~zooko/cryptopp/trunk

// arc4.cpp - written and placed in the public domain by Wei Dai

// The ARC4 algorithm was first revealed in an anonymous email to the

// cypherpunks mailing list. This file originally contained some

// code copied from this email. The code has since been rewritten in order

// to clarify the copyright status of this file. It should now be

// completely in the public domain.

#include "pch.h"

#define CRYPTOPP_ENABLE_NAMESPACE_WEAK 1

#include "arc4.h"

NAMESPACE_BEGIN(CryptoPP)

namespace Weak1 {

void ARC4_TestInstantiations()

{

	ARC4 x;

}

ARC4_Base::~ARC4_Base()

{

	m_x = m_y = 0;

}

void ARC4_Base::UncheckedSetKey(const byte *key, unsigned int keyLen, const NameValuePairs &params)

{

	AssertValidKeyLength(keyLen);

	m_x = 1;

	m_y = 0;

	unsigned int i;

	for (i=0; i<256; i++)

		m_state[i] = i;

	unsigned int keyIndex = 0, stateIndex = 0;

	for (i=0; i<256; i++)

	{

		unsigned int a = m_state[i];

		stateIndex += key[keyIndex] + a;

		stateIndex &= 0xff;

		m_state[i] = m_state[stateIndex];

		m_state[stateIndex] = a;

		if (++keyIndex >= keyLen)

			keyIndex = 0;

	}

	int discardBytes = params.GetIntValueWithDefault("DiscardBytes", GetDefaultDiscardBytes());

	DiscardBytes(discardBytes);

}

template <class T>

static inline unsigned int MakeByte(T &x, T &y, byte *s)

{

	unsigned int a = s[x];

	y = (y+a) & 0xff;

	unsigned int b = s[y];

	s[x] = b;

	s[y] = a;

	x = (x+1) & 0xff;

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

}

void ARC4_Base::GenerateBlock(byte *output, size_t size)

{

	while (size--)

		*output++ = MakeByte(m_x, m_y, m_state);

}

void ARC4_Base::ProcessData(byte *outString, const byte *inString, size_t length)

{

	if (length == 0)

		return;

	byte *const s = m_state;

	unsigned int x = m_x;

	unsigned int y = m_y;

	if (inString == outString)

	{

		do

		{

			*outString++ ^= MakeByte(x, y, s);

		} while (--length);

	}

	else

	{

		do

		{

			*outString++ = *inString++ ^ MakeByte(x, y, s);

		}

		while(--length);

	}

	m_x = x;

	m_y = y;

}

void ARC4_Base::DiscardBytes(size_t length)

{

	if (length == 0)

		return;

	byte *const s = m_state;

	unsigned int x = m_x;

	unsigned int y = m_y;

	do

	{

		MakeByte(x, y, s);

	}

	while(--length);

	m_x = x;

	m_y = y;

}

}

NAMESPACE_END