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libavutil/rc4.c

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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 }

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