cbc.c 4.37 KB
Newer Older
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
/* cbc.c
 *
 * Cipher block chaining mode.
 */

/* nettle, low-level cryptographics library
 *
 * Copyright (C) 2001 Niels Mller
 *  
 * The nettle library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 * 
 * The nettle library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with the nettle library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

26
27
28
#if HAVE_CONFIG_H
# include <config.h>
#endif
Niels Möller's avatar
Niels Möller committed
29

30
#include <assert.h>
Niels Möller's avatar
Niels Möller committed
31
32
#include <stdlib.h>
#include <string.h>
33

34
35
36
37
#include "cbc.h"

#include "memxor.h"

38
39
40
41
42
43
44
45
46
47
48
49
50
void
cbc_encrypt(void *ctx, void (*f)(void *ctx,
				 unsigned length, uint8_t *dst,
				 const uint8_t *src),
	    unsigned block_size, uint8_t *iv,
	    unsigned length, uint8_t *dst,
	    const uint8_t *src)
{
  assert(!(length % block_size));

  for ( ; length; length -= block_size, src += block_size, dst += block_size)
    {
      memxor(iv, src, block_size);
51
      f(ctx, block_size, dst, iv);
52
53
54
55
      memcpy(iv, dst, block_size);
    }
}

56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
/* Reqires that dst != src */
static void
cbc_decrypt_internal(void *ctx, void (*f)(void *ctx,
					  unsigned length, uint8_t *dst,
					  const uint8_t *src),
		     unsigned block_size, uint8_t *iv,
		     unsigned length, uint8_t *dst,
		     const uint8_t *src)
{
  assert(length);
  assert( !(length % block_size) );
  assert(src != dst);
  
  /* Decrypt in ECB mode */
  f(ctx, length, dst, src);

  /* XOR the cryptotext, shifted one block */
  memxor(dst, iv, block_size);
  memxor(dst + block_size, src, length - block_size);
  memcpy(iv, src + length - block_size, block_size);
}

/* Don't allocate any more space than this on the stack */
#define CBC_BUFFER_LIMIT 4096

81
82
83
84
85
86
87
88
89
90
91
92
93
void
cbc_decrypt(void *ctx, void (*f)(void *ctx,
				 unsigned length, uint8_t *dst,
				 const uint8_t *src),
	    unsigned block_size, uint8_t *iv,
	    unsigned length, uint8_t *dst,
	    const uint8_t *src)
{
  assert(!(length % block_size));

  if (!length)
    return;

94
95
96
97
  if (src != dst)
    cbc_decrypt_internal(ctx, f, block_size, iv,
			 length, dst, src);
  else
98
    {
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
      /* We need a copy of the ciphertext, so we can't ECB decrypt in
       * place.
       *
       * If length is small, we allocate a complete copy of src on the
       * stack. Otherwise, we allocate a block of size at most
       * CBC_BUFFER_LIMIT, and process that amount of data at a
       * time.
       *
       * NOTE: We assume that block_size <= CBC_BUFFER_LIMIT. */

      uint8_t *buffer;
      
      if (length <= CBC_BUFFER_LIMIT)
	buffer = alloca(length);
      else
	{
	  /* The buffer size must be an integral number of blocks. */
	  unsigned buffer_size
	    = CBC_BUFFER_LIMIT - (CBC_BUFFER_LIMIT % block_size);

	  buffer = alloca(buffer_size);

	  for ( ; length >= buffer_size;
		length -= buffer_size, dst += buffer_size, src += buffer_size)
	    {
	      memcpy(buffer, src, buffer_size);
	      cbc_decrypt_internal(ctx, f, block_size, iv,
				   buffer_size, dst, buffer);
	    }
	  if (!length)
	    return;
	}
      /* Now, we have at most CBC_BUFFER_LIMIT octets left */
      memcpy(buffer, src, length);

      cbc_decrypt_internal(ctx, f, block_size, iv,
			   length, dst, buffer);
136
137
    }
}
Niels Möller's avatar
Niels Möller committed
138

Niels Möller's avatar
Niels Möller committed
139
140
141
142
#if 0
#include "twofish.h"
#include "aes.h"

Niels Möller's avatar
Niels Möller committed
143
144
static void foo(void)
{
Niels Möller's avatar
Niels Möller committed
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
  struct CBC_CTX(struct twofish_ctx, TWOFISH_BLOCK_SIZE) ctx;
  uint8_t src[TWOFISH_BLOCK_SIZE];
  uint8_t dst[TWOFISH_BLOCK_SIZE];
  
  CBC_ENCRYPT(&ctx, twofish_encrypt, TWOFISH_BLOCK_SIZE, dst, src);

  /* Should result in a warning */
  CBC_ENCRYPT(&ctx, aes_encrypt, TWOFISH_BLOCK_SIZE, dst, src);
  
}

static void foo2(void)
{
  struct twofish_ctx ctx;
  uint8_t iv[TWOFISH_BLOCK_SIZE];
  uint8_t src[TWOFISH_BLOCK_SIZE];
  uint8_t dst[TWOFISH_BLOCK_SIZE];
Niels Möller's avatar
Niels Möller committed
162
  
Niels Möller's avatar
Niels Möller committed
163
164
165
  CBC_ENCRYPT2(&ctx, twofish_encrypt, TWOFISH_BLOCK_SIZE, iv, TWOFISH_BLOCK_SIZE, dst, src);
  /* Should result in a warning */
  CBC_ENCRYPT2(&ctx, aes_encrypt, TWOFISH_BLOCK_SIZE, iv, TWOFISH_BLOCK_SIZE, dst, src);
Niels Möller's avatar
Niels Möller committed
166
}
Niels Möller's avatar
Niels Möller committed
167
168

#endif