xref: /openbsd/usr.bin/ssh/cipher.c (revision 414d371c) 
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 <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 
54 struct 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 
63 struct 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 
82 static 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. */
110 char *
111 cipher_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 
136 const char *
137 compression_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 
147 u_int
148 cipher_blocksize(const struct sshcipher *c)
149 {
150 	return (c->block_size);
151 }
152 
153 u_int
154 cipher_keylen(const struct sshcipher *c)
155 {
156 	return (c->key_len);
157 }
158 
159 u_int
160 cipher_seclen(const struct sshcipher *c)
161 {
162 	if (strcmp("3des-cbc", c->name) == 0)
163 		return 14;
164 	return cipher_keylen(c);
165 }
166 
167 u_int
168 cipher_authlen(const struct sshcipher *c)
169 {
170 	return (c->auth_len);
171 }
172 
173 u_int
174 cipher_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 
184 u_int
185 cipher_is_cbc(const struct sshcipher *c)
186 {
187 	return (c->flags & CFLAG_CBC) != 0;
188 }
189 
190 u_int
191 cipher_ctx_is_plaintext(struct sshcipher_ctx *cc)
192 {
193 	return cc->plaintext;
194 }
195 
196 const struct sshcipher *
197 cipher_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	","
207 int
208 ciphers_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 
230 const char *
231 cipher_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 
239 int
240 cipher_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  */
338 int
339 cipher_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 decyption */
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 */
401 int
402 cipher_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 
414 void
415 cipher_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 
431 int
432 cipher_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 
470 int
471 cipher_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