1 /* $OpenBSD: cipher.c,v 1.126 2026/02/14 00:18:34 jsg 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
51 #include "openbsd-compat/openssl-compat.h"
52
53 #ifndef WITH_OPENSSL
54 #define EVP_CIPHER_CTX void
55 #endif
56
57 struct sshcipher_ctx {
58 int plaintext;
59 int encrypt;
60 EVP_CIPHER_CTX *evp;
61 struct chachapoly_ctx *cp_ctx;
62 struct aesctr_ctx ac_ctx; /* XXX union with evp? */
63 const struct sshcipher *cipher;
64 };
65
66 struct sshcipher {
67 char *name;
68 u_int block_size;
69 u_int key_len;
70 u_int iv_len; /* defaults to block_size */
71 u_int auth_len;
72 u_int flags;
73 #define CFLAG_CBC (1<<0)
74 #define CFLAG_CHACHAPOLY (1<<1)
75 #define CFLAG_AESCTR (1<<2)
76 #define CFLAG_NONE (1<<3)
77 #define CFLAG_INTERNAL CFLAG_NONE /* Don't use "none" for packets */
78 #ifdef WITH_OPENSSL
79 const EVP_CIPHER *(*evptype)(void);
80 #else
81 void *ignored;
82 #endif
83 };
84
85 static const struct sshcipher ciphers[] = {
86 #ifdef WITH_OPENSSL
87 #ifndef OPENSSL_NO_DES
88 { "3des-cbc", 8, 24, 0, 0, CFLAG_CBC, EVP_des_ede3_cbc },
89 #endif
90 { "aes128-cbc", 16, 16, 0, 0, CFLAG_CBC, EVP_aes_128_cbc },
91 { "aes192-cbc", 16, 24, 0, 0, CFLAG_CBC, EVP_aes_192_cbc },
92 { "aes256-cbc", 16, 32, 0, 0, CFLAG_CBC, EVP_aes_256_cbc },
93 { "aes128-ctr", 16, 16, 0, 0, 0, EVP_aes_128_ctr },
94 { "aes192-ctr", 16, 24, 0, 0, 0, EVP_aes_192_ctr },
95 { "aes256-ctr", 16, 32, 0, 0, 0, EVP_aes_256_ctr },
96 { "aes128-gcm@openssh.com",
97 16, 16, 12, 16, 0, EVP_aes_128_gcm },
98 { "aes256-gcm@openssh.com",
99 16, 32, 12, 16, 0, EVP_aes_256_gcm },
100 #else
101 { "aes128-ctr", 16, 16, 0, 0, CFLAG_AESCTR, NULL },
102 { "aes192-ctr", 16, 24, 0, 0, CFLAG_AESCTR, NULL },
103 { "aes256-ctr", 16, 32, 0, 0, CFLAG_AESCTR, NULL },
104 #endif
105 { "chacha20-poly1305@openssh.com",
106 8, 64, 0, 16, CFLAG_CHACHAPOLY, NULL },
107 { "none", 8, 0, 0, 0, CFLAG_NONE, NULL },
108
109 { NULL, 0, 0, 0, 0, 0, NULL }
110 };
111
112 /*--*/
113
114 /* Returns a comma-separated list of supported ciphers. */
115 char *
cipher_alg_list(char sep,int auth_only)116 cipher_alg_list(char sep, int auth_only)
117 {
118 char *ret = NULL;
119 const struct sshcipher *c;
120 char sep_str[2] = {sep, '\0'};
121
122 for (c = ciphers; c->name != NULL; c++) {
123 if ((c->flags & CFLAG_INTERNAL) != 0)
124 continue;
125 if (auth_only && c->auth_len == 0)
126 continue;
127 xextendf(&ret, sep_str, "%s", c->name);
128 }
129 return ret;
130 }
131
132 const char *
compression_alg_list(int compression)133 compression_alg_list(int compression)
134 {
135 #ifdef WITH_ZLIB
136 return compression ? "zlib@openssh.com,none" :
137 "none,zlib@openssh.com";
138 #else
139 return "none";
140 #endif
141 }
142
143 u_int
cipher_blocksize(const struct sshcipher * c)144 cipher_blocksize(const struct sshcipher *c)
145 {
146 return (c->block_size);
147 }
148
149 u_int
cipher_keylen(const struct sshcipher * c)150 cipher_keylen(const struct sshcipher *c)
151 {
152 return (c->key_len);
153 }
154
155 u_int
cipher_seclen(const struct sshcipher * c)156 cipher_seclen(const struct sshcipher *c)
157 {
158 if (strcmp("3des-cbc", c->name) == 0)
159 return 14;
160 return cipher_keylen(c);
161 }
162
163 u_int
cipher_authlen(const struct sshcipher * c)164 cipher_authlen(const struct sshcipher *c)
165 {
166 return (c->auth_len);
167 }
168
169 u_int
cipher_ivlen(const struct sshcipher * c)170 cipher_ivlen(const struct sshcipher *c)
171 {
172 /*
173 * Default is cipher block size, except for chacha20+poly1305 that
174 * needs no IV. XXX make iv_len == -1 default?
