1/* $OpenBSD: cipher.c,v 1.120 2023/10/10 06:49:54 tb 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
58struct 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
67struct 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
86static 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	{ "aes128-gcm@openssh.com",
98				16, 16, 12, 16, 0, EVP_aes_128_gcm },
99	{ "aes256-gcm@openssh.com",
100				16, 32, 12, 16, 0, EVP_aes_256_gcm },
101#else
102	{ "aes128-ctr",		16, 16, 0, 0, CFLAG_AESCTR, NULL },
103	{ "aes192-ctr",		16, 24, 0, 0, CFLAG_AESCTR, NULL },
104	{ "aes256-ctr",		16, 32, 0, 0, CFLAG_AESCTR, NULL },
105#endif
106	{ "chacha20-poly1305@openssh.com",
107				8, 64, 0, 16, CFLAG_CHACHAPOLY, NULL },
108	{ "none",		8, 0, 0, 0, CFLAG_NONE, NULL },
109
110	{ NULL,			0, 0, 0, 0, 0, NULL }
111};
112
113/*--*/
114
115/* Returns a comma-separated list of supported ciphers. */
116char *
117cipher_alg_list(char sep, int auth_only)
118{
119	char *tmp, *ret = NULL;
120	size_t nlen, rlen = 0;
121	const struct sshcipher *c;
122
123	for (c = ciphers; c->name != NULL; c++) {
124		if ((c->flags & CFLAG_INTERNAL) != 0)
125			continue;
126		if (auth_only && c->auth_len == 0)
127			continue;
128		if (ret != NULL)
129			ret[rlen++] = sep;
130		nlen = strlen(c->name);
131		if ((tmp = realloc(ret, rlen + nlen + 2)) == NULL) {
132			free(ret);
133			return NULL;
134		}
135		ret = tmp;
136		memcpy(ret + rlen, c->name, nlen + 1);
137		rlen += nlen;
138	}
139	return ret;
140}
141
142const char *
143compression_alg_list(int compression)
144{
145#ifdef WITH_ZLIB
146	return compression ? "zlib@openssh.com,zlib,none" :
147	    "none,zlib@openssh.com,zlib";
148#else
149	return "none";
150#endif
151}
152
153u_int
154cipher_blocksize(const struct sshcipher *c)
155{
156	return (c->block_size);
157}
158
159u_int
160cipher_keylen(const struct sshcipher *c)
161{
162	return (c->key_len);
163}
164
165u_int
166cipher_seclen(const struct sshcipher *c)
167{
168	if (strcmp("3des-cbc", c->name) == 0)
169		return 14;
170	return cipher_keylen(c);
171}
172
173u_int
174cipher_authlen(const struct sshcipher *c)
175{
176	return (c->auth_len);
177}
178
179u_int
180cipher_ivlen(const struct sshcipher *c)
181{
182	/*
183	 * Default is cipher block size, except for chacha20+poly1305 that
184	 * needs no IV. XXX make iv_len == -1 default?
185	 */
186	return (c->iv_len != 0 || (c->flags & CFLAG_CHACHAPOLY) != 0) ?
187	    c->iv_len : c->block_size;
188}
189
190u_int
191cipher_is_cbc(const struct sshcipher *c)
192{
193	return (c->flags & CFLAG_CBC) != 0;
194}
195
196u_int
197cipher_ctx_is_plaintext(struct sshcipher_ctx *cc)
198{
199	return cc->plaintext;
200}
201
202const struct sshcipher *
203cipher_by_name(const char *name)
204{
205	const struct sshcipher *c;
206	for (c = ciphers; c->name != NULL; c++)
207		if (strcmp(c->name, name) == 0)
208			return c;
209	return NULL;
210}
211
212#define	CIPHER_SEP	","
213int
214ciphers_valid(const char *names)
215{
216	const struct sshcipher *c;
217	char *cipher_list, *cp;
218	char *p;
219
220	if (names == NULL || strcmp(names, "") == 0)
221		return 0;
222	if ((cipher_list = cp = strdup(names)) == NULL)
223		return 0;
224	for ((p = strsep(&cp, CIPHER_SEP)); p && *p != '\0';
225	    (p = strsep(&cp, CIPHER_SEP))) {
226		c = cipher_by_name(p);
227		if (c == NULL || (c->flags & CFLAG_INTERNAL) != 0) {
228			free(cipher_list);
229			return 0;
230		}
231	}
232	free(cipher_list);
233	return 1;
234}
235
236const char *
237cipher_warning_message(const struct sshcipher_ctx *cc)
238{
239	if (cc == NULL || cc->cipher == NULL)
240		return NULL;
241	/* XXX repurpose for CBC warning */
242	return NULL;
243}
244
245int
246cipher_init(struct sshcipher_ctx **ccp, const struct sshcipher *cipher,
247    const u_char *key, u_int keylen, const u_char *iv, u_int ivlen,
248    int do_encrypt)
249{
250	struct sshcipher_ctx *cc = NULL;
251	int ret = SSH_ERR_INTERNAL_ERROR;
252#ifdef WITH_OPENSSL
253	const EVP_CIPHER *type;
254	int klen;
255#endif
256
257	*ccp = NULL;
258	if ((cc = calloc(sizeof(*cc), 1)) == NULL)
259		return SSH_ERR_ALLOC_FAIL;
260
261	cc->plaintext = (cipher->flags & CFLAG_NONE) != 0;
