xref: /openbsd-src/usr.bin/ssh/cipher.c (revision a28daedfc357b214be5c701aa8ba8adb29a7f1c2)
1 /* $OpenBSD: cipher.c,v 1.82 2009/01/26 09:58:15 markus 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 <openssl/md5.h>
41 
42 #include <string.h>
43 #include <stdarg.h>
44 
45 #include "xmalloc.h"
46 #include "log.h"
47 #include "cipher.h"
48 
49 extern const EVP_CIPHER *evp_ssh1_bf(void);
50 extern const EVP_CIPHER *evp_ssh1_3des(void);
51 extern void ssh1_3des_iv(EVP_CIPHER_CTX *, int, u_char *, int);
52 extern const EVP_CIPHER *evp_aes_128_ctr(void);
53 extern void ssh_aes_ctr_iv(EVP_CIPHER_CTX *, int, u_char *, u_int);
54 
55 struct Cipher {
56 	char	*name;
57 	int	number;		/* for ssh1 only */
58 	u_int	block_size;
59 	u_int	key_len;
60 	u_int	discard_len;
61 	u_int	cbc_mode;
62 	const EVP_CIPHER	*(*evptype)(void);
63 } ciphers[] = {
64 	{ "none",		SSH_CIPHER_NONE, 8, 0, 0, 0, EVP_enc_null },
65 	{ "des",		SSH_CIPHER_DES, 8, 8, 0, 1, EVP_des_cbc },
66 	{ "3des",		SSH_CIPHER_3DES, 8, 16, 0, 1, evp_ssh1_3des },
67 	{ "blowfish",		SSH_CIPHER_BLOWFISH, 8, 32, 0, 1, evp_ssh1_bf },
68 
69 	{ "3des-cbc",		SSH_CIPHER_SSH2, 8, 24, 0, 1, EVP_des_ede3_cbc },
70 	{ "blowfish-cbc",	SSH_CIPHER_SSH2, 8, 16, 0, 1, EVP_bf_cbc },
71 	{ "cast128-cbc",	SSH_CIPHER_SSH2, 8, 16, 0, 1, EVP_cast5_cbc },
72 	{ "arcfour",		SSH_CIPHER_SSH2, 8, 16, 0, 0, EVP_rc4 },
73 	{ "arcfour128",		SSH_CIPHER_SSH2, 8, 16, 1536, 0, EVP_rc4 },
74 	{ "arcfour256",		SSH_CIPHER_SSH2, 8, 32, 1536, 0, EVP_rc4 },
75 	{ "aes128-cbc",		SSH_CIPHER_SSH2, 16, 16, 0, 1, EVP_aes_128_cbc },
76 	{ "aes192-cbc",		SSH_CIPHER_SSH2, 16, 24, 0, 1, EVP_aes_192_cbc },
77 	{ "aes256-cbc",		SSH_CIPHER_SSH2, 16, 32, 0, 1, EVP_aes_256_cbc },
78 	{ "rijndael-cbc@lysator.liu.se",
79 				SSH_CIPHER_SSH2, 16, 32, 0, 1, EVP_aes_256_cbc },
80 	{ "aes128-ctr",		SSH_CIPHER_SSH2, 16, 16, 0, 0, evp_aes_128_ctr },
81 	{ "aes192-ctr",		SSH_CIPHER_SSH2, 16, 24, 0, 0, evp_aes_128_ctr },
82 	{ "aes256-ctr",		SSH_CIPHER_SSH2, 16, 32, 0, 0, evp_aes_128_ctr },
83 	{ "acss@openssh.org",	SSH_CIPHER_SSH2, 16, 5, 0, 0, EVP_acss },
84 
85 	{ NULL,			SSH_CIPHER_INVALID, 0, 0, 0, 0, NULL }
86 };
87 
88 /*--*/
89 
90 u_int
91 cipher_blocksize(const Cipher *c)
92 {
93 	return (c->block_size);
94 }
95 
96 u_int
97 cipher_keylen(const Cipher *c)
98 {
99 	return (c->key_len);
100 }
101 
102 u_int
103 cipher_get_number(const Cipher *c)
104 {
105 	return (c->number);
106 }
107 
108 u_int
109 cipher_is_cbc(const Cipher *c)
110 {
111 	return (c->cbc_mode);
112 }
113 
114 u_int
115 cipher_mask_ssh1(int client)
116 {
117 	u_int mask = 0;
118 	mask |= 1 << SSH_CIPHER_3DES;		/* Mandatory */
119 	mask |= 1 << SSH_CIPHER_BLOWFISH;
120 	if (client) {
121 		mask |= 1 << SSH_CIPHER_DES;
122 	}
123 	return mask;
124 }
125 
126 Cipher *
127 cipher_by_name(const char *name)
128 {
129 	Cipher *c;
130 	for (c = ciphers; c->name != NULL; c++)
131 		if (strcmp(c->name, name) == 0)
132 			return c;
133 	return NULL;
134 }
135 
136 Cipher *
137 cipher_by_number(int id)
138 {
139 	Cipher *c;
140 	for (c = ciphers; c->name != NULL; c++)
141 		if (c->number == id)
142 			return c;
143 	return NULL;
144 }
145 
146 #define	CIPHER_SEP	","
147 int
148 ciphers_valid(const char *names)
149 {
150 	Cipher *c;
151 	char *cipher_list, *cp;
152 	char *p;
153 
154 	if (names == NULL || strcmp(names, "") == 0)
155 		return 0;
156 	cipher_list = cp = xstrdup(names);
157 	for ((p = strsep(&cp, CIPHER_SEP)); p && *p != '\0';
158 	    (p = strsep(&cp, CIPHER_SEP))) {
159 		c = cipher_by_name(p);
160 		if (c == NULL || c->number != SSH_CIPHER_SSH2) {
161 			debug("bad cipher %s [%s]", p, names);
162 			xfree(cipher_list);
163 			return 0;
164 		} else {
165 			debug3("cipher ok: %s [%s]", p, names);
166 		}
167 	}
168 	debug3("ciphers ok: [%s]", names);
169 	xfree(cipher_list);
170 	return 1;
171 }
172 
173 /*
174  * Parses the name of the cipher.  Returns the number of the corresponding
175  * cipher, or -1 on error.
