1 /* $OpenBSD: ssh-dss.c,v 1.31 2014/02/02 03:44:31 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 <sys/types.h> 27 28 #include <openssl/bn.h> 29 #include <openssl/evp.h> 30 31 #include <string.h> 32 33 #include "xmalloc.h" 34 #include "buffer.h" 35 #include "compat.h" 36 #include "log.h" 37 #include "key.h" 38 #include "digest.h" 39 40 #define INTBLOB_LEN 20 41 #define SIGBLOB_LEN (2*INTBLOB_LEN) 42 43 int 44 ssh_dss_sign(const Key *key, u_char **sigp, u_int *lenp, 45 const u_char *data, u_int datalen) 46 { 47 DSA_SIG *sig; 48 u_char digest[SSH_DIGEST_MAX_LENGTH], sigblob[SIGBLOB_LEN]; 49 u_int rlen, slen, len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1); 50 Buffer b; 51 52 if (key == NULL || key_type_plain(key->type) != KEY_DSA || 53 key->dsa == NULL) { 54 error("%s: no DSA key", __func__); 55 return -1; 56 } 57 58 if (ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen, 59 digest, sizeof(digest)) != 0) { 60 error("%s: ssh_digest_memory failed", __func__); 61 return -1; 62 } 63 64 sig = DSA_do_sign(digest, dlen, key->dsa); 65 explicit_bzero(digest, 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 explicit_bzero(sigblob, 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 u_char digest[SSH_DIGEST_MAX_LENGTH], *sigblob; 113 u_int len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1); 114 int rlen, ret; 115 Buffer b; 116 117 if (key == NULL || key_type_plain(key->type) != KEY_DSA || 118 key->dsa == NULL) { 119 error("%s: no DSA key", __func__); 120 return -1; 121 } 122 123 /* fetch signature */ 124 if (datafellows & SSH_BUG_SIGBLOB) { 125 sigblob = xmalloc(signaturelen); 126 memcpy(sigblob, signature, signaturelen); 127 len = signaturelen; 128 } else { 129 /* ietf-drafts */ 130 char *ktype; 131 buffer_init(&b); 132 buffer_append(&b, signature, signaturelen); 133 ktype = buffer_get_cstring(&b, NULL); 134 if (strcmp("ssh-dss", ktype) != 0) { 135 error("%s: cannot handle type %s", __func__, ktype); 136 buffer_free(&b); 137 free(ktype); 138 return -1; 139 } 140 free(ktype); 141 sigblob = buffer_get_string(&b, &len); 142 rlen = buffer_len(&b); 143 buffer_free(&b); 144 if (rlen != 0) { 145 error("%s: remaining bytes in signature %d", 146 __func__, rlen); 147 free(sigblob); 148 return -1; 149 } 150 } 151 152 if (len != SIGBLOB_LEN) { 153 fatal("bad sigbloblen %u != SIGBLOB_LEN", len); 154 } 155 156 /* parse signature */ 157 if ((sig = DSA_SIG_new()) == NULL) 158 fatal("%s: DSA_SIG_new failed", __func__); 159 if ((sig->r = BN_new()) == NULL) 160 fatal("%s: BN_new failed", __func__); 161 if ((sig->s = BN_new()) == NULL) 162 fatal("ssh_dss_verify: BN_new failed"); 163 if ((BN_bin2bn(sigblob, INTBLOB_LEN, sig->r) == NULL) || 164 (BN_bin2bn(sigblob+ INTBLOB_LEN, INTBLOB_LEN, sig->s) == NULL)) 165 fatal("%s: BN_bin2bn failed", __func__); 166 167 /* clean up */ 168 explicit_bzero(sigblob, len); 169 free(sigblob); 170 171 /* sha1 the data */ 172 if (ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen, 173 digest, sizeof(digest)) != 0) { 174 error("%s: digest_memory failed", __func__); 175 return -1; 176 } 177 178 ret = DSA_do_verify(digest, dlen, sig, key->dsa); 179 explicit_bzero(digest, sizeof(digest)); 180 181 DSA_SIG_free(sig); 182 183 debug("%s: signature %s", __func__, 184 ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error"); 185 return ret; 186 } 187