/*

 * 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 "error.h"

#include "macros.h"

#include "mem.h"

#include "rc4.h"

AVRC4 *av_rc4_alloc(void)

{

    return av_mallocz(sizeof(struct AVRC4));

}

int av_rc4_init(AVRC4 *r, const uint8_t *key, int key_bits, int decrypt) {

    int i, j;

    uint8_t y;

    uint8_t *state = r->state;

    int keylen = key_bits >> 3;

    if (key_bits & 7)

        return AVERROR(EINVAL);

    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]);

    }

    r->x = 1;

    r->y = state[1];

    return 0;

}

void av_rc4_crypt(AVRC4 *r, uint8_t *dst, const uint8_t *src, int count, uint8_t *iv, int decrypt) {

    uint8_t x = r->x, y = r->y;

    uint8_t *state = r->state;

    while (count-- > 0) {

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

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

        *dst++ = src ? *src++ ^ state[sum] : state[sum];

        x++;

        y += state[x];

    }

    r->x = x; r->y = y;

}