xref: /freebsd/crypto/openssh/ssh-rsa.c (revision b6a05070fa77edc7ce6e60b61623fd806e807be6)
1 /* $OpenBSD: ssh-rsa.c,v 1.51 2014/02/02 03:44:31 djm Exp $ */
2 /*
3  * Copyright (c) 2000, 2003 Markus Friedl <markus@openbsd.org>
4  *
5  * Permission to use, copy, modify, and distribute this software for any
6  * purpose with or without fee is hereby granted, provided that the above
7  * copyright notice and this permission notice appear in all copies.
8  *
9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16  */
17 
18 #include "includes.h"
19 
20 #include <sys/types.h>
21 
22 #include <openssl/evp.h>
23 #include <openssl/err.h>
24 
25 #include <stdarg.h>
26 #include <string.h>
27 
28 #include "xmalloc.h"
29 #include "log.h"
30 #include "buffer.h"
31 #include "key.h"
32 #include "compat.h"
33 #include "misc.h"
34 #include "ssh.h"
35 #include "digest.h"
36 
37 static int openssh_RSA_verify(int, u_char *, u_int, u_char *, u_int, RSA *);
38 
39 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
40 int
41 ssh_rsa_sign(const Key *key, u_char **sigp, u_int *lenp,
42     const u_char *data, u_int datalen)
43 {
44 	int hash_alg;
45 	u_char digest[SSH_DIGEST_MAX_LENGTH], *sig;
46 	u_int slen, dlen, len;
47 	int ok, nid;
48 	Buffer b;
49 
50 	if (key == NULL || key_type_plain(key->type) != KEY_RSA ||
51 	    key->rsa == NULL) {
52 		error("%s: no RSA key", __func__);
53 		return -1;
54 	}
55 
56 	/* hash the data */
57 	hash_alg = SSH_DIGEST_SHA1;
58 	nid = NID_sha1;
59 	if ((dlen = ssh_digest_bytes(hash_alg)) == 0) {
60 		error("%s: bad hash algorithm %d", __func__, hash_alg);
61 		return -1;
62 	}
63 	if (ssh_digest_memory(hash_alg, data, datalen,
64 	    digest, sizeof(digest)) != 0) {
65 		error("%s: ssh_digest_memory failed", __func__);
66 		return -1;
67 	}
68 
69 	slen = RSA_size(key->rsa);
70 	sig = xmalloc(slen);
71 
72 	ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa);
73 	explicit_bzero(digest, sizeof(digest));
74 
75 	if (ok != 1) {
76 		int ecode = ERR_get_error();
77 
78 		error("%s: RSA_sign failed: %s", __func__,
79 		    ERR_error_string(ecode, NULL));
80 		free(sig);
81 		return -1;
82 	}
83 	if (len < slen) {
84 		u_int diff = slen - len;
85 		debug("slen %u > len %u", slen, len);
86 		memmove(sig + diff, sig, len);
87 		explicit_bzero(sig, diff);
88 	} else if (len > slen) {
89 		error("%s: slen %u slen2 %u", __func__, slen, len);
90 		free(sig);
91 		return -1;
92 	}
93 	/* encode signature */
94 	buffer_init(&b);
95 	buffer_put_cstring(&b, "ssh-rsa");
96 	buffer_put_string(&b, sig, slen);
97 	len = buffer_len(&b);
98 	if (lenp != NULL)
99 		*lenp = len;
100 	if (sigp != NULL) {
101 		*sigp = xmalloc(len);
102 		memcpy(*sigp, buffer_ptr(&b), len);
103 	}
104 	buffer_free(&b);
105 	explicit_bzero(sig, slen);
106 	free(sig);
107 
108 	return 0;
109 }
110 
111 int
112 ssh_rsa_verify(const Key *key, const u_char *signature, u_int signaturelen,
113     const u_char *data, u_int datalen)
114 {
115 	Buffer b;
116 	int hash_alg;
117 	char *ktype;
118 	u_char digest[SSH_DIGEST_MAX_LENGTH], *sigblob;
119 	u_int len, dlen, modlen;
120 	int rlen, ret;
121 
122 	if (key == NULL || key_type_plain(key->type) != KEY_RSA ||
123 	    key->rsa == NULL) {
124 		error("%s: no RSA key", __func__);
125 		return -1;
126 	}
127 
128 	if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
129 		error("%s: RSA modulus too small: %d < minimum %d bits",
130 		    __func__, BN_num_bits(key->rsa->n),
131 		    SSH_RSA_MINIMUM_MODULUS_SIZE);
132 		return -1;
