xref: /openssh-portable/cipher.c (revision d081f017) 
1 /* $OpenBSD: cipher.c,v 1.116 2020/03/13 03:17:07 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; /* XXX union with evp? */
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 	{ "rijndael-cbc@lysator.liu.se",
95 				16, 32, 0, 0, CFLAG_CBC, EVP_aes_256_cbc },
96 	{ "aes128-ctr",		16, 16, 0, 0, 0, EVP_aes_128_ctr },
97 	{ "aes192-ctr",		16, 24, 0, 0, 0, EVP_aes_192_ctr },
98 	{ "aes256-ctr",		16, 32, 0, 0, 0, EVP_aes_256_ctr },
99 # ifdef OPENSSL_HAVE_EVPGCM
100 	{ "aes128-gcm@openssh.com",
101 				16, 16, 12, 16, 0, EVP_aes_128_gcm },
102 	{ "aes256-gcm@openssh.com",
103 				16, 32, 12, 16, 0, EVP_aes_256_gcm },
104 # endif /* OPENSSL_HAVE_EVPGCM */
105 #else
106 	{ "aes128-ctr",		16, 16, 0, 0, CFLAG_AESCTR, NULL },
107 	{ "aes192-ctr",		16, 24, 0, 0, CFLAG_AESCTR, NULL },
108 	{ "aes256-ctr",		16, 32, 0, 0, CFLAG_AESCTR, NULL },
109 #endif
110 	{ "chacha20-poly1305@openssh.com",
111 				8, 64, 0, 16, CFLAG_CHACHAPOLY, NULL },
112 	{ "none",		8, 0, 0, 0, CFLAG_NONE, NULL },
113 
114 	{ NULL,			0, 0, 0, 0, 0, NULL }
115 };
116 
117 /*--*/
118 
119 /* Returns a comma-separated list of supported ciphers. */
120 char *
121 cipher_alg_list(char sep, int auth_only)
122 {
123 	char *tmp, *ret = NULL;
124 	size_t nlen, rlen = 0;
125 	const struct sshcipher *c;
126 
127 	for (c = ciphers; c->name != NULL; c++) {
128 		if ((c->flags & CFLAG_INTERNAL) != 0)
129 			continue;
130 		if (auth_only && c->auth_len == 0)
131 			continue;
132 		if (ret != NULL)
133 			ret[rlen++] = sep;
134 		nlen = strlen(c->name);
135 		if ((tmp = realloc(ret, rlen + nlen + 2)) == NULL) {
136 			free(ret);
137 			return NULL;
138 		}
139 		ret = tmp;
140 		memcpy(ret + rlen, c->name, nlen + 1);
141 		rlen += nlen;
142 	}
143 	return ret;
144 }
145 
146 const char *
147 compression_alg_list(int compression)
148 {
149 #ifdef WITH_ZLIB
150 	return compression ? "zlib@openssh.com,zlib,none" :
151 	    "none,zlib@openssh.com,zlib";
152 #else
153 	return "none";
154 #endif
155 }
156 
157 u_int
158 cipher_blocksize(const struct sshcipher *c)
159 {
160 	return (c->block_size);
161 }
162 
163 u_int
164 cipher_keylen(const struct sshcipher *c)
165 {
166 	return (c->key_len);
167 }
168 
169 u_int
170 cipher_seclen(const struct sshcipher *c)
171 {
172 	if (strcmp("3des-cbc", c->name) == 0)
173 		return 14;
174 	return cipher_keylen(c);
175 }
176 
177 u_int
178 cipher_authlen(const struct sshcipher *c)
179 {
180 	return (c->auth_len);
181 }
182 
183 u_int
184 cipher_ivlen(const struct sshcipher *c)
185 {
186 	/*
187 	 * Default is cipher block size, except for chacha20+poly1305 that
188 	 * needs no IV. XXX make iv_len == -1 default?
189 	 */
190 	return (c->iv_len != 0 || (c->flags & CFLAG_CHACHAPOLY) != 0) ?
