1 /* $NetBSD: cipher.c,v 1.24 2025/04/09 15:49:32 christos Exp $ */
2 /* $OpenBSD: cipher.c,v 1.124 2025/03/14 09:49:49 tb Exp $ */
3
4 /*
5 * Author: Tatu Ylonen <ylo@cs.hut.fi>
6 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
7 * All rights reserved
8 *
9 * As far as I am concerned, the code I have written for this software
10 * can be used freely for any purpose. Any derived versions of this
11 * software must be clearly marked as such, and if the derived work is
12 * incompatible with the protocol description in the RFC file, it must be
13 * called by a name other than "ssh" or "Secure Shell".
14 *
15 *
16 * Copyright (c) 1999 Niels Provos. All rights reserved.
17 * Copyright (c) 1999, 2000 Markus Friedl. All rights reserved.
18 *
19 * Redistribution and use in source and binary forms, with or without
20 * modification, are permitted provided that the following conditions
21 * are met:
22 * 1. Redistributions of source code must retain the above copyright
23 * notice, this list of conditions and the following disclaimer.
24 * 2. Redistributions in binary form must reproduce the above copyright
25 * notice, this list of conditions and the following disclaimer in the
26 * documentation and/or other materials provided with the distribution.
27 *
28 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
29 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
30 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
31 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
32 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
33 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
34 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
35 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
36 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
37 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
38 */
39
40 #include "includes.h"
41 __RCSID("$NetBSD: cipher.c,v 1.24 2025/04/09 15:49:32 christos Exp $");
42 #include <sys/types.h>
43
44 #include <string.h>
45 #include <stdarg.h>
46 #include <stdio.h>
47
48 #include "cipher.h"
49 #include "misc.h"
50 #include "sshbuf.h"
51 #include "ssherr.h"
52 #include "digest.h"
53
54 #ifndef WITH_OPENSSL
55 #define EVP_CIPHER_CTX void
56 #endif
57
58 // XXX: from libressl
59 #define HAVE_EVP_CIPHER_CTX_IV
60
61 static int
EVP_CIPHER_CTX_get_iv(const EVP_CIPHER_CTX * ctx,unsigned char * iv,size_t len)62 EVP_CIPHER_CTX_get_iv(const EVP_CIPHER_CTX *ctx, unsigned char *iv, size_t len)
63 {
64 if (ctx == NULL)
65 return 0;
66 if (EVP_CIPHER_CTX_iv_length(ctx) < 0)
67 return 0;
68 if (len != (size_t)EVP_CIPHER_CTX_iv_length(ctx))
69 return 0;
70 if (len > EVP_MAX_IV_LENGTH)
71 return 0; /* sanity check; shouldn't happen */
72 /*
73 * Skip the memcpy entirely when the requested IV length is zero,
74 * since the iv pointer may be NULL or invalid.
75 */
76 if (len != 0) {
77 if (iv == NULL)
78 return 0;
79 # ifdef HAVE_EVP_CIPHER_CTX_IV
80 memcpy(iv, EVP_CIPHER_CTX_iv(ctx), len);
81 # else
82 memcpy(iv, ctx->iv, len);
83 # endif /* HAVE_EVP_CIPHER_CTX_IV */
84 }
85 return 1;
86 }
87 // XXX: end
88
89 struct sshcipher_ctx {
90 int plaintext;
91 int encrypt;
92 EVP_CIPHER_CTX *evp;
93 struct chachapoly_ctx *cp_ctx;
94 struct aesctr_ctx ac_ctx; /* XXX union with evp? */
95 const struct sshcipher *cipher;
96 };
97
98 struct sshcipher {
