xref: /openbsd-src/usr.bin/ssh/cipher.c (revision ae3cb403620ab940fbaabb3055fac045a63d56b7) 
1 /* $OpenBSD: cipher.c,v 1.108 2017/11/03 02:22:41 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 <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 
51 struct sshcipher_ctx {
52 	int	plaintext;
53 	int	encrypt;
54 	EVP_CIPHER_CTX *evp;
55 	struct chachapoly_ctx cp_ctx; /* XXX union with evp? */
56 	struct aesctr_ctx ac_ctx; /* XXX union with evp? */
57 	const struct sshcipher *cipher;
58 };
59 
60 struct sshcipher {
61 	char	*name;
62 	u_int	block_size;
63 	u_int	key_len;
64 	u_int	iv_len;		/* defaults to block_size */
65 	u_int	auth_len;
66 	u_int	flags;
67 #define CFLAG_CBC		(1<<0)
68 #define CFLAG_CHACHAPOLY	(1<<1)
69 #define CFLAG_AESCTR		(1<<2)
70 #define CFLAG_NONE		(1<<3)
71 #define CFLAG_INTERNAL		CFLAG_NONE /* Don't use "none" for packets */
72 #ifdef WITH_OPENSSL
73 	const EVP_CIPHER	*(*evptype)(void);
74 #else
75 	void	*ignored;
76 #endif
77 };
78 
79 static const struct sshcipher ciphers[] = {
80 #ifdef WITH_OPENSSL
81 	{ "3des-cbc",		8, 24, 0, 0, CFLAG_CBC, EVP_des_ede3_cbc },
82 	{ "aes128-cbc",		16, 16, 0, 0, CFLAG_CBC, EVP_aes_128_cbc },
83 	{ "aes192-cbc",		16, 24, 0, 0, CFLAG_CBC, EVP_aes_192_cbc },
84 	{ "aes256-cbc",		16, 32, 0, 0, CFLAG_CBC, EVP_aes_256_cbc },
85 	{ "rijndael-cbc@lysator.liu.se",
86 				16, 32, 0, 0, CFLAG_CBC, EVP_aes_256_cbc },
87 	{ "aes128-ctr",		16, 16, 0, 0, 0, EVP_aes_128_ctr },
88 	{ "aes192-ctr",		16, 24, 0, 0, 0, EVP_aes_192_ctr },
89 	{ "aes256-ctr",		16, 32, 0, 0, 0, EVP_aes_256_ctr },
90 	{ "aes128-gcm@openssh.com",
91 				16, 16, 12, 16, 0, EVP_aes_128_gcm },
92 	{ "aes256-gcm@openssh.com",
93 				16, 32, 12, 16, 0, EVP_aes_256_gcm },
94 #else
95 	{ "aes128-ctr",		16, 16, 0, 0, CFLAG_AESCTR, NULL },
96 	{ "aes192-ctr",		16, 24, 0, 0, CFLAG_AESCTR, NULL },
97 	{ "aes256-ctr",		16, 32, 0, 0, CFLAG_AESCTR, NULL },
98 #endif
99 	{ "chacha20-poly1305@openssh.com",
100 				8, 64, 0, 16, CFLAG_CHACHAPOLY, NULL },
101 	{ "none",		8, 0, 0, 0, CFLAG_NONE, NULL },
102 
103 	{ NULL,			0, 0, 0, 0, 0, NULL }
104 };
105 
106 /*--*/
107 
108 /* Returns a comma-separated list of supported ciphers. */
109 char *
110 cipher_alg_list(char sep, int auth_only)
111 {
112 	char *tmp, *ret = NULL;
113 	size_t nlen, rlen = 0;
114 	const struct sshcipher *c;
115 
116 	for (c = ciphers; c->name != NULL; c++) {
117 		if ((c->flags & CFLAG_INTERNAL) != 0)
118 			continue;
119 		if (auth_only && c->auth_len == 0)
120 			continue;
121 		if (ret != NULL)
122 			ret[rlen++] = sep;
123 		nlen = strlen(c->name);
124 		if ((tmp = realloc(ret, rlen + nlen + 2)) == NULL) {
125 			free(ret);
126 			return NULL;
127 		}
128 		ret = tmp;
129 		memcpy(ret + rlen, c->name, nlen + 1);
130 		rlen += nlen;
131 	}
132 	return ret;
133 }
134 
135 u_int
136 cipher_blocksize(const struct sshcipher *c)
137 {
138 	return (c->block_size);
139 }
140 
141 u_int
142 cipher_keylen(const struct sshcipher *c)
143 {
144 	return (c->key_len);
145 }
146 
147 u_int
148 cipher_seclen(const struct sshcipher *c)
149 {
150 	if (strcmp("3des-cbc", c->name) == 0)
151 		return 14;
152 	return cipher_keylen(c);
153 }
154 
155 u_int
156 cipher_authlen(const struct sshcipher *c)
157 {
158 	return (c->auth_len);
159 }
160 
161 u_int
162 cipher_ivlen(const struct sshcipher *c)
163 {
164 	/*
165 	 * Default is cipher block size, except for chacha20+poly1305 that
166 	 * needs no IV. XXX make iv_len == -1 default?
