yading@11: /*
yading@11:  * RC4 encryption/decryption/pseudo-random number generator
yading@11:  * Copyright (c) 2007 Reimar Doeffinger
yading@11:  *
yading@11:  * loosely based on LibTomCrypt by Tom St Denis
yading@11:  *
yading@11:  * This file is part of FFmpeg.
yading@11:  *
yading@11:  * FFmpeg is free software; you can redistribute it and/or
yading@11:  * modify it under the terms of the GNU Lesser General Public
yading@11:  * License as published by the Free Software Foundation; either
yading@11:  * version 2.1 of the License, or (at your option) any later version.
yading@11:  *
yading@11:  * FFmpeg is distributed in the hope that it will be useful,
yading@11:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@11:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@11:  * Lesser General Public License for more details.
yading@11:  *
yading@11:  * You should have received a copy of the GNU Lesser General Public
yading@11:  * License along with FFmpeg; if not, write to the Free Software
yading@11:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@11:  */
yading@11: #include "avutil.h"
yading@11: #include "common.h"
yading@11: #include "rc4.h"
yading@11: 
yading@11: typedef struct AVRC4 AVRC4;
yading@11: 
yading@11: int av_rc4_init(AVRC4 *r, const uint8_t *key, int key_bits, int decrypt) {
yading@11:     int i, j;
yading@11:     uint8_t y;
yading@11:     uint8_t *state = r->state;
yading@11:     int keylen = key_bits >> 3;
yading@11:     if (key_bits & 7)
yading@11:         return -1;
yading@11:     for (i = 0; i < 256; i++)
yading@11:         state[i] = i;
yading@11:     y = 0;
yading@11:     // j is i % keylen
yading@11:     for (j = 0, i = 0; i < 256; i++, j++) {
yading@11:         if (j == keylen) j = 0;
yading@11:         y += state[i] + key[j];
yading@11:         FFSWAP(uint8_t, state[i], state[y]);
yading@11:     }
yading@11:     r->x = 1;
yading@11:     r->y = state[1];
yading@11:     return 0;
yading@11: }
yading@11: 
yading@11: void av_rc4_crypt(AVRC4 *r, uint8_t *dst, const uint8_t *src, int count, uint8_t *iv, int decrypt) {
yading@11:     uint8_t x = r->x, y = r->y;
yading@11:     uint8_t *state = r->state;
yading@11:     while (count-- > 0) {
yading@11:         uint8_t sum = state[x] + state[y];
yading@11:         FFSWAP(uint8_t, state[x], state[y]);
yading@11:         *dst++ = src ? *src++ ^ state[sum] : state[sum];
yading@11:         x++;
yading@11:         y += state[x];
yading@11:     }
yading@11:     r->x = x; r->y = y;
yading@11: }