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/*
* arc4.c : Implementation for the Alleged-RC4 stream cipher
*
* Part of the Python Cryptography Toolkit
*
* Originally written by: A.M. Kuchling
*
* ===================================================================
* 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 _ARC4
#define BLOCK_SIZE 1
#define KEY_SIZE 0
typedef struct
{
unsigned char state[256];
unsigned char x,y;
} stream_state;
/* Encryption and decryption are symmetric */
#define stream_decrypt stream_encrypt
static void stream_encrypt(stream_state *self, unsigned char *block,
int len)
{
register int i, x=self->x, y=self->y;
for (i=0; i<len; i++)
{
x = (x + 1) % 256;
y = (y + self->state[x]) % 256;
{
register int t; /* Exchange state[x] and state[y] */
t = self->state[x];
self->state[x] = self->state[y];
self->state[y] = t;
}
{
register int xorIndex; /* XOR the data with the stream data */
xorIndex=(self->state[x]+self->state[y]) % 256;
block[i] ^= self->state[xorIndex];
}
}
self->x=x;
self->y=y;
}
static void stream_init(stream_state *self, unsigned char *key, int keylen)
{
register int i, index1, index2;
for(i=0; i<256; i++) self->state[i]=i;
self->x=0; self->y=0;
index1=0; index2=0;
for(i=0; i<256; i++)
{
register int t;
index2 = ( key[index1] + self->state[i] + index2) % 256;
t = self->state[i];
self->state[i] = self->state[index2];
self->state[index2] = t;
index1 = (index1 + 1) % keylen;
}
}
#include "stream_template.c"
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