1 /*
2 * RC4 stream cipher
3 * Copyright (c) 2002-2005, Jouni Malinen <j@w1.fi>
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License version 2 as
7 * published by the Free Software Foundation.
8 *
9 * Alternatively, this software may be distributed under the terms of BSD
10 * license.
11 *
12 * See README and COPYING for more details.
13 */
14
15 #include "includes.h"
16
17 #include "common.h"
18 #include "crypto.h"
19
20 #define S_SWAP(a,b) do { u8 t = S[a]; S[a] = S[b]; S[b] = t; } while(0)
21
rc4_skip(const u8 * key,size_t keylen,size_t skip,u8 * data,size_t data_len)22 int rc4_skip(const u8 *key, size_t keylen, size_t skip,
23 u8 *data, size_t data_len)
24 {
25 u32 i, j, k;
26 u8 S[256], *pos;
27 size_t kpos;
28
29 /* Setup RC4 state */
30 for (i = 0; i < 256; i++)
31 S[i] = i;
32 j = 0;
33 kpos = 0;
34 for (i = 0; i < 256; i++) {
35 j = (j + S[i] + key[kpos]) & 0xff;
36 kpos++;
37 if (kpos >= keylen)
38 kpos = 0;
39 S_SWAP(i, j);
40 }
41
42 /* Skip the start of the stream */
43 i = j = 0;
44 for (k = 0; k < skip; k++) {
45 i = (i + 1) & 0xff;
46 j = (j + S[i]) & 0xff;
47 S_SWAP(i, j);
48 }
49
50 /* Apply RC4 to data */
51 pos = data;
52 for (k = 0; k < data_len; k++) {
53 i = (i + 1) & 0xff;
54 j = (j + S[i]) & 0xff;
55 S_SWAP(i, j);
56 *pos++ ^= S[(S[i] + S[j]) & 0xff];
57 }
58
59 return 0;
60 }
61