ssh-dss.c revision 113908 
1/*
2 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 *    notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 *    notice, this list of conditions and the following disclaimer in the
11 *    documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
14 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
15 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
16 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
17 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
18 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
22 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
23 */
24
25#include "includes.h"
26RCSID("$OpenBSD: ssh-dss.c,v 1.18 2003/02/12 09:33:04 markus Exp $");
27
28#include <openssl/bn.h>
29#include <openssl/evp.h>
30
31#include "xmalloc.h"
32#include "buffer.h"
33#include "bufaux.h"
34#include "compat.h"
35#include "log.h"
36#include "key.h"
37
38#define INTBLOB_LEN	20
39#define SIGBLOB_LEN	(2*INTBLOB_LEN)
40
41int
42ssh_dss_sign(Key *key, u_char **sigp, u_int *lenp,
43    u_char *data, u_int datalen)
44{
45	DSA_SIG *sig;
46	const EVP_MD *evp_md = EVP_sha1();
47	EVP_MD_CTX md;
48	u_char digest[EVP_MAX_MD_SIZE], sigblob[SIGBLOB_LEN];
49	u_int rlen, slen, len, dlen;
50	Buffer b;
51
52	if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) {
53		error("ssh_dss_sign: no DSA key");
54		return -1;
55	}
56	EVP_DigestInit(&md, evp_md);
57	EVP_DigestUpdate(&md, data, datalen);
58	EVP_DigestFinal(&md, digest, &dlen);
59
60	sig = DSA_do_sign(digest, dlen, key->dsa);
61	memset(digest, 'd', sizeof(digest));
62
63	if (sig == NULL) {
64		error("ssh_dss_sign: sign failed");
65		return -1;
66	}
67
68	rlen = BN_num_bytes(sig->r);
69	slen = BN_num_bytes(sig->s);
70	if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
71		error("bad sig size %u %u", rlen, slen);
72		DSA_SIG_free(sig);
73		return -1;
74	}
75	memset(sigblob, 0, SIGBLOB_LEN);
76	BN_bn2bin(sig->r, sigblob+ SIGBLOB_LEN - INTBLOB_LEN - rlen);
77	BN_bn2bin(sig->s, sigblob+ SIGBLOB_LEN - slen);
78	DSA_SIG_free(sig);
79
80	if (datafellows & SSH_BUG_SIGBLOB) {
81		if (lenp != NULL)
82			*lenp = SIGBLOB_LEN;
83		if (sigp != NULL) {
84			*sigp = xmalloc(SIGBLOB_LEN);
85			memcpy(*sigp, sigblob, SIGBLOB_LEN);
86		}
87	} else {
88		/* ietf-drafts */
89		buffer_init(&b);
90		buffer_put_cstring(&b, "ssh-dss");
91		buffer_put_string(&b, sigblob, SIGBLOB_LEN);
92		len = buffer_len(&b);
93		if (lenp != NULL)
94			*lenp = len;
95		if (sigp != NULL) {
96			*sigp = xmalloc(len);
97			memcpy(*sigp, buffer_ptr(&b), len);
98		}
99		buffer_free(&b);
100	}
101	return 0;
102}
103int
104ssh_dss_verify(Key *key, u_char *signature, u_int signaturelen,
105    u_char *data, u_int datalen)
106{
107	DSA_SIG *sig;
108	const EVP_MD *evp_md = EVP_sha1();
109	EVP_MD_CTX md;
110	u_char digest[EVP_MAX_MD_SIZE], *sigblob;
111	u_int len, dlen;
112	int rlen, ret;
113	Buffer b;
114
115	if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) {
116		error("ssh_dss_verify: no DSA key");
117		return -1;
118	}
119
120	/* fetch signature */
121	if (datafellows & SSH_BUG_SIGBLOB) {
122		sigblob = signature;
123		len = signaturelen;
124	} else {
125		/* ietf-drafts */
126		char *ktype;
127		buffer_init(&b);
128		buffer_append(&b, signature, signaturelen);
129		ktype = buffer_get_string(&b, NULL);
130		if (strcmp("ssh-dss", ktype) != 0) {
131			error("ssh_dss_verify: cannot handle type %s", ktype);
132			buffer_free(&b);
133			xfree(ktype);
134			return -1;
135		}
136		xfree(ktype);
137		sigblob = buffer_get_string(&b, &len);
138		rlen = buffer_len(&b);
139		buffer_free(&b);
140		if (rlen != 0) {
141			error("ssh_dss_verify: "
142			    "remaining bytes in signature %d", rlen);
143			xfree(sigblob);
144			return -1;
145		}
146	}
147
148	if (len != SIGBLOB_LEN) {
149		fatal("bad sigbloblen %u != SIGBLOB_LEN", len);
150	}
151
152	/* parse signature */
153	if ((sig = DSA_SIG_new()) == NULL)
154		fatal("ssh_dss_verify: DSA_SIG_new failed");
155	if ((sig->r = BN_new()) == NULL)
156		fatal("ssh_dss_verify: BN_new failed");
157	if ((sig->s = BN_new()) == NULL)
158		fatal("ssh_dss_verify: BN_new failed");
159	BN_bin2bn(sigblob, INTBLOB_LEN, sig->r);
160	BN_bin2bn(sigblob+ INTBLOB_LEN, INTBLOB_LEN, sig->s);
161
162	if (!(datafellows & SSH_BUG_SIGBLOB)) {
163		memset(sigblob, 0, len);
164		xfree(sigblob);
165	}
166
167	/* sha1 the data */
168	EVP_DigestInit(&md, evp_md);
169	EVP_DigestUpdate(&md, data, datalen);
170	EVP_DigestFinal(&md, digest, &dlen);
171
172	ret = DSA_do_verify(digest, dlen, sig, key->dsa);
173	memset(digest, 'd', sizeof(digest));
174
175	DSA_SIG_free(sig);
176
177	debug("ssh_dss_verify: signature %s",
178	    ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error");
179	return ret;
180}
181