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/*
* 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 "avutil.h"
#include "common.h"
#include "rc4.h"
typedef struct AVRC4 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 -1;
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;
}
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