## ffmpeg / libavutil / rc4.c @ 1fc81e73

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1 | 80b1c5a8 | Reimar Döffinger | ```
/*
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2 | ```
* RC4 encryption/decryption/pseudo-random number generator
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3 | ```
* Copyright (c) 2007 Reimar Doeffinger
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4 | ```
*
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5 | d5a8a023 | Diego Biurrun | ```
* loosely based on LibTomCrypt by Tom St Denis
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6 | ```
*
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7 | 80b1c5a8 | Reimar Döffinger | ```
* This file is part of FFmpeg.
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8 | ```
*
``` |
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9 | ```
* FFmpeg is free software; you can redistribute it and/or
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10 | ```
* modify it under the terms of the GNU Lesser General Public
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11 | ```
* License as published by the Free Software Foundation; either
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12 | ```
* version 2.1 of the License, or (at your option) any later version.
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13 | ```
*
``` |
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14 | ```
* FFmpeg is distributed in the hope that it will be useful,
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15 | ```
* but WITHOUT ANY WARRANTY; without even the implied warranty of
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16 | ```
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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17 | ```
* Lesser General Public License for more details.
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18 | ```
*
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19 | ```
* You should have received a copy of the GNU Lesser General Public
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20 | ```
* License along with FFmpeg; if not, write to the Free Software
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21 | ```
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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22 | ```
*/
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23 | 1a534c7f | Reimar Döffinger | #include "avutil.h" |

24 | 80b1c5a8 | Reimar Döffinger | #include "common.h" |

25 | #include "rc4.h" |
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26 | |||

27 | 1a534c7f | Reimar Döffinger | typedef struct AVRC4 AVRC4; |

28 | |||

29 | int av_rc4_init(AVRC4 *r, const uint8_t *key, int key_bits, int decrypt) { |
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30 | 80b1c5a8 | Reimar Döffinger | ```
int i, j;
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31 | 1a534c7f | Reimar Döffinger | uint8_t y; |

32 | uint8_t *state = r->state; |
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33 | int keylen = key_bits >> 3; |
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34 | if (key_bits & 7) |
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35 | return -1; |
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36 | 80b1c5a8 | Reimar Döffinger | for (i = 0; i < 256; i++) |

37 | state[i] = i; |
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38 | ```
y = 0;
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39 | ```
// j is i % keylen
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40 | for (j = 0, i = 0; i < 256; i++, j++) { |
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41 | if (j == keylen) j = 0; |
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42 | y += state[i] + key[j]; |
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43 | FFSWAP(uint8_t, state[i], state[y]); |
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44 | } |
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45 | 1a534c7f | Reimar Döffinger | ```
r->x = 1;
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46 | ```
r->y = state[1];
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47 | return 0; |
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48 | } |
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49 | |||

50 | void av_rc4_crypt(AVRC4 *r, uint8_t *dst, const uint8_t *src, int count, uint8_t *iv, int decrypt) { |
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51 | uint8_t x = r->x, y = r->y; |
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52 | uint8_t *state = r->state; |
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53 | while (count-- > 0) { |
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54 | 80b1c5a8 | Reimar Döffinger | uint8_t sum = state[x] + state[y]; |

55 | FFSWAP(uint8_t, state[x], state[y]); |
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56 | 1a534c7f | Reimar Döffinger | *dst++ = src ? *src++ ^ state[sum] : state[sum]; |

57 | 80b1c5a8 | Reimar Döffinger | x++; |

58 | y += state[x]; |
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59 | } |
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60 | 1a534c7f | Reimar Döffinger | r->x = x; r->y = y; |

61 | } |