191 	    c->iv_len : c->block_size;
192 }
193 
194 u_int
195 cipher_is_cbc(const struct sshcipher *c)
196 {
197 	return (c->flags & CFLAG_CBC) != 0;
198 }
199 
200 u_int
201 cipher_ctx_is_plaintext(struct sshcipher_ctx *cc)
202 {
203 	return cc->plaintext;
204 }
205 
206 const struct sshcipher *
207 cipher_by_name(const char *name)
208 {
209 	const struct sshcipher *c;
210 	for (c = ciphers; c->name != NULL; c++)
211 		if (strcmp(c->name, name) == 0)
212 			return c;
213 	return NULL;
214 }
215 
216 #define	CIPHER_SEP	","
217 int
218 ciphers_valid(const char *names)
219 {
220 	const struct sshcipher *c;
221 	char *cipher_list, *cp;
222 	char *p;
223 
224 	if (names == NULL || strcmp(names, "") == 0)
225 		return 0;
226 	if ((cipher_list = cp = strdup(names)) == NULL)
227 		return 0;
228 	for ((p = strsep(&cp, CIPHER_SEP)); p && *p != '\0';
229 	    (p = strsep(&cp, CIPHER_SEP))) {
230 		c = cipher_by_name(p);
231 		if (c == NULL || (c->flags & CFLAG_INTERNAL) != 0) {
232 			free(cipher_list);
233 			return 0;
234 		}
235 	}
236 	free(cipher_list);
237 	return 1;
238 }
239 
240 const char *
241 cipher_warning_message(const struct sshcipher_ctx *cc)
242 {
243 	if (cc == NULL || cc->cipher == NULL)
244 		return NULL;
245 	/* XXX repurpose for CBC warning */
246 	return NULL;
247 }
248 
249 int
250 cipher_init(struct sshcipher_ctx **ccp, const struct sshcipher *cipher,
251     const u_char *key, u_int keylen, const u_char *iv, u_int ivlen,
252     int do_encrypt)
253 {
254 	struct sshcipher_ctx *cc = NULL;
255 	int ret = SSH_ERR_INTERNAL_ERROR;
256 #ifdef WITH_OPENSSL
257 	const EVP_CIPHER *type;
258 	int klen;
259 #endif
260 
261 	*ccp = NULL;
262 	if ((cc = calloc(sizeof(*cc), 1)) == NULL)
263 		return SSH_ERR_ALLOC_FAIL;
264 
265 	cc->plaintext = (cipher->flags & CFLAG_NONE) != 0;
266 	cc->encrypt = do_encrypt;
267 
268 	if (keylen < cipher->key_len ||
269 	    (iv != NULL && ivlen < cipher_ivlen(cipher))) {
270 		ret = SSH_ERR_INVALID_ARGUMENT;
271 		goto out;
272 	}
273 
274 	cc->cipher = cipher;
275 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
276 		ret = chachapoly_init(&cc->cp_ctx, key, keylen);
277 		goto out;
278 	}
279 	if ((cc->cipher->flags & CFLAG_NONE) != 0) {
280 		ret = 0;
281 		goto out;
282 	}
283 #ifndef WITH_OPENSSL
284 	if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
285 		aesctr_keysetup(&cc->ac_ctx, key, 8 * keylen, 8 * ivlen);
286 		aesctr_ivsetup(&cc->ac_ctx, iv);
287 		ret = 0;
288 		goto out;
289 	}
290 	ret = SSH_ERR_INVALID_ARGUMENT;
291 	goto out;
292 #else /* WITH_OPENSSL */
293 	type = (*cipher->evptype)();
294 	if ((cc->evp = EVP_CIPHER_CTX_new()) == NULL) {
295 		ret = SSH_ERR_ALLOC_FAIL;
296 		goto out;
297 	}
298 	if (EVP_CipherInit(cc->evp, type, NULL, (u_char *)iv,
299 	    (do_encrypt == CIPHER_ENCRYPT)) == 0) {
300 		ret = SSH_ERR_LIBCRYPTO_ERROR;
301 		goto out;
302 	}
303 	if (cipher_authlen(cipher) &&
304 	    !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_IV_FIXED,
305 	    -1, (u_char *)iv)) {
306 		ret = SSH_ERR_LIBCRYPTO_ERROR;
307 		goto out;
308 	}
309 	klen = EVP_CIPHER_CTX_key_length(cc->evp);
310 	if (klen > 0 && keylen != (u_int)klen) {
311 		if (EVP_CIPHER_CTX_set_key_length(cc->evp, keylen) == 0) {
312 			ret = SSH_ERR_LIBCRYPTO_ERROR;
313 			goto out;
314 		}
315 	}
316 	if (EVP_CipherInit(cc->evp, NULL, (u_char *)key, NULL, -1) == 0) {
317 		ret = SSH_ERR_LIBCRYPTO_ERROR;
318 		goto out;
319 	}
320 	ret = 0;
321 #endif /* WITH_OPENSSL */
322  out:
323 	if (ret == 0) {
324 		/* success */
325 		*ccp = cc;
326 	} else {
327 		if (cc != NULL) {
328 #ifdef WITH_OPENSSL
329 			EVP_CIPHER_CTX_free(cc->evp);
330 #endif /* WITH_OPENSSL */
331 			freezero(cc, sizeof(*cc));
332 		}
333 	}
334 	return ret;
335 }
336 
337 /*
338  * cipher_crypt() operates as following:
339  * Copy 'aadlen' bytes (without en/decryption) from 'src' to 'dest'.
