ssh-dss.c revision 1.10 
1/*	$NetBSD: ssh-dss.c,v 1.10 2016/12/25 00:07:47 christos Exp $	*/
2/* $OpenBSD: ssh-dss.c,v 1.35 2016/04/21 06:08:02 djm Exp $ */
3/*
4 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 *    notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice, this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27#include "includes.h"
28__RCSID("$NetBSD: ssh-dss.c,v 1.10 2016/12/25 00:07:47 christos Exp $");
29#include <sys/types.h>
30
31#include <openssl/bn.h>
32#include <openssl/evp.h>
33
34#include <string.h>
35
36#include "sshbuf.h"
37#include "compat.h"
38#include "ssherr.h"
39#include "digest.h"
40#define SSHKEY_INTERNAL
41#include "sshkey.h"
42
43#define INTBLOB_LEN	20
44#define SIGBLOB_LEN	(2*INTBLOB_LEN)
45
46int
47ssh_dss_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
48    const u_char *data, size_t datalen, u_int compat)
49{
50	DSA_SIG *sig = NULL;
51	u_char digest[SSH_DIGEST_MAX_LENGTH], sigblob[SIGBLOB_LEN];
52	size_t rlen, slen, len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1);
53	struct sshbuf *b = NULL;
54	int ret = SSH_ERR_INVALID_ARGUMENT;
55
56	if (lenp != NULL)
57		*lenp = 0;
58	if (sigp != NULL)
59		*sigp = NULL;
60
61	if (key == NULL || key->dsa == NULL ||
62	    sshkey_type_plain(key->type) != KEY_DSA)
63		return SSH_ERR_INVALID_ARGUMENT;
64	if (dlen == 0)
65		return SSH_ERR_INTERNAL_ERROR;
66
67	if ((ret = ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen,
68	    digest, sizeof(digest))) != 0)
69		goto out;
70
71	if ((sig = DSA_do_sign(digest, dlen, key->dsa)) == NULL) {
72		ret = SSH_ERR_LIBCRYPTO_ERROR;
73		goto out;
74	}
75
76	rlen = BN_num_bytes(sig->r);
77	slen = BN_num_bytes(sig->s);
78	if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
79		ret = SSH_ERR_INTERNAL_ERROR;
80		goto out;
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
86	if (compat & SSH_BUG_SIGBLOB) {
87		if (sigp != NULL) {
88			if ((*sigp = malloc(SIGBLOB_LEN)) == NULL) {
89				ret = SSH_ERR_ALLOC_FAIL;
90				goto out;
91			}
92			memcpy(*sigp, sigblob, SIGBLOB_LEN);
93		}
94		if (lenp != NULL)
95			*lenp = SIGBLOB_LEN;
96		ret = 0;
97	} else {
98		/* ietf-drafts */
99		if ((b = sshbuf_new()) == NULL) {
100			ret = SSH_ERR_ALLOC_FAIL;
101			goto out;
102		}
103		if ((ret = sshbuf_put_cstring(b, "ssh-dss")) != 0 ||
104		    (ret = sshbuf_put_string(b, sigblob, SIGBLOB_LEN)) != 0)
105			goto out;
106		len = sshbuf_len(b);
107		if (sigp != NULL) {
108			if ((*sigp = malloc(len)) == NULL) {
109				ret = SSH_ERR_ALLOC_FAIL;
110				goto out;
111			}
112			memcpy(*sigp, sshbuf_ptr(b), len);
113		}
114		if (lenp != NULL)
115			*lenp = len;
116		ret = 0;
117	}
118 out:
119	explicit_bzero(digest, sizeof(digest));
120	if (sig != NULL)
121		DSA_SIG_free(sig);
122	sshbuf_free(b);
123	return ret;
124}
125
126int
127ssh_dss_verify(const struct sshkey *key,
128    const u_char *signature, size_t signaturelen,
129    const u_char *data, size_t datalen, u_int compat)
130{
131	DSA_SIG *sig = NULL;
132	u_char digest[SSH_DIGEST_MAX_LENGTH], *sigblob = NULL;
133	size_t len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1);
134	int ret = SSH_ERR_INTERNAL_ERROR;
135	struct sshbuf *b = NULL;
136	char *ktype = NULL;
137
138	if (key == NULL || key->dsa == NULL ||
139	    sshkey_type_plain(key->type) != KEY_DSA ||
140	    signature == NULL || signaturelen == 0)
141		return SSH_ERR_INVALID_ARGUMENT;
142	if (dlen == 0)
143		return SSH_ERR_INTERNAL_ERROR;
144
145	/* fetch signature */
146	if (compat & SSH_BUG_SIGBLOB) {
147		if ((sigblob = malloc(signaturelen)) == NULL)
148			return SSH_ERR_ALLOC_FAIL;
149		memcpy(sigblob, signature, signaturelen);
150		len = signaturelen;
151	} else {
152		/* ietf-drafts */
153		if ((b = sshbuf_from(signature, signaturelen)) == NULL)
154			return SSH_ERR_ALLOC_FAIL;
155		if (sshbuf_get_cstring(b, &ktype, NULL) != 0 ||
156		    sshbuf_get_string(b, &sigblob, &len) != 0) {
157			ret = SSH_ERR_INVALID_FORMAT;
158			goto out;
159		}
160		if (strcmp("ssh-dss", ktype) != 0) {
161			ret = SSH_ERR_KEY_TYPE_MISMATCH;
162			goto out;
163		}
164		if (sshbuf_len(b) != 0) {
165			ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
166			goto out;
167		}
168	}
169
170	if (len != SIGBLOB_LEN) {
171		ret = SSH_ERR_INVALID_FORMAT;
172		goto out;
173	}
174
175	/* parse signature */
176	if ((sig = DSA_SIG_new()) == NULL ||
177	    (sig->r = BN_new()) == NULL ||
178	    (sig->s = BN_new()) == NULL) {
179		ret = SSH_ERR_ALLOC_FAIL;
180		goto out;
181	}
182	if ((BN_bin2bn(sigblob, INTBLOB_LEN, sig->r) == NULL) ||
183	    (BN_bin2bn(sigblob+ INTBLOB_LEN, INTBLOB_LEN, sig->s) == NULL)) {
184		ret = SSH_ERR_LIBCRYPTO_ERROR;
185		goto out;
186	}
187
188	/* sha1 the data */
189	if ((ret = ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen,
190	    digest, sizeof(digest))) != 0)
191		goto out;
192
193	switch (DSA_do_verify(digest, dlen, sig, key->dsa)) {
194	case 1:
195		ret = 0;
196		break;
197	case 0:
198		ret = SSH_ERR_SIGNATURE_INVALID;
199		goto out;
200	default:
201		ret = SSH_ERR_LIBCRYPTO_ERROR;
202		goto out;
203	}
204
205 out:
206	explicit_bzero(digest, sizeof(digest));
207	if (sig != NULL)
208		DSA_SIG_free(sig);
209	sshbuf_free(b);
210	free(ktype);
211	if (sigblob != NULL) {
212		explicit_bzero(sigblob, len);
213		free(sigblob);
214	}
215	return ret;
216}
217