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 "rc4.h"
19
20 #define S_SWAP(a,b) do { u8 t = S[a]; S[a] = S[b]; S[b] = t; } while(0)
21
22 /**
23 * rc4 - XOR RC4 stream to given data with skip-stream-start
24 * @key: RC4 key
25 * @keylen: RC4 key length
26 * @skip: number of bytes to skip from the beginning of the RC4 stream
27 * @data: data to be XOR'ed with RC4 stream
28 * @data_len: buf length
29 *
30 * Generate RC4 pseudo random stream for the given key, skip beginning of the
31 * stream, and XOR the end result with the data buffer to perform RC4
32 * encryption/decryption.
33 */
rc4_skip(const u8 * key,size_t keylen,size_t skip,u8 * data,size_t data_len)34 void rc4_skip(const u8 *key, size_t keylen, size_t skip,
35 u8 *data, size_t data_len)
36 {
37 u32 i, j, k;
38 u8 S[256], *pos;
39 size_t kpos;
40
41 /* Setup RC4 state */
42 for (i = 0; i < 256; i++)
43 S[i] = i;
44 j = 0;
45 kpos = 0;
46 for (i = 0; i < 256; i++) {
47 j = (j + S[i] + key[kpos]) & 0xff;
48 kpos++;
49 if (kpos >= keylen)
50 kpos = 0;
51 S_SWAP(i, j);
52 }
53
54 /* Skip the start of the stream */
55 i = j = 0;
56 for (k = 0; k < skip; k++) {
57 i = (i + 1) & 0xff;
58 j = (j + S[i]) & 0xff;
59 S_SWAP(i, j);
60 }
61
62 /* Apply RC4 to data */
63 pos = data;
64 for (k = 0; k < data_len; k++) {
65 i = (i + 1) & 0xff;
66 j = (j + S[i]) & 0xff;
67 S_SWAP(i, j);
68 *pos++ ^= S[(S[i] + S[j]) & 0xff];
69 }
70 }
71
72
73 /**
74 * rc4 - XOR RC4 stream to given data
75 * @buf: data to be XOR'ed with RC4 stream
76 * @len: buf length
77 * @key: RC4 key
78 * @key_len: RC4 key length
79 *
80 * Generate RC4 pseudo random stream for the given key and XOR this with the
81 * data buffer to perform RC4 encryption/decryption.
82 */
rc4(u8 * buf,size_t len,const u8 * key,size_t key_len)83 void rc4(u8 *buf, size_t len, const u8 *key, size_t key_len)
84 {
85 rc4_skip(key, key_len, 0, buf, len);
86 }
87