ssh-rsa.c revision 124208
1/*
2 * Copyright (c) 2000, 2003 Markus Friedl <markus@openbsd.org>
3 *
4 * Permission to use, copy, modify, and distribute this software for any
5 * purpose with or without fee is hereby granted, provided that the above
6 * copyright notice and this permission notice appear in all copies.
7 *
8 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15 */
16#include "includes.h"
17RCSID("$OpenBSD: ssh-rsa.c,v 1.30 2003/06/18 11:28:11 markus Exp $");
18
19#include <openssl/evp.h>
20#include <openssl/err.h>
21
22#include "xmalloc.h"
23#include "log.h"
24#include "buffer.h"
25#include "bufaux.h"
26#include "key.h"
27#include "compat.h"
28#include "ssh.h"
29
30static int openssh_RSA_verify(int, u_char *, u_int, u_char *, u_int, RSA *);
31
32/* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
33int
34ssh_rsa_sign(Key *key, u_char **sigp, u_int *lenp,
35    u_char *data, u_int datalen)
36{
37	const EVP_MD *evp_md;
38	EVP_MD_CTX md;
39	u_char digest[EVP_MAX_MD_SIZE], *sig;
40	u_int slen, dlen, len;
41	int ok, nid;
42	Buffer b;
43
44	if (key == NULL || key->type != KEY_RSA || key->rsa == NULL) {
45		error("ssh_rsa_sign: no RSA key");
46		return -1;
47	}
48	nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
49	if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
50		error("ssh_rsa_sign: EVP_get_digestbynid %d failed", nid);
51		return -1;
52	}
53	EVP_DigestInit(&md, evp_md);
54	EVP_DigestUpdate(&md, data, datalen);
55	EVP_DigestFinal(&md, digest, &dlen);
56
57	slen = RSA_size(key->rsa);
58	sig = xmalloc(slen);
59
60	ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa);
61	memset(digest, 'd', sizeof(digest));
62
63	if (ok != 1) {
64		int ecode = ERR_get_error();
65		error("ssh_rsa_sign: RSA_sign failed: %s",
66		    ERR_error_string(ecode, NULL));
67		xfree(sig);
68		return -1;
69	}
70	if (len < slen) {
71		u_int diff = slen - len;
72		debug("slen %u > len %u", slen, len);
73		memmove(sig + diff, sig, len);
74		memset(sig, 0, diff);
75	} else if (len > slen) {
76		error("ssh_rsa_sign: slen %u slen2 %u", slen, len);
77		xfree(sig);
78		return -1;
79	}
80	/* encode signature */
81	buffer_init(&b);
82	buffer_put_cstring(&b, "ssh-rsa");
83	buffer_put_string(&b, sig, slen);
84	len = buffer_len(&b);
85	if (lenp != NULL)
86		*lenp = len;
87	if (sigp != NULL) {
88		*sigp = xmalloc(len);
89		memcpy(*sigp, buffer_ptr(&b), len);
90	}
91	buffer_free(&b);
92	memset(sig, 's', slen);
93	xfree(sig);
94
95	return 0;
96}
97
98int
99ssh_rsa_verify(Key *key, u_char *signature, u_int signaturelen,
100    u_char *data, u_int datalen)
101{
102	Buffer b;
103	const EVP_MD *evp_md;
104	EVP_MD_CTX md;
105	char *ktype;
106	u_char digest[EVP_MAX_MD_SIZE], *sigblob;
107	u_int len, dlen, modlen;
108	int rlen, ret, nid;
109
110	if (key == NULL || key->type != KEY_RSA || key->rsa == NULL) {
111		error("ssh_rsa_verify: no RSA key");
112		return -1;
113	}
114	if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
115		error("ssh_rsa_verify: RSA modulus too small: %d < minimum %d bits",
116		    BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
117		return -1;
118	}
119	buffer_init(&b);
120	buffer_append(&b, signature, signaturelen);
121	ktype = buffer_get_string(&b, NULL);
122	if (strcmp("ssh-rsa", ktype) != 0) {
123		error("ssh_rsa_verify: cannot handle type %s", ktype);
124		buffer_free(&b);
125		xfree(ktype);
126		return -1;
