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1  /*  
2  * RC4 encryption/decryption/pseudorandom 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 021101301 USA  
22  */  
23  
24  #include "error.h"  
25  #include "macros.h"  
26  #include "mem.h"  
27  #include "rc4.h"  
28  
29  543  AVRC4 *av_rc4_alloc(void)  
30  {  
31  543  return av_mallocz(sizeof(struct AVRC4));  
32  }  
33  
34  1086  int av_rc4_init(AVRC4 *r, const uint8_t *key, int key_bits, int decrypt) {  
35  int i, j;  
36  uint8_t y;  
37  1086  uint8_t *state = r>state;  
38  1086  int keylen = key_bits >> 3;  
39 
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1086  if (key_bits & 7) 
40  ✗  return AVERROR(EINVAL);  
41 
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279102  for (i = 0; i < 256; i++) 
42  278016  state[i] = i;  
43  1086  y = 0;  
44  // j is i % keylen  
45 
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279102  for (j = 0, i = 0; i < 256; i++, j++) { 
46 
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278016  if (j == keylen) j = 0; 
47  278016  y += state[i] + key[j];  
48  278016  FFSWAP(uint8_t, state[i], state[y]);  
49  }  
50  1086  r>x = 1;  
51  1086  r>y = state[1];  
52  1086  return 0;  
53  }  
54  
55  1086  void av_rc4_crypt(AVRC4 *r, uint8_t *dst, const uint8_t *src, int count, uint8_t *iv, int decrypt) {  
56  1086  uint8_t x = r>x, y = r>y;  
57  1086  uint8_t *state = r>state;  
58 
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403302  while (count > 0) { 
59  402216  uint8_t sum = state[x] + state[y];  
60  402216  FFSWAP(uint8_t, state[x], state[y]);  
61 
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402216  *dst++ = src ? *src++ ^ state[sum] : state[sum]; 
62  402216  x++;  
63  402216  y += state[x];  
64  }  
65  1086  r>x = x; r>y = y;  
66  1086  }  
67 