xref: /freebsd/crypto/openssh/cipher.c (revision 67f7f2781daa9bd398b424ffe2bd0be67f37f03d) 
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 *
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 *
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
144 cipher_blocksize(const struct sshcipher *c)
145 {
146 	return (c->block_size);
147 }
148 
149 u_int
150 cipher_keylen(const struct sshcipher *c)
151 {
152 	return (c->key_len);
153 }
154 
155 u_int
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
164 cipher_authlen(const struct sshcipher *c)
165 {
166 	return (c->auth_len);
167 }
168 
169 u_int
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
181 cipher_is_cbc(const struct sshcipher *c)
182 {
183 	return (c->flags & CFLAG_CBC) != 0;
184 }
185 
186 u_int
187 cipher_ctx_is_plaintext(struct sshcipher_ctx *cc)
188 {
189 	return cc->plaintext;
190 }
191 
192 const struct sshcipher *
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
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 *
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
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
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
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
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
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
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