127	}
128	xfree(ktype);
129	sigblob = buffer_get_string(&b, &len);
130	rlen = buffer_len(&b);
131	buffer_free(&b);
132	if (rlen != 0) {
133		error("ssh_rsa_verify: remaining bytes in signature %d", rlen);
134		xfree(sigblob);
135		return -1;
136	}
137	/* RSA_verify expects a signature of RSA_size */
138	modlen = RSA_size(key->rsa);
139	if (len > modlen) {
140		error("ssh_rsa_verify: len %u > modlen %u", len, modlen);
141		xfree(sigblob);
142		return -1;
143	} else if (len < modlen) {
144		u_int diff = modlen - len;
145		debug("ssh_rsa_verify: add padding: modlen %u > len %u",
146		    modlen, len);
147		sigblob = xrealloc(sigblob, modlen);
148		memmove(sigblob + diff, sigblob, len);
149		memset(sigblob, 0, diff);
150		len = modlen;
151	}
152	nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
153	if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
154		error("ssh_rsa_verify: EVP_get_digestbynid %d failed", nid);
155		xfree(sigblob);
156		return -1;
157	}
158	EVP_DigestInit(&md, evp_md);
159	EVP_DigestUpdate(&md, data, datalen);
160	EVP_DigestFinal(&md, digest, &dlen);
161
162	ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa);
163	memset(digest, 'd', sizeof(digest));
164	memset(sigblob, 's', len);
165	xfree(sigblob);
166	debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : "");
167	return ret;
168}
169
170/*
171 * See:
172 * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
173 * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
174 */
175/*
176 * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
177 *	oiw(14) secsig(3) algorithms(2) 26 }
178 */
179static const u_char id_sha1[] = {
180	0x30, 0x21, /* type Sequence, length 0x21 (33) */
181	0x30, 0x09, /* type Sequence, length 0x09 */
182	0x06, 0x05, /* type OID, length 0x05 */
183	0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
184	0x05, 0x00, /* NULL */
185	0x04, 0x14  /* Octet string, length 0x14 (20), followed by sha1 hash */
186};
187/*
188 * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
189 *	rsadsi(113549) digestAlgorithm(2) 5 }
190 */
191static const u_char id_md5[] = {
192	0x30, 0x20, /* type Sequence, length 0x20 (32) */
193	0x30, 0x0c, /* type Sequence, length 0x09 */
194	0x06, 0x08, /* type OID, length 0x05 */
195	0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */
196	0x05, 0x00, /* NULL */
197	0x04, 0x10  /* Octet string, length 0x10 (16), followed by md5 hash */
198};
199
200static int
201openssh_RSA_verify(int type, u_char *hash, u_int hashlen,
202    u_char *sigbuf, u_int siglen, RSA *rsa)
203{
204	u_int ret, rsasize, oidlen = 0, hlen = 0;
205	int len;
206	const u_char *oid = NULL;
207	u_char *decrypted = NULL;
208
209	ret = 0;
210	switch (type) {
211	case NID_sha1:
212		oid = id_sha1;
213		oidlen = sizeof(id_sha1);
214		hlen = 20;
215		break;
216	case NID_md5:
217		oid = id_md5;
218		oidlen = sizeof(id_md5);
219		hlen = 16;
220		break;
221	default:
222		goto done;
223		break;
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 != hlen + oidlen) {
242		error("bad decrypted len: %d != %d + %d", len, hlen, oidlen);
243		goto done;
244	}
245	if (memcmp(decrypted, oid, oidlen) != 0) {
246		error("oid mismatch");
247		goto done;
248	}
249	if (memcmp(decrypted + oidlen, hash, hlen) != 0) {
250		error("hash mismatch");
251		goto done;
252	}
253	ret = 1;
254done:
255	if (decrypted)
256		xfree(decrypted);
257	return ret;
258}
259