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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 | #include "avutil.h" | |
24 | #include "common.h" | |
25 | #include "rc4.h" | |
26 | ||
27 | typedef struct AVRC4 AVRC4; | |
28 | ||
29 | int 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 | ||
50 | void 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 | } |