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 <sys/types.h> 27 28 #include <openssl/bn.h> 29 #include <openssl/evp.h> 30 31 #include <string.h> 32 33 #include "sshbuf.h" 34 #include "compat.h" 35 #include "ssherr.h" 36 #include "digest.h" 37 #define SSHKEY_INTERNAL 38 #include "sshkey.h" 39 40 #define INTBLOB_LEN 20 41 #define SIGBLOB_LEN (2*INTBLOB_LEN) 42 43 int 44 ssh_dss_sign(const struct sshkey *key, u_char **sigp, size_t *lenp, 45 const u_char *data, size_t datalen, u_int compat) 46 { 47 DSA_SIG *sig = NULL; 48 const BIGNUM *sig_r, *sig_s; 49 u_char digest[SSH_DIGEST_MAX_LENGTH], sigblob[SIGBLOB_LEN]; 50 size_t rlen, slen, len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1); 51 struct sshbuf *b = NULL; 52 int ret = SSH_ERR_INVALID_ARGUMENT; 53 54 if (lenp != NULL) 55 *lenp = 0; 56 if (sigp != NULL) 57 *sigp = NULL; 58 59 if (key == NULL || key->dsa == NULL || 60 sshkey_type_plain(key->type) != KEY_DSA) 61 return SSH_ERR_INVALID_ARGUMENT; 62 if (dlen == 0) 63 return SSH_ERR_INTERNAL_ERROR; 64 65 if ((ret = ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen, 66 digest, sizeof(digest))) != 0) 67 goto out; 68 69 if ((sig = DSA_do_sign(digest, dlen, key->dsa)) == NULL) { 70 ret = SSH_ERR_LIBCRYPTO_ERROR; 71 goto out; 72 } 73 74 DSA_SIG_get0(sig, &sig_r, &sig_s); 75 rlen = BN_num_bytes(sig_r); 76 slen = BN_num_bytes(sig_s); 77 if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) { 78 ret = SSH_ERR_INTERNAL_ERROR; 79 goto out; 80 } 81 explicit_bzero(sigblob, SIGBLOB_LEN); 82 BN_bn2bin(sig_r, sigblob + SIGBLOB_LEN - INTBLOB_LEN - rlen); 83 BN_bn2bin(sig_s, sigblob + SIGBLOB_LEN - slen); 84 85 if ((b = sshbuf_new()) == NULL) { 86 ret = SSH_ERR_ALLOC_FAIL; 87 goto out; 88 } 89 if ((ret = sshbuf_put_cstring(b, "ssh-dss")) != 0 || 90 (ret = sshbuf_put_string(b, sigblob, SIGBLOB_LEN)) != 0) 91 goto out; 92 93 len = sshbuf_len(b); 94 if (sigp != NULL) { 95 if ((*sigp = malloc(len)) == NULL) { 96 ret = SSH_ERR_ALLOC_FAIL; 97 goto out; 98 } 99 memcpy(*sigp, sshbuf_ptr(b), len); 100 } 101 if (lenp != NULL) 102 *lenp = len; 103 ret = 0; 104 out: 105 explicit_bzero(digest, sizeof(digest)); 106 DSA_SIG_free(sig); 107 sshbuf_free(b); 108 return ret; 109 } 110 111 int 112 ssh_dss_verify(const struct sshkey *key, 113 const u_char *signature, size_t signaturelen, 114 const u_char *data, size_t datalen, u_int compat) 115 { 116 DSA_SIG *sig = NULL; 117 BIGNUM *sig_r = NULL, *sig_s = NULL; 118 u_char digest[SSH_DIGEST_MAX_LENGTH], *sigblob = NULL; 119 size_t len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1); 120 int ret = SSH_ERR_INTERNAL_ERROR; 121 struct sshbuf *b = NULL; 122 char *ktype = NULL; 123 124 if (key == NULL || key->dsa == NULL || 125 sshkey_type_plain(key->type) != KEY_DSA || 126 signature == NULL || signaturelen == 0) 127 return SSH_ERR_INVALID_ARGUMENT; 128 if (dlen == 0) 129 return SSH_ERR_INTERNAL_ERROR; 130 131 /* fetch signature */ 132 if ((b = sshbuf_from(signature, signaturelen)) == NULL) 133 return SSH_ERR_ALLOC_FAIL; 134 if (sshbuf_get_cstring(b, &ktype, NULL) != 0 || 135 sshbuf_get_string(b, &sigblob, &len) != 0) { 136 ret = SSH_ERR_INVALID_FORMAT; 137 goto out; 138 } 139 if (strcmp("ssh-dss", ktype) != 0) { 140 ret = SSH_ERR_KEY_TYPE_MISMATCH; 141 goto out; 142 } 143 if (sshbuf_len(b) != 0) { 144 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA; 145 goto out; 146 } 147 148 if (len != SIGBLOB_LEN) { 149 ret = SSH_ERR_INVALID_FORMAT; 150 goto out; 151 } 152 153 /* parse signature */ 154 if ((sig = DSA_SIG_new()) == NULL || 155 (sig_r = BN_new()) == NULL || 156 (sig_s = BN_new()) == NULL) { 157 ret = SSH_ERR_ALLOC_FAIL; 158 goto out; 159 } 160 if ((BN_bin2bn(sigblob, INTBLOB_LEN, sig_r) == NULL) || 161 (BN_bin2bn(sigblob + INTBLOB_LEN, INTBLOB_LEN, sig_s) == NULL)) { 162 ret = SSH_ERR_LIBCRYPTO_ERROR; 163 goto out; 164 } 165 if (!DSA_SIG_set0(sig, sig_r, sig_s)) { 166 ret = SSH_ERR_LIBCRYPTO_ERROR; 167 goto out; 168 } 169 sig_r = sig_s = NULL; /* transferred */ 170 171 /* sha1 the data */ 172 if ((ret = ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen, 173 digest, sizeof(digest))) != 0) 174 goto out; 175 176 switch (DSA_do_verify(digest, dlen, sig, key->dsa)) { 177 case 1: 178 ret = 0; 179 break; 180 case 0: 181 ret = SSH_ERR_SIGNATURE_INVALID; 182 goto out; 183 default: 184 ret = SSH_ERR_LIBCRYPTO_ERROR; 185 goto out; 186 } 187 188 out: 189 explicit_bzero(digest, sizeof(digest)); 190 DSA_SIG_free(sig); 191 BN_clear_free(sig_r); 192 BN_clear_free(sig_s); 193 sshbuf_free(b); 194 free(ktype); 195 if (sigblob != NULL) 196 freezero(sigblob, len); 197 return ret; 198 } 199