176  */
177 
178 int
179 cipher_number(const char *name)
180 {
181 	Cipher *c;
182 	if (name == NULL)
183 		return -1;
184 	for (c = ciphers; c->name != NULL; c++)
185 		if (strcasecmp(c->name, name) == 0)
186 			return c->number;
187 	return -1;
188 }
189 
190 char *
191 cipher_name(int id)
192 {
193 	Cipher *c = cipher_by_number(id);
194 	return (c==NULL) ? "<unknown>" : c->name;
195 }
196 
197 void
198 cipher_init(CipherContext *cc, Cipher *cipher,
199     const u_char *key, u_int keylen, const u_char *iv, u_int ivlen,
200     int do_encrypt)
201 {
202 	static int dowarn = 1;
203 	const EVP_CIPHER *type;
204 	int klen;
205 	u_char *junk, *discard;
206 
207 	if (cipher->number == SSH_CIPHER_DES) {
208 		if (dowarn) {
209 			error("Warning: use of DES is strongly discouraged "
210 			    "due to cryptographic weaknesses");
211 			dowarn = 0;
212 		}
213 		if (keylen > 8)
214 			keylen = 8;
215 	}
216 	cc->plaintext = (cipher->number == SSH_CIPHER_NONE);
217 
218 	if (keylen < cipher->key_len)
219 		fatal("cipher_init: key length %d is insufficient for %s.",
220 		    keylen, cipher->name);
221 	if (iv != NULL && ivlen < cipher->block_size)
222 		fatal("cipher_init: iv length %d is insufficient for %s.",
223 		    ivlen, cipher->name);
224 	cc->cipher = cipher;
225 
226 	type = (*cipher->evptype)();
227 
228 	EVP_CIPHER_CTX_init(&cc->evp);
229 	if (EVP_CipherInit(&cc->evp, type, NULL, (u_char *)iv,
230 	    (do_encrypt == CIPHER_ENCRYPT)) == 0)
231 		fatal("cipher_init: EVP_CipherInit failed for %s",
232 		    cipher->name);
233 	klen = EVP_CIPHER_CTX_key_length(&cc->evp);
234 	if (klen > 0 && keylen != (u_int)klen) {
235 		debug2("cipher_init: set keylen (%d -> %d)", klen, keylen);
236 		if (EVP_CIPHER_CTX_set_key_length(&cc->evp, keylen) == 0)
237 			fatal("cipher_init: set keylen failed (%d -> %d)",
238 			    klen, keylen);
239 	}
240 	if (EVP_CipherInit(&cc->evp, NULL, (u_char *)key, NULL, -1) == 0)
241 		fatal("cipher_init: EVP_CipherInit: set key failed for %s",
242 		    cipher->name);
243 
244 	if (cipher->discard_len > 0) {
245 		junk = xmalloc(cipher->discard_len);
246 		discard = xmalloc(cipher->discard_len);
247 		if (EVP_Cipher(&cc->evp, discard, junk,
248 		    cipher->discard_len) == 0)
249 			fatal("evp_crypt: EVP_Cipher failed during discard");
250 		memset(discard, 0, cipher->discard_len);
251 		xfree(junk);
252 		xfree(discard);
253 	}
254 }
255 
256 void
257 cipher_crypt(CipherContext *cc, u_char *dest, const u_char *src, u_int len)
258 {
259 	if (len % cc->cipher->block_size)
260 		fatal("cipher_encrypt: bad plaintext length %d", len);
261 	if (EVP_Cipher(&cc->evp, dest, (u_char *)src, len) == 0)
262 		fatal("evp_crypt: EVP_Cipher failed");
263 }
264 
265 void
266 cipher_cleanup(CipherContext *cc)
267 {
268 	if (EVP_CIPHER_CTX_cleanup(&cc->evp) == 0)
269 		error("cipher_cleanup: EVP_CIPHER_CTX_cleanup failed");
270 }
271 
272 /*
273  * Selects the cipher, and keys if by computing the MD5 checksum of the
274  * passphrase and using the resulting 16 bytes as the key.
