1 /* $OpenBSD: ssh-rsa.c,v 1.67 2018/07/03 11:39:54 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 #include "log.h"
37
38 #include "openbsd-compat/openssl-compat.h"
39
40 static int openssh_RSA_verify(int, u_char *, size_t, u_char *, size_t, RSA *);
41
42 static const char *
rsa_hash_alg_ident(int hash_alg)43 rsa_hash_alg_ident(int hash_alg)
44 {
45 switch (hash_alg) {
46 case SSH_DIGEST_SHA1:
47 return "ssh-rsa";
48 case SSH_DIGEST_SHA256:
49 return "rsa-sha2-256";
50 case SSH_DIGEST_SHA512:
51 return "rsa-sha2-512";
52 }
53 return NULL;
54 }
55
56 /*
57 * Returns the hash algorithm ID for a given algorithm identifier as used
58 * inside the signature blob,
59 */
60 static int
rsa_hash_id_from_ident(const char * ident)61 rsa_hash_id_from_ident(const char *ident)
62 {
63 if (strcmp(ident, "ssh-rsa") == 0)
64 return SSH_DIGEST_SHA1;
65 if (strcmp(ident, "rsa-sha2-256") == 0)
66 return SSH_DIGEST_SHA256;
67 if (strcmp(ident, "rsa-sha2-512") == 0)
68 return SSH_DIGEST_SHA512;
69 return -1;
70 }
71
72 /*
73 * Return the hash algorithm ID for the specified key name. This includes
74 * all the cases of rsa_hash_id_from_ident() but also the certificate key
75 * types.
76 */
77 static int
rsa_hash_id_from_keyname(const char * alg)78 rsa_hash_id_from_keyname(const char *alg)
79 {
80 int r;
81
82 if ((r = rsa_hash_id_from_ident(alg)) != -1)
83 return r;
84 if (strcmp(alg, "ssh-rsa-cert-v01@openssh.com") == 0)
85 return SSH_DIGEST_SHA1;
86 if (strcmp(alg, "rsa-sha2-256-cert-v01@openssh.com") == 0)
87 return SSH_DIGEST_SHA256;
88 if (strcmp(alg, "rsa-sha2-512-cert-v01@openssh.com") == 0)
89 return SSH_DIGEST_SHA512;
90 return -1;
91 }
92
93 static int
rsa_hash_alg_nid(int type)94 rsa_hash_alg_nid(int type)
95 {
96 switch (type) {
97 case SSH_DIGEST_SHA1:
98 return NID_sha1;
99 case SSH_DIGEST_SHA256:
100 return NID_sha256;
101 case SSH_DIGEST_SHA512:
102 return NID_sha512;
103 default:
104 return -1;
105 }
106 }
107
108 int
ssh_rsa_complete_crt_parameters(struct sshkey * key,const BIGNUM * iqmp)109 ssh_rsa_complete_crt_parameters(struct sshkey *key, const BIGNUM *iqmp)
110 {
111 const BIGNUM *rsa_p, *rsa_q, *rsa_d;
112 BIGNUM *aux = NULL, *d_consttime = NULL;
113 BIGNUM *rsa_dmq1 = NULL, *rsa_dmp1 = NULL, *rsa_iqmp = NULL;
114 BN_CTX *ctx = NULL;
115 int r;
116
117 if (key == NULL || key->rsa == NULL ||
118 sshkey_type_plain(key->type) != KEY_RSA)
119 return SSH_ERR_INVALID_ARGUMENT;
120
121 RSA_get0_key(key->rsa, NULL, NULL, &rsa_d);
122 RSA_get0_factors(key->rsa, &rsa_p, &rsa_q);
123
124 if ((ctx = BN_CTX_new()) == NULL)
125 return SSH_ERR_ALLOC_FAIL;
126 if ((aux = BN_new()) == NULL ||
127 (rsa_dmq1 = BN_new()) == NULL ||
128 (rsa_dmp1 = BN_new()) == NULL)
129 return SSH_ERR_ALLOC_FAIL;
130 if ((d_consttime = BN_dup(rsa_d)) == NULL ||
131 (rsa_iqmp = BN_dup(iqmp)) == NULL) {
132 r = SSH_ERR_ALLOC_FAIL;
133 goto out;
134 }
135 #if !defined(OPENSSL_IS_BORINGSSL)
136 BN_set_flags(aux, BN_FLG_CONSTTIME);
137 BN_set_flags(d_consttime, BN_FLG_CONSTTIME);
138 #endif
139
140 if ((BN_sub(aux, rsa_q, BN_value_one()) == 0) ||
141 (BN_mod(rsa_dmq1, d_consttime, aux, ctx) == 0) ||
142 (BN_sub(aux, rsa_p, BN_value_one()) == 0) ||
