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