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/* cbc.c
*
* Cipher block chaining mode.
*/
/* nettle, low-level cryptographics library
*
* Copyright (C) 2001 Niels Möller
*
* 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.
*/
#include "cbc.h"
#include "memxor.h"
#include <assert.h>
#include <stdlib.h>
#include <string.h>
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);
f(ctx, block_size, dst, iv);
memcpy(iv, dst, block_size);
}
}
/* 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
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;
if (src != dst)
cbc_decrypt_internal(ctx, f, block_size, iv,
length, dst, src);
else
{
/* 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);
}
}
#if 0
#include "twofish.h"
#include "aes.h"
static void foo(void)
{
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];
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);
}
#endif
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