99 const char *name;
100 u_int block_size;
101 u_int key_len;
102 u_int iv_len; /* defaults to block_size */
103 u_int auth_len;
104 u_int flags;
105 #define CFLAG_CBC (1<<0)
106 #define CFLAG_CHACHAPOLY (1<<1)
107 #define CFLAG_AESCTR (1<<2)
108 #define CFLAG_NONE (1<<3)
109 #define CFLAG_INTERNAL CFLAG_NONE /* Don't use "none" for packets */
110 #ifdef WITH_OPENSSL
111 const EVP_CIPHER *(*evptype)(void);
112 #else
113 void *ignored;
114 #endif
115 };
116
117 static const struct sshcipher ciphers[] = {
118 #ifdef WITH_OPENSSL
119 { "3des-cbc", 8, 24, 0, 0, CFLAG_CBC, EVP_des_ede3_cbc },
120 { "aes128-cbc", 16, 16, 0, 0, CFLAG_CBC, EVP_aes_128_cbc },
121 { "aes192-cbc", 16, 24, 0, 0, CFLAG_CBC, EVP_aes_192_cbc },
122 { "aes256-cbc", 16, 32, 0, 0, CFLAG_CBC, EVP_aes_256_cbc },
123 { "aes128-ctr", 16, 16, 0, 0, 0, EVP_aes_128_ctr },
124 { "aes192-ctr", 16, 24, 0, 0, 0, EVP_aes_192_ctr },
125 { "aes256-ctr", 16, 32, 0, 0, 0, EVP_aes_256_ctr },
126 { "aes128-gcm@openssh.com",
127 16, 16, 12, 16, 0, EVP_aes_128_gcm },
128 { "aes256-gcm@openssh.com",
129 16, 32, 12, 16, 0, EVP_aes_256_gcm },
130 #else
131 { "aes128-ctr", 16, 16, 0, 0, CFLAG_AESCTR, NULL },
132 { "aes192-ctr", 16, 24, 0, 0, CFLAG_AESCTR, NULL },
133 { "aes256-ctr", 16, 32, 0, 0, CFLAG_AESCTR, NULL },
134 #endif
135 { "chacha20-poly1305@openssh.com",
136 8, 64, 0, 16, CFLAG_CHACHAPOLY, NULL },
137 { "none", 8, 0, 0, 0, CFLAG_NONE, NULL },
138
139 { NULL, 0, 0, 0, 0, 0, NULL }
140 };
141
142 /*--*/
143
144 /* Returns a comma-separated list of supported ciphers. */
145 char *
cipher_alg_list(char sep,int auth_only)146 cipher_alg_list(char sep, int auth_only)
147 {
148 char *tmp, *ret = NULL;
149 size_t nlen, rlen = 0;
150 const struct sshcipher *c;
151
152 for (c = ciphers; c->name != NULL; c++) {
153 if ((c->flags & CFLAG_INTERNAL) != 0)
154 continue;
155 if (auth_only && c->auth_len == 0)
156 continue;
157 if (ret != NULL)
158 ret[rlen++] = sep;
159 nlen = strlen(c->name);
160 if ((tmp = realloc(ret, rlen + nlen + 2)) == NULL) {
161 free(ret);
162 return NULL;
163 }
164 ret = tmp;
165 memcpy(ret + rlen, c->name, nlen + 1);
166 rlen += nlen;
167 }
168 return ret;
169 }
170
171 const char *
compression_alg_list(int compression)172 compression_alg_list(int compression)
173 {
174 #ifdef WITH_ZLIB
175 return compression ? "zlib@openssh.com,none" :
176 "none,zlib@openssh.com";
177 #else
178 return "none";
179 #endif
180 }
181
182 u_int
cipher_blocksize(const struct sshcipher * c)183 cipher_blocksize(const struct sshcipher *c)
184 {
185 return (c->block_size);
186 }
187
188 u_int
cipher_keylen(const struct sshcipher * c)189 cipher_keylen(const struct sshcipher *c)
190 {
191 return (c->key_len);
192 }
193
194 u_int
cipher_seclen(const struct sshcipher * c)195 cipher_seclen(const struct sshcipher *c)
196 {
197 if (strcmp("3des-cbc", c->name) == 0)
198 return 14;
199 return cipher_keylen(c);
200 }
201
202 u_int
cipher_authlen(const struct sshcipher * c)203 cipher_authlen(const struct sshcipher *c)
204 {
205 return (c->auth_len);
206 }
207
208 u_int
cipher_ivlen(const struct sshcipher * c)209 cipher_ivlen(const struct sshcipher *c)
210 {
211 /*
212 * Default is cipher block size, except for chacha20+poly1305 that
213 * needs no IV. XXX make iv_len == -1 default?
214 */
215 return (c->iv_len != 0 || (c->flags & CFLAG_CHACHAPOLY) != 0) ?