340  * These bytes are treated as additional authenticated data for
341  * authenticated encryption modes.
342  * En/Decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'.
343  * Use 'authlen' bytes at offset 'len'+'aadlen' as the authentication tag.
344  * This tag is written on encryption and verified on decryption.
345  * Both 'aadlen' and 'authlen' can be set to 0.
346  */
347 int
348 cipher_crypt(struct sshcipher_ctx *cc, u_int seqnr, u_char *dest,
349    const u_char *src, u_int len, u_int aadlen, u_int authlen)
350 {
351 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
352 		return chachapoly_crypt(&cc->cp_ctx, seqnr, dest, src,
353 		    len, aadlen, authlen, cc->encrypt);
354 	}
355 	if ((cc->cipher->flags & CFLAG_NONE) != 0) {
356 		memcpy(dest, src, aadlen + len);
357 		return 0;
358 	}
359 #ifndef WITH_OPENSSL
360 	if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
361 		if (aadlen)
362 			memcpy(dest, src, aadlen);
363 		aesctr_encrypt_bytes(&cc->ac_ctx, src + aadlen,
364 		    dest + aadlen, len);
365 		return 0;
366 	}
367 	return SSH_ERR_INVALID_ARGUMENT;
368 #else
369 	if (authlen) {
370 		u_char lastiv[1];
371 
372 		if (authlen != cipher_authlen(cc->cipher))
373 			return SSH_ERR_INVALID_ARGUMENT;
374 		/* increment IV */
375 		if (!EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN,
376 		    1, lastiv))
377 			return SSH_ERR_LIBCRYPTO_ERROR;
378 		/* set tag on decyption */
379 		if (!cc->encrypt &&
380 		    !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_TAG,
381 		    authlen, (u_char *)src + aadlen + len))
382 			return SSH_ERR_LIBCRYPTO_ERROR;
383 	}
384 	if (aadlen) {
385 		if (authlen &&
386 		    EVP_Cipher(cc->evp, NULL, (u_char *)src, aadlen) < 0)
387 			return SSH_ERR_LIBCRYPTO_ERROR;
388 		memcpy(dest, src, aadlen);
389 	}
390 	if (len % cc->cipher->block_size)
391 		return SSH_ERR_INVALID_ARGUMENT;
392 	if (EVP_Cipher(cc->evp, dest + aadlen, (u_char *)src + aadlen,
393 	    len) < 0)
394 		return SSH_ERR_LIBCRYPTO_ERROR;
395 	if (authlen) {
396 		/* compute tag (on encrypt) or verify tag (on decrypt) */
397 		if (EVP_Cipher(cc->evp, NULL, NULL, 0) < 0)
398 			return cc->encrypt ?
399 			    SSH_ERR_LIBCRYPTO_ERROR : SSH_ERR_MAC_INVALID;
400 		if (cc->encrypt &&
401 		    !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_GET_TAG,
402 		    authlen, dest + aadlen + len))
403 			return SSH_ERR_LIBCRYPTO_ERROR;
404 	}
405 	return 0;
406 #endif
407 }
408 
409 /* Extract the packet length, including any decryption necessary beforehand */
410 int
411 cipher_get_length(struct sshcipher_ctx *cc, u_int *plenp, u_int seqnr,
412     const u_char *cp, u_int len)
413 {
414 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
415 		return chachapoly_get_length(&cc->cp_ctx, plenp, seqnr,
416 		    cp, len);
417 	if (len < 4)
418 		return SSH_ERR_MESSAGE_INCOMPLETE;
419 	*plenp = PEEK_U32(cp);
420 	return 0;
421 }
422 
423 void
424 cipher_free(struct sshcipher_ctx *cc)
425 {
426 	if (cc == NULL)
427 		return;
428 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
429 		explicit_bzero(&cc->cp_ctx, sizeof(cc->cp_ctx));
430 	else if ((cc->cipher->flags & CFLAG_AESCTR) != 0)
431 		explicit_bzero(&cc->ac_ctx, sizeof(cc->ac_ctx));
432 #ifdef WITH_OPENSSL
433 	EVP_CIPHER_CTX_free(cc->evp);
434 	cc->evp = NULL;
435 #endif
436 	freezero(cc, sizeof(*cc));
437 }
438 
439 /*
440  * Exports an IV from the sshcipher_ctx required to export the key
441  * state back from the unprivileged child to the privileged parent
442  * process.
