1 /* $OpenBSD: ssh-rsa.c,v 1.45 2010/08/31 09:58:37 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
36 static int openssh_RSA_verify(int, u_char *, u_int, u_char *, u_int, RSA *);
37
38 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
39 int
ssh_rsa_sign(const Key * key,u_char ** sigp,u_int * lenp,const u_char * data,u_int datalen)40 ssh_rsa_sign(const Key *key, u_char **sigp, u_int *lenp,
41 const u_char *data, u_int datalen)
42 {
43 const EVP_MD *evp_md;
44 EVP_MD_CTX md;
45 u_char digest[EVP_MAX_MD_SIZE], *sig;
46 u_int slen, dlen, len;
47 int ok, nid;
48 Buffer b;
49
50 if (key == NULL || key->rsa == NULL || (key->type != KEY_RSA &&
51 key->type != KEY_RSA_CERT && key->type != KEY_RSA_CERT_V00)) {
52 error("ssh_rsa_sign: no RSA key");
53 return -1;
54 }
55 nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
56 if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
57 error("ssh_rsa_sign: EVP_get_digestbynid %d failed", nid);
58 return -1;
59 }
60 EVP_DigestInit(&md, evp_md);
61 EVP_DigestUpdate(&md, data, datalen);
62 EVP_DigestFinal(&md, digest, &dlen);
63
64 slen = RSA_size(key->rsa);
65 sig = xmalloc(slen);
66
67 ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa);
68 memset(digest, 'd', sizeof(digest));
69
70 if (ok != 1) {
71 int ecode = ERR_get_error();
72
73 error("ssh_rsa_sign: RSA_sign failed: %s",
74 ERR_error_string(ecode, NULL));
75 xfree(sig);
76 return -1;
77 }
78 if (len < slen) {
79 u_int diff = slen - len;
80 debug("slen %u > len %u", slen, len);
81 memmove(sig + diff, sig, len);
82 memset(sig, 0, diff);
83 } else if (len > slen) {
84 error("ssh_rsa_sign: slen %u slen2 %u", slen, len);
85 xfree(sig);
86 return -1;
87 }
88 /* encode signature */
89 buffer_init(&b);
90 buffer_put_cstring(&b, "ssh-rsa");
91 buffer_put_string(&b, sig, slen);
92 len = buffer_len(&b);
93 if (lenp != NULL)
94 *lenp = len;
95 if (sigp != NULL) {
96 *sigp = xmalloc(len);
97 memcpy(*sigp, buffer_ptr(&b), len);
98 }
99 buffer_free(&b);
100 memset(sig, 's', slen);
101 xfree(sig);
102
103 return 0;
104 }
105
106 int
ssh_rsa_verify(const Key * key,const u_char * signature,u_int signaturelen,const u_char * data,u_int datalen)107 ssh_rsa_verify(const Key *key, const u_char *signature, u_int signaturelen,
108 const u_char *data, u_int datalen)
109 {
110 Buffer b;
111 const EVP_MD *evp_md;
112 EVP_MD_CTX md;
113 char *ktype;
114 u_char digest[EVP_MAX_MD_SIZE], *sigblob;
115 u_int len, dlen, modlen;
116 int rlen, ret, nid;
117
118 if (key == NULL || key->rsa == NULL || (key->type != KEY_RSA &&
119 key->type != KEY_RSA_CERT && key->type != KEY_RSA_CERT_V00)) {
120 error("ssh_rsa_verify: no RSA key");
121 return -1;
122 }
123 if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
124 error("ssh_rsa_verify: RSA modulus too small: %d < minimum %d bits",
125 BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
126 return -1;
127 }
128 buffer_init(&b);
129 buffer_append(&b, signature, signaturelen);
130 ktype = buffer_get_cstring(&b, NULL);
131 if (strcmp("ssh-rsa", ktype) != 0) {
132 error("ssh_rsa_verify: cannot handle type %s", ktype);
133 buffer_free(&b);
134 xfree(ktype);
135 return -1;
136 }
137 xfree(ktype);
138 sigblob = buffer_get_string(&b, &len);
139 rlen = buffer_len(&b);
140 buffer_free(&b);
141 if (rlen != 0) {
142 error("ssh_rsa_verify: remaining bytes in signature %d", rlen);
143 xfree(sigblob);
144 return -1;
145 }
146 /* RSA_verify expects a signature of RSA_size */
147 modlen = RSA_size(key->rsa);
148 if (len > modlen) {
149 error("ssh_rsa_verify: len %u > modlen %u", len, modlen);