216 c->iv_len : c->block_size;
217 }
218
219 u_int
cipher_is_cbc(const struct sshcipher * c)220 cipher_is_cbc(const struct sshcipher *c)
221 {
222 return (c->flags & CFLAG_CBC) != 0;
223 }
224
225 u_int
cipher_ctx_is_plaintext(struct sshcipher_ctx * cc)226 cipher_ctx_is_plaintext(struct sshcipher_ctx *cc)
227 {
228 return cc->plaintext;
229 }
230
231 const struct sshcipher *
cipher_by_name(const char * name)232 cipher_by_name(const char *name)
233 {
234 const struct sshcipher *c;
235 for (c = ciphers; c->name != NULL; c++)
236 if (strcmp(c->name, name) == 0)
237 return c;
238 return NULL;
239 }
240
241 #define CIPHER_SEP ","
242 int
ciphers_valid(const char * names)243 ciphers_valid(const char *names)
244 {
245 const struct sshcipher *c;
246 char *cipher_list, *cp;
247 char *p;
248
249 if (names == NULL || strcmp(names, "") == 0)
250 return 0;
251 if ((cipher_list = cp = strdup(names)) == NULL)
252 return 0;
253 for ((p = strsep(&cp, CIPHER_SEP)); p && *p != '\0';
254 (p = strsep(&cp, CIPHER_SEP))) {
255 c = cipher_by_name(p);
256 if (c == NULL || (c->flags & (CFLAG_INTERNAL|CFLAG_NONE)) != 0) {
257 free(cipher_list);
258 return 0;
259 }
260 }
261 free(cipher_list);
262 return 1;
263 }
264
265 const char *
cipher_warning_message(const struct sshcipher_ctx * cc)266 cipher_warning_message(const struct sshcipher_ctx *cc)
267 {
268 if (cc == NULL || cc->cipher == NULL)
269 return NULL;
270 /* XXX repurpose for CBC warning */
271 return NULL;
272 }
273
274 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)275 cipher_init(struct sshcipher_ctx **ccp, const struct sshcipher *cipher,
276 const u_char *key, u_int keylen, const u_char *iv, u_int ivlen,
277 int do_encrypt)
278 {
279 struct sshcipher_ctx *cc = NULL;
280 int ret = SSH_ERR_INTERNAL_ERROR;
281 #ifdef WITH_OPENSSL
282 const EVP_CIPHER *type;
283 int klen;
284 #endif
285
286 *ccp = NULL;
287 if ((cc = calloc(1, sizeof(*cc))) == NULL)
288 return SSH_ERR_ALLOC_FAIL;
289
290 cc->plaintext = (cipher->flags & CFLAG_NONE) != 0;
291 cc->encrypt = do_encrypt;
292
293 if (keylen < cipher->key_len ||
294 (iv != NULL && ivlen < cipher_ivlen(cipher))) {
295 ret = SSH_ERR_INVALID_ARGUMENT;
296 goto out;
297 }
298
299 cc->cipher = cipher;
300 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
301 cc->cp_ctx = chachapoly_new(key, keylen);
302 ret = cc->cp_ctx != NULL ? 0 : SSH_ERR_INVALID_ARGUMENT;
303 goto out;
304 }
305 if ((cc->cipher->flags & CFLAG_NONE) != 0) {
306 ret = 0;
307 goto out;
308 }
309 #ifndef WITH_OPENSSL
310 if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
311 aesctr_keysetup(&cc->ac_ctx, key, 8 * keylen, 8 * ivlen);
312 aesctr_ivsetup(&cc->ac_ctx, iv);
313 ret = 0;
314 goto out;
315 }
316 ret = SSH_ERR_INVALID_ARGUMENT;
317 goto out;
318 #else /* WITH_OPENSSL */
319 type = (*cipher->evptype)();
320 if ((cc->evp = EVP_CIPHER_CTX_new()) == NULL) {
321 ret = SSH_ERR_ALLOC_FAIL;
322 goto out;
323 }
324 if (EVP_CipherInit(cc->evp, type, NULL, (const u_char *)iv,
325 (do_encrypt == CIPHER_ENCRYPT)) == 0) {
326 ret = SSH_ERR_LIBCRYPTO_ERROR;
327 goto out;
328 }
329 if (cipher_authlen(cipher) &&
