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Reactos
1/*
2 * Copyright 2006 Mike McCormack
3 *
4 * based on arc4.cpp - written and placed in the public domain by Wei Dai
5 *
6 * This library is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
9 * version 2.1 of the License, or (at your option) any later version.
10 *
11 * This library is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with this library; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
19 */
20
21/* http://cryptopp.sourceforge.net/docs/ref521/arc4_8cpp-source.html */
22
23#include "rc4.h"
24
25void rc4_init(RC4_CONTEXT *a4i, const unsigned char *key, unsigned int keyLen)
26{
27 unsigned int keyIndex = 0, stateIndex = 0;
28 unsigned int i, a;
29
30 a4i->x = a4i->y = 0;
31
32 for (i=0; i<256; i++)
33 a4i->state[i] = i;
34
35 for (i=0; i<256; i++)
36 {
37 a = a4i->state[i];
38 stateIndex += key[keyIndex] + a;
39 stateIndex &= 0xff;
40 a4i->state[i] = a4i->state[stateIndex];
41 a4i->state[stateIndex] = a;
42 if (++keyIndex >= keyLen)
43 keyIndex = 0;
44 }
45}
46
47void rc4_crypt(RC4_CONTEXT *a4i, unsigned char *inoutString, unsigned int length)
48{
49 unsigned char *const s=a4i->state;
50 unsigned int x = a4i->x;
51 unsigned int y = a4i->y;
52 unsigned int a, b;
53
54 while(length--)
55 {
56 x = (x+1) & 0xff;
57 a = s[x];
58 y = (y+a) & 0xff;
59 b = s[y];
60 s[x] = b;
61 s[y] = a;
62 *inoutString++ ^= s[(a+b) & 0xff];
63 }
64
65 a4i->x = x;
66 a4i->y = y;
67}