150 xfree(sigblob);
151 return -1;
152 } else if (len < modlen) {
153 u_int diff = modlen - len;
154 debug("ssh_rsa_verify: add padding: modlen %u > len %u",
155 modlen, len);
156 sigblob = xrealloc(sigblob, 1, modlen);
157 memmove(sigblob + diff, sigblob, len);
158 memset(sigblob, 0, diff);
159 len = modlen;
160 }
161 nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
162 if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
163 error("ssh_rsa_verify: EVP_get_digestbynid %d failed", nid);
164 xfree(sigblob);
165 return -1;
166 }
167 EVP_DigestInit(&md, evp_md);
168 EVP_DigestUpdate(&md, data, datalen);
169 EVP_DigestFinal(&md, digest, &dlen);
170
171 ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa);
172 memset(digest, 'd', sizeof(digest));
173 memset(sigblob, 's', len);
174 xfree(sigblob);
175 debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : "");
176 return ret;
177 }
178
179 /*
180 * See:
181 * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
182 * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
183 */
184 /*
185 * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
186 * oiw(14) secsig(3) algorithms(2) 26 }
187 */
188 static const u_char id_sha1[] = {
189 0x30, 0x21, /* type Sequence, length 0x21 (33) */
190 0x30, 0x09, /* type Sequence, length 0x09 */
191 0x06, 0x05, /* type OID, length 0x05 */
192 0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
193 0x05, 0x00, /* NULL */
194 0x04, 0x14 /* Octet string, length 0x14 (20), followed by sha1 hash */
195 };
196 /*
197 * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
198 * rsadsi(113549) digestAlgorithm(2) 5 }
199 */
200 static const u_char id_md5[] = {
201 0x30, 0x20, /* type Sequence, length 0x20 (32) */
202 0x30, 0x0c, /* type Sequence, length 0x09 */
203 0x06, 0x08, /* type OID, length 0x05 */
204 0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */
205 0x05, 0x00, /* NULL */
206 0x04, 0x10 /* Octet string, length 0x10 (16), followed by md5 hash */
207 };
208
209 static int
openssh_RSA_verify(int type,u_char * hash,u_int hashlen,u_char * sigbuf,u_int siglen,RSA * rsa)210 openssh_RSA_verify(int type, u_char *hash, u_int hashlen,
211 u_char *sigbuf, u_int siglen, RSA *rsa)
212 {
213 u_int ret, rsasize, oidlen = 0, hlen = 0;
214 int len, oidmatch, hashmatch;
215 const u_char *oid = NULL;
216 u_char *decrypted = NULL;
217
218 ret = 0;
219 switch (type) {
220 case NID_sha1:
221 oid = id_sha1;
222 oidlen = sizeof(id_sha1);
223 hlen = 20;
224 break;
225 case NID_md5:
226 oid = id_md5;
227 oidlen = sizeof(id_md5);
228 hlen = 16;
229 break;
230 default:
231 goto done;
232 }
233 if (hashlen != hlen) {
234 error("bad hashlen");
235 goto done;
236 }
237 rsasize = RSA_size(rsa);
238 if (siglen == 0 || siglen > rsasize) {
239 error("bad siglen");
240 goto done;
241 }
242 decrypted = xmalloc(rsasize);
243 if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
244 RSA_PKCS1_PADDING)) < 0) {
245 error("RSA_public_decrypt failed: %s",
246 ERR_error_string(ERR_get_error(), NULL));
247 goto done;
248 }
249 if (len < 0 || (u_int)len != hlen + oidlen) {
250 error("bad decrypted len: %d != %d + %d", len, hlen, oidlen);
251 goto done;
252 }
253 oidmatch = timingsafe_bcmp(decrypted, oid, oidlen) == 0;
254 hashmatch = timingsafe_bcmp(decrypted + oidlen, hash, hlen) == 0;
255 if (!oidmatch) {
256 error("oid mismatch");
257 goto done;
258 }
259 if (!hashmatch) {
260 error("hash mismatch");
261 goto done;
262 }
263 ret = 1;
264 done:
265 if (decrypted)
266 xfree(decrypted);
267 return ret;
268 }
269