167 	 */
168 	return (c->iv_len != 0 || (c->flags & CFLAG_CHACHAPOLY) != 0) ?
169 	    c->iv_len : c->block_size;
170 }
171 
172 u_int
173 cipher_is_cbc(const struct sshcipher *c)
174 {
175 	return (c->flags & CFLAG_CBC) != 0;
176 }
177 
178 u_int
179 cipher_ctx_is_plaintext(struct sshcipher_ctx *cc)
180 {
181 	return cc->plaintext;
182 }
183 
184 const struct sshcipher *
185 cipher_by_name(const char *name)
186 {
187 	const struct sshcipher *c;
188 	for (c = ciphers; c->name != NULL; c++)
189 		if (strcmp(c->name, name) == 0)
190 			return c;
191 	return NULL;
192 }
193 
194 #define	CIPHER_SEP	","
195 int
196 ciphers_valid(const char *names)
197 {
198 	const struct sshcipher *c;
199 	char *cipher_list, *cp;
200 	char *p;
201 
202 	if (names == NULL || strcmp(names, "") == 0)
203 		return 0;
204 	if ((cipher_list = cp = strdup(names)) == NULL)
205 		return 0;
206 	for ((p = strsep(&cp, CIPHER_SEP)); p && *p != '\0';
207 	    (p = strsep(&cp, CIPHER_SEP))) {
208 		c = cipher_by_name(p);
209 		if (c == NULL || (c->flags & CFLAG_INTERNAL) != 0) {
210 			free(cipher_list);
211 			return 0;
212 		}
213 	}
214 	free(cipher_list);
215 	return 1;
216 }
217 
218 const char *
219 cipher_warning_message(const struct sshcipher_ctx *cc)
220 {
221 	if (cc == NULL || cc->cipher == NULL)
222 		return NULL;
223 	/* XXX repurpose for CBC warning */
224 	return NULL;
225 }
226 
227 int
228 cipher_init(struct sshcipher_ctx **ccp, const struct sshcipher *cipher,
229     const u_char *key, u_int keylen, const u_char *iv, u_int ivlen,
230     int do_encrypt)
231 {
232 	struct sshcipher_ctx *cc = NULL;
233 	int ret = SSH_ERR_INTERNAL_ERROR;
234 #ifdef WITH_OPENSSL
235 	const EVP_CIPHER *type;
236 	int klen;
237 #endif
238 
239 	*ccp = NULL;
240 	if ((cc = calloc(sizeof(*cc), 1)) == NULL)
241 		return SSH_ERR_ALLOC_FAIL;
242 
243 	cc->plaintext = (cipher->flags & CFLAG_NONE) != 0;
244 	cc->encrypt = do_encrypt;
245 
246 	if (keylen < cipher->key_len ||
247 	    (iv != NULL && ivlen < cipher_ivlen(cipher))) {
248 		ret = SSH_ERR_INVALID_ARGUMENT;
249 		goto out;
250 	}
251 
252 	cc->cipher = cipher;
253 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
254 		ret = chachapoly_init(&cc->cp_ctx, key, keylen);
255 		goto out;
256 	}
257 	if ((cc->cipher->flags & CFLAG_NONE) != 0) {
258 		ret = 0;
259 		goto out;
260 	}
261 #ifndef WITH_OPENSSL
262 	if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
263 		aesctr_keysetup(&cc->ac_ctx, key, 8 * keylen, 8 * ivlen);
264 		aesctr_ivsetup(&cc->ac_ctx, iv);
265 		ret = 0;
266 		goto out;
267 	}
268 	ret = SSH_ERR_INVALID_ARGUMENT;
269 	goto out;
270 #else /* WITH_OPENSSL */
271 	type = (*cipher->evptype)();
272 	if ((cc->evp = EVP_CIPHER_CTX_new()) == NULL) {
273 		ret = SSH_ERR_ALLOC_FAIL;
274 		goto out;
275 	}
276 	if (EVP_CipherInit(cc->evp, type, NULL, (u_char *)iv,
277 	    (do_encrypt == CIPHER_ENCRYPT)) == 0) {
278 		ret = SSH_ERR_LIBCRYPTO_ERROR;
279 		goto out;
280 	}
281 	if (cipher_authlen(cipher) &&
282 	    !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_IV_FIXED,
283 	    -1, (u_char *)iv)) {
