1/* $OpenBSD: cipher.c,v 1.121 2024/05/17 02:39:11 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 <sys/types.h>
39
40#include <string.h>
41#include <stdarg.h>
42#include <stdio.h>
43
44#include "cipher.h"
45#include "misc.h"
46#include "sshbuf.h"
47#include "ssherr.h"
48#include "digest.h"
49
50#ifndef WITH_OPENSSL
51#define EVP_CIPHER_CTX void
52#endif
53
54struct sshcipher_ctx {
55	int	plaintext;
56	int	encrypt;
57	EVP_CIPHER_CTX *evp;
58	struct chachapoly_ctx *cp_ctx;
59	struct aesctr_ctx ac_ctx; /* XXX union with evp? */
60	const struct sshcipher *cipher;
61};
62
63struct sshcipher {
64	char	*name;
65	u_int	block_size;
66	u_int	key_len;
67	u_int	iv_len;		/* defaults to block_size */
68	u_int	auth_len;
69	u_int	flags;
70#define CFLAG_CBC		(1<<0)
71#define CFLAG_CHACHAPOLY	(1<<1)
72#define CFLAG_AESCTR		(1<<2)
73#define CFLAG_NONE		(1<<3)
74#define CFLAG_INTERNAL		CFLAG_NONE /* Don't use "none" for packets */
75#ifdef WITH_OPENSSL
76	const EVP_CIPHER	*(*evptype)(void);
77#else
78	void	*ignored;
79#endif
80};
81
82static const struct sshcipher ciphers[] = {
83#ifdef WITH_OPENSSL
84	{ "3des-cbc",		8, 24, 0, 0, CFLAG_CBC, EVP_des_ede3_cbc },
85	{ "aes128-cbc",		16, 16, 0, 0, CFLAG_CBC, EVP_aes_128_cbc },
86	{ "aes192-cbc",		16, 24, 0, 0, CFLAG_CBC, EVP_aes_192_cbc },
87	{ "aes256-cbc",		16, 32, 0, 0, CFLAG_CBC, EVP_aes_256_cbc },
88	{ "aes128-ctr",		16, 16, 0, 0, 0, EVP_aes_128_ctr },
89	{ "aes192-ctr",		16, 24, 0, 0, 0, EVP_aes_192_ctr },
90	{ "aes256-ctr",		16, 32, 0, 0, 0, EVP_aes_256_ctr },
91	{ "aes128-gcm@openssh.com",
92				16, 16, 12, 16, 0, EVP_aes_128_gcm },
93	{ "aes256-gcm@openssh.com",
94				16, 32, 12, 16, 0, EVP_aes_256_gcm },
95#else
96	{ "aes128-ctr",		16, 16, 0, 0, CFLAG_AESCTR, NULL },
97	{ "aes192-ctr",		16, 24, 0, 0, CFLAG_AESCTR, NULL },
98	{ "aes256-ctr",		16, 32, 0, 0, CFLAG_AESCTR, NULL },
99#endif
100	{ "chacha20-poly1305@openssh.com",
101				8, 64, 0, 16, CFLAG_CHACHAPOLY, NULL },
102	{ "none",		8, 0, 0, 0, CFLAG_NONE, NULL },
103
104	{ NULL,			0, 0, 0, 0, 0, NULL }
105};
106
107/*--*/
108
109/* Returns a comma-separated list of supported ciphers. */
110char *
111cipher_alg_list(char sep, int auth_only)
112{
113	char *tmp, *ret = NULL;
114	size_t nlen, rlen = 0;
115	const struct sshcipher *c;
116
117	for (c = ciphers; c->name != NULL; c++) {
118		if ((c->flags & CFLAG_INTERNAL) != 0)
119			continue;
120		if (auth_only && c->auth_len == 0)
121			continue;
122		if (ret != NULL)
123			ret[rlen++] = sep;
124		nlen = strlen(c->name);
125		if ((tmp = realloc(ret, rlen + nlen + 2)) == NULL) {
126			free(ret);
127			return NULL;
128		}
129		ret = tmp;
130		memcpy(ret + rlen, c->name, nlen + 1);
131		rlen += nlen;
132	}
133	return ret;
134}
135
136const char *
137compression_alg_list(int compression)
138{
139#ifdef WITH_ZLIB
140	return compression ? "zlib@openssh.com,zlib,none" :
141	    "none,zlib@openssh.com,zlib";
142#else
143	return "none";
144#endif
145}
146
147u_int
148cipher_blocksize(const struct sshcipher *c)
149{
150	return (c->block_size);
151}
152
153u_int
154cipher_keylen(const struct sshcipher *c)
155{
156	return (c->key_len);
157}
158
159u_int
160cipher_seclen(const struct sshcipher *c)
161{
162	if (strcmp("3des-cbc", c->name) == 0)
163		return 14;
164	return cipher_keylen(c);
165}
166
167u_int
168cipher_authlen(const struct sshcipher *c)
169{
170	return (c->auth_len);
171}
172
173u_int
174cipher_ivlen(const struct sshcipher *c)
175{
176	/*
177	 * Default is cipher block size, except for chacha20+poly1305 that
178	 * needs no IV. XXX make iv_len == -1 default?