330 EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_IV_FIXED,
331 -1, __UNCONST(iv)) <= 0) {
332 ret = SSH_ERR_LIBCRYPTO_ERROR;
333 goto out;
334 }
335 klen = EVP_CIPHER_CTX_key_length(cc->evp);
336 if (klen > 0 && keylen != (u_int)klen) {
337 if (EVP_CIPHER_CTX_set_key_length(cc->evp, keylen) == 0) {
338 ret = SSH_ERR_LIBCRYPTO_ERROR;
339 goto out;
340 }
341 }
342 /* in OpenSSL 1.1.0, EVP_CipherInit clears all previous setups;
343 use EVP_CipherInit_ex for augmenting */
344 if (EVP_CipherInit_ex(cc->evp, NULL, NULL, __UNCONST(key), NULL, -1) == 0) {
345 ret = SSH_ERR_LIBCRYPTO_ERROR;
346 goto out;
347 }
348 ret = 0;
349 #endif /* WITH_OPENSSL */
350 out:
351 if (ret == 0) {
352 /* success */
353 *ccp = cc;
354 } else {
355 if (cc != NULL) {
356 #ifdef WITH_OPENSSL
357 EVP_CIPHER_CTX_free(cc->evp);
358 #endif /* WITH_OPENSSL */
359 freezero(cc, sizeof(*cc));
360 }
361 }
362 return ret;
363 }
364
365 /*
366 * cipher_crypt() operates as following:
367 * Copy 'aadlen' bytes (without en/decryption) from 'src' to 'dest'.
368 * These bytes are treated as additional authenticated data for
369 * authenticated encryption modes.
370 * En/Decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'.
371 * Use 'authlen' bytes at offset 'len'+'aadlen' as the authentication tag.
372 * This tag is written on encryption and verified on decryption.
373 * Both 'aadlen' and 'authlen' can be set to 0.
374 */
375 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)376 cipher_crypt(struct sshcipher_ctx *cc, u_int seqnr, u_char *dest,
377 const u_char *src, u_int len, u_int aadlen, u_int authlen)
378 {
379 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
380 return chachapoly_crypt(cc->cp_ctx, seqnr, dest, src,
381 len, aadlen, authlen, cc->encrypt);
382 }
383 if ((cc->cipher->flags & CFLAG_NONE) != 0) {
384 memcpy(dest, src, aadlen + len);
385 return 0;
386 }
387 #ifndef WITH_OPENSSL
388 if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
389 if (aadlen)
390 memcpy(dest, src, aadlen);
391 aesctr_encrypt_bytes(&cc->ac_ctx, src + aadlen,
392 dest + aadlen, len);
393 return 0;
394 }
395 return SSH_ERR_INVALID_ARGUMENT;
396 #else
397 if (authlen) {
398 u_char lastiv[1];
399
400 if (authlen != cipher_authlen(cc->cipher))
401 return SSH_ERR_INVALID_ARGUMENT;
402 /* increment IV */
403 if (EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN,
404 1, lastiv) <= 0)
405 return SSH_ERR_LIBCRYPTO_ERROR;
406 /* set tag on decryption */
407 if (!cc->encrypt &&
408 EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_TAG,
409 authlen, __UNCONST(src + aadlen + len)) <= 0)
410 return SSH_ERR_LIBCRYPTO_ERROR;
411 }
412 if (aadlen) {
413 if (authlen &&
414 EVP_Cipher(cc->evp, NULL, (const u_char *)src, aadlen) < 0)
415 return SSH_ERR_LIBCRYPTO_ERROR;
416 memcpy(dest, src, aadlen);
417 }
418 if (len % cc->cipher->block_size)
419 return SSH_ERR_INVALID_ARGUMENT;
420 if (EVP_Cipher(cc->evp, dest + aadlen, (const u_char *)src + aadlen,
421 len) < 0)
422 return SSH_ERR_LIBCRYPTO_ERROR;
423 if (authlen) {
424 /* compute tag (on encrypt) or verify tag (on decrypt) */
425 if (EVP_Cipher(cc->evp, NULL, NULL, 0) < 0)
426 return cc->encrypt ?
