cipher.c revision 57430 
1/*
2 *
3 * cipher.c
4 *
5 * Author: Tatu Ylonen <ylo@cs.hut.fi>
6 *
7 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
8 *                    All rights reserved
9 *
10 * Created: Wed Apr 19 17:41:39 1995 ylo
11 *
12 */
13
14#include "includes.h"
15RCSID("$Id: cipher.c,v 1.19 2000/02/22 15:19:29 markus Exp $");
16
17#include "ssh.h"
18#include "cipher.h"
19
20#include <ssl/md5.h>
21
22/*
23 * What kind of tripple DES are these 2 routines?
24 *
25 * Why is there a redundant initialization vector?
26 *
27 * If only iv3 was used, then, this would till effect have been
28 * outer-cbc. However, there is also a private iv1 == iv2 which
29 * perhaps makes differential analysis easier. On the other hand, the
30 * private iv1 probably makes the CRC-32 attack ineffective. This is a
31 * result of that there is no longer any known iv1 to use when
32 * choosing the X block.
33 */
34void
35SSH_3CBC_ENCRYPT(des_key_schedule ks1,
36		 des_key_schedule ks2, des_cblock * iv2,
37		 des_key_schedule ks3, des_cblock * iv3,
38		 unsigned char *dest, unsigned char *src,
39		 unsigned int len)
40{
41	des_cblock iv1;
42
43	memcpy(&iv1, iv2, 8);
44
45	des_cbc_encrypt(src, dest, len, ks1, &iv1, DES_ENCRYPT);
46	memcpy(&iv1, dest + len - 8, 8);
47
48	des_cbc_encrypt(dest, dest, len, ks2, iv2, DES_DECRYPT);
49	memcpy(iv2, &iv1, 8);	/* Note how iv1 == iv2 on entry and exit. */
50
51	des_cbc_encrypt(dest, dest, len, ks3, iv3, DES_ENCRYPT);
52	memcpy(iv3, dest + len - 8, 8);
53}
54
55void
56SSH_3CBC_DECRYPT(des_key_schedule ks1,
57		 des_key_schedule ks2, des_cblock * iv2,
58		 des_key_schedule ks3, des_cblock * iv3,
59		 unsigned char *dest, unsigned char *src,
60		 unsigned int len)
61{
62	des_cblock iv1;
63
64	memcpy(&iv1, iv2, 8);
65
66	des_cbc_encrypt(src, dest, len, ks3, iv3, DES_DECRYPT);
67	memcpy(iv3, src + len - 8, 8);
68
69	des_cbc_encrypt(dest, dest, len, ks2, iv2, DES_ENCRYPT);
70	memcpy(iv2, dest + len - 8, 8);
71
72	des_cbc_encrypt(dest, dest, len, ks1, &iv1, DES_DECRYPT);
73	/* memcpy(&iv1, iv2, 8); */
74	/* Note how iv1 == iv2 on entry and exit. */
75}
76
77/*
78 * SSH uses a variation on Blowfish, all bytes must be swapped before
79 * and after encryption/decryption. Thus the swap_bytes stuff (yuk).
80 */
81static void
82swap_bytes(const unsigned char *src, unsigned char *dst_, int n)
83{
84	/* dst must be properly aligned. */
85	u_int32_t *dst = (u_int32_t *) dst_;
86	union {
87		u_int32_t i;
88		char c[4];
89	} t;
90
91	/* Process 8 bytes every lap. */
92	for (n = n / 8; n > 0; n--) {
93		t.c[3] = *src++;
94		t.c[2] = *src++;
95		t.c[1] = *src++;
96		t.c[0] = *src++;
97		*dst++ = t.i;
98
99		t.c[3] = *src++;
100		t.c[2] = *src++;
101		t.c[1] = *src++;
102		t.c[0] = *src++;
103		*dst++ = t.i;
104	}
105}
106
107void (*cipher_attack_detected) (const char *fmt,...) = fatal;
108
109static inline void
110detect_cbc_attack(const unsigned char *src,
111		  unsigned int len)
112{
113	return;
114
115	log("CRC-32 CBC insertion attack detected");
116	cipher_attack_detected("CRC-32 CBC insertion attack detected");
117}
118
119/*
120 * Names of all encryption algorithms.
121 * These must match the numbers defined in cipher.h.
122 */
123static char *cipher_names[] =
124{
125	"none",
126	"idea",
127	"des",
128	"3des",
129	"tss",
130	"rc4",
131	"blowfish"
132};
133
134/*
135 * Returns a bit mask indicating which ciphers are supported by this
136 * implementation.  The bit mask has the corresponding bit set of each
137 * supported cipher.
138 */
139
140unsigned int
141cipher_mask()
142{
143	unsigned int mask = 0;
144	mask |= 1 << SSH_CIPHER_3DES;		/* Mandatory */
145	mask |= 1 << SSH_CIPHER_BLOWFISH;
146	return mask;
147}
148
149/* Returns the name of the cipher. */
150
151const char *
152cipher_name(int cipher)
153{
154	if (cipher < 0 || cipher >= sizeof(cipher_names) / sizeof(cipher_names[0]) ||
155	    cipher_names[cipher] == NULL)
156		fatal("cipher_name: bad cipher number: %d", cipher);
157	return cipher_names[cipher];
158}
159
160/*
161 * Parses the name of the cipher.  Returns the number of the corresponding
162 * cipher, or -1 on error.