179	 */
180	return (c->iv_len != 0 || (c->flags & CFLAG_CHACHAPOLY) != 0) ?
181	    c->iv_len : c->block_size;
182}
183
184u_int
185cipher_is_cbc(const struct sshcipher *c)
186{
187	return (c->flags & CFLAG_CBC) != 0;
188}
189
190u_int
191cipher_ctx_is_plaintext(struct sshcipher_ctx *cc)
192{
193	return cc->plaintext;
194}
195
196const struct sshcipher *
197cipher_by_name(const char *name)
198{
199	const struct sshcipher *c;
200	for (c = ciphers; c->name != NULL; c++)
201		if (strcmp(c->name, name) == 0)
202			return c;
203	return NULL;
204}
205
206#define	CIPHER_SEP	","
207int
208ciphers_valid(const char *names)
209{
210	const struct sshcipher *c;
211	char *cipher_list, *cp;
212	char *p;
213
214	if (names == NULL || strcmp(names, "") == 0)
215		return 0;
216	if ((cipher_list = cp = strdup(names)) == NULL)
217		return 0;
218	for ((p = strsep(&cp, CIPHER_SEP)); p && *p != '\0';
219	    (p = strsep(&cp, CIPHER_SEP))) {
220		c = cipher_by_name(p);
221		if (c == NULL || (c->flags & CFLAG_INTERNAL) != 0) {
222			free(cipher_list);
223			return 0;
224		}
225	}
226	free(cipher_list);
227	return 1;
228}
229
230const char *
231cipher_warning_message(const struct sshcipher_ctx *cc)
232{
233	if (cc == NULL || cc->cipher == NULL)
234		return NULL;
235	/* XXX repurpose for CBC warning */
236	return NULL;
237}
238
239int
240cipher_init(struct sshcipher_ctx **ccp, const struct sshcipher *cipher,
241    const u_char *key, u_int keylen, const u_char *iv, u_int ivlen,
242    int do_encrypt)
243{
244	struct sshcipher_ctx *cc = NULL;
245	int ret = SSH_ERR_INTERNAL_ERROR;
246#ifdef WITH_OPENSSL
247	const EVP_CIPHER *type;
248	int klen;
249#endif
250
251	*ccp = NULL;
252	if ((cc = calloc(sizeof(*cc), 1)) == NULL)
253		return SSH_ERR_ALLOC_FAIL;
254
255	cc->plaintext = (cipher->flags & CFLAG_NONE) != 0;
256	cc->encrypt = do_encrypt;
257
258	if (keylen < cipher->key_len ||
259	    (iv != NULL && ivlen < cipher_ivlen(cipher))) {
260		ret = SSH_ERR_INVALID_ARGUMENT;
261		goto out;
262	}
263
264	cc->cipher = cipher;
265	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
266		cc->cp_ctx = chachapoly_new(key, keylen);
267		ret = cc->cp_ctx != NULL ? 0 : SSH_ERR_INVALID_ARGUMENT;
268		goto out;
269	}
270	if ((cc->cipher->flags & CFLAG_NONE) != 0) {
271		ret = 0;
272		goto out;
273	}
274#ifndef WITH_OPENSSL
275	if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
276		aesctr_keysetup(&cc->ac_ctx, key, 8 * keylen, 8 * ivlen);
277		aesctr_ivsetup(&cc->ac_ctx, iv);
278		ret = 0;
279		goto out;
280	}
281	ret = SSH_ERR_INVALID_ARGUMENT;
282	goto out;
283#else /* WITH_OPENSSL */
284	type = (*cipher->evptype)();
285	if ((cc->evp = EVP_CIPHER_CTX_new()) == NULL) {
286		ret = SSH_ERR_ALLOC_FAIL;
287		goto out;
288	}
289	if (EVP_CipherInit(cc->evp, type, NULL, (u_char *)iv,
290	    (do_encrypt == CIPHER_ENCRYPT)) == 0) {
291		ret = SSH_ERR_LIBCRYPTO_ERROR;
292		goto out;
293	}
294	if (cipher_authlen(cipher) &&
295	    !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_IV_FIXED,
