blob: ffcb11214292b77b99baf679b89148899caf339f
| 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 "mem.h" |
| 26 | #include "rc4.h" |
| 27 | |
| 28 | AVRC4 *av_rc4_alloc(void) |
| 29 | { |
| 30 | return av_mallocz(sizeof(struct AVRC4)); |
| 31 | } |
| 32 | |
| 33 | int av_rc4_init(AVRC4 *r, const uint8_t *key, int key_bits, int decrypt) { |
| 34 | int i, j; |
| 35 | uint8_t y; |
| 36 | uint8_t *state = r->state; |
| 37 | int keylen = key_bits >> 3; |
| 38 | if (key_bits & 7) |
| 39 | return AVERROR(EINVAL); |
| 40 | for (i = 0; i < 256; i++) |
| 41 | state[i] = i; |
| 42 | y = 0; |
| 43 | // j is i % keylen |
| 44 | for (j = 0, i = 0; i < 256; i++, j++) { |
| 45 | if (j == keylen) j = 0; |
| 46 | y += state[i] + key[j]; |
| 47 | FFSWAP(uint8_t, state[i], state[y]); |
| 48 | } |
| 49 | r->x = 1; |
| 50 | r->y = state[1]; |
| 51 | return 0; |
| 52 | } |
| 53 | |
| 54 | void av_rc4_crypt(AVRC4 *r, uint8_t *dst, const uint8_t *src, int count, uint8_t *iv, int decrypt) { |
| 55 | uint8_t x = r->x, y = r->y; |
| 56 | uint8_t *state = r->state; |
| 57 | while (count-- > 0) { |
| 58 | uint8_t sum = state[x] + state[y]; |
| 59 | FFSWAP(uint8_t, state[x], state[y]); |
| 60 | *dst++ = src ? *src++ ^ state[sum] : state[sum]; |
| 61 | x++; |
| 62 | y += state[x]; |
| 63 | } |
| 64 | r->x = x; r->y = y; |
| 65 | } |
| 66 |