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
ssh_dss_sign(const Key * key,u_char ** sigp,u_int * lenp,const u_char * data,u_int datalen)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
ssh_dss_verify(const Key * key,const u_char * signature,u_int signaturelen,const u_char * data,u_int datalen)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