1 /* $OpenBSD: ssh-dss.c,v 1.24 2006/11/06 21:25:28 markus 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 39 #define INTBLOB_LEN 20 40 #define SIGBLOB_LEN (2*INTBLOB_LEN) 41 42 int 43 ssh_dss_sign(const Key *key, u_char **sigp, u_int *lenp, 44 const u_char *data, u_int datalen) 45 { 46 DSA_SIG *sig; 47 const EVP_MD *evp_md = EVP_sha1(); 48 EVP_MD_CTX md; 49 u_char digest[EVP_MAX_MD_SIZE], sigblob[SIGBLOB_LEN]; 50 u_int rlen, slen, len, dlen; 51 Buffer b; 52 53 if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) { 54 error("ssh_dss_sign: no DSA key"); 55 return -1; 56 } 57 EVP_DigestInit(&md, evp_md); 58 EVP_DigestUpdate(&md, data, datalen); 59 EVP_DigestFinal(&md, digest, &dlen); 60 61 sig = DSA_do_sign(digest, dlen, key->dsa); 62 memset(digest, 'd', sizeof(digest)); 63 64 if (sig == NULL) { 65 error("ssh_dss_sign: sign failed"); 66 return -1; 67 } 68 69 rlen = BN_num_bytes(sig->r); 70 slen = BN_num_bytes(sig->s); 71 if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) { 72 error("bad sig size %u %u", rlen, slen); 73 DSA_SIG_free(sig); 74 return -1; 75 } 76 memset(sigblob, 0, SIGBLOB_LEN); 77 BN_bn2bin(sig->r, sigblob+ SIGBLOB_LEN - INTBLOB_LEN - rlen); 78 BN_bn2bin(sig->s, sigblob+ SIGBLOB_LEN - slen); 79 DSA_SIG_free(sig); 80 81 if (datafellows & SSH_BUG_SIGBLOB) { 82 if (lenp != NULL) 83 *lenp = SIGBLOB_LEN; 84 if (sigp != NULL) { 85 *sigp = xmalloc(SIGBLOB_LEN); 86 memcpy(*sigp, sigblob, SIGBLOB_LEN); 87 } 88 } else { 89 /* ietf-drafts */ 90 buffer_init(&b); 91 buffer_put_cstring(&b, "ssh-dss"); 92 buffer_put_string(&b, sigblob, SIGBLOB_LEN); 93 len = buffer_len(&b); 94 if (lenp != NULL) 95 *lenp = len; 96 if (sigp != NULL) { 97 *sigp = xmalloc(len); 98 memcpy(*sigp, buffer_ptr(&b), len); 99 } 100 buffer_free(&b); 101 } 102 return 0; 103 } 104 int 105 ssh_dss_verify(const Key *key, const u_char *signature, u_int signaturelen, 106 const u_char *data, u_int datalen) 107 { 108 DSA_SIG *sig; 109 const EVP_MD *evp_md = EVP_sha1(); 110 EVP_MD_CTX md; 111 u_char digest[EVP_MAX_MD_SIZE], *sigblob; 112 u_int len, dlen; 113 int rlen, ret; 114 Buffer b; 115 116 if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) { 117 error("ssh_dss_verify: no DSA key"); 118 return -1; 119 } 120 121 /* fetch signature */ 122 if (datafellows & SSH_BUG_SIGBLOB) { 123 sigblob = xmalloc(signaturelen); 124 memcpy(sigblob, signature, signaturelen); 125 len = signaturelen; 126 } else { 127 /* ietf-drafts */ 128 char *ktype; 129 buffer_init(&b); 130 buffer_append(&b, signature, signaturelen); 131 ktype = buffer_get_string(&b, NULL); 132 if (strcmp("ssh-dss", ktype) != 0) { 133 error("ssh_dss_verify: cannot handle type %s", ktype); 134 buffer_free(&b); 135 xfree(ktype); 136 return -1; 137 } 138 xfree(ktype); 139 sigblob = buffer_get_string(&b, &len); 140 rlen = buffer_len(&b); 141 buffer_free(&b); 142 if (rlen != 0) { 143 error("ssh_dss_verify: " 144 "remaining bytes in signature %d", rlen); 145 xfree(sigblob); 146 return -1; 147 } 148 } 149 150 if (len != SIGBLOB_LEN) { 151 fatal("bad sigbloblen %u != SIGBLOB_LEN", len); 152 } 153 154 /* parse signature */ 155 if ((sig = DSA_SIG_new()) == NULL) 156 fatal("ssh_dss_verify: DSA_SIG_new failed"); 157 if ((sig->r = BN_new()) == NULL) 158 fatal("ssh_dss_verify: BN_new failed"); 159 if ((sig->s = BN_new()) == NULL) 160 fatal("ssh_dss_verify: BN_new failed"); 161 if ((BN_bin2bn(sigblob, INTBLOB_LEN, sig->r) == NULL) || 162 (BN_bin2bn(sigblob+ INTBLOB_LEN, INTBLOB_LEN, sig->s) == NULL)) 163 fatal("ssh_dss_verify: BN_bin2bn failed"); 164 165 /* clean up */ 166 memset(sigblob, 0, len); 167 xfree(sigblob); 168 169 /* sha1 the data */ 170 EVP_DigestInit(&md, evp_md); 171 EVP_DigestUpdate(&md, data, datalen); 172 EVP_DigestFinal(&md, digest, &dlen); 173 174 ret = DSA_do_verify(digest, dlen, sig, key->dsa); 175 memset(digest, 'd', sizeof(digest)); 176 177 DSA_SIG_free(sig); 178 179 debug("ssh_dss_verify: signature %s", 180 ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error"); 181 return ret; 182 } 183