src/XOR.c

/*
 *  xor.c : Source for the trivial cipher which XORs the message with the key.
 *          The key can be up to 32 bytes long.
 *
 * Part of the Python Cryptography Toolkit
 *
 * Contributed by Barry Warsaw and others.
 *
 * =======================================================================
 * The contents of this file are dedicated to the public domain.  To the
 * extent that dedication to the public domain is not available, everyone
 * is granted a worldwide, perpetual, royalty-free, non-exclusive license
 * to exercise all rights associated with the contents of this file for
 * any purpose whatsoever.  No rights are reserved.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 * =======================================================================
 */

#include "pycrypto_common.h"

#define MODULE_NAME _XOR
#define BLOCK_SIZE 1
#define KEY_SIZE 0

#define MAX_KEY_SIZE 32

typedef struct 
{
	unsigned char key[MAX_KEY_SIZE];
	int keylen, last_pos;
} stream_state;

static void
stream_init(stream_state *self, unsigned char *key, int len)
{
	int i;

        if (len > MAX_KEY_SIZE)
        {
		PyErr_Format(PyExc_ValueError,
				"XOR key must be no longer than %d bytes",
                                MAX_KEY_SIZE);
		return;
        }
	self->keylen = len;
	self->last_pos = 0;

	for(i=0; i<len; i++)
	{
		self->key[i] = key[i];
	}
}

/* Encryption and decryption are symmetric */
#define stream_decrypt stream_encrypt	

static void stream_encrypt(stream_state *self, unsigned char *block, 
			   int len)
{
	int i, j = self->last_pos;
	for(i=0; i<len; i++, j=(j+1) % self->keylen)
	{
		block[i] ^= self->key[j];
	}
	self->last_pos = j;
}

#include "stream_template.c"