284 		ret = SSH_ERR_LIBCRYPTO_ERROR;
285 		goto out;
286 	}
287 	klen = EVP_CIPHER_CTX_key_length(cc->evp);
288 	if (klen > 0 && keylen != (u_int)klen) {
289 		if (EVP_CIPHER_CTX_set_key_length(cc->evp, keylen) == 0) {
290 			ret = SSH_ERR_LIBCRYPTO_ERROR;
291 			goto out;
292 		}
293 	}
294 	if (EVP_CipherInit(cc->evp, NULL, (u_char *)key, NULL, -1) == 0) {
295 		ret = SSH_ERR_LIBCRYPTO_ERROR;
296 		goto out;
297 	}
298 	ret = 0;
299 #endif /* WITH_OPENSSL */
300  out:
301 	if (ret == 0) {
302 		/* success */
303 		*ccp = cc;
304 	} else {
305 		if (cc != NULL) {
306 #ifdef WITH_OPENSSL
307 			if (cc->evp != NULL)
308 				EVP_CIPHER_CTX_free(cc->evp);
309 #endif /* WITH_OPENSSL */
310 			explicit_bzero(cc, sizeof(*cc));
311 			free(cc);
312 		}
313 	}
314 	return ret;
315 }
316 
317 /*
318  * cipher_crypt() operates as following:
319  * Copy 'aadlen' bytes (without en/decryption) from 'src' to 'dest'.
320  * Theses bytes are treated as additional authenticated data for
321  * authenticated encryption modes.
322  * En/Decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'.
323  * Use 'authlen' bytes at offset 'len'+'aadlen' as the authentication tag.
324  * This tag is written on encryption and verified on decryption.
325  * Both 'aadlen' and 'authlen' can be set to 0.
326  */
327 int
328 cipher_crypt(struct sshcipher_ctx *cc, u_int seqnr, u_char *dest,
329    const u_char *src, u_int len, u_int aadlen, u_int authlen)
330 {
331 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
332 		return chachapoly_crypt(&cc->cp_ctx, seqnr, dest, src,
333 		    len, aadlen, authlen, cc->encrypt);
334 	}
335 	if ((cc->cipher->flags & CFLAG_NONE) != 0) {
336 		memcpy(dest, src, aadlen + len);
337 		return 0;
338 	}
339 #ifndef WITH_OPENSSL
340 	if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
341 		if (aadlen)
342 			memcpy(dest, src, aadlen);
343 		aesctr_encrypt_bytes(&cc->ac_ctx, src + aadlen,
344 		    dest + aadlen, len);
345 		return 0;
346 	}
347 	return SSH_ERR_INVALID_ARGUMENT;
348 #else
349 	if (authlen) {
350 		u_char lastiv[1];
351 
352 		if (authlen != cipher_authlen(cc->cipher))
353 			return SSH_ERR_INVALID_ARGUMENT;
354 		/* increment IV */
355 		if (!EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN,
356 		    1, lastiv))
357 			return SSH_ERR_LIBCRYPTO_ERROR;
358 		/* set tag on decyption */
359 		if (!cc->encrypt &&
360 		    !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_TAG,
361 		    authlen, (u_char *)src + aadlen + len))
362 			return SSH_ERR_LIBCRYPTO_ERROR;
363 	}
364 	if (aadlen) {
365 		if (authlen &&
366 		    EVP_Cipher(cc->evp, NULL, (u_char *)src, aadlen) < 0)
367 			return SSH_ERR_LIBCRYPTO_ERROR;
368 		memcpy(dest, src, aadlen);
369 	}
370 	if (len % cc->cipher->block_size)
371 		return SSH_ERR_INVALID_ARGUMENT;
372 	if (EVP_Cipher(cc->evp, dest + aadlen, (u_char *)src + aadlen,
373 	    len) < 0)
374 		return SSH_ERR_LIBCRYPTO_ERROR;
375 	if (authlen) {
376 		/* compute tag (on encrypt) or verify tag (on decrypt) */
377 		if (EVP_Cipher(cc->evp, NULL, NULL, 0) < 0)
378 			return cc->encrypt ?
