1 /* $OpenBSD: cipher.c,v 1.118 2020/12/21 11:09:32 dtucker Exp $ */
2 /*
3 * Author: Tatu Ylonen <ylo@cs.hut.fi>
4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 * All rights reserved
6 *
7 * As far as I am concerned, the code I have written for this software
8 * can be used freely for any purpose. Any derived versions of this
9 * software must be clearly marked as such, and if the derived work is
10 * incompatible with the protocol description in the RFC file, it must be
11 * called by a name other than "ssh" or "Secure Shell".
12 *
13 *
14 * Copyright (c) 1999 Niels Provos. All rights reserved.
15 * Copyright (c) 1999, 2000 Markus Friedl. All rights reserved.
16 *
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions
19 * are met:
20 * 1. Redistributions of source code must retain the above copyright
21 * notice, this list of conditions and the following disclaimer.
22 * 2. Redistributions in binary form must reproduce the above copyright
23 * notice, this list of conditions and the following disclaimer in the
24 * documentation and/or other materials provided with the distribution.
25 *
26 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
27 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
28 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
29 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
30 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
31 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
32 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
36 */
37
38 #include "includes.h"
39
40 #include <sys/types.h>
41
42 #include <string.h>
43 #include <stdarg.h>
44 #include <stdio.h>
45
46 #include "cipher.h"
47 #include "misc.h"
48 #include "sshbuf.h"
49 #include "ssherr.h"
50 #include "digest.h"
51
52 #include "openbsd-compat/openssl-compat.h"
53
54 #ifndef WITH_OPENSSL
55 #define EVP_CIPHER_CTX void
56 #endif
57
58 struct sshcipher_ctx {
59 int plaintext;
60 int encrypt;
61 EVP_CIPHER_CTX *evp;
62 struct chachapoly_ctx *cp_ctx;
63 struct aesctr_ctx ac_ctx; /* XXX union with evp? */
64 const struct sshcipher *cipher;
65 };
66
67 struct sshcipher {
68 char *name;
69 u_int block_size;
70 u_int key_len;
71 u_int iv_len; /* defaults to block_size */
72 u_int auth_len;
73 u_int flags;
74 #define CFLAG_CBC (1<<0)
75 #define CFLAG_CHACHAPOLY (1<<1)
76 #define CFLAG_AESCTR (1<<2)
77 #define CFLAG_NONE (1<<3)
78 #define CFLAG_INTERNAL CFLAG_NONE /* Don't use "none" for packets */
79 #ifdef WITH_OPENSSL
80 const EVP_CIPHER *(*evptype)(void);
81 #else
82 void *ignored;
83 #endif
84 };
85
86 static const struct sshcipher ciphers[] = {
87 #ifdef WITH_OPENSSL
88 #ifndef OPENSSL_NO_DES
89 { "3des-cbc", 8, 24, 0, 0, CFLAG_CBC, EVP_des_ede3_cbc },
90 #endif
91 { "aes128-cbc", 16, 16, 0, 0, CFLAG_CBC, EVP_aes_128_cbc },
92 { "aes192-cbc", 16, 24, 0, 0, CFLAG_CBC, EVP_aes_192_cbc },
93 { "aes256-cbc", 16, 32, 0, 0, CFLAG_CBC, EVP_aes_256_cbc },
94 { "aes128-ctr", 16, 16, 0, 0, 0, EVP_aes_128_ctr },
95 { "aes192-ctr", 16, 24, 0, 0, 0, EVP_aes_192_ctr },
96 { "aes256-ctr", 16, 32, 0, 0, 0, EVP_aes_256_ctr },
97 # ifdef OPENSSL_HAVE_EVPGCM
98 { "aes128-gcm@openssh.com",
99 16, 16, 12, 16, 0, EVP_aes_128_gcm },
100 { "aes256-gcm@openssh.com",