133 	}
134 	buffer_init(&b);
135 	buffer_append(&b, signature, signaturelen);
136 	ktype = buffer_get_cstring(&b, NULL);
137 	if (strcmp("ssh-rsa", 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", __func__, rlen);
149 		free(sigblob);
150 		return -1;
151 	}
152 	/* RSA_verify expects a signature of RSA_size */
153 	modlen = RSA_size(key->rsa);
154 	if (len > modlen) {
155 		error("%s: len %u > modlen %u", __func__, len, modlen);
156 		free(sigblob);
157 		return -1;
158 	} else if (len < modlen) {
159 		u_int diff = modlen - len;
160 		debug("%s: add padding: modlen %u > len %u", __func__,
161 		    modlen, len);
162 		sigblob = xrealloc(sigblob, 1, modlen);
163 		memmove(sigblob + diff, sigblob, len);
164 		explicit_bzero(sigblob, diff);
165 		len = modlen;
166 	}
167 	/* hash the data */
168 	hash_alg = SSH_DIGEST_SHA1;
169 	if ((dlen = ssh_digest_bytes(hash_alg)) == 0) {
170 		error("%s: bad hash algorithm %d", __func__, hash_alg);
171 		return -1;
172 	}
173 	if (ssh_digest_memory(hash_alg, data, datalen,
174 	    digest, sizeof(digest)) != 0) {
175 		error("%s: ssh_digest_memory failed", __func__);
176 		return -1;
177 	}
178 
179 	ret = openssh_RSA_verify(hash_alg, digest, dlen, sigblob, len,
180 	    key->rsa);
181 	explicit_bzero(digest, sizeof(digest));
182 	explicit_bzero(sigblob, len);
183 	free(sigblob);
184 	debug("%s: signature %scorrect", __func__, (ret == 0) ? "in" : "");
185 	return ret;
186 }
187 
188 /*
189  * See:
190  * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
191  * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
192  */
193 /*
194  * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
195  *	oiw(14) secsig(3) algorithms(2) 26 }
196  */
197 static const u_char id_sha1[] = {
198 	0x30, 0x21, /* type Sequence, length 0x21 (33) */
199 	0x30, 0x09, /* type Sequence, length 0x09 */
200 	0x06, 0x05, /* type OID, length 0x05 */
201 	0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
202 	0x05, 0x00, /* NULL */
203 	0x04, 0x14  /* Octet string, length 0x14 (20), followed by sha1 hash */
204 };
205 
206 static int
207 openssh_RSA_verify(int hash_alg, u_char *hash, u_int hashlen,
208     u_char *sigbuf, u_int siglen, RSA *rsa)
209 {
210 	u_int ret, rsasize, oidlen = 0, hlen = 0;
211 	int len, oidmatch, hashmatch;
212 	const u_char *oid = NULL;
213 	u_char *decrypted = NULL;
214 
215 	ret = 0;
216 	switch (hash_alg) {
217 	case SSH_DIGEST_SHA1:
218 		oid = id_sha1;
219 		oidlen = sizeof(id_sha1);
220 		hlen = 20;
221 		break;
222 	default:
223 		goto done;
224 	}
225 	if (hashlen != hlen) {
226 		error("bad hashlen");
227 		goto done;
228 	}
229 	rsasize = RSA_size(rsa);
230 	if (siglen == 0 || siglen > rsasize) {
231 		error("bad siglen");
232 		goto done;
233 	}
234 	decrypted = xmalloc(rsasize);
235 	if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
236 	    RSA_PKCS1_PADDING)) < 0) {
237 		error("RSA_public_decrypt failed: %s",
238 		    ERR_error_string(ERR_get_error(), NULL));
239 		goto done;
240 	}
241 	if (len < 0 || (u_int)len != hlen + oidlen) {
242 		error("bad decrypted len: %d != %d + %d", len, hlen, oidlen);
243 		goto done;
244 	}
245 	oidmatch = timingsafe_bcmp(decrypted, oid, oidlen) == 0;
246 	hashmatch = timingsafe_bcmp(decrypted + oidlen, hash, hlen) == 0;
247 	if (!oidmatch) {
248 		error("oid mismatch");
249 		goto done;
250 	}
251 	if (!hashmatch) {
252 		error("hash mismatch");
253 		goto done;
254 	}
255 	ret = 1;
256 done:
257 	free(decrypted);
258 	return ret;
259 }
260