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
ssh_rsa_sign(const Key * key,u_char ** sigp,u_int * lenp,const u_char * data,u_int datalen)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
ssh_rsa_verify(const Key * key,const u_char * signature,u_int signaturelen,const u_char * data,u_int datalen)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
openssh_RSA_verify(int hash_alg,u_char * hash,u_int hashlen,u_char * sigbuf,u_int siglen,RSA * rsa)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