143 (BN_mod(rsa_dmp1, d_consttime, aux, ctx) == 0)) {
144 r = SSH_ERR_LIBCRYPTO_ERROR;
145 goto out;
146 }
147 if (!RSA_set0_crt_params(key->rsa, rsa_dmp1, rsa_dmq1, rsa_iqmp)) {
148 r = SSH_ERR_LIBCRYPTO_ERROR;
149 goto out;
150 }
151 rsa_dmp1 = rsa_dmq1 = rsa_iqmp = NULL; /* transferred */
152 /* success */
153 r = 0;
154 out:
155 BN_clear_free(aux);
156 BN_clear_free(d_consttime);
157 BN_clear_free(rsa_dmp1);
158 BN_clear_free(rsa_dmq1);
159 BN_clear_free(rsa_iqmp);
160 BN_CTX_free(ctx);
161 return r;
162 }
163
164 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
165 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)166 ssh_rsa_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
167 const u_char *data, size_t datalen, const char *alg_ident)
168 {
169 const BIGNUM *rsa_n;
170 u_char digest[SSH_DIGEST_MAX_LENGTH], *sig = NULL;
171 size_t slen = 0;
172 u_int dlen, len;
173 int nid, hash_alg, ret = SSH_ERR_INTERNAL_ERROR;
174 struct sshbuf *b = NULL;
175
176 if (lenp != NULL)
177 *lenp = 0;
178 if (sigp != NULL)
179 *sigp = NULL;
180
181 if (alg_ident == NULL || strlen(alg_ident) == 0)
182 hash_alg = SSH_DIGEST_SHA1;
183 else
184 hash_alg = rsa_hash_id_from_keyname(alg_ident);
185 if (key == NULL || key->rsa == NULL || hash_alg == -1 ||
186 sshkey_type_plain(key->type) != KEY_RSA)
187 return SSH_ERR_INVALID_ARGUMENT;
188 RSA_get0_key(key->rsa, &rsa_n, NULL, NULL);
189 if (BN_num_bits(rsa_n) < SSH_RSA_MINIMUM_MODULUS_SIZE)
190 return SSH_ERR_KEY_LENGTH;
191 slen = RSA_size(key->rsa);
192 if (slen <= 0 || slen > SSHBUF_MAX_BIGNUM)
193 return SSH_ERR_INVALID_ARGUMENT;
194
195 /* hash the data */
196 nid = rsa_hash_alg_nid(hash_alg);
197 if ((dlen = ssh_digest_bytes(hash_alg)) == 0)
198 return SSH_ERR_INTERNAL_ERROR;
199 if ((ret = ssh_digest_memory(hash_alg, data, datalen,
200 digest, sizeof(digest))) != 0)
201 goto out;
202
203 if ((sig = malloc(slen)) == NULL) {
204 ret = SSH_ERR_ALLOC_FAIL;
205 goto out;
206 }
207
208 if (RSA_sign(nid, digest, dlen, sig, &len, key->rsa) != 1) {
209 ret = SSH_ERR_LIBCRYPTO_ERROR;
210 goto out;
211 }
212 if (len < slen) {
213 size_t diff = slen - len;
214 memmove(sig + diff, sig, len);
215 explicit_bzero(sig, diff);
216 } else if (len > slen) {
217 ret = SSH_ERR_INTERNAL_ERROR;
218 goto out;
219 }
220 /* encode signature */
221 if ((b = sshbuf_new()) == NULL) {
222 ret = SSH_ERR_ALLOC_FAIL;
223 goto out;
224 }
225 if ((ret = sshbuf_put_cstring(b, rsa_hash_alg_ident(hash_alg))) != 0 ||
226 (ret = sshbuf_put_string(b, sig, slen)) != 0)
227 goto out;
228 len = sshbuf_len(b);
229 if (sigp != NULL) {
230 if ((*sigp = malloc(len)) == NULL) {
231 ret = SSH_ERR_ALLOC_FAIL;
232 goto out;
233 }
234 memcpy(*sigp, sshbuf_ptr(b), len);
235 }
236 if (lenp != NULL)
237 *lenp = len;
238 ret = 0;
239 out:
240 explicit_bzero(digest, sizeof(digest));
241 freezero(sig, slen);
242 sshbuf_free(b);
243 return ret;
244 }
245
246 int
ssh_rsa_verify(const struct sshkey * key,const u_char * sig,size_t siglen,const u_char * data,size_t datalen,const char * alg)247 ssh_rsa_verify(const struct sshkey *key,
248 const u_char *sig, size_t siglen, const u_char *data, size_t datalen,
249 const char *alg)
250 {
251 const BIGNUM *rsa_n;