296	    -1, (u_char *)iv)) {
297		ret = SSH_ERR_LIBCRYPTO_ERROR;
298		goto out;
299	}
300	klen = EVP_CIPHER_CTX_key_length(cc->evp);
301	if (klen > 0 && keylen != (u_int)klen) {
302		if (EVP_CIPHER_CTX_set_key_length(cc->evp, keylen) == 0) {
303			ret = SSH_ERR_LIBCRYPTO_ERROR;
304			goto out;
305		}
306	}
307	if (EVP_CipherInit(cc->evp, NULL, (u_char *)key, NULL, -1) == 0) {
308		ret = SSH_ERR_LIBCRYPTO_ERROR;
309		goto out;
310	}
311	ret = 0;
312#endif /* WITH_OPENSSL */
313 out:
314	if (ret == 0) {
315		/* success */
316		*ccp = cc;
317	} else {
318		if (cc != NULL) {
319#ifdef WITH_OPENSSL
320			EVP_CIPHER_CTX_free(cc->evp);
321#endif /* WITH_OPENSSL */
322			freezero(cc, sizeof(*cc));
323		}
324	}
325	return ret;
326}
327
328/*
329 * cipher_crypt() operates as following:
330 * Copy 'aadlen' bytes (without en/decryption) from 'src' to 'dest'.
331 * These bytes are treated as additional authenticated data for
332 * authenticated encryption modes.
333 * En/Decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'.
334 * Use 'authlen' bytes at offset 'len'+'aadlen' as the authentication tag.
335 * This tag is written on encryption and verified on decryption.
336 * Both 'aadlen' and 'authlen' can be set to 0.
337 */
338int
339cipher_crypt(struct sshcipher_ctx *cc, u_int seqnr, u_char *dest,
340   const u_char *src, u_int len, u_int aadlen, u_int authlen)
341{
342	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
343		return chachapoly_crypt(cc->cp_ctx, seqnr, dest, src,
344		    len, aadlen, authlen, cc->encrypt);
345	}
346	if ((cc->cipher->flags & CFLAG_NONE) != 0) {
347		memcpy(dest, src, aadlen + len);
348		return 0;
349	}
350#ifndef WITH_OPENSSL
351	if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
352		if (aadlen)
353			memcpy(dest, src, aadlen);
354		aesctr_encrypt_bytes(&cc->ac_ctx, src + aadlen,
355		    dest + aadlen, len);
356		return 0;
357	}
358	return SSH_ERR_INVALID_ARGUMENT;
359#else
360	if (authlen) {
361		u_char lastiv[1];
362
363		if (authlen != cipher_authlen(cc->cipher))
364			return SSH_ERR_INVALID_ARGUMENT;
365		/* increment IV */
366		if (!EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN,
367		    1, lastiv))
368			return SSH_ERR_LIBCRYPTO_ERROR;
369		/* set tag on decryption */
370		if (!cc->encrypt &&
371		    !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_TAG,
372		    authlen, (u_char *)src + aadlen + len))
373			return SSH_ERR_LIBCRYPTO_ERROR;
374	}
375	if (aadlen) {
376		if (authlen &&
377		    EVP_Cipher(cc->evp, NULL, (u_char *)src, aadlen) < 0)
378			return SSH_ERR_LIBCRYPTO_ERROR;
379		memcpy(dest, src, aadlen);
380	}
381	if (len % cc->cipher->block_size)
382		return SSH_ERR_INVALID_ARGUMENT;
383	if (EVP_Cipher(cc->evp, dest + aadlen, (u_char *)src + aadlen,
384	    len) < 0)
385		return SSH_ERR_LIBCRYPTO_ERROR;
386	if (authlen) {
387		/* compute tag (on encrypt) or verify tag (on decrypt) */
388		if (EVP_Cipher(cc->evp, NULL, NULL, 0) < 0)
389			return cc->encrypt ?