175 */
176 return (c->iv_len != 0 || (c->flags & CFLAG_CHACHAPOLY) != 0) ?
177 c->iv_len : c->block_size;
178 }
179
180 u_int
cipher_is_cbc(const struct sshcipher * c)181 cipher_is_cbc(const struct sshcipher *c)
182 {
183 return (c->flags & CFLAG_CBC) != 0;
184 }
185
186 u_int
cipher_ctx_is_plaintext(struct sshcipher_ctx * cc)187 cipher_ctx_is_plaintext(struct sshcipher_ctx *cc)
188 {
189 return cc->plaintext;
190 }
191
192 const struct sshcipher *
cipher_by_name(const char * name)193 cipher_by_name(const char *name)
194 {
195 const struct sshcipher *c;
196 for (c = ciphers; c->name != NULL; c++)
197 if (strcmp(c->name, name) == 0)
198 return c;
199 return NULL;
200 }
201
202 #define CIPHER_SEP ","
203 int
ciphers_valid(const char * names)204 ciphers_valid(const char *names)
205 {
206 const struct sshcipher *c;
207 char *cipher_list, *cp;
208 char *p;
209
210 if (names == NULL || strcmp(names, "") == 0)
211 return 0;
212 if ((cipher_list = cp = strdup(names)) == NULL)
213 return 0;
214 for ((p = strsep(&cp, CIPHER_SEP)); p && *p != '\0';
215 (p = strsep(&cp, CIPHER_SEP))) {
216 c = cipher_by_name(p);
217 if (c == NULL || (c->flags & CFLAG_INTERNAL) != 0) {
218 free(cipher_list);
219 return 0;
220 }
221 }
222 free(cipher_list);
223 return 1;
224 }
225
226 const char *
cipher_warning_message(const struct sshcipher_ctx * cc)227 cipher_warning_message(const struct sshcipher_ctx *cc)
228 {
229 if (cc == NULL || cc->cipher == NULL)
230 return NULL;
231 /* XXX repurpose for CBC warning */
232 return NULL;
233 }
234
235 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)236 cipher_init(struct sshcipher_ctx **ccp, const struct sshcipher *cipher,
237 const u_char *key, u_int keylen, const u_char *iv, u_int ivlen,
238 int do_encrypt)
239 {
240 struct sshcipher_ctx *cc = NULL;
241 int ret = SSH_ERR_INTERNAL_ERROR;
242 #ifdef WITH_OPENSSL
243 const EVP_CIPHER *type;
244 int klen;
245 #endif
246
247 *ccp = NULL;
248 if ((cc = calloc(1, sizeof(*cc))) == NULL)
249 return SSH_ERR_ALLOC_FAIL;
250
251 cc->plaintext = (cipher->flags & CFLAG_NONE) != 0;
252 cc->encrypt = do_encrypt;
253
254 if (keylen < cipher->key_len ||
255 (iv != NULL && ivlen < cipher_ivlen(cipher))) {
256 ret = SSH_ERR_INVALID_ARGUMENT;
257 goto out;
258 }
259
260 cc->cipher = cipher;
261 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
262 cc->cp_ctx = chachapoly_new(key, keylen);
263 ret = cc->cp_ctx != NULL ? 0 : SSH_ERR_INVALID_ARGUMENT;
264 goto out;
265 }
266 if ((cc->cipher->flags & CFLAG_NONE) != 0) {
267 ret = 0;
268 goto out;
269 }
270 #ifndef WITH_OPENSSL
271 if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
272 aesctr_keysetup(&cc->ac_ctx, key, 8 * keylen, 8 * ivlen);
273 aesctr_ivsetup(&cc->ac_ctx, iv);
274 ret = 0;
275 goto out;
276 }
277 ret = SSH_ERR_INVALID_ARGUMENT;
278 goto out;
279 #else /* WITH_OPENSSL */
280 type = (*cipher->evptype)();
281 if ((cc->evp = EVP_CIPHER_CTX_new()) == NULL) {
282 ret = SSH_ERR_ALLOC_FAIL;
283 goto out;
284 }
285 if (EVP_CipherInit(cc->evp, type, NULL, (u_char *)iv,
286 (do_encrypt == CIPHER_ENCRYPT)) == 0) {
287 ret = SSH_ERR_LIBCRYPTO_ERROR;