101 16, 32, 12, 16, 0, EVP_aes_256_gcm },
102 # endif /* OPENSSL_HAVE_EVPGCM */
103 #else
104 { "aes128-ctr", 16, 16, 0, 0, CFLAG_AESCTR, NULL },
105 { "aes192-ctr", 16, 24, 0, 0, CFLAG_AESCTR, NULL },
106 { "aes256-ctr", 16, 32, 0, 0, CFLAG_AESCTR, NULL },
107 #endif
108 { "chacha20-poly1305@openssh.com",
109 8, 64, 0, 16, CFLAG_CHACHAPOLY, NULL },
110 { "none", 8, 0, 0, 0, CFLAG_NONE, NULL },
111
112 { NULL, 0, 0, 0, 0, 0, NULL }
113 };
114
115 /*--*/
116
117 /* Returns a comma-separated list of supported ciphers. */
118 char *
cipher_alg_list(char sep,int auth_only)119 cipher_alg_list(char sep, int auth_only)
120 {
121 char *tmp, *ret = NULL;
122 size_t nlen, rlen = 0;
123 const struct sshcipher *c;
124
125 for (c = ciphers; c->name != NULL; c++) {
126 if ((c->flags & CFLAG_INTERNAL) != 0)
127 continue;
128 if (auth_only && c->auth_len == 0)
129 continue;
130 if (ret != NULL)
131 ret[rlen++] = sep;
132 nlen = strlen(c->name);
133 if ((tmp = realloc(ret, rlen + nlen + 2)) == NULL) {
134 free(ret);
135 return NULL;
136 }
137 ret = tmp;
138 memcpy(ret + rlen, c->name, nlen + 1);
139 rlen += nlen;
140 }
141 return ret;
142 }
143
144 const char *
compression_alg_list(int compression)145 compression_alg_list(int compression)
146 {
147 #ifdef WITH_ZLIB
148 return compression ? "zlib@openssh.com,zlib,none" :
149 "none,zlib@openssh.com,zlib";
150 #else
151 return "none";
152 #endif
153 }
154
155 u_int
cipher_blocksize(const struct sshcipher * c)156 cipher_blocksize(const struct sshcipher *c)
157 {
158 return (c->block_size);
159 }
160
161 u_int
cipher_keylen(const struct sshcipher * c)162 cipher_keylen(const struct sshcipher *c)
163 {
164 return (c->key_len);
165 }
166
167 u_int
cipher_seclen(const struct sshcipher * c)168 cipher_seclen(const struct sshcipher *c)
169 {
170 if (strcmp("3des-cbc", c->name) == 0)
171 return 14;
172 return cipher_keylen(c);
173 }
174
175 u_int
cipher_authlen(const struct sshcipher * c)176 cipher_authlen(const struct sshcipher *c)
177 {
178 return (c->auth_len);
179 }
180
181 u_int
cipher_ivlen(const struct sshcipher * c)182 cipher_ivlen(const struct sshcipher *c)
183 {
184 /*
185 * Default is cipher block size, except for chacha20+poly1305 that
186 * needs no IV. XXX make iv_len == -1 default?
187 */
188 return (c->iv_len != 0 || (c->flags & CFLAG_CHACHAPOLY) != 0) ?
189 c->iv_len : c->block_size;
190 }
191
192 u_int
cipher_is_cbc(const struct sshcipher * c)193 cipher_is_cbc(const struct sshcipher *c)
194 {
195 return (c->flags & CFLAG_CBC) != 0;
196 }
197
198 u_int
cipher_ctx_is_plaintext(struct sshcipher_ctx * cc)199 cipher_ctx_is_plaintext(struct sshcipher_ctx *cc)
200 {
201 return cc->plaintext;
202 }
203
204 const struct sshcipher *
cipher_by_name(const char * name)205 cipher_by_name(const char *name)
206 {
207 const struct sshcipher *c;
208 for (c = ciphers; c->name != NULL; c++)
209 if (strcmp(c->name, name) == 0)
210 return c;
211 return NULL;
212 }
213
214 #define CIPHER_SEP ","
215 int
ciphers_valid(const char * names)216 ciphers_valid(const char *names)
217 {
218 const struct sshcipher *c;
219 char *cipher_list, *cp;
220 char *p;
221
222 if (names == NULL || strcmp(names, "") == 0)
223 return 0;
224 if ((cipher_list = cp = strdup(names)) == NULL)
