xref: /openssh-portable/ssh-dss.c (revision d5ba1c03)
1 /* $OpenBSD: ssh-dss.c,v 1.39 2020/02/26 13:40:09 jsg 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 #ifdef WITH_OPENSSL
29 
30 #include <sys/types.h>
31 
32 #include <openssl/bn.h>
33 #include <openssl/dsa.h>
34 #include <openssl/evp.h>
35 
36 #include <stdarg.h>
37 #include <string.h>
38 
39 #include "sshbuf.h"
40 #include "compat.h"
41 #include "ssherr.h"
42 #include "digest.h"
43 #define SSHKEY_INTERNAL
44 #include "sshkey.h"
45 
46 #include "openbsd-compat/openssl-compat.h"
47 
48 #define INTBLOB_LEN	20
49 #define SIGBLOB_LEN	(2*INTBLOB_LEN)
50 
51 int
ssh_dss_sign(const struct sshkey * key,u_char ** sigp,size_t * lenp,const u_char * data,size_t datalen,u_int compat)52 ssh_dss_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
53     const u_char *data, size_t datalen, u_int compat)
54 {
55 	DSA_SIG *sig = NULL;
56 	const BIGNUM *sig_r, *sig_s;
57 	u_char digest[SSH_DIGEST_MAX_LENGTH], sigblob[SIGBLOB_LEN];
58 	size_t rlen, slen, len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1);
59 	struct sshbuf *b = NULL;
60 	int ret = SSH_ERR_INVALID_ARGUMENT;
61 
62 	if (lenp != NULL)
63 		*lenp = 0;
64 	if (sigp != NULL)
65 		*sigp = NULL;
66 
67 	if (key == NULL || key->dsa == NULL ||
68 	    sshkey_type_plain(key->type) != KEY_DSA)
69 		return SSH_ERR_INVALID_ARGUMENT;
70 	if (dlen == 0)
71 		return SSH_ERR_INTERNAL_ERROR;
72 
73 	if ((ret = ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen,
74 	    digest, sizeof(digest))) != 0)
75 		goto out;
76 
77 	if ((sig = DSA_do_sign(digest, dlen, key->dsa)) == NULL) {
78 		ret = SSH_ERR_LIBCRYPTO_ERROR;
79 		goto out;
80 	}
81 
82 	DSA_SIG_get0(sig, &sig_r, &sig_s);
83 	rlen = BN_num_bytes(sig_r);
84 	slen = BN_num_bytes(sig_s);
85 	if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
86 		ret = SSH_ERR_INTERNAL_ERROR;
87 		goto out;
88 	}
89 	explicit_bzero(sigblob, SIGBLOB_LEN);
90 	BN_bn2bin(sig_r, sigblob + SIGBLOB_LEN - INTBLOB_LEN - rlen);
91 	BN_bn2bin(sig_s, sigblob + SIGBLOB_LEN - slen);
92 
93 	if ((b = sshbuf_new()) == NULL) {
94 		ret = SSH_ERR_ALLOC_FAIL;
95 		goto out;
96 	}
97 	if ((ret = sshbuf_put_cstring(b, "ssh-dss")) != 0 ||
98 	    (ret = sshbuf_put_string(b, sigblob, SIGBLOB_LEN)) != 0)
99 		goto out;
100 
101 	len = sshbuf_len(b);
102 	if (sigp != NULL) {
103 		if ((*sigp = malloc(len)) == NULL) {
104 			ret = SSH_ERR_ALLOC_FAIL;
105 			goto out;
106 		}
107 		memcpy(*sigp, sshbuf_ptr(b), len);
108 	}
109 	if (lenp != NULL)
110 		*lenp = len;
111 	ret = 0;
112  out:
113 	explicit_bzero(digest, sizeof(digest));
114 	DSA_SIG_free(sig);
115 	sshbuf_free(b);
116 	return ret;
117 }
118 
119 int
ssh_dss_verify(const struct sshkey * key,const u_char * signature,size_t signaturelen,const u_char * data,size_t datalen,u_int compat)120 ssh_dss_verify(const struct sshkey *key,
121     const u_char *signature, size_t signaturelen,
122     const u_char *data, size_t datalen, u_int compat)
123 {
124 	DSA_SIG *sig = NULL;
125 	BIGNUM *sig_r = NULL, *sig_s = NULL;
126 	u_char digest[SSH_DIGEST_MAX_LENGTH], *sigblob = NULL;
127 	size_t len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1);
128 	int ret = SSH_ERR_INTERNAL_ERROR;
129 	struct sshbuf *b = NULL;
130 	char *ktype = NULL;
131 
132 	if (key == NULL || key->dsa == NULL ||
133 	    sshkey_type_plain(key->type) != KEY_DSA ||
134 	    signature == NULL || signaturelen == 0)
135 		return SSH_ERR_INVALID_ARGUMENT;
136 	if (dlen == 0)
137 		return SSH_ERR_INTERNAL_ERROR;
138 
139 	/* fetch signature */
140 	if ((b = sshbuf_from(signature, signaturelen)) == NULL)
141 		return SSH_ERR_ALLOC_FAIL;
142 	if (sshbuf_get_cstring(b, &ktype, NULL) != 0 ||
143 	    sshbuf_get_string(b, &sigblob, &len) != 0) {
144 		ret = SSH_ERR_INVALID_FORMAT;
145 		goto out;
146 	}
147 	if (strcmp("ssh-dss", ktype) != 0) {
148 		ret = SSH_ERR_KEY_TYPE_MISMATCH;
149 		goto out;
150 	}
151 	if (sshbuf_len(b) != 0) {
152 		ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
153 		goto out;
154 	}
155 
156 	if (len != SIGBLOB_LEN) {
157 		ret = SSH_ERR_INVALID_FORMAT;
158 		goto out;
159 	}
160 
161 	/* parse signature */
162 	if ((sig = DSA_SIG_new()) == NULL ||
163 	    (sig_r = BN_new()) == NULL ||
164 	    (sig_s = BN_new()) == NULL) {
165 		ret = SSH_ERR_ALLOC_FAIL;
166 		goto out;
167 	}
168 	if ((BN_bin2bn(sigblob, INTBLOB_LEN, sig_r) == NULL) ||
169 	    (BN_bin2bn(sigblob + INTBLOB_LEN, INTBLOB_LEN, sig_s) == NULL)) {
170 		ret = SSH_ERR_LIBCRYPTO_ERROR;
171 		goto out;
172 	}
173 	if (!DSA_SIG_set0(sig, sig_r, sig_s)) {
174 		ret = SSH_ERR_LIBCRYPTO_ERROR;
175 		goto out;
176 	}
177 	sig_r = sig_s = NULL; /* transferred */
178 
179 	/* sha1 the data */
180 	if ((ret = ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen,
181 	    digest, sizeof(digest))) != 0)
182 		goto out;
183 
184 	switch (DSA_do_verify(digest, dlen, sig, key->dsa)) {
185 	case 1:
186 		ret = 0;
187 		break;
188 	case 0:
189 		ret = SSH_ERR_SIGNATURE_INVALID;
190 		goto out;
191 	default:
192 		ret = SSH_ERR_LIBCRYPTO_ERROR;
193 		goto out;
194 	}
195 
196  out:
197 	explicit_bzero(digest, sizeof(digest));
198 	DSA_SIG_free(sig);
199 	BN_clear_free(sig_r);
200 	BN_clear_free(sig_s);
201 	sshbuf_free(b);
202 	free(ktype);
203 	if (sigblob != NULL)
204 		freezero(sigblob, len);
205 	return ret;
206 }
207 #endif /* WITH_OPENSSL */
208