xref: /freebsd/crypto/openssh/cipher.c (revision 7ef62cebc2f965b0f640263e179276928885e33d) 
1 /* $OpenBSD: cipher.c,v 1.119 2021/04/03 06:18:40 djm 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 
58 struct 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 
67 struct 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 
86 static 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. */
116 char *
117 cipher_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 
142 const char *
143 compression_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 
153 u_int
154 cipher_blocksize(const struct sshcipher *c)
155 {
156 	return (c->block_size);
157 }
158 
159 u_int
160 cipher_keylen(const struct sshcipher *c)
161 {
162 	return (c->key_len);
163 }
164 
165 u_int
166 cipher_seclen(const struct sshcipher *c)
167 {
168 	if (strcmp("3des-cbc", c->name) == 0)
169 		return 14;
170 	return cipher_keylen(c);
171 }
172 
173 u_int
174 cipher_authlen(const struct sshcipher *c)
175 {
176 	return (c->auth_len);
177 }
178 
179 u_int
180 cipher_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 
190 u_int
191 cipher_is_cbc(const struct sshcipher *c)
192 {
193 	return (c->flags & CFLAG_CBC) != 0;
194 }
195 
196 u_int
197 cipher_ctx_is_plaintext(struct sshcipher_ctx *cc)
198 {
199 	return cc->plaintext;
200 }
201 
202 const struct sshcipher *
203 cipher_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	","
213 int
214 ciphers_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 
236 const char *
237 cipher_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 
245 int
246 cipher_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  */
344 int
345 cipher_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 */
407 int
408 cipher_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 
420 void
421 cipher_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 
437 /*
438  * Exports an IV from the sshcipher_ctx required to export the key
439  * state back from the unprivileged child to the privileged parent
440  * process.
441  */
442 int
443 cipher_get_keyiv_len(const struct sshcipher_ctx *cc)
444 {
445 	const struct sshcipher *c = cc->cipher;
446 
447 	if ((c->flags & CFLAG_CHACHAPOLY) != 0)
448 		return 0;
449 	else if ((c->flags & CFLAG_AESCTR) != 0)
450 		return sizeof(cc->ac_ctx.ctr);
451 #ifdef WITH_OPENSSL
452 	return EVP_CIPHER_CTX_iv_length(cc->evp);
453 #else
454 	return 0;
455 #endif
456 }
457 
458 int
459 cipher_get_keyiv(struct sshcipher_ctx *cc, u_char *iv, size_t len)
460 {
461 #ifdef WITH_OPENSSL
462 	const struct sshcipher *c = cc->cipher;
463 	int evplen;
464 #endif
465 
466 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
467 		if (len != 0)
468 			return SSH_ERR_INVALID_ARGUMENT;
469 		return 0;
470 	}
471 	if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
472 		if (len != sizeof(cc->ac_ctx.ctr))
473 			return SSH_ERR_INVALID_ARGUMENT;
474 		memcpy(iv, cc->ac_ctx.ctr, len);
475 		return 0;
476 	}
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 0;
484 	else if (evplen < 0)
485 		return SSH_ERR_LIBCRYPTO_ERROR;
486 	if ((size_t)evplen != len)
487 		return SSH_ERR_INVALID_ARGUMENT;
488 	if (cipher_authlen(c)) {
489 		if (!EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN,
490 		    len, iv))
491 			return SSH_ERR_LIBCRYPTO_ERROR;
492 	} else if (!EVP_CIPHER_CTX_get_iv(cc->evp, iv, len))
493 		return SSH_ERR_LIBCRYPTO_ERROR;
494 #endif
495 	return 0;
496 }
497 
498 int
499 cipher_set_keyiv(struct sshcipher_ctx *cc, const u_char *iv, size_t len)
500 {
501 #ifdef WITH_OPENSSL
502 	const struct sshcipher *c = cc->cipher;
503 	int evplen = 0;
504 #endif
505 
506 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
507 		return 0;
508 	if ((cc->cipher->flags & CFLAG_NONE) != 0)
509 		return 0;
510 
511 #ifdef WITH_OPENSSL
512 	evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
513 	if (evplen <= 0)
514 		return SSH_ERR_LIBCRYPTO_ERROR;
515 	if ((size_t)evplen != len)
516 		return SSH_ERR_INVALID_ARGUMENT;
517 	if (cipher_authlen(c)) {
518 		/* XXX iv arg is const, but EVP_CIPHER_CTX_ctrl isn't */
519 		if (!EVP_CIPHER_CTX_ctrl(cc->evp,
520 		    EVP_CTRL_GCM_SET_IV_FIXED, -1, (void *)iv))
521 			return SSH_ERR_LIBCRYPTO_ERROR;
522 	} else if (!EVP_CIPHER_CTX_set_iv(cc->evp, iv, evplen))
523 		return SSH_ERR_LIBCRYPTO_ERROR;
524 #endif
525 	return 0;
526 }
527