225 return 0;
226 for ((p = strsep(&cp, CIPHER_SEP)); p && *p != '\0';
227 (p = strsep(&cp, CIPHER_SEP))) {
228 c = cipher_by_name(p);
229 if (c == NULL || (c->flags & CFLAG_INTERNAL) != 0) {
230 free(cipher_list);
231 return 0;
232 }
233 }
234 free(cipher_list);
235 return 1;
236 }
237
238 const char *
cipher_warning_message(const struct sshcipher_ctx * cc)239 cipher_warning_message(const struct sshcipher_ctx *cc)
240 {
241 if (cc == NULL || cc->cipher == NULL)
242 return NULL;
243 /* XXX repurpose for CBC warning */
244 return NULL;
245 }
246
247 int
cipher_init(struct sshcipher_ctx ** ccp,const struct sshcipher * cipher,const u_char * key,u_int keylen,const u_char * iv,u_int ivlen,int do_encrypt)248 cipher_init(struct sshcipher_ctx **ccp, const struct sshcipher *cipher,
249 const u_char *key, u_int keylen, const u_char *iv, u_int ivlen,
250 int do_encrypt)
251 {
252 struct sshcipher_ctx *cc = NULL;
253 int ret = SSH_ERR_INTERNAL_ERROR;
254 #ifdef WITH_OPENSSL
255 const EVP_CIPHER *type;
256 int klen;
257 #endif
258
259 *ccp = NULL;
260 if ((cc = calloc(sizeof(*cc), 1)) == NULL)
261 return SSH_ERR_ALLOC_FAIL;
262
263 cc->plaintext = (cipher->flags & CFLAG_NONE) != 0;
264 cc->encrypt = do_encrypt;
265
266 if (keylen < cipher->key_len ||
267 (iv != NULL && ivlen < cipher_ivlen(cipher))) {
268 ret = SSH_ERR_INVALID_ARGUMENT;
269 goto out;
270 }
271
272 cc->cipher = cipher;
273 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
274 cc->cp_ctx = chachapoly_new(key, keylen);
275 ret = cc->cp_ctx != NULL ? 0 : SSH_ERR_INVALID_ARGUMENT;
276 goto out;
277 }
278 if ((cc->cipher->flags & CFLAG_NONE) != 0) {
279 ret = 0;
280 goto out;
281 }
282 #ifndef WITH_OPENSSL
283 if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
284 aesctr_keysetup(&cc->ac_ctx, key, 8 * keylen, 8 * ivlen);
285 aesctr_ivsetup(&cc->ac_ctx, iv);
286 ret = 0;
287 goto out;
288 }
289 ret = SSH_ERR_INVALID_ARGUMENT;
290 goto out;
291 #else /* WITH_OPENSSL */
292 type = (*cipher->evptype)();
293 if ((cc->evp = EVP_CIPHER_CTX_new()) == NULL) {
294 ret = SSH_ERR_ALLOC_FAIL;
295 goto out;
296 }
297 if (EVP_CipherInit(cc->evp, type, NULL, (u_char *)iv,
298 (do_encrypt == CIPHER_ENCRYPT)) == 0) {
299 ret = SSH_ERR_LIBCRYPTO_ERROR;
300 goto out;
301 }
302 if (cipher_authlen(cipher) &&
303 !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_IV_FIXED,
304 -1, (u_char *)iv)) {
305 ret = SSH_ERR_LIBCRYPTO_ERROR;
306 goto out;
307 }
308 klen = EVP_CIPHER_CTX_key_length(cc->evp);
309 if (klen > 0 && keylen != (u_int)klen) {
310 if (EVP_CIPHER_CTX_set_key_length(cc->evp, keylen) == 0) {
311 ret = SSH_ERR_LIBCRYPTO_ERROR;
312 goto out;
313 }
314 }
315 if (EVP_CipherInit(cc->evp, NULL, (u_char *)key, NULL, -1) == 0) {
316 ret = SSH_ERR_LIBCRYPTO_ERROR;
317 goto out;
318 }
319 ret = 0;
320 #endif /* WITH_OPENSSL */
321 out:
322 if (ret == 0) {
323 /* success */
324 *ccp = cc;
325 } else {
326 if (cc != NULL) {
327 #ifdef WITH_OPENSSL
328 EVP_CIPHER_CTX_free(cc->evp);
329 #endif /* WITH_OPENSSL */
330 freezero(cc, sizeof(*cc));
331 }
332 }
333 return ret;
334 }
335
336 /*
337 * cipher_crypt() operates as following:
338 * Copy 'aadlen' bytes (without en/decryption) from 'src' to 'dest'.
