Libav
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00001 /* 00002 * RC4 encryption/decryption/pseudo-random number generator 00003 * Copyright (c) 2007 Reimar Doeffinger 00004 * 00005 * loosely based on LibTomCrypt by Tom St Denis 00006 * 00007 * This file is part of FFmpeg. 00008 * 00009 * FFmpeg is free software; you can redistribute it and/or 00010 * modify it under the terms of the GNU Lesser General Public 00011 * License as published by the Free Software Foundation; either 00012 * version 2.1 of the License, or (at your option) any later version. 00013 * 00014 * FFmpeg is distributed in the hope that it will be useful, 00015 * but WITHOUT ANY WARRANTY; without even the implied warranty of 00016 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 00017 * Lesser General Public License for more details. 00018 * 00019 * You should have received a copy of the GNU Lesser General Public 00020 * License along with FFmpeg; if not, write to the Free Software 00021 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 00022 */ 00023 #include "avutil.h" 00024 #include "common.h" 00025 #include "rc4.h" 00026 00027 typedef struct AVRC4 AVRC4; 00028 00029 int av_rc4_init(AVRC4 *r, const uint8_t *key, int key_bits, int decrypt) { 00030 int i, j; 00031 uint8_t y; 00032 uint8_t *state = r->state; 00033 int keylen = key_bits >> 3; 00034 if (key_bits & 7) 00035 return -1; 00036 for (i = 0; i < 256; i++) 00037 state[i] = i; 00038 y = 0; 00039 // j is i % keylen 00040 for (j = 0, i = 0; i < 256; i++, j++) { 00041 if (j == keylen) j = 0; 00042 y += state[i] + key[j]; 00043 FFSWAP(uint8_t, state[i], state[y]); 00044 } 00045 r->x = 1; 00046 r->y = state[1]; 00047 return 0; 00048 } 00049 00050 void av_rc4_crypt(AVRC4 *r, uint8_t *dst, const uint8_t *src, int count, uint8_t *iv, int decrypt) { 00051 uint8_t x = r->x, y = r->y; 00052 uint8_t *state = r->state; 00053 while (count-- > 0) { 00054 uint8_t sum = state[x] + state[y]; 00055 FFSWAP(uint8_t, state[x], state[y]); 00056 *dst++ = src ? *src++ ^ state[sum] : state[sum]; 00057 x++; 00058 y += state[x]; 00059 } 00060 r->x = x; r->y = y; 00061 }