252 char *sigtype = NULL;
253 int hash_alg, want_alg, ret = SSH_ERR_INTERNAL_ERROR;
254 size_t len = 0, diff, modlen, dlen;
255 struct sshbuf *b = NULL;
256 u_char digest[SSH_DIGEST_MAX_LENGTH], *osigblob, *sigblob = NULL;
257
258 if (key == NULL || key->rsa == NULL ||
259 sshkey_type_plain(key->type) != KEY_RSA ||
260 sig == NULL || siglen == 0)
261 return SSH_ERR_INVALID_ARGUMENT;
262 RSA_get0_key(key->rsa, &rsa_n, NULL, NULL);
263 if (BN_num_bits(rsa_n) < SSH_RSA_MINIMUM_MODULUS_SIZE)
264 return SSH_ERR_KEY_LENGTH;
265
266 if ((b = sshbuf_from(sig, siglen)) == NULL)
267 return SSH_ERR_ALLOC_FAIL;
268 if (sshbuf_get_cstring(b, &sigtype, NULL) != 0) {
269 ret = SSH_ERR_INVALID_FORMAT;
270 goto out;
271 }
272 if ((hash_alg = rsa_hash_id_from_ident(sigtype)) == -1) {
273 ret = SSH_ERR_KEY_TYPE_MISMATCH;
274 goto out;
275 }
276 /*
277 * Allow ssh-rsa-cert-v01 certs to generate SHA2 signatures for
278 * legacy reasons, but otherwise the signature type should match.
279 */
280 if (alg != NULL && strcmp(alg, "ssh-rsa-cert-v01@openssh.com") != 0) {
281 if ((want_alg = rsa_hash_id_from_keyname(alg)) == -1) {
282 ret = SSH_ERR_INVALID_ARGUMENT;
283 goto out;
284 }
285 if (hash_alg != want_alg) {
286 ret = SSH_ERR_SIGNATURE_INVALID;
287 goto out;
288 }
289 }
290 if (sshbuf_get_string(b, &sigblob, &len) != 0) {
291 ret = SSH_ERR_INVALID_FORMAT;
292 goto out;
293 }
294 if (sshbuf_len(b) != 0) {
295 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
296 goto out;
297 }
298 /* RSA_verify expects a signature of RSA_size */
299 modlen = RSA_size(key->rsa);
300 if (len > modlen) {
301 ret = SSH_ERR_KEY_BITS_MISMATCH;
302 goto out;
303 } else if (len < modlen) {
304 diff = modlen - len;
305 osigblob = sigblob;
306 if ((sigblob = realloc(sigblob, modlen)) == NULL) {
307 sigblob = osigblob; /* put it back for clear/free */
308 ret = SSH_ERR_ALLOC_FAIL;
309 goto out;
310 }
311 memmove(sigblob + diff, sigblob, len);
312 explicit_bzero(sigblob, diff);
313 len = modlen;
314 }
315 if ((dlen = ssh_digest_bytes(hash_alg)) == 0) {
316 ret = SSH_ERR_INTERNAL_ERROR;
317 goto out;
318 }
319 if ((ret = ssh_digest_memory(hash_alg, data, datalen,
320 digest, sizeof(digest))) != 0)
321 goto out;
322
323 ret = openssh_RSA_verify(hash_alg, digest, dlen, sigblob, len,
324 key->rsa);
325 out:
326 freezero(sigblob, len);
327 free(sigtype);
328 sshbuf_free(b);
329 explicit_bzero(digest, sizeof(digest));
330 return ret;
331 }
332
333 /*
334 * See:
335 * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
336 * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
337 */
338
339 /*
340 * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
341 * oiw(14) secsig(3) algorithms(2) 26 }
342 */
343 static const u_char id_sha1[] = {
344 0x30, 0x21, /* type Sequence, length 0x21 (33) */
345 0x30, 0x09, /* type Sequence, length 0x09 */
346 0x06, 0x05, /* type OID, length 0x05 */
347 0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
348 0x05, 0x00, /* NULL */
349 0x04, 0x14 /* Octet string, length 0x14 (20), followed by sha1 hash */
350 };
351
352 /*
353 * See http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html
354 * id-sha256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840)
