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/* arc4.cpp
*
* Copyright (C) 2003 Sawtooth Consulting Ltd.
*
* This file is part of yaSSL.
*
* yaSSL 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.
*
* yaSSL 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
*/
/* based on Wei Dai's arc4.cpp from CryptoPP */
#include "runtime.hpp"
#include "arc4.hpp"
namespace TaoCrypt {
void ARC4::SetKey(const byte* key, word32 length)
{
x_ = 1;
y_ = 0;
word32 i;
for (i = 0; i < STATE_SIZE; i++)
state_[i] = i;
word32 keyIndex = 0, stateIndex = 0;
for (i = 0; i < STATE_SIZE; i++) {
word32 a = state_[i];
stateIndex += key[keyIndex] + a;
stateIndex &= 0xFF;
state_[i] = state_[stateIndex];
state_[stateIndex] = a;
if (++keyIndex >= length)
keyIndex = 0;
}
}
// local
namespace {
inline unsigned int MakeByte(word32& x, word32& y, byte* s)
{
word32 a = s[x];
y = (y+a) & 0xff;
word32 b = s[y];
s[x] = b;
s[y] = a;
x = (x+1) & 0xff;
return s[(a+b) & 0xff];
}
} // namespace
void ARC4::Process(byte* out, const byte* in, word32 length)
{
if (length == 0) return;
byte *const s = state_;
word32 x = x_;
word32 y = y_;
if (in == out)
while (length--)
*out++ ^= MakeByte(x, y, s);
else
while(length--)
*out++ = *in++ ^ MakeByte(x, y, s);
x_ = x;
y_ = y;
}
} // namespace
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