FFmpeg: libavutil/rc4.c Source File

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libavutil

rc4.c

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1 /*

2 * RC4 encryption/decryption/pseudo-random number generator

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"

27 typedef struct AVRC4 AVRC4;

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 }

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 }

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