62 lines
1.9 KiB
C
62 lines
1.9 KiB
C
/*
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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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}
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