339 * These bytes are treated as additional authenticated data for
340 * authenticated encryption modes.
341 * En/Decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'.
342 * Use 'authlen' bytes at offset 'len'+'aadlen' as the authentication tag.
343 * This tag is written on encryption and verified on decryption.
344 * Both 'aadlen' and 'authlen' can be set to 0.
345 */
346 int
cipher_crypt(struct sshcipher_ctx * cc,u_int seqnr,u_char * dest,const u_char * src,u_int len,u_int aadlen,u_int authlen)347 cipher_crypt(struct sshcipher_ctx *cc, u_int seqnr, u_char *dest,
348 const u_char *src, u_int len, u_int aadlen, u_int authlen)
349 {
350 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
351 return chachapoly_crypt(cc->cp_ctx, seqnr, dest, src,
352 len, aadlen, authlen, cc->encrypt);
353 }
354 if ((cc->cipher->flags & CFLAG_NONE) != 0) {
355 memcpy(dest, src, aadlen + len);
356 return 0;
357 }
358 #ifndef WITH_OPENSSL
359 if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
360 if (aadlen)
361 memcpy(dest, src, aadlen);
362 aesctr_encrypt_bytes(&cc->ac_ctx, src + aadlen,
363 dest + aadlen, len);
364 return 0;
365 }
366 return SSH_ERR_INVALID_ARGUMENT;
367 #else
368 if (authlen) {
369 u_char lastiv[1];
370
371 if (authlen != cipher_authlen(cc->cipher))
372 return SSH_ERR_INVALID_ARGUMENT;
373 /* increment IV */
374 if (!EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN,
375 1, lastiv))
376 return SSH_ERR_LIBCRYPTO_ERROR;
377 /* set tag on decyption */
378 if (!cc->encrypt &&
379 !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_TAG,
380 authlen, (u_char *)src + aadlen + len))
381 return SSH_ERR_LIBCRYPTO_ERROR;
382 }
383 if (aadlen) {
384 if (authlen &&
385 EVP_Cipher(cc->evp, NULL, (u_char *)src, aadlen) < 0)
386 return SSH_ERR_LIBCRYPTO_ERROR;
387 memcpy(dest, src, aadlen);
388 }
389 if (len % cc->cipher->block_size)
390 return SSH_ERR_INVALID_ARGUMENT;
391 if (EVP_Cipher(cc->evp, dest + aadlen, (u_char *)src + aadlen,
392 len) < 0)
393 return SSH_ERR_LIBCRYPTO_ERROR;
394 if (authlen) {
395 /* compute tag (on encrypt) or verify tag (on decrypt) */
396 if (EVP_Cipher(cc->evp, NULL, NULL, 0) < 0)
397 return cc->encrypt ?
398 SSH_ERR_LIBCRYPTO_ERROR : SSH_ERR_MAC_INVALID;
399 if (cc->encrypt &&
400 !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_GET_TAG,
401 authlen, dest + aadlen + len))
402 return SSH_ERR_LIBCRYPTO_ERROR;
403 }
404 return 0;
405 #endif
406 }
407
408 /* Extract the packet length, including any decryption necessary beforehand */
409 int
cipher_get_length(struct sshcipher_ctx * cc,u_int * plenp,u_int seqnr,const u_char * cp,u_int len)410 cipher_get_length(struct sshcipher_ctx *cc, u_int *plenp, u_int seqnr,
411 const u_char *cp, u_int len)
412 {
413 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
414 return chachapoly_get_length(cc->cp_ctx, plenp, seqnr,
415 cp, len);
416 if (len < 4)
417 return SSH_ERR_MESSAGE_INCOMPLETE;
418 *plenp = PEEK_U32(cp);
419 return 0;
420 }
421
422 void
cipher_free(struct sshcipher_ctx * cc)423 cipher_free(struct sshcipher_ctx *cc)
424 {
425 if (cc == NULL)
426 return;
427 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
428 chachapoly_free(cc->cp_ctx);
429 cc->cp_ctx = NULL;
430 } else if ((cc->cipher->flags & CFLAG_AESCTR) != 0)
431 explicit_bzero(&cc->ac_ctx, sizeof(cc->ac_ctx));
432 #ifdef WITH_OPENSSL
433 EVP_CIPHER_CTX_free(cc->evp);
434 cc->evp = NULL;
435 #endif
436 freezero(cc, sizeof(*cc));
437 }
438
439 /*
440 * Exports an IV from the sshcipher_ctx required to export the key
441 * state back from the unprivileged child to the privileged parent
442 * process.