288 goto out;
289 }
290 if (cipher_authlen(cipher) &&
291 EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_IV_FIXED,
292 -1, (u_char *)iv) <= 0) {
293 ret = SSH_ERR_LIBCRYPTO_ERROR;
294 goto out;
295 }
296 klen = EVP_CIPHER_CTX_key_length(cc->evp);
297 if (klen > 0 && keylen != (u_int)klen) {
298 if (EVP_CIPHER_CTX_set_key_length(cc->evp, keylen) == 0) {
299 ret = SSH_ERR_LIBCRYPTO_ERROR;
300 goto out;
301 }
302 }
303 if (EVP_CipherInit(cc->evp, NULL, (u_char *)key, NULL, -1) == 0) {
304 ret = SSH_ERR_LIBCRYPTO_ERROR;
305 goto out;
306 }
307 ret = 0;
308 #endif /* WITH_OPENSSL */
309 out:
310 if (ret == 0) {
311 /* success */
312 *ccp = cc;
313 } else {
314 if (cc != NULL) {
315 #ifdef WITH_OPENSSL
316 EVP_CIPHER_CTX_free(cc->evp);
317 #endif /* WITH_OPENSSL */
318 freezero(cc, sizeof(*cc));
319 }
320 }
321 return ret;
322 }
323
324 /*
325 * cipher_crypt() operates as following:
326 * Copy 'aadlen' bytes (without en/decryption) from 'src' to 'dest'.
327 * These bytes are treated as additional authenticated data for
328 * authenticated encryption modes.
329 * En/Decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'.
330 * Use 'authlen' bytes at offset 'len'+'aadlen' as the authentication tag.
331 * This tag is written on encryption and verified on decryption.
332 * Both 'aadlen' and 'authlen' can be set to 0.
333 */
334 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)335 cipher_crypt(struct sshcipher_ctx *cc, u_int seqnr, u_char *dest,
336 const u_char *src, u_int len, u_int aadlen, u_int authlen)
337 {
338 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
339 return chachapoly_crypt(cc->cp_ctx, seqnr, dest, src,
340 len, aadlen, authlen, cc->encrypt);
341 }
342 if ((cc->cipher->flags & CFLAG_NONE) != 0) {
343 memcpy(dest, src, aadlen + len);
344 return 0;
345 }
346 #ifndef WITH_OPENSSL
347 if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
348 if (aadlen)
349 memcpy(dest, src, aadlen);
350 aesctr_encrypt_bytes(&cc->ac_ctx, src + aadlen,
351 dest + aadlen, len);
352 return 0;
353 }
354 return SSH_ERR_INVALID_ARGUMENT;
355 #else
356 if (authlen) {
357 u_char lastiv[1];
358
359 if (authlen != cipher_authlen(cc->cipher))
360 return SSH_ERR_INVALID_ARGUMENT;
361 /* increment IV */
362 if (EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN,
363 1, lastiv) <= 0)
364 return SSH_ERR_LIBCRYPTO_ERROR;
365 /* set tag on decryption */
366 if (!cc->encrypt &&
367 EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_TAG,
368 authlen, (u_char *)src + aadlen + len) <= 0)
369 return SSH_ERR_LIBCRYPTO_ERROR;
370 }
371 if (aadlen) {
372 if (authlen &&
373 EVP_Cipher(cc->evp, NULL, (u_char *)src, aadlen) < 0)
374 return SSH_ERR_LIBCRYPTO_ERROR;
375 memcpy(dest, src, aadlen);
376 }
377 if (len % cc->cipher->block_size)
378 return SSH_ERR_INVALID_ARGUMENT;
379 if (EVP_Cipher(cc->evp, dest + aadlen, (u_char *)src + aadlen,
380 len) < 0)
381 return SSH_ERR_LIBCRYPTO_ERROR;
382 if (authlen) {
383 /* compute tag (on encrypt) or verify tag (on decrypt) */
384 if (EVP_Cipher(cc->evp, NULL, NULL, 0) < 0)
385 return cc->encrypt ?
