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