reactos/sdk/lib/cryptlib/rc4.c

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/*
* Copyright 2006 Mike McCormack
*
* based on arc4.cpp - written and placed in the public domain by Wei Dai
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
*/
/* http://cryptopp.sourceforge.net/docs/ref521/arc4_8cpp-source.html */
#include "rc4.h"
void rc4_init(RC4_CONTEXT *a4i, const unsigned char *key, unsigned int keyLen)
{
unsigned int keyIndex = 0, stateIndex = 0;
unsigned int i, a;
a4i->x = a4i->y = 0;
for (i=0; i<256; i++)
a4i->state[i] = i;
for (i=0; i<256; i++)
{
a = a4i->state[i];
stateIndex += key[keyIndex] + a;
stateIndex &= 0xff;
a4i->state[i] = a4i->state[stateIndex];
a4i->state[stateIndex] = a;
if (++keyIndex >= keyLen)
keyIndex = 0;
}
}
void rc4_crypt(RC4_CONTEXT *a4i, unsigned char *inoutString, unsigned int length)
{
unsigned char *const s=a4i->state;
unsigned int x = a4i->x;
unsigned int y = a4i->y;
unsigned int a, b;
while(length--)
{
x = (x+1) & 0xff;
a = s[x];
y = (y+a) & 0xff;
b = s[y];
s[x] = b;
s[y] = a;
*inoutString++ ^= s[(a+b) & 0xff];
}
a4i->x = x;
a4i->y = y;
}