262	cc->encrypt = do_encrypt;
263
264	if (keylen < cipher->key_len ||
265	    (iv != NULL && ivlen < cipher_ivlen(cipher))) {
266		ret = SSH_ERR_INVALID_ARGUMENT;
267		goto out;
268	}
269
270	cc->cipher = cipher;
271	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
272		cc->cp_ctx = chachapoly_new(key, keylen);
273		ret = cc->cp_ctx != NULL ? 0 : SSH_ERR_INVALID_ARGUMENT;
274		goto out;
275	}
276	if ((cc->cipher->flags & CFLAG_NONE) != 0) {
277		ret = 0;
278		goto out;
279	}
280#ifndef WITH_OPENSSL
281	if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
282		aesctr_keysetup(&cc->ac_ctx, key, 8 * keylen, 8 * ivlen);
283		aesctr_ivsetup(&cc->ac_ctx, iv);
284		ret = 0;
285		goto out;
286	}
287	ret = SSH_ERR_INVALID_ARGUMENT;
288	goto out;
289#else /* WITH_OPENSSL */
290	type = (*cipher->evptype)();
291	if ((cc->evp = EVP_CIPHER_CTX_new()) == NULL) {
292		ret = SSH_ERR_ALLOC_FAIL;
293		goto out;
294	}
295	if (EVP_CipherInit(cc->evp, type, NULL, (u_char *)iv,
296	    (do_encrypt == CIPHER_ENCRYPT)) == 0) {
297		ret = SSH_ERR_LIBCRYPTO_ERROR;
298		goto out;
299	}
300	if (cipher_authlen(cipher) &&
301	    !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_IV_FIXED,
302	    -1, (u_char *)iv)) {
303		ret = SSH_ERR_LIBCRYPTO_ERROR;
304		goto out;
305	}
306	klen = EVP_CIPHER_CTX_key_length(cc->evp);
307	if (klen > 0 && keylen != (u_int)klen) {
308		if (EVP_CIPHER_CTX_set_key_length(cc->evp, keylen) == 0) {
309			ret = SSH_ERR_LIBCRYPTO_ERROR;
310			goto out;
311		}
312	}
313	if (EVP_CipherInit(cc->evp, NULL, (u_char *)key, NULL, -1) == 0) {
314		ret = SSH_ERR_LIBCRYPTO_ERROR;
315		goto out;
316	}
317	ret = 0;
318#endif /* WITH_OPENSSL */
319 out:
320	if (ret == 0) {
321		/* success */
322		*ccp = cc;
323	} else {
324		if (cc != NULL) {
325#ifdef WITH_OPENSSL
326			EVP_CIPHER_CTX_free(cc->evp);
327#endif /* WITH_OPENSSL */
328			freezero(cc, sizeof(*cc));
329		}
330	}
331	return ret;
332}
333
334/*
335 * cipher_crypt() operates as following:
336 * Copy 'aadlen' bytes (without en/decryption) from 'src' to 'dest'.
337 * These bytes are treated as additional authenticated data for
338 * authenticated encryption modes.
339 * En/Decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'.
340 * Use 'authlen' bytes at offset 'len'+'aadlen' as the authentication tag.
341 * This tag is written on encryption and verified on decryption.
342 * Both 'aadlen' and 'authlen' can be set to 0.
343 */
344int
345cipher_crypt(struct sshcipher_ctx *cc, u_int seqnr, u_char *dest,
346   const u_char *src, u_int len, u_int aadlen, u_int authlen)
347{
348	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
349		return chachapoly_crypt(cc->cp_ctx, seqnr, dest, src,
350		    len, aadlen, authlen, cc->encrypt);
351	}
352	if ((cc->cipher->flags & CFLAG_NONE) != 0) {
353		memcpy(dest, src, aadlen + len);
354		return 0;
355	}
356#ifndef WITH_OPENSSL
357	if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
358		if (aadlen)
359			memcpy(dest, src, aadlen);
360		aesctr_encrypt_bytes(&cc->ac_ctx, src + aadlen,
361		    dest + aadlen, len);
362		return 0;
363	}
364	return SSH_ERR_INVALID_ARGUMENT;
365#else
366	if (authlen) {
367		u_char lastiv[1];
368
369		if (authlen != cipher_authlen(cc->cipher))
370			return SSH_ERR_INVALID_ARGUMENT;
371		/* increment IV */
372		if (!EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN,
373		    1, lastiv))
374			return SSH_ERR_LIBCRYPTO_ERROR;
375		/* set tag on decyption */
376		if (!cc->encrypt &&
377		    !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_TAG,
378		    authlen, (u_char *)src + aadlen + len))
379			return SSH_ERR_LIBCRYPTO_ERROR;
380	}
381	if (aadlen) {
382		if (authlen &&
383		    EVP_Cipher(cc->evp, NULL, (u_char *)src, aadlen) < 0)
384			return SSH_ERR_LIBCRYPTO_ERROR;
385		memcpy(dest, src, aadlen);
386	}
387	if (len % cc->cipher->block_size)
388		return SSH_ERR_INVALID_ARGUMENT;
389	if (EVP_Cipher(cc->evp, dest + aadlen, (u_char *)src + aadlen,
390	    len) < 0)
391		return SSH_ERR_LIBCRYPTO_ERROR;
392	if (authlen) {
393		/* compute tag (on encrypt) or verify tag (on decrypt) */
394		if (EVP_Cipher(cc->evp, NULL, NULL, 0) < 0)
395			return cc->encrypt ?
