1/* 2 * RC4 encryption/decryption/pseudo-random number generator 3 * Copyright (c) 2007 Reimar Doeffinger 4 * 5 * loosely based on LibTomCrypt by Tom St Denis 6 * 7 * This file is part of Libav. 8 * 9 * Libav is free software; you can redistribute it and/or 10 * modify it under the terms of the GNU Lesser General Public 11 * License as published by the Free Software Foundation; either 12 * version 2.1 of the License, or (at your option) any later version. 13 * 14 * Libav is distributed in the hope that it will be useful, 15 * but WITHOUT ANY WARRANTY; without even the implied warranty of 16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 17 * Lesser General Public License for more details. 18 * 19 * You should have received a copy of the GNU Lesser General Public 20 * License along with Libav; if not, write to the Free Software 21 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 22 */ 23#include "avutil.h" 24#include "common.h" 25#include "rc4.h" 26 27typedef struct AVRC4 AVRC4; 28 29int av_rc4_init(AVRC4 *r, const uint8_t *key, int key_bits, int decrypt) { 30 int i, j; 31 uint8_t y; 32 uint8_t *state = r->state; 33 int keylen = key_bits >> 3; 34 if (key_bits & 7) 35 return -1; 36 for (i = 0; i < 256; i++) 37 state[i] = i; 38 y = 0; 39 // j is i % keylen 40 for (j = 0, i = 0; i < 256; i++, j++) { 41 if (j == keylen) j = 0; 42 y += state[i] + key[j]; 43 FFSWAP(uint8_t, state[i], state[y]); 44 } 45 r->x = 1; 46 r->y = state[1]; 47 return 0; 48} 49 50void av_rc4_crypt(AVRC4 *r, uint8_t *dst, const uint8_t *src, int count, uint8_t *iv, int decrypt) { 51 uint8_t x = r->x, y = r->y; 52 uint8_t *state = r->state; 53 while (count-- > 0) { 54 uint8_t sum = state[x] + state[y]; 55 FFSWAP(uint8_t, state[x], state[y]); 56 *dst++ = src ? *src++ ^ state[sum] : state[sum]; 57 x++; 58 y += state[x]; 59 } 60 r->x = x; r->y = y; 61} 62