379 			    SSH_ERR_LIBCRYPTO_ERROR : SSH_ERR_MAC_INVALID;
380 		if (cc->encrypt &&
381 		    !EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_GET_TAG,
382 		    authlen, dest + aadlen + len))
383 			return SSH_ERR_LIBCRYPTO_ERROR;
384 	}
385 	return 0;
386 #endif
387 }
388 
389 /* Extract the packet length, including any decryption necessary beforehand */
390 int
391 cipher_get_length(struct sshcipher_ctx *cc, u_int *plenp, u_int seqnr,
392     const u_char *cp, u_int len)
393 {
394 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
395 		return chachapoly_get_length(&cc->cp_ctx, plenp, seqnr,
396 		    cp, len);
397 	if (len < 4)
398 		return SSH_ERR_MESSAGE_INCOMPLETE;
399 	*plenp = get_u32(cp);
400 	return 0;
401 }
402 
403 void
404 cipher_free(struct sshcipher_ctx *cc)
405 {
406 	if (cc == NULL)
407 		return;
408 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
409 		explicit_bzero(&cc->cp_ctx, sizeof(cc->cp_ctx));
410 	else if ((cc->cipher->flags & CFLAG_AESCTR) != 0)
411 		explicit_bzero(&cc->ac_ctx, sizeof(cc->ac_ctx));
412 #ifdef WITH_OPENSSL
413 	if (cc->evp != NULL) {
414 		EVP_CIPHER_CTX_free(cc->evp);
415 		cc->evp = NULL;
416 	}
417 #endif
418 	explicit_bzero(cc, sizeof(*cc));
419 	free(cc);
420 }
421 
422 /*
423  * Exports an IV from the sshcipher_ctx required to export the key
424  * state back from the unprivileged child to the privileged parent
425  * process.
426  */
427 int
428 cipher_get_keyiv_len(const struct sshcipher_ctx *cc)
429 {
430 	const struct sshcipher *c = cc->cipher;
431 
432 	if ((c->flags & CFLAG_CHACHAPOLY) != 0)
433 		return 0;
434 	else if ((c->flags & CFLAG_AESCTR) != 0)
435 		return sizeof(cc->ac_ctx.ctr);
436 #ifdef WITH_OPENSSL
437 	return EVP_CIPHER_CTX_iv_length(cc->evp);
438 #else
439 	return 0;
440 #endif
441 }
442 
443 int
444 cipher_get_keyiv(struct sshcipher_ctx *cc, u_char *iv, u_int len)
445 {
446 #ifdef WITH_OPENSSL
447 	const struct sshcipher *c = cc->cipher;
448  	int evplen;
449 #endif
450 
451 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
452 		if (len != 0)
453 			return SSH_ERR_INVALID_ARGUMENT;
454 		return 0;
455 	}
456 	if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {
457 		if (len != sizeof(cc->ac_ctx.ctr))
458 			return SSH_ERR_INVALID_ARGUMENT;
459 		memcpy(iv, cc->ac_ctx.ctr, len);
460 		return 0;
461 	}
462 	if ((cc->cipher->flags & CFLAG_NONE) != 0)
463 		return 0;
464 
465 #ifdef WITH_OPENSSL
466 	evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
467 	if (evplen == 0)
468 		return 0;
469 	else if (evplen < 0)
470 		return SSH_ERR_LIBCRYPTO_ERROR;
471 	if ((u_int)evplen != len)
472 		return SSH_ERR_INVALID_ARGUMENT;
473 	if (cipher_authlen(c)) {
474 		if (!EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN,
475 		   len, iv))
476 		       return SSH_ERR_LIBCRYPTO_ERROR;
477 	} else
478 		memcpy(iv, cc->evp->iv, len);
479 #endif
480 	return 0;
481 }
482 
483 int
484 cipher_set_keyiv(struct sshcipher_ctx *cc, const u_char *iv)
485 {
486 #ifdef WITH_OPENSSL
487 	const struct sshcipher *c = cc->cipher;
488  	int evplen = 0;
489 #endif
490 
491 	if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
492 		return 0;
493 	if ((cc->cipher->flags & CFLAG_NONE) != 0)
494 		return 0;
495 
496 #ifdef WITH_OPENSSL
497 	evplen = EVP_CIPHER_CTX_iv_length(cc->evp);
498 	if (evplen <= 0)
499 		return SSH_ERR_LIBCRYPTO_ERROR;
500 	if (cipher_authlen(c)) {
501 		/* XXX iv arg is const, but EVP_CIPHER_CTX_ctrl isn't */
502 		if (!EVP_CIPHER_CTX_ctrl(cc->evp,
503 		    EVP_CTRL_GCM_SET_IV_FIXED, -1, (void *)iv))
504 			return SSH_ERR_LIBCRYPTO_ERROR;
505 	} else
506 		memcpy(cc->evp->iv, iv, evplen);
507 #endif
508 	return 0;
509 }
510 
511