355 * organization(1) gov(101) csor(3) nistAlgorithm(4) hashAlgs(2)
356 * id-sha256(1) }
357 */
358 static const u_char id_sha256[] = {
359 0x30, 0x31, /* type Sequence, length 0x31 (49) */
360 0x30, 0x0d, /* type Sequence, length 0x0d (13) */
361 0x06, 0x09, /* type OID, length 0x09 */
362 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, /* id-sha256 */
363 0x05, 0x00, /* NULL */
364 0x04, 0x20 /* Octet string, length 0x20 (32), followed by sha256 hash */
365 };
366
367 /*
368 * See http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html
369 * id-sha512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840)
370 * organization(1) gov(101) csor(3) nistAlgorithm(4) hashAlgs(2)
371 * id-sha256(3) }
372 */
373 static const u_char id_sha512[] = {
374 0x30, 0x51, /* type Sequence, length 0x51 (81) */
375 0x30, 0x0d, /* type Sequence, length 0x0d (13) */
376 0x06, 0x09, /* type OID, length 0x09 */
377 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, /* id-sha512 */
378 0x05, 0x00, /* NULL */
379 0x04, 0x40 /* Octet string, length 0x40 (64), followed by sha512 hash */
380 };
381
382 static int
rsa_hash_alg_oid(int hash_alg,const u_char ** oidp,size_t * oidlenp)383 rsa_hash_alg_oid(int hash_alg, const u_char **oidp, size_t *oidlenp)
384 {
385 switch (hash_alg) {
386 case SSH_DIGEST_SHA1:
387 *oidp = id_sha1;
388 *oidlenp = sizeof(id_sha1);
389 break;
390 case SSH_DIGEST_SHA256:
391 *oidp = id_sha256;
392 *oidlenp = sizeof(id_sha256);
393 break;
394 case SSH_DIGEST_SHA512:
395 *oidp = id_sha512;
396 *oidlenp = sizeof(id_sha512);
397 break;
398 default:
399 return SSH_ERR_INVALID_ARGUMENT;
400 }
401 return 0;
402 }
403
404 static int
openssh_RSA_verify(int hash_alg,u_char * hash,size_t hashlen,u_char * sigbuf,size_t siglen,RSA * rsa)405 openssh_RSA_verify(int hash_alg, u_char *hash, size_t hashlen,
406 u_char *sigbuf, size_t siglen, RSA *rsa)
407 {
408 size_t rsasize = 0, oidlen = 0, hlen = 0;
409 int ret, len, oidmatch, hashmatch;
410 const u_char *oid = NULL;
411 u_char *decrypted = NULL;
412
413 if ((ret = rsa_hash_alg_oid(hash_alg, &oid, &oidlen)) != 0)
414 return ret;
415 ret = SSH_ERR_INTERNAL_ERROR;
416 hlen = ssh_digest_bytes(hash_alg);
417 if (hashlen != hlen) {
418 ret = SSH_ERR_INVALID_ARGUMENT;
419 goto done;
420 }
421 rsasize = RSA_size(rsa);
422 if (rsasize <= 0 || rsasize > SSHBUF_MAX_BIGNUM ||
423 siglen == 0 || siglen > rsasize) {
424 ret = SSH_ERR_INVALID_ARGUMENT;
425 goto done;
426 }
427 if ((decrypted = malloc(rsasize)) == NULL) {
428 ret = SSH_ERR_ALLOC_FAIL;
429 goto done;
430 }
431 if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
432 RSA_PKCS1_PADDING)) < 0) {
433 ret = SSH_ERR_LIBCRYPTO_ERROR;
434 goto done;
435 }
436 if (len < 0 || (size_t)len != hlen + oidlen) {
437 ret = SSH_ERR_INVALID_FORMAT;
438 goto done;
439 }
440 oidmatch = timingsafe_bcmp(decrypted, oid, oidlen) == 0;
441 hashmatch = timingsafe_bcmp(decrypted + oidlen, hash, hlen) == 0;
442 if (!oidmatch || !hashmatch) {
443 ret = SSH_ERR_SIGNATURE_INVALID;
444 goto done;
445 }
446 ret = 0;
447 done:
448 freezero(decrypted, rsasize);
449 return ret;
450 }
451 #endif /* WITH_OPENSSL */
452