1 /* $OpenBSD: ssh-rsa.c,v 1.60 2016/09/12 23:39:34 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 #ifdef WITH_OPENSSL
21
22 #include <sys/types.h>
23
24 #include <openssl/evp.h>
25 #include <openssl/err.h>
26
27 #include <stdarg.h>
28 #include <string.h>
29
30 #include "sshbuf.h"
31 #include "compat.h"
32 #include "ssherr.h"
33 #define SSHKEY_INTERNAL
34 #include "sshkey.h"
35 #include "digest.h"
36
37 static int openssh_RSA_verify(int, u_char *, size_t, u_char *, size_t, RSA *);
38
39 static const char *
rsa_hash_alg_ident(int hash_alg)40 rsa_hash_alg_ident(int hash_alg)
41 {
42 switch (hash_alg) {
43 case SSH_DIGEST_SHA1:
44 return "ssh-rsa";
45 case SSH_DIGEST_SHA256:
46 return "rsa-sha2-256";
47 case SSH_DIGEST_SHA512:
48 return "rsa-sha2-512";
49 }
50 return NULL;
51 }
52
53 static int
rsa_hash_alg_from_ident(const char * ident)54 rsa_hash_alg_from_ident(const char *ident)
55 {
56 if (strcmp(ident, "ssh-rsa") == 0 ||
57 strcmp(ident, "ssh-rsa-cert-v01@openssh.com") == 0)
58 return SSH_DIGEST_SHA1;
59 if (strcmp(ident, "rsa-sha2-256") == 0)
60 return SSH_DIGEST_SHA256;
61 if (strcmp(ident, "rsa-sha2-512") == 0)
62 return SSH_DIGEST_SHA512;
63 return -1;
64 }
65
66 static int
rsa_hash_alg_nid(int type)67 rsa_hash_alg_nid(int type)
68 {
69 switch (type) {
70 case SSH_DIGEST_SHA1:
71 return NID_sha1;
72 case SSH_DIGEST_SHA256:
73 return NID_sha256;
74 case SSH_DIGEST_SHA512:
75 return NID_sha512;
76 default:
77 return -1;
78 }
79 }
80
81 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
82 int
ssh_rsa_sign(const struct sshkey * key,u_char ** sigp,size_t * lenp,const u_char * data,size_t datalen,const char * alg_ident)83 ssh_rsa_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
84 const u_char *data, size_t datalen, const char *alg_ident)
85 {
86 u_char digest[SSH_DIGEST_MAX_LENGTH], *sig = NULL;
87 size_t slen;
88 u_int dlen, len;
89 int nid, hash_alg, ret = SSH_ERR_INTERNAL_ERROR;
90 struct sshbuf *b = NULL;
91
92 if (lenp != NULL)
93 *lenp = 0;
94 if (sigp != NULL)
95 *sigp = NULL;
96
97 if (alg_ident == NULL || strlen(alg_ident) == 0)
98 hash_alg = SSH_DIGEST_SHA1;
99 else
100 hash_alg = rsa_hash_alg_from_ident(alg_ident);
101 if (key == NULL || key->rsa == NULL || hash_alg == -1 ||
102 sshkey_type_plain(key->type) != KEY_RSA ||
103 BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE)
104 return SSH_ERR_INVALID_ARGUMENT;
105 slen = RSA_size(key->rsa);
106 if (slen <= 0 || slen > SSHBUF_MAX_BIGNUM)
107 return SSH_ERR_INVALID_ARGUMENT;
108
109 /* hash the data */
110 nid = rsa_hash_alg_nid(hash_alg);
111 if ((dlen = ssh_digest_bytes(hash_alg)) == 0)
112 return SSH_ERR_INTERNAL_ERROR;
113 if ((ret = ssh_digest_memory(hash_alg, data, datalen,
114 digest, sizeof(digest))) != 0)
115 goto out;
116
117 if ((sig = malloc(slen)) == NULL) {
118 ret = SSH_ERR_ALLOC_FAIL;
119 goto out;
120 }
121
122 if (RSA_sign(nid, digest, dlen, sig, &len, key->rsa) != 1) {
123 ret = SSH_ERR_LIBCRYPTO_ERROR;
124 goto out;
125 }
126 if (len < slen) {
127 size_t diff = slen - len;
128 memmove(sig + diff, sig, len);
129 explicit_bzero(sig, diff);
130 } else if (len > slen) {
131 ret = SSH_ERR_INTERNAL_ERROR;
132 goto out;
133 }
134 /* encode signature */
135 if ((b = sshbuf_new()) == NULL) {
136 ret = SSH_ERR_ALLOC_FAIL;
137 goto out;
138 }
139 if ((ret = sshbuf_put_cstring(b, rsa_hash_alg_ident(hash_alg))) != 0 ||
