PeerStreamer

/*

 * RC4 encryption/decryption/pseudo-random number generator

 * Copyright (c) 2007 Reimar Doeffinger

 *

 * loosely based on LibTomCrypt by Tom St Denis

 *

 * This file is part of FFmpeg.

 *

 * FFmpeg 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.

 *

 * FFmpeg 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 FFmpeg; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

#include "common.h"

#include "rc4.h"

void ff_rc4_enc(const uint8_t *key, int keylen, uint8_t *data, int datalen) {

    int i, j;

    uint8_t x, y;

    uint8_t state[256];

    for (i = 0; i < 256; i++)

        state[i] = i;

    y = 0;

    // j is i % keylen

    for (j = 0, i = 0; i < 256; i++, j++) {

        if (j == keylen) j = 0;

        y += state[i] + key[j];

        FFSWAP(uint8_t, state[i], state[y]);

    }

    // state initialized, now do the real encryption

    x = 1; y = state[1];

    while (datalen-- > 0) {

        uint8_t sum = state[x] + state[y];

        FFSWAP(uint8_t, state[x], state[y]);

        *data++ ^= state[sum];

        x++;

        y += state[x];

    }

}