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"
26 RCSID("$OpenBSD: ssh-rsa.c,v 1.26 2002/08/27 17:13:56 stevesk Exp $");
27
28 #pragma ident "%Z%%M% %I% %E% SMI"
29
30 #include <openssl/evp.h>
31 #include <openssl/err.h>
32
33 #include "xmalloc.h"
34 #include "log.h"
35 #include "buffer.h"
36 #include "bufaux.h"
37 #include "key.h"
38 #include "ssh-rsa.h"
39 #include "compat.h"
40 #include "ssh.h"
41
42 static int openssh_RSA_verify(int, u_char *, u_int, u_char *, u_int , RSA *);
43
44 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
45 int
46 ssh_rsa_sign(Key *key, u_char **sigp, u_int *lenp,
47 u_char *data, u_int datalen)
48 {
49 const EVP_MD *evp_md;
50 EVP_MD_CTX md;
51 u_char digest[EVP_MAX_MD_SIZE], *sig;
52 u_int slen, dlen, len;
53 int ok, nid;
54 Buffer b;
55
56 if (key == NULL || key->type != KEY_RSA || key->rsa == NULL) {
57 error("ssh_rsa_sign: no RSA key");
58 return -1;
59 }
60 nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
61 if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
62 error("ssh_rsa_sign: EVP_get_digestbynid %d failed", nid);
63 return -1;
64 }
65 EVP_DigestInit(&md, evp_md);
66 EVP_DigestUpdate(&md, data, datalen);
67 EVP_DigestFinal(&md, digest, &dlen);
68
69 slen = RSA_size(key->rsa);
70 sig = xmalloc(slen);
71
72 ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa);
73 memset(digest, 'd', sizeof(digest));
74
75 if (ok != 1) {
76 int ecode = ERR_get_error();
77 error("ssh_rsa_sign: RSA_sign failed: %s",
78 ERR_error_string(ecode, NULL));
79 xfree(sig);
80 return -1;
81 }
82 if (len < slen) {
83 u_int diff = slen - len;
84 debug("slen %u > len %u", slen, len);
85 memmove(sig + diff, sig, len);
86 memset(sig, 0, diff);
87 } else if (len > slen) {
88 error("ssh_rsa_sign: slen %u slen2 %u", slen, len);
89 xfree(sig);
90 return -1;
91 }
92 /* encode signature */
93 buffer_init(&b);
94 buffer_put_cstring(&b, "ssh-rsa");
95 buffer_put_string(&b, sig, slen);
96 len = buffer_len(&b);
97 if (lenp != NULL)
98 *lenp = len;
99 if (sigp != NULL) {
100 *sigp = xmalloc(len);
101 memcpy(*sigp, buffer_ptr(&b), len);
102 }
103 buffer_free(&b);
104 memset(sig, 's', slen);
105 xfree(sig);
106
107 return 0;
108 }
109
110 int
111 ssh_rsa_verify(Key *key, u_char *signature, u_int signaturelen,
112 u_char *data, u_int datalen)
113 {
114 Buffer b;
115 const EVP_MD *evp_md;
116 EVP_MD_CTX md;
117 char *ktype;
118 u_char digest[EVP_MAX_MD_SIZE], *sigblob;
119 u_int len, dlen, modlen;
120 int rlen, ret, nid;
121
122 if (key == NULL || key->type != KEY_RSA || key->rsa == NULL) {
123 error("ssh_rsa_verify: no RSA key");
124 return -1;
125 }
126 if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
127 error("ssh_rsa_verify: RSA modulus too small: %d < minimum %d bits",
128 BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
129 return -1;
130 }
131 buffer_init(&b);
132 buffer_append(&b, signature, signaturelen);
133 ktype = buffer_get_string(&b, NULL);
134 if (strcmp("ssh-rsa", ktype) != 0) {
135 error("ssh_rsa_verify: cannot handle type %s", ktype);
136 buffer_free(&b);
137 xfree(ktype);
138 return -1;
139 }
140 xfree(ktype);
141 sigblob = buffer_get_string(&b, &len);
142 rlen = buffer_len(&b);
143 buffer_free(&b);
144 if (rlen != 0) {
145 error("ssh_rsa_verify: remaining bytes in signature %d", rlen);
146 xfree(sigblob);
147 return -1;
148 }
149 /* RSA_verify expects a signature of RSA_size */
150 modlen = RSA_size(key->rsa);
