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 "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 #include "digest.h"
42
43 #define INTBLOB_LEN 20
44 #define SIGBLOB_LEN (2*INTBLOB_LEN)
45
46 int
ssh_dss_sign(const Key * key,u_char ** sigp,u_int * lenp,const u_char * data,u_int datalen)47 ssh_dss_sign(const Key *key, u_char **sigp, u_int *lenp,
48 const u_char *data, u_int datalen)
49 {
50 DSA_SIG *sig;
51 u_char digest[SSH_DIGEST_MAX_LENGTH], sigblob[SIGBLOB_LEN];
52 u_int rlen, slen, len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1);
53 Buffer b;
54
55 if (key == NULL || key_type_plain(key->type) != KEY_DSA ||
56 key->dsa == NULL) {
57 error("%s: no DSA key", __func__);
58 return -1;
59 }
60
61 if (ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen,
62 digest, sizeof(digest)) != 0) {
63 error("%s: ssh_digest_memory failed", __func__);
64 return -1;
65 }
66
67 sig = DSA_do_sign(digest, dlen, key->dsa);
68 explicit_bzero(digest, sizeof(digest));
69
70 if (sig == NULL) {
71 error("ssh_dss_sign: sign failed");
72 return -1;
73 }
74
75 rlen = BN_num_bytes(sig->r);
76 slen = BN_num_bytes(sig->s);
77 if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
78 error("bad sig size %u %u", rlen, slen);
79 DSA_SIG_free(sig);
80 return -1;
81 }
82 explicit_bzero(sigblob, SIGBLOB_LEN);
83 BN_bn2bin(sig->r, sigblob+ SIGBLOB_LEN - INTBLOB_LEN - rlen);
84 BN_bn2bin(sig->s, sigblob+ SIGBLOB_LEN - slen);
85 DSA_SIG_free(sig);
86
87 if (datafellows & SSH_BUG_SIGBLOB) {
88 if (lenp != NULL)
89 *lenp = SIGBLOB_LEN;
90 if (sigp != NULL) {
91 *sigp = xmalloc(SIGBLOB_LEN);
92 memcpy(*sigp, sigblob, SIGBLOB_LEN);
93 }
94 } else {
95 /* ietf-drafts */
96 buffer_init(&b);
97 buffer_put_cstring(&b, "ssh-dss");
98 buffer_put_string(&b, sigblob, SIGBLOB_LEN);
99 len = buffer_len(&b);
100 if (lenp != NULL)
101 *lenp = len;
102 if (sigp != NULL) {
103 *sigp = xmalloc(len);
104 memcpy(*sigp, buffer_ptr(&b), len);
105 }
106 buffer_free(&b);
107 }
108 return 0;
109 }
110 int
ssh_dss_verify(const Key * key,const u_char * signature,u_int signaturelen,const u_char * data,u_int datalen)111 ssh_dss_verify(const Key *key, const u_char *signature, u_int signaturelen,
112 const u_char *data, u_int datalen)
113 {
114 DSA_SIG *sig;
115 u_char digest[SSH_DIGEST_MAX_LENGTH], *sigblob;
116 u_int len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1);
117 int rlen, ret;
118 Buffer b;
119
120 if (key == NULL || key_type_plain(key->type) != KEY_DSA ||
121 key->dsa == NULL) {
122 error("%s: no DSA key", __func__);
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("%s: cannot handle type %s", __func__, ktype);
139 buffer_free(&b);
140 free(ktype);
141 return -1;
142 }
143 free(ktype);
144 sigblob = buffer_get_string(&b, &len);
145 rlen = buffer_len(&b);
146 buffer_free(&b);
147 if (rlen != 0) {
148 error("%s: remaining bytes in signature %d",
149 __func__, rlen);
150 free(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("%s: DSA_SIG_new failed", __func__);
162 if ((sig->r = BN_new()) == NULL)
163 fatal("%s: BN_new failed", __func__);
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("%s: BN_bin2bn failed", __func__);
169
170 /* clean up */
171 explicit_bzero(sigblob, len);
172 free(sigblob);
173
174 /* sha1 the data */
175 if (ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen,
176 digest, sizeof(digest)) != 0) {
177 error("%s: digest_memory failed", __func__);
178 return -1;
179 }
180
181 ret = DSA_do_verify(digest, dlen, sig, key->dsa);
182 explicit_bzero(digest, sizeof(digest));
183
184 DSA_SIG_free(sig);
185
186 debug("%s: signature %s", __func__,
187 ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error");
188 return ret;
189 }
190