140 (ret = sshbuf_put_string(b, sig, slen)) != 0)
141 goto out;
142 len = sshbuf_len(b);
143 if (sigp != NULL) {
144 if ((*sigp = malloc(len)) == NULL) {
145 ret = SSH_ERR_ALLOC_FAIL;
146 goto out;
147 }
148 memcpy(*sigp, sshbuf_ptr(b), len);
149 }
150 if (lenp != NULL)
151 *lenp = len;
152 ret = 0;
153 out:
154 explicit_bzero(digest, sizeof(digest));
155 if (sig != NULL) {
156 explicit_bzero(sig, slen);
157 free(sig);
158 }
159 sshbuf_free(b);
160 return ret;
161 }
162
163 int
ssh_rsa_verify(const struct sshkey * key,const u_char * sig,size_t siglen,const u_char * data,size_t datalen)164 ssh_rsa_verify(const struct sshkey *key,
165 const u_char *sig, size_t siglen, const u_char *data, size_t datalen)
166 {
167 char *ktype = NULL;
168 int hash_alg, ret = SSH_ERR_INTERNAL_ERROR;
169 size_t len, diff, modlen, dlen;
170 struct sshbuf *b = NULL;
171 u_char digest[SSH_DIGEST_MAX_LENGTH], *osigblob, *sigblob = NULL;
172
173 if (key == NULL || key->rsa == NULL ||
174 sshkey_type_plain(key->type) != KEY_RSA ||
175 BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE ||
176 sig == NULL || siglen == 0)
177 return SSH_ERR_INVALID_ARGUMENT;
178
179 if ((b = sshbuf_from(sig, siglen)) == NULL)
180 return SSH_ERR_ALLOC_FAIL;
181 if (sshbuf_get_cstring(b, &ktype, NULL) != 0) {
182 ret = SSH_ERR_INVALID_FORMAT;
183 goto out;
184 }
185 if ((hash_alg = rsa_hash_alg_from_ident(ktype)) == -1) {
186 ret = SSH_ERR_KEY_TYPE_MISMATCH;
187 goto out;
188 }
189 if (sshbuf_get_string(b, &sigblob, &len) != 0) {
190 ret = SSH_ERR_INVALID_FORMAT;
191 goto out;
192 }
193 if (sshbuf_len(b) != 0) {
194 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
195 goto out;
196 }
197 /* RSA_verify expects a signature of RSA_size */
198 modlen = RSA_size(key->rsa);
199 if (len > modlen) {
200 ret = SSH_ERR_KEY_BITS_MISMATCH;
201 goto out;
202 } else if (len < modlen) {
203 diff = modlen - len;
204 osigblob = sigblob;
205 if ((sigblob = realloc(sigblob, modlen)) == NULL) {
206 sigblob = osigblob; /* put it back for clear/free */
207 ret = SSH_ERR_ALLOC_FAIL;
208 goto out;
209 }
210 memmove(sigblob + diff, sigblob, len);
211 explicit_bzero(sigblob, diff);
212 len = modlen;
213 }
214 if ((dlen = ssh_digest_bytes(hash_alg)) == 0) {
215 ret = SSH_ERR_INTERNAL_ERROR;
216 goto out;
217 }
218 if ((ret = ssh_digest_memory(hash_alg, data, datalen,
219 digest, sizeof(digest))) != 0)
220 goto out;
221
222 ret = openssh_RSA_verify(hash_alg, digest, dlen, sigblob, len,
223 key->rsa);
224 out:
225 if (sigblob != NULL) {
226 explicit_bzero(sigblob, len);
227 free(sigblob);
228 }
229 free(ktype);
230 sshbuf_free(b);
231 explicit_bzero(digest, sizeof(digest));
232 return ret;
233 }
234
235 /*
236 * See:
237 * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
238 * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
239 */
240
241 /*
242 * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
243 * oiw(14) secsig(3) algorithms(2) 26 }
244 */
245 static const u_char id_sha1[] = {
246 0x30, 0x21, /* type Sequence, length 0x21 (33) */
247 0x30, 0x09, /* type Sequence, length 0x09 */
248 0x06, 0x05, /* type OID, length 0x05 */
249 0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
250 0x05, 0x00, /* NULL */
251 0x04, 0x14 /* Octet string, length 0x14 (20), followed by sha1 hash */
252 };
253
254 /*
