wolfssl/ctaocrypt/src/arc4.c

/* arc4.c
 *
 * Copyright (C) 2006-2011 Sawtooth Consulting Ltd.
 *
 * This file is part of CyaSSL.
 *
 * CyaSSL is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * CyaSSL 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */


#include "arc4.h"



void Arc4SetKey(Arc4* arc4, const byte* key, word32 length)
{
    word32 i;
    word32 keyIndex = 0, stateIndex = 0;

    arc4->x = 1;
    arc4->y = 0;

    for (i = 0; i < ARC4_STATE_SIZE; i++)
        arc4->state[i] = i;

    for (i = 0; i < ARC4_STATE_SIZE; i++) {
        word32 a = arc4->state[i];
        stateIndex += key[keyIndex] + a;
        stateIndex &= 0xFF;
        arc4->state[i] = arc4->state[stateIndex];
        arc4->state[stateIndex] = a;

        if (++keyIndex >= length)
            keyIndex = 0;
    }
}


static INLINE word32 MakeByte(word32* x, word32* y, byte* s)
{
    word32 a = s[*x], b;
    *y = (*y+a) & 0xff;

    b = s[*y];
    s[*x] = b;
    s[*y] = a;
    *x = (*x+1) & 0xff;

    return s[(a+b) & 0xff];
}


void Arc4Process(Arc4* arc4, byte* out, const byte* in, word32 length)
{
    word32 x = arc4->x;
    word32 y = arc4->y;

    while(length--)
        *out++ = *in++ ^ MakeByte(&x, &y, arc4->state);

    arc4->x = x;
    arc4->y = y;
}