151 if (len > modlen) {
152 error("ssh_rsa_verify: len %u > modlen %u", len, modlen);
153 xfree(sigblob);
154 return -1;
155 } else if (len < modlen) {
156 u_int diff = modlen - len;
157 debug("ssh_rsa_verify: add padding: modlen %u > len %u",
158 modlen, len);
159 sigblob = xrealloc(sigblob, modlen);
160 memmove(sigblob + diff, sigblob, len);
161 memset(sigblob, 0, diff);
162 len = modlen;
163 }
164 nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
165 if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
166 error("ssh_rsa_verify: EVP_get_digestbynid %d failed", nid);
167 xfree(sigblob);
168 return -1;
169 }
170 EVP_DigestInit(&md, evp_md);
171 EVP_DigestUpdate(&md, data, datalen);
172 EVP_DigestFinal(&md, digest, &dlen);
173
174 ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa);
175 memset(digest, 'd', sizeof(digest));
176 memset(sigblob, 's', len);
177 xfree(sigblob);
178 debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : "");
179 return ret;
180 }
181
182 /*
183 * See:
184 * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
185 * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
186 */
187 /*
188 * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
189 * oiw(14) secsig(3) algorithms(2) 26 }
190 */
191 static const u_char id_sha1[] = {
192 0x30, 0x21, /* type Sequence, length 0x21 (33) */
193 0x30, 0x09, /* type Sequence, length 0x09 */
194 0x06, 0x05, /* type OID, length 0x05 */
195 0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
196 0x05, 0x00, /* NULL */
197 0x04, 0x14 /* Octet string, length 0x14 (20), followed by sha1 hash */
198 };
199 /*
200 * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
201 * rsadsi(113549) digestAlgorithm(2) 5 }
202 */
203 static const u_char id_md5[] = {
204 0x30, 0x20, /* type Sequence, length 0x20 (32) */
205 0x30, 0x0c, /* type Sequence, length 0x09 */
206 0x06, 0x08, /* type OID, length 0x05 */
207 0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */
208 0x05, 0x00, /* NULL */
209 0x04, 0x10 /* Octet string, length 0x10 (16), followed by md5 hash */
210 };
211
212 static int
213 openssh_RSA_verify(int type, u_char *hash, u_int hashlen,
214 u_char *sigbuf, u_int siglen, RSA *rsa)
215 {
216 u_int ret, rsasize, oidlen = 0, hlen = 0;
217 int len;
218 const u_char *oid = NULL;
219 u_char *decrypted = NULL;
220
221 ret = 0;
222 switch (type) {
223 case NID_sha1:
224 oid = id_sha1;
225 oidlen = sizeof(id_sha1);
226 hlen = 20;
227 break;
228 case NID_md5:
229 oid = id_md5;
230 oidlen = sizeof(id_md5);
231 hlen = 16;
232 break;
233 default:
234 goto done;
235 break;
236 }
237 if (hashlen != hlen) {
238 error("bad hashlen");
239 goto done;
240 }
241 rsasize = RSA_size(rsa);
242 if (siglen == 0 || siglen > rsasize) {
243 error("bad siglen");
244 goto done;
245 }
246 decrypted = xmalloc(rsasize);
247 if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
248 RSA_PKCS1_PADDING)) < 0) {
249 error("RSA_public_decrypt failed: %s",
250 ERR_error_string(ERR_get_error(), NULL));
251 goto done;
252 }
253 if (len != hlen + oidlen) {
254 error("bad decrypted len: %d != %d + %d", len, hlen, oidlen);
255 goto done;
256 }
257 if (memcmp(decrypted, oid, oidlen) != 0) {
258 error("oid mismatch");
259 goto done;
260 }
261 if (memcmp(decrypted + oidlen, hash, hlen) != 0) {
262 error("hash mismatch");
263 goto done;
264 }
265 ret = 1;
266 done:
267 if (decrypted)
268 xfree(decrypted);
269 return ret;
270 }