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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 FFmpeg.
8  *
9  * FFmpeg 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  * FFmpeg 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 FFmpeg; if not, write to the Free Software
21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
22  */
23 
24 #include "error.h"
25 #include "macros.h"
26 #include "mem.h"
27 #include "rc4.h"
28 
av_rc4_alloc(void)29 AVRC4 *av_rc4_alloc(void)
30 {
31     return av_mallocz(sizeof(struct AVRC4));
32 }
33 
av_rc4_init(AVRC4 * r,const uint8_t * key,int key_bits,int decrypt)34 int av_rc4_init(AVRC4 *r, const uint8_t *key, int key_bits, int decrypt) {
35     int i, j;
36     uint8_t y;
37     uint8_t *state = r->state;
38     int keylen = key_bits >> 3;
39     if (key_bits & 7)
40         return AVERROR(EINVAL);
41     for (i = 0; i < 256; i++)
42         state[i] = i;
43     y = 0;
44     // j is i % keylen
45     for (j = 0, i = 0; i < 256; i++, j++) {
46         if (j == keylen) j = 0;
47         y += state[i] + key[j];
48         FFSWAP(uint8_t, state[i], state[y]);
49     }
50     r->x = 1;
51     r->y = state[1];
52     return 0;
53 }
54 
av_rc4_crypt(AVRC4 * r,uint8_t * dst,const uint8_t * src,int count,uint8_t * iv,int decrypt)55 void av_rc4_crypt(AVRC4 *r, uint8_t *dst, const uint8_t *src, int count, uint8_t *iv, int decrypt) {
56     uint8_t x = r->x, y = r->y;
57     uint8_t *state = r->state;
58     while (count-- > 0) {
59         uint8_t sum = state[x] + state[y];
60         FFSWAP(uint8_t, state[x], state[y]);
61         *dst++ = src ? *src++ ^ state[sum] : state[sum];
62         x++;
63         y += state[x];
64     }
65     r->x = x; r->y = y;
66 }
67