390			    SSH_ERR_LIBCRYPTO_ERROR : SSH_ERR_MAC_INVALID;
391		if (cc->encrypt &&
392		    !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_GET_TAG,
393		    authlen, dest + aadlen + len))
394			return SSH_ERR_LIBCRYPTO_ERROR;
395	}
396	return 0;
397#endif
398}
399
400/* Extract the packet length, including any decryption necessary beforehand */
401int
402cipher_get_length(struct sshcipher_ctx *cc, u_int *plenp, u_int seqnr,
403    const u_char *cp, u_int len)
404{
405	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
406		return chachapoly_get_length(cc->cp_ctx, plenp, seqnr,
407		    cp, len);
408	if (len < 4)
409		return SSH_ERR_MESSAGE_INCOMPLETE;
410	*plenp = PEEK_U32(cp);
411	return 0;
412}
413
414void
415cipher_free(struct sshcipher_ctx *cc)
416{
417	if (cc == NULL)
418		return;
419	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
420		chachapoly_free(cc->cp_ctx);
421		cc->cp_ctx = NULL;
422	} else if ((cc->cipher->flags & CFLAG_AESCTR) != 0)
423		explicit_bzero(&cc->ac_ctx, sizeof(cc->ac_ctx));
424#ifdef WITH_OPENSSL
425	EVP_CIPHER_CTX_free(cc->evp);
426	cc->evp = NULL;
427#endif
428	freezero(cc, sizeof(*cc));
429}
430
431int
432cipher_get_keyiv(struct sshcipher_ctx *cc, u_char *iv, size_t len)
433{
434#ifdef WITH_OPENSSL
435	const struct sshcipher *c = cc->cipher;
436	int evplen;
437#endif
438
439	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
440		if (len != 0)
441			return SSH_ERR_INVALID_ARGUMENT;
442		return 0;
443	}
444	if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
445		if (len != sizeof(cc->ac_ctx.ctr))
446			return SSH_ERR_INVALID_ARGUMENT;
447		memcpy(iv, cc->ac_ctx.ctr, len);
448		return 0;
449	}
450	if ((cc->cipher->flags & CFLAG_NONE) != 0)
451		return 0;
452
453#ifdef WITH_OPENSSL
454	evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
455	if (evplen == 0)
456		return 0;
457	else if (evplen < 0)
458		return SSH_ERR_LIBCRYPTO_ERROR;
459	if ((size_t)evplen != len)
460		return SSH_ERR_INVALID_ARGUMENT;
461	if (cipher_authlen(c)) {
462		if (!EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN, len, iv))
463			return SSH_ERR_LIBCRYPTO_ERROR;
464	} else if (!EVP_CIPHER_CTX_get_iv(cc->evp, iv, len))
465		return SSH_ERR_LIBCRYPTO_ERROR;
466#endif
467	return 0;
468}
469
470int
471cipher_set_keyiv(struct sshcipher_ctx *cc, const u_char *iv, size_t len)
472{
473#ifdef WITH_OPENSSL
474	const struct sshcipher *c = cc->cipher;
475	int evplen = 0;
476#endif
477
478	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
479		return 0;
480	if ((cc->cipher->flags & CFLAG_NONE) != 0)
481		return 0;
482
483#ifdef WITH_OPENSSL
484	evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
485	if (evplen <= 0)
486		return SSH_ERR_LIBCRYPTO_ERROR;
487	if ((size_t)evplen != len)
488		return SSH_ERR_INVALID_ARGUMENT;
489	if (cipher_authlen(c)) {
490		/* XXX iv arg is const, but EVP_CIPHER_CTX_ctrl isn't */
491		if (!EVP_CIPHER_CTX_ctrl(cc->evp,
492		    EVP_CTRL_GCM_SET_IV_FIXED, -1, (void *)iv))
493			return SSH_ERR_LIBCRYPTO_ERROR;
494	} else if (!EVP_CIPHER_CTX_set_iv(cc->evp, iv, evplen))
495		return SSH_ERR_LIBCRYPTO_ERROR;
496#endif
497	return 0;
498}
499
500