = 0; 59 if (sigp != NULL) 60 *sigp = NULL; 61 62 if (key == NULL || key->dsa == NULL || 63 sshkey_type_plain(key->type) != KEY_DSA) 64 return SSH_ERR_INVALID_ARGUMENT; 65 if (dlen == 0) 66 return SSH_ERR_INTERNAL_ERROR; 67 68 if ((ret = ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen, 69 digest, sizeof(digest))) != 0) 70 goto out; 71 72 if ((sig = DSA_do_sign(digest, dlen, key->dsa)) == NULL) { 73 ret = SSH_ERR_LIBCRYPTO_ERROR; 74 goto out; 75 } 76 77 DSA_SIG_get0(sig, &sig_r, &sig_s); 78 rlen = BN_num_bytes(sig_r); 79 slen = BN_num_bytes(sig_s); 80 if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) { 81 ret = SSH_ERR_INTERNAL_ERROR; 82 goto out; 83 } 84 explicit_bzero(sigblob, SIGBLOB_LEN); 85 BN_bn2bin(sig_r, sigblob + SIGBLOB_LEN - INTBLOB_LEN - rlen); 86 BN_bn2bin(sig_s, sigblob + SIGBLOB_LEN - slen); 87 88 if ((b = sshbuf_new()) == NULL) { 89 ret = SSH_ERR_ALLOC_FAIL; 90 goto out; 91 } 92 if ((ret = sshbuf_put_cstring(b, "ssh-dss")) != 0 || 93 (ret = sshbuf_put_string(b, sigblob, SIGBLOB_LEN)) != 0) 94 goto out; 95 96 len = sshbuf_len(b); 97 if (sigp != NULL) { 98 if ((*sigp = malloc(len)) == NULL) { 99 ret = SSH_ERR_ALLOC_FAIL; 100 goto out; 101 } 102 memcpy(*sigp, sshbuf_ptr(b), len); 103 } 104 if (lenp != NULL) 105 *lenp = len; 106 ret = 0; 107 out: 108 explicit_bzero(digest, sizeof(digest)); 109 DSA_SIG_free(sig); 110 sshbuf_free(b); 111 return ret; 112 } 113 114 int 115 ssh_dss_verify(const struct sshkey *key, 116 const u_char *signature, size_t signaturelen, 117 const u_char *data, size_t datalen, u_int compat) 118 { 119 DSA_SIG *sig = NULL; 120 BIGNUM *sig_r = NULL, *sig_s = NULL; 121 u_char digest[SSH_DIGEST_MAX_LENGTH], *sigblob = NULL; 122 size_t len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1); 123 int ret = SSH_ERR_INTERNAL_ERROR; 124 struct sshbuf *b = NULL; 125 char *ktype = NULL; 126 127 if (key == NULL || key->dsa == NULL || 128 sshkey_type_plain(key->type) != KEY_DSA || 129 signature == NULL || signaturelen == 0) 130 return SSH_ERR_INVALID_ARGUMENT; 131 if (dlen == 0) 132 return SSH_ERR_INTERNAL_ERROR; 133 134 /* fetch signature */ 135 if ((b = sshbuf_from(signature, signaturelen)) == NULL) 136 return SSH_ERR_ALLOC_FAIL; 137 if (sshbuf_get_cstring(b, &ktype, NULL) != 0 || 138 sshbuf_get_string(b, &sigblob, &len) != 0) { 139 ret = SSH_ERR_INVALID_FORMAT; 140 goto out; 141 } 142 if (strcmp("ssh-dss", ktype) != 0) { 143 ret = SSH_ERR_KEY_TYPE_MISMATCH; 144 goto out; 145 } 146 if (sshbuf_len(b) != 0) { 147 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA; 148 goto out; 149 } 150 151 if (len != SIGBLOB_LEN) { 152 ret = SSH_ERR_INVALID_FORMAT; 153 goto out; 154 } 155 156 /* parse signature */ 157 if ((sig = DSA_SIG_new()) == NULL || 158 (sig_r = BN_new()) == NULL || 159 (sig_s = BN_new()) == NULL) { 160 ret = SSH_ERR_ALLOC_FAIL; 161 goto out; 162 } 163 if ((BN_bin2bn(sigblob, INTBLOB_LEN, sig_r) == NULL) || 164 (BN_bin2bn(sigblob + INTBLOB_LEN, INTBLOB_LEN, sig_s) == NULL)) { 165 ret = SSH_ERR_LIBCRYPTO_ERROR; 166 goto out; 167 } 168 if (!DSA_SIG_set0(sig, sig_r, sig_s)) { 169 ret = SSH_ERR_LIBCRYPTO_ERROR; 170 goto out; 171 } 172 sig_r = sig_s = NULL; /* transferred */ 173 174 /* sha1 the data */ 175 if ((ret = ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen, 176 digest, sizeof(digest))) != 0) 177 goto out; 178 179 switch (DSA_do_verify(digest, dlen, sig, key->dsa)) { 180 case 1: 181 ret = 0; 182 break; 183 case 0: 184 ret = SSH_ERR_SIGNATURE_INVALID; 185 goto out; 186 default: 187 ret = SSH_ERR_LIBCRYPTO_ERROR; 188 goto out; 189 } 190 191 out: 192 explicit_bzero(digest, sizeof(digest)); 193 DSA_SIG_free(sig); 194 BN_clear_free(sig_r); 195 BN_clear_free(sig_s); 196 sshbuf_free(b); 197 free(ktype); 198 if (sigblob != NULL) 199 freezero(sigblob, len); 200 return ret; 201 } 202