255 * See http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html
256 * id-sha256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840)
257 * organization(1) gov(101) csor(3) nistAlgorithm(4) hashAlgs(2)
258 * id-sha256(1) }
259 */
260 static const u_char id_sha256[] = {
261 0x30, 0x31, /* type Sequence, length 0x31 (49) */
262 0x30, 0x0d, /* type Sequence, length 0x0d (13) */
263 0x06, 0x09, /* type OID, length 0x09 */
264 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, /* id-sha256 */
265 0x05, 0x00, /* NULL */
266 0x04, 0x20 /* Octet string, length 0x20 (32), followed by sha256 hash */
267 };
268
269 /*
270 * See http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html
271 * id-sha512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840)
272 * organization(1) gov(101) csor(3) nistAlgorithm(4) hashAlgs(2)
273 * id-sha256(3) }
274 */
275 static const u_char id_sha512[] = {
276 0x30, 0x51, /* type Sequence, length 0x51 (81) */
277 0x30, 0x0d, /* type Sequence, length 0x0d (13) */
278 0x06, 0x09, /* type OID, length 0x09 */
279 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, /* id-sha512 */
280 0x05, 0x00, /* NULL */
281 0x04, 0x40 /* Octet string, length 0x40 (64), followed by sha512 hash */
282 };
283
284 static int
rsa_hash_alg_oid(int hash_alg,const u_char ** oidp,size_t * oidlenp)285 rsa_hash_alg_oid(int hash_alg, const u_char **oidp, size_t *oidlenp)
286 {
287 switch (hash_alg) {
288 case SSH_DIGEST_SHA1:
289 *oidp = id_sha1;
290 *oidlenp = sizeof(id_sha1);
291 break;
292 case SSH_DIGEST_SHA256:
293 *oidp = id_sha256;
294 *oidlenp = sizeof(id_sha256);
295 break;
296 case SSH_DIGEST_SHA512:
297 *oidp = id_sha512;
298 *oidlenp = sizeof(id_sha512);
299 break;
300 default:
301 return SSH_ERR_INVALID_ARGUMENT;
302 }
303 return 0;
304 }
305
306 static int
openssh_RSA_verify(int hash_alg,u_char * hash,size_t hashlen,u_char * sigbuf,size_t siglen,RSA * rsa)307 openssh_RSA_verify(int hash_alg, u_char *hash, size_t hashlen,
308 u_char *sigbuf, size_t siglen, RSA *rsa)
309 {
310 size_t rsasize = 0, oidlen = 0, hlen = 0;
311 int ret, len, oidmatch, hashmatch;
312 const u_char *oid = NULL;
313 u_char *decrypted = NULL;
314
315 if ((ret = rsa_hash_alg_oid(hash_alg, &oid, &oidlen)) != 0)
316 return ret;
317 ret = SSH_ERR_INTERNAL_ERROR;
318 hlen = ssh_digest_bytes(hash_alg);
319 if (hashlen != hlen) {
320 ret = SSH_ERR_INVALID_ARGUMENT;
321 goto done;
322 }
323 rsasize = RSA_size(rsa);
324 if (rsasize <= 0 || rsasize > SSHBUF_MAX_BIGNUM ||
325 siglen == 0 || siglen > rsasize) {
326 ret = SSH_ERR_INVALID_ARGUMENT;
327 goto done;
328 }
329 if ((decrypted = malloc(rsasize)) == NULL) {
330 ret = SSH_ERR_ALLOC_FAIL;
331 goto done;
332 }
333 if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
334 RSA_PKCS1_PADDING)) < 0) {
335 ret = SSH_ERR_LIBCRYPTO_ERROR;
336 goto done;
337 }
338 if (len < 0 || (size_t)len != hlen + oidlen) {
339 ret = SSH_ERR_INVALID_FORMAT;
340 goto done;
341 }
342 oidmatch = timingsafe_bcmp(decrypted, oid, oidlen) == 0;
343 hashmatch = timingsafe_bcmp(decrypted + oidlen, hash, hlen) == 0;
344 if (!oidmatch || !hashmatch) {
345 ret = SSH_ERR_SIGNATURE_INVALID;
346 goto done;
347 }
348 ret = 0;
349 done:
350 if (decrypted) {
351 explicit_bzero(decrypted, rsasize);
352 free(decrypted);
353 }
354 return ret;
355 }
356 #endif /* WITH_OPENSSL */
357