443 */
444 int
cipher_get_keyiv_len(const struct sshcipher_ctx * cc)445 cipher_get_keyiv_len(const struct sshcipher_ctx *cc)
446 {
447 const struct sshcipher *c = cc->cipher;
448
449 if ((c->flags & CFLAG_CHACHAPOLY) != 0)
450 return 0;
451 else if ((c->flags & CFLAG_AESCTR) != 0)
452 return sizeof(cc->ac_ctx.ctr);
453 #ifdef WITH_OPENSSL
454 return EVP_CIPHER_CTX_iv_length(cc->evp);
455 #else
456 return 0;
457 #endif
458 }
459
460 int
cipher_get_keyiv(struct sshcipher_ctx * cc,u_char * iv,size_t len)461 cipher_get_keyiv(struct sshcipher_ctx *cc, u_char *iv, size_t len)
462 {
463 #ifdef WITH_OPENSSL
464 const struct sshcipher *c = cc->cipher;
465 int evplen;
466 #endif
467
468 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
469 if (len != 0)
470 return SSH_ERR_INVALID_ARGUMENT;
471 return 0;
472 }
473 if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
474 if (len != sizeof(cc->ac_ctx.ctr))
475 return SSH_ERR_INVALID_ARGUMENT;
476 memcpy(iv, cc->ac_ctx.ctr, len);
477 return 0;
478 }
479 if ((cc->cipher->flags & CFLAG_NONE) != 0)
480 return 0;
481
482 #ifdef WITH_OPENSSL
483 evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
484 if (evplen == 0)
485 return 0;
486 else if (evplen < 0)
487 return SSH_ERR_LIBCRYPTO_ERROR;
488 if ((size_t)evplen != len)
489 return SSH_ERR_INVALID_ARGUMENT;
490 #ifndef OPENSSL_HAVE_EVPCTR
491 if (c->evptype == evp_aes_128_ctr)
492 ssh_aes_ctr_iv(cc->evp, 0, iv, len);
493 else
494 #endif
495 if (cipher_authlen(c)) {
496 if (!EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN,
497 len, iv))
498 return SSH_ERR_LIBCRYPTO_ERROR;
499 } else if (!EVP_CIPHER_CTX_get_iv(cc->evp, iv, len))
500 return SSH_ERR_LIBCRYPTO_ERROR;
501 #endif
502 return 0;
503 }
504
505 int
cipher_set_keyiv(struct sshcipher_ctx * cc,const u_char * iv,size_t len)506 cipher_set_keyiv(struct sshcipher_ctx *cc, const u_char *iv, size_t len)
507 {
508 #ifdef WITH_OPENSSL
509 const struct sshcipher *c = cc->cipher;
510 int evplen = 0;
511 #endif
512
513 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
514 return 0;
515 if ((cc->cipher->flags & CFLAG_NONE) != 0)
516 return 0;
517
518 #ifdef WITH_OPENSSL
519 evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
520 if (evplen <= 0)
521 return SSH_ERR_LIBCRYPTO_ERROR;
522 if ((size_t)evplen != len)
523 return SSH_ERR_INVALID_ARGUMENT;
524 #ifndef OPENSSL_HAVE_EVPCTR
525 /* XXX iv arg is const, but ssh_aes_ctr_iv isn't */
526 if (c->evptype == evp_aes_128_ctr)
527 ssh_aes_ctr_iv(cc->evp, 1, (u_char *)iv, evplen);
528 else
529 #endif
530 if (cipher_authlen(c)) {
531 /* XXX iv arg is const, but EVP_CIPHER_CTX_ctrl isn't */
532 if (!EVP_CIPHER_CTX_ctrl(cc->evp,
533 EVP_CTRL_GCM_SET_IV_FIXED, -1, (void *)iv))
534 return SSH_ERR_LIBCRYPTO_ERROR;
535 } else if (!EVP_CIPHER_CTX_set_iv(cc->evp, iv, evplen))
536 return SSH_ERR_LIBCRYPTO_ERROR;
537 #endif
538 return 0;
539 }
540