386 SSH_ERR_LIBCRYPTO_ERROR : SSH_ERR_MAC_INVALID;
387 if (cc->encrypt &&
388 EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_GET_TAG,
389 authlen, dest + aadlen + len) <= 0)
390 return SSH_ERR_LIBCRYPTO_ERROR;
391 }
392 return 0;
393 #endif
394 }
395
396 /* Extract the packet length, including any decryption necessary beforehand */
397 int
cipher_get_length(struct sshcipher_ctx * cc,u_int * plenp,u_int seqnr,const u_char * cp,u_int len)398 cipher_get_length(struct sshcipher_ctx *cc, u_int *plenp, u_int seqnr,
399 const u_char *cp, u_int len)
400 {
401 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
402 return chachapoly_get_length(cc->cp_ctx, plenp, seqnr,
403 cp, len);
404 if (len < 4)
405 return SSH_ERR_MESSAGE_INCOMPLETE;
406 *plenp = PEEK_U32(cp);
407 return 0;
408 }
409
410 void
cipher_free(struct sshcipher_ctx * cc)411 cipher_free(struct sshcipher_ctx *cc)
412 {
413 if (cc == NULL)
414 return;
415 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
416 chachapoly_free(cc->cp_ctx);
417 cc->cp_ctx = NULL;
418 } else if ((cc->cipher->flags & CFLAG_AESCTR) != 0)
419 explicit_bzero(&cc->ac_ctx, sizeof(cc->ac_ctx));
420 #ifdef WITH_OPENSSL
421 EVP_CIPHER_CTX_free(cc->evp);
422 cc->evp = NULL;
423 #endif
424 freezero(cc, sizeof(*cc));
425 }
426
427 int
cipher_get_keyiv(struct sshcipher_ctx * cc,u_char * iv,size_t len)428 cipher_get_keyiv(struct sshcipher_ctx *cc, u_char *iv, size_t len)
429 {
430 #ifdef WITH_OPENSSL
431 const struct sshcipher *c = cc->cipher;
432 int evplen;
433 #endif
434
435 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
436 if (len != 0)
437 return SSH_ERR_INVALID_ARGUMENT;
438 return 0;
439 }
440 if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
441 if (len != sizeof(cc->ac_ctx.ctr))
442 return SSH_ERR_INVALID_ARGUMENT;
443 memcpy(iv, cc->ac_ctx.ctr, len);
444 return 0;
445 }
446 if ((cc->cipher->flags & CFLAG_NONE) != 0)
447 return 0;
448
449 #ifdef WITH_OPENSSL
450 evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
451 if (evplen == 0)
452 return 0;
453 else if (evplen < 0)
454 return SSH_ERR_LIBCRYPTO_ERROR;
455 if ((size_t)evplen != len)
456 return SSH_ERR_INVALID_ARGUMENT;
457 if (cipher_authlen(c)) {
458 if (EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN, len,
459 iv) <= 0)
460 return SSH_ERR_LIBCRYPTO_ERROR;
461 } else if (EVP_CIPHER_CTX_get_iv(cc->evp, iv, len) <= 0)
462 return SSH_ERR_LIBCRYPTO_ERROR;
463 #endif
464 return 0;
465 }
466
467 int
cipher_set_keyiv(struct sshcipher_ctx * cc,const u_char * iv,size_t len)468 cipher_set_keyiv(struct sshcipher_ctx *cc, const u_char *iv, size_t len)
469 {
470 #ifdef WITH_OPENSSL
471 const struct sshcipher *c = cc->cipher;
472 int evplen = 0;
473 #endif
474
475 if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
476 return 0;
477 if ((cc->cipher->flags & CFLAG_NONE) != 0)
478 return 0;
479
480 #ifdef WITH_OPENSSL
481 evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
482 if (evplen <= 0)
483 return SSH_ERR_LIBCRYPTO_ERROR;
484 if ((size_t)evplen != len)
485 return SSH_ERR_INVALID_ARGUMENT;
486 if (cipher_authlen(c)) {
487 /* XXX iv arg is const, but EVP_CIPHER_CTX_ctrl isn't */
488 if (EVP_CIPHER_CTX_ctrl(cc->evp,
489 EVP_CTRL_GCM_SET_IV_FIXED, -1, (void *)iv) <= 0)
490 return SSH_ERR_LIBCRYPTO_ERROR;
491 } else if (!EVP_CIPHER_CTX_set_iv(cc->evp, iv, evplen))
492 return SSH_ERR_LIBCRYPTO_ERROR;
493 #endif
494 return 0;
495 }
496