275  */
276 
277 void
278 cipher_set_key_string(CipherContext *cc, Cipher *cipher,
279     const char *passphrase, int do_encrypt)
280 {
281 	MD5_CTX md;
282 	u_char digest[16];
283 
284 	MD5_Init(&md);
285 	MD5_Update(&md, (const u_char *)passphrase, strlen(passphrase));
286 	MD5_Final(digest, &md);
287 
288 	cipher_init(cc, cipher, digest, 16, NULL, 0, do_encrypt);
289 
290 	memset(digest, 0, sizeof(digest));
291 	memset(&md, 0, sizeof(md));
292 }
293 
294 /*
295  * Exports an IV from the CipherContext required to export the key
296  * state back from the unprivileged child to the privileged parent
297  * process.
298  */
299 
300 int
301 cipher_get_keyiv_len(const CipherContext *cc)
302 {
303 	Cipher *c = cc->cipher;
304 	int ivlen;
305 
306 	if (c->number == SSH_CIPHER_3DES)
307 		ivlen = 24;
308 	else
309 		ivlen = EVP_CIPHER_CTX_iv_length(&cc->evp);
310 	return (ivlen);
311 }
312 
313 void
314 cipher_get_keyiv(CipherContext *cc, u_char *iv, u_int len)
315 {
316 	Cipher *c = cc->cipher;
317 	int evplen;
318 
319 	switch (c->number) {
320 	case SSH_CIPHER_SSH2:
321 	case SSH_CIPHER_DES:
322 	case SSH_CIPHER_BLOWFISH:
323 		evplen = EVP_CIPHER_CTX_iv_length(&cc->evp);
324 		if (evplen <= 0)
325 			return;
326 		if ((u_int)evplen != len)
327 			fatal("%s: wrong iv length %d != %d", __func__,
328 			    evplen, len);
329 		if (c->evptype == evp_aes_128_ctr)
330 			ssh_aes_ctr_iv(&cc->evp, 0, iv, len);
331 		else
332 			memcpy(iv, cc->evp.iv, len);
333 		break;
334 	case SSH_CIPHER_3DES:
335 		ssh1_3des_iv(&cc->evp, 0, iv, 24);
336 		break;
337 	default:
338 		fatal("%s: bad cipher %d", __func__, c->number);
339 	}
340 }
341 
342 void
343 cipher_set_keyiv(CipherContext *cc, u_char *iv)
344 {
345 	Cipher *c = cc->cipher;
346 	int evplen = 0;
347 
348 	switch (c->number) {
349 	case SSH_CIPHER_SSH2:
350 	case SSH_CIPHER_DES:
351 	case SSH_CIPHER_BLOWFISH:
352 		evplen = EVP_CIPHER_CTX_iv_length(&cc->evp);
353 		if (evplen == 0)
354 			return;
355 		if (c->evptype == evp_aes_128_ctr)
356 			ssh_aes_ctr_iv(&cc->evp, 1, iv, evplen);
357 		else
358 			memcpy(cc->evp.iv, iv, evplen);
359 		break;
360 	case SSH_CIPHER_3DES:
361 		ssh1_3des_iv(&cc->evp, 1, iv, 24);
362 		break;
363 	default:
364 		fatal("%s: bad cipher %d", __func__, c->number);
365 	}
366 }
367 
368 #define EVP_X_STATE(evp)	(evp).cipher_data
369 #define EVP_X_STATE_LEN(evp)	(evp).cipher->ctx_size
370 
371 int
372 cipher_get_keycontext(const CipherContext *cc, u_char *dat)
373 {
374 	Cipher *c = cc->cipher;
375 	int plen = 0;
376 
377 	if (c->evptype == EVP_rc4 || c->evptype == EVP_acss) {
378 		plen = EVP_X_STATE_LEN(cc->evp);
379 		if (dat == NULL)
380 			return (plen);
381 		memcpy(dat, EVP_X_STATE(cc->evp), plen);
382 	}
383 	return (plen);
384 }
385 
386 void
387 cipher_set_keycontext(CipherContext *cc, u_char *dat)
388 {
389 	Cipher *c = cc->cipher;
390 	int plen;
391 
392 	if (c->evptype == EVP_rc4 || c->evptype == EVP_acss) {
393 		plen = EVP_X_STATE_LEN(cc->evp);
394 		memcpy(EVP_X_STATE(cc->evp), dat, plen);
395 	}
396 }
397