1 /* $OpenBSD: ssh-dss.c,v 1.27 2010/08/31 09:58:37 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 || key->dsa == NULL || (key->type != KEY_DSA && 57 key->type != KEY_DSA_CERT && key->type != KEY_DSA_CERT_V00)) { 58 error("ssh_dss_sign: no DSA key"); 59 return -1; 60 } 61 EVP_DigestInit(&md, evp_md); 62 EVP_DigestUpdate(&md, data, datalen); 63 EVP_DigestFinal(&md, digest, &dlen); 64 65 sig = DSA_do_sign(digest, dlen, key->dsa); 66 memset(digest, 'd', sizeof(digest)); 67 68 if (sig == NULL) { 69 error("ssh_dss_sign: sign failed"); 70 return -1; 71 } 72 73 rlen = BN_num_bytes(sig->r); 74 slen = BN_num_bytes(sig->s); 75 if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) { 76 error("bad sig size %u %u", rlen, slen); 77 DSA_SIG_free(sig); 78 return -1; 79 } 80 memset(sigblob, 0, SIGBLOB_LEN); 81 BN_bn2bin(sig->r, sigblob+ SIGBLOB_LEN - INTBLOB_LEN - rlen); 82 BN_bn2bin(sig->s, sigblob+ SIGBLOB_LEN - slen); 83 DSA_SIG_free(sig); 84 85 if (datafellows & SSH_BUG_SIGBLOB) { 86 if (lenp != NULL) 87 *lenp = SIGBLOB_LEN; 88 if (sigp != NULL) { 89 *sigp = xmalloc(SIGBLOB_LEN); 90 memcpy(*sigp, sigblob, SIGBLOB_LEN); 91 } 92 } else { 93 /* ietf-drafts */ 94 buffer_init(&b); 95 buffer_put_cstring(&b, "ssh-dss"); 96 buffer_put_string(&b, sigblob, SIGBLOB_LEN); 97 len = buffer_len(&b); 98 if (lenp != NULL) 99 *lenp = len; 100 if (sigp != NULL) { 101 *sigp = xmalloc(len); 102 memcpy(*sigp, buffer_ptr(&b), len); 103 } 104 buffer_free(&b); 105 } 106 return 0; 107 } 108 int 109 ssh_dss_verify(const Key *key, const u_char *signature, u_int signaturelen, 110 const u_char *data, u_int datalen) 111 { 112 DSA_SIG *sig; 113 const EVP_MD *evp_md = EVP_sha1(); 114 EVP_MD_CTX md; 115 u_char digest[EVP_MAX_MD_SIZE], *sigblob; 116 u_int len, dlen; 117 int rlen, ret; 118 Buffer b; 119 120 if (key == NULL || key->dsa == NULL || (key->type != KEY_DSA && 121 key->type != KEY_DSA_CERT && key->type != KEY_DSA_CERT_V00)) { 122 error("ssh_dss_verify: no DSA key"); 123 return -1; 124 } 125 126 /* fetch signature */ 127 if (datafellows & SSH_BUG_SIGBLOB) { 128 sigblob = xmalloc(signaturelen); 129 memcpy(sigblob, signature, signaturelen); 130 len = signaturelen; 131 } else { 132 /* ietf-drafts */ 133 char *ktype; 134 buffer_init(&b); 135 buffer_append(&b, signature, signaturelen); 136 ktype = buffer_get_cstring(&b, NULL); 137 if (strcmp("ssh-dss", ktype) != 0) { 138 error("ssh_dss_verify: cannot handle type %s", ktype); 139 buffer_free(&b); 140 xfree(ktype); 141 return -1; 142 } 143 xfree(ktype); 144 sigblob = buffer_get_string(&b, &len); 145 rlen = buffer_len(&b); 146 buffer_free(&b); 147 if (rlen != 0) { 148 error("ssh_dss_verify: " 149 "remaining bytes in signature %d", rlen); 150 xfree(sigblob); 151 return -1; 152 } 153 } 154 155 if (len != SIGBLOB_LEN) { 156 fatal("bad sigbloblen %u != SIGBLOB_LEN", len); 157 } 158 159 /* parse signature */ 160 if ((sig = DSA_SIG_new()) == NULL) 161 fatal("ssh_dss_verify: DSA_SIG_new failed"); 162 if ((sig->r = BN_new()) == NULL) 163 fatal("ssh_dss_verify: BN_new failed"); 164 if ((sig->s = BN_new()) == NULL) 165 fatal("ssh_dss_verify: BN_new failed"); 166 if ((BN_bin2bn(sigblob, INTBLOB_LEN, sig->r) == NULL) || 167 (BN_bin2bn(sigblob+ INTBLOB_LEN, INTBLOB_LEN, sig->s) == NULL)) 168 fatal("ssh_dss_verify: BN_bin2bn failed"); 169 170 /* clean up */ 171 memset(sigblob, 0, len); 172 xfree(sigblob); 173 174 /* sha1 the data */ 175 EVP_DigestInit(&md, evp_md); 176 EVP_DigestUpdate(&md, data, datalen); 177 EVP_DigestFinal(&md, digest, &dlen); 178 179 ret = DSA_do_verify(digest, dlen, sig, key->dsa); 180 memset(digest, 'd', sizeof(digest)); 181 182 DSA_SIG_free(sig); 183 184 debug("ssh_dss_verify: signature %s", 185 ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error"); 186 return ret; 187 } 188