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ffmpeg / libavutil / rc4.c @ 80a07f6e

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