arc4.c

00001 /* arc4.c
00002  *
00003  * Copyright (C) 2006-2009 Sawtooth Consulting Ltd.
00004  *
00005  * This file is part of CyaSSL.
00006  *
00007  * CyaSSL is free software; you can redistribute it and/or modify
00008  * it under the terms of the GNU General Public License as published by
00009  * the Free Software Foundation; either version 2 of the License, or
00010  * (at your option) any later version.
00011  *
00012  * CyaSSL is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00015  * GNU General Public License for more details.
00016  *
00017  * You should have received a copy of the GNU General Public License
00018  * along with this program; if not, write to the Free Software
00019  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
00020  */
00021 
00022 
00023 #include "arc4.h"
00024 
00025 
00026 
00027 void Arc4SetKey(Arc4* arc4, const byte* key, word32 length)
00028 {
00029     word32 i;
00030     word32 keyIndex = 0, stateIndex = 0;
00031 
00032     arc4->x = 1;
00033     arc4->y = 0;
00034 
00035     for (i = 0; i < ARC4_STATE_SIZE; i++)
00036         arc4->state[i] = i;
00037 
00038     for (i = 0; i < ARC4_STATE_SIZE; i++) {
00039         word32 a = arc4->state[i];
00040         stateIndex += key[keyIndex] + a;
00041         stateIndex &= 0xFF;
00042         arc4->state[i] = arc4->state[stateIndex];
00043         arc4->state[stateIndex] = a;
00044 
00045         if (++keyIndex >= length)
00046             keyIndex = 0;
00047     }
00048 }
00049 
00050 
00051 static INLINE word32 MakeByte(word32* x, word32* y, byte* s)
00052 {
00053     word32 a = s[*x], b;
00054     *y = (*y+a) & 0xff;
00055 
00056     b = s[*y];
00057     s[*x] = b;
00058     s[*y] = a;
00059     *x = (*x+1) & 0xff;
00060 
00061     return s[(a+b) & 0xff];
00062 }
00063 
00064 
00065 void Arc4Process(Arc4* arc4, byte* out, const byte* in, word32 length)
00066 {
00067     word32 x = arc4->x;
00068     word32 y = arc4->y;
00069 
00070     while(length--)
00071         *out++ = *in++ ^ MakeByte(&x, &y, arc4->state);
00072 
00073     arc4->x = x;
00074     arc4->y = y;
00075 }
00076