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 } 190