396			    SSH_ERR_LIBCRYPTO_ERROR : SSH_ERR_MAC_INVALID;
397		if (cc->encrypt &&
398		    !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_GET_TAG,
399		    authlen, dest + aadlen + len))
400			return SSH_ERR_LIBCRYPTO_ERROR;
401	}
402	return 0;
403#endif
404}
405
406/* Extract the packet length, including any decryption necessary beforehand */
407int
408cipher_get_length(struct sshcipher_ctx *cc, u_int *plenp, u_int seqnr,
409    const u_char *cp, u_int len)
410{
411	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
412		return chachapoly_get_length(cc->cp_ctx, plenp, seqnr,
413		    cp, len);
414	if (len < 4)
415		return SSH_ERR_MESSAGE_INCOMPLETE;
416	*plenp = PEEK_U32(cp);
417	return 0;
418}
419
420void
421cipher_free(struct sshcipher_ctx *cc)
422{
423	if (cc == NULL)
424		return;
425	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
426		chachapoly_free(cc->cp_ctx);
427		cc->cp_ctx = NULL;
428	} else if ((cc->cipher->flags & CFLAG_AESCTR) != 0)
429		explicit_bzero(&cc->ac_ctx, sizeof(cc->ac_ctx));
430#ifdef WITH_OPENSSL
431	EVP_CIPHER_CTX_free(cc->evp);
432	cc->evp = NULL;
433#endif
434	freezero(cc, sizeof(*cc));
435}
436
437int
438cipher_get_keyiv(struct sshcipher_ctx *cc, u_char *iv, size_t len)
439{
440#ifdef WITH_OPENSSL
441	const struct sshcipher *c = cc->cipher;
442	int evplen;
443#endif
444
445	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
446		if (len != 0)
447			return SSH_ERR_INVALID_ARGUMENT;
448		return 0;
449	}
450	if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
451		if (len != sizeof(cc->ac_ctx.ctr))
452			return SSH_ERR_INVALID_ARGUMENT;
453		memcpy(iv, cc->ac_ctx.ctr, len);
454		return 0;
455	}
456	if ((cc->cipher->flags & CFLAG_NONE) != 0)
457		return 0;
458
459#ifdef WITH_OPENSSL
460	evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
461	if (evplen == 0)
462		return 0;
463	else if (evplen < 0)
464		return SSH_ERR_LIBCRYPTO_ERROR;
465	if ((size_t)evplen != len)
466		return SSH_ERR_INVALID_ARGUMENT;
467	if (cipher_authlen(c)) {
468		if (!EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN,
469		    len, iv))
470			return SSH_ERR_LIBCRYPTO_ERROR;
471	} else if (!EVP_CIPHER_CTX_get_iv(cc->evp, iv, len))
472		return SSH_ERR_LIBCRYPTO_ERROR;
473#endif
474	return 0;
475}
476
477int
478cipher_set_keyiv(struct sshcipher_ctx *cc, const u_char *iv, size_t len)
479{
480#ifdef WITH_OPENSSL
481	const struct sshcipher *c = cc->cipher;
482	int evplen = 0;
483#endif
484
485	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
486		return 0;
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 SSH_ERR_LIBCRYPTO_ERROR;
494	if ((size_t)evplen != len)
495		return SSH_ERR_INVALID_ARGUMENT;
496	if (cipher_authlen(c)) {
497		/* XXX iv arg is const, but EVP_CIPHER_CTX_ctrl isn't */
498		if (!EVP_CIPHER_CTX_ctrl(cc->evp,
499		    EVP_CTRL_GCM_SET_IV_FIXED, -1, (void *)iv))
500			return SSH_ERR_LIBCRYPTO_ERROR;
501	} else if (!EVP_CIPHER_CTX_set_iv(cc->evp, iv, evplen))
502		return SSH_ERR_LIBCRYPTO_ERROR;
503#endif
504	return 0;
505}
506