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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