427 SSH_ERR_LIBCRYPTO_ERROR : SSH_ERR_MAC_INVALID;
428 if (cc->encrypt &&
429 EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_GET_TAG,
430 authlen, dest + aadlen + len) <= 0)
431 return SSH_ERR_LIBCRYPTO_ERROR;
432 }
433 return 0;
434 #endif
435 }
436
437 /* Extract the packet length, including any decryption necessary beforehand */
438 int
cipher_get_length(struct sshcipher_ctx * cc,u_int * plenp,u_int seqnr,const u_char * cp,u_int len)439 cipher_get_length(struct sshcipher_ctx *cc, u_int *plenp, u_int seqnr,
440 const u_char *cp, u_int len)
441 {
442 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
443 return chachapoly_get_length(cc->cp_ctx, plenp, seqnr,
444 cp, len);
445 if (len < 4)
446 return SSH_ERR_MESSAGE_INCOMPLETE;
447 *plenp = PEEK_U32(cp);
448 return 0;
449 }
450
451 void
cipher_free(struct sshcipher_ctx * cc)452 cipher_free(struct sshcipher_ctx *cc)
453 {
454 if (cc == NULL)
455 return;
456 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
457 chachapoly_free(cc->cp_ctx);
458 cc->cp_ctx = NULL;
459 } else if ((cc->cipher->flags & CFLAG_AESCTR) != 0)
460 explicit_bzero(&cc->ac_ctx, sizeof(cc->ac_ctx));
461 #ifdef WITH_OPENSSL
462 EVP_CIPHER_CTX_free(cc->evp);
463 cc->evp = NULL;
464 #endif
465 freezero(cc, sizeof(*cc));
466 }
467
468 int
cipher_get_keyiv(struct sshcipher_ctx * cc,u_char * iv,size_t len)469 cipher_get_keyiv(struct sshcipher_ctx *cc, u_char *iv, size_t len)
470 {
471 #ifdef WITH_OPENSSL
472 const struct sshcipher *c = cc->cipher;
473 int evplen;
474 #endif
475
476 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
477 if (len != 0)
478 return SSH_ERR_INVALID_ARGUMENT;
479 return 0;
480 }
481 if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
482 if (len != sizeof(cc->ac_ctx.ctr))
483 return SSH_ERR_INVALID_ARGUMENT;
484 memcpy(iv, cc->ac_ctx.ctr, len);
485 return 0;
486 }
487 if ((cc->cipher->flags & CFLAG_NONE) != 0)
488 return 0;
489
490 #ifdef WITH_OPENSSL
491 evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
492 if (evplen == 0)
493 return 0;
494 else if (evplen < 0)
495 return SSH_ERR_LIBCRYPTO_ERROR;
496 if ((size_t)evplen != len)
497 return SSH_ERR_INVALID_ARGUMENT;
498 if (cipher_authlen(c)) {
499 if (EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN, len,
500 iv) <= 0)
501 return SSH_ERR_LIBCRYPTO_ERROR;
502 } else if (EVP_CIPHER_CTX_get_iv(cc->evp, iv, len) <= 0)
503 return SSH_ERR_LIBCRYPTO_ERROR;
504 #endif
505 return 0;
506 }
507
508 int
cipher_set_keyiv(struct sshcipher_ctx * cc,const u_char * iv,size_t len)509 cipher_set_keyiv(struct sshcipher_ctx *cc, const u_char *iv, size_t len)
510 {
511 #ifdef WITH_OPENSSL
512 const struct sshcipher *c = cc->cipher;
513 int evplen = 0;
514 #endif
515
516 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
517 return 0;
518 if ((cc->cipher->flags & CFLAG_NONE) != 0)
519 return 0;
520
521 #ifdef WITH_OPENSSL
522 evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
523 if (evplen <= 0)
524 return SSH_ERR_LIBCRYPTO_ERROR;
525 if ((size_t)evplen != len)
526 return SSH_ERR_INVALID_ARGUMENT;
527 if (cipher_authlen(c)) {
528 /* XXX iv arg is const, but EVP_CIPHER_CTX_ctrl isn't */
529 if (EVP_CIPHER_CTX_ctrl(cc->evp,
530 EVP_CTRL_GCM_SET_IV_FIXED, -1, __UNCONST(iv)) <= 0)
531 return SSH_ERR_LIBCRYPTO_ERROR;
532 } else
533 memcpy(EVP_CIPHER_CTX_iv_noconst(cc->evp), iv, evplen);
534 #endif
535 return 0;
536 }
537