443  */
444 int
445 cipher_get_keyiv_len(const struct sshcipher_ctx *cc)
446 {
447 	const struct sshcipher *c = cc->cipher;
448 
449 	if ((c->flags & CFLAG_CHACHAPOLY) != 0)
450 		return 0;
451 	else if ((c->flags & CFLAG_AESCTR) != 0)
452 		return sizeof(cc->ac_ctx.ctr);
453 #ifdef WITH_OPENSSL
454 	return EVP_CIPHER_CTX_iv_length(cc->evp);
455 #else
456 	return 0;
457 #endif
458 }
459 
460 int
461 cipher_get_keyiv(struct sshcipher_ctx *cc, u_char *iv, size_t len)
462 {
463 #ifdef WITH_OPENSSL
464 	const struct sshcipher *c = cc->cipher;
465 	int evplen;
466 #endif
467 
468 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
469 		if (len != 0)
470 			return SSH_ERR_INVALID_ARGUMENT;
471 		return 0;
472 	}
473 	if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
474 		if (len != sizeof(cc->ac_ctx.ctr))
475 			return SSH_ERR_INVALID_ARGUMENT;
476 		memcpy(iv, cc->ac_ctx.ctr, len);
477 		return 0;
478 	}
479 	if ((cc->cipher->flags & CFLAG_NONE) != 0)
480 		return 0;
481 
482 #ifdef WITH_OPENSSL
483 	evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
484 	if (evplen == 0)
485 		return 0;
486 	else if (evplen < 0)
487 		return SSH_ERR_LIBCRYPTO_ERROR;
488 	if ((size_t)evplen != len)
489 		return SSH_ERR_INVALID_ARGUMENT;
490 #ifndef OPENSSL_HAVE_EVPCTR
491 	if (c->evptype == evp_aes_128_ctr)
492 		ssh_aes_ctr_iv(cc->evp, 0, iv, len);
493 	else
494 #endif
495 	if (cipher_authlen(c)) {
496 		if (!EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN,
497 		   len, iv))
498 		       return SSH_ERR_LIBCRYPTO_ERROR;
499 	} else if (!EVP_CIPHER_CTX_get_iv(cc->evp, iv, len))
500 	       return SSH_ERR_LIBCRYPTO_ERROR;
501 #endif
502 	return 0;
503 }
504 
505 int
506 cipher_set_keyiv(struct sshcipher_ctx *cc, const u_char *iv, size_t len)
507 {
508 #ifdef WITH_OPENSSL
509 	const struct sshcipher *c = cc->cipher;
510 	int evplen = 0;
511 #endif
512 
513 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
514 		return 0;
515 	if ((cc->cipher->flags & CFLAG_NONE) != 0)
516 		return 0;
517 
518 #ifdef WITH_OPENSSL
519 	evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
520 	if (evplen <= 0)
521 		return SSH_ERR_LIBCRYPTO_ERROR;
522 	if ((size_t)evplen != len)
523 		return SSH_ERR_INVALID_ARGUMENT;
524 #ifndef OPENSSL_HAVE_EVPCTR
525 	/* XXX iv arg is const, but ssh_aes_ctr_iv isn't */
526 	if (c->evptype == evp_aes_128_ctr)
527 		ssh_aes_ctr_iv(cc->evp, 1, (u_char *)iv, evplen);
528 	else
529 #endif
530 	if (cipher_authlen(c)) {
531 		/* XXX iv arg is const, but EVP_CIPHER_CTX_ctrl isn't */
532 		if (!EVP_CIPHER_CTX_ctrl(cc->evp,
533 		    EVP_CTRL_GCM_SET_IV_FIXED, -1, (void *)iv))
534 			return SSH_ERR_LIBCRYPTO_ERROR;
535 	} else if (!EVP_CIPHER_CTX_set_iv(cc->evp, iv, evplen))
536 		return SSH_ERR_LIBCRYPTO_ERROR;
537 #endif
538 	return 0;
539 }
540