163 */
164
165int
166cipher_number(const char *name)
167{
168	int i;
169	for (i = 0; i < sizeof(cipher_names) / sizeof(cipher_names[0]); i++)
170		if (strcmp(cipher_names[i], name) == 0 &&
171		    (cipher_mask() & (1 << i)))
172			return i;
173	return -1;
174}
175
176/*
177 * Selects the cipher, and keys if by computing the MD5 checksum of the
178 * passphrase and using the resulting 16 bytes as the key.
179 */
180
181void
182cipher_set_key_string(CipherContext *context, int cipher,
183		      const char *passphrase, int for_encryption)
184{
185	MD5_CTX md;
186	unsigned char digest[16];
187
188	MD5_Init(&md);
189	MD5_Update(&md, (const unsigned char *) passphrase, strlen(passphrase));
190	MD5_Final(digest, &md);
191
192	cipher_set_key(context, cipher, digest, 16, for_encryption);
193
194	memset(digest, 0, sizeof(digest));
195	memset(&md, 0, sizeof(md));
196}
197
198/* Selects the cipher to use and sets the key. */
199
200void
201cipher_set_key(CipherContext *context, int cipher,
202	       const unsigned char *key, int keylen, int for_encryption)
203{
204	unsigned char padded[32];
205
206	/* Set cipher type. */
207	context->type = cipher;
208
209	/* Get 32 bytes of key data.  Pad if necessary.  (So that code
210	   below does not need to worry about key size). */
211	memset(padded, 0, sizeof(padded));
212	memcpy(padded, key, keylen < sizeof(padded) ? keylen : sizeof(padded));
213
214	/* Initialize the initialization vector. */
215	switch (cipher) {
216	case SSH_CIPHER_NONE:
217		/*
218		 * Has to stay for authfile saving of private key with no
219		 * passphrase
220		 */
221		break;
222
223	case SSH_CIPHER_3DES:
224		/*
225		 * Note: the least significant bit of each byte of key is
226		 * parity, and must be ignored by the implementation.  16
227		 * bytes of key are used (first and last keys are the same).
228		 */
229		if (keylen < 16)
230			error("Key length %d is insufficient for 3DES.", keylen);
231		des_set_key((void *) padded, context->u.des3.key1);
232		des_set_key((void *) (padded + 8), context->u.des3.key2);
233		if (keylen <= 16)
234			des_set_key((void *) padded, context->u.des3.key3);
235		else
236			des_set_key((void *) (padded + 16), context->u.des3.key3);
237		memset(context->u.des3.iv2, 0, sizeof(context->u.des3.iv2));
238		memset(context->u.des3.iv3, 0, sizeof(context->u.des3.iv3));
239		break;
240
241	case SSH_CIPHER_BLOWFISH:
242		BF_set_key(&context->u.bf.key, keylen, padded);
243		memset(context->u.bf.iv, 0, 8);
244		break;
245
246	default:
247		fatal("cipher_set_key: unknown cipher: %s", cipher_name(cipher));
248	}
249	memset(padded, 0, sizeof(padded));
250}
251
252/* Encrypts data using the cipher. */
253
254void
255cipher_encrypt(CipherContext *context, unsigned char *dest,
256	       const unsigned char *src, unsigned int len)
257{
258	if ((len & 7) != 0)
259		fatal("cipher_encrypt: bad plaintext length %d", len);
260
261	switch (context->type) {
262	case SSH_CIPHER_NONE:
263		memcpy(dest, src, len);
264		break;
265
266	case SSH_CIPHER_3DES:
267		SSH_3CBC_ENCRYPT(context->u.des3.key1,
268				 context->u.des3.key2, &context->u.des3.iv2,
269				 context->u.des3.key3, &context->u.des3.iv3,
270				 dest, (unsigned char *) src, len);
271		break;
272
273	case SSH_CIPHER_BLOWFISH:
274		swap_bytes(src, dest, len);
275		BF_cbc_encrypt(dest, dest, len,
276		               &context->u.bf.key, context->u.bf.iv,
277			       BF_ENCRYPT);
278		swap_bytes(dest, dest, len);
279		break;
280
281	default:
282		fatal("cipher_encrypt: unknown cipher: %s", cipher_name(context->type));
283	}
284}
285
286/* Decrypts data using the cipher. */
287
288void
289cipher_decrypt(CipherContext *context, unsigned char *dest,
290	       const unsigned char *src, unsigned int len)
291{
292	if ((len & 7) != 0)
293		fatal("cipher_decrypt: bad ciphertext length %d", len);
294
295	switch (context->type) {
296	case SSH_CIPHER_NONE:
297		memcpy(dest, src, len);
298		break;
299
300	case SSH_CIPHER_3DES:
301		/* CRC-32 attack? */
302		SSH_3CBC_DECRYPT(context->u.des3.key1,
303				 context->u.des3.key2, &context->u.des3.iv2,
304				 context->u.des3.key3, &context->u.des3.iv3,
305				 dest, (unsigned char *) src, len);
306		break;
307
308	case SSH_CIPHER_BLOWFISH:
309		detect_cbc_attack(src, len);
310		swap_bytes(src, dest, len);
311		BF_cbc_encrypt((void *) dest, dest, len,
312			       &context->u.bf.key, context->u.bf.iv,
313			       BF_DECRYPT);
314		swap_bytes(dest, dest, len);
315		break;
316
317	default:
318		fatal("cipher_decrypt: unknown cipher: %s", cipher_name(context->type));
319	}
320}
321