/*

* Copyright (c) 2002-2009 Nokia Corporation and/or its subsidiary(-ies).

* All rights reserved.

* This component and the accompanying materials are made available

* under the terms of the License "Eclipse Public License v1.0"

* which accompanies this distribution, and is available

* at the URL "http://www.eclipse.org/legal/epl-v10.html".

*

* Initial Contributors:

* Nokia Corporation - initial contribution.

*

* Contributors:

*

* Description: 

* ** IMPORTANT ** PublishedPartner API's in this file are published to 3rd party developers via the 

* Symbian website. Changes to these API's should be treated as PublishedAll API changes and the Security TA should be consulted.

* RC4 implementation

*

*/

/**

 @file 

 @internalAll

*/

#ifndef __ARC4_H__

#define __ARC4_H__

#include "streamcipher.h"

/** The size of the substitution box (i.e. lookup table) in bytes. */

const TInt KSBoxSize = 256;

/** Maximum ARC4 key size in bytes. */

const TInt KMaxARC4KeyBytes = 256; //2048 bits

/** Number of bytes to discard by default from an ARC4 key stream. */

const TUint KDefaultDiscardBytes = 768;

/**

* Implements an RC4-compatible stream cipher that outputs a pseudorandom stream

* of bits, having been initialised with a key. 

*

* @publishedPartner

* @released 

*/

class CARC4 : public CStreamCipher

{

public:

	/**

	* Constructs an instance of a CARC4 object, and initialises it with a key and

	* (optionally) the number of initial bytes to discard. Defaults to 256. 

	*

	* The number of dropped bytes <b>must</b> be agreed with the other

	* party, with which information is to be exchanged, prior to encipherment.

	*

	* @note	Several papers have been published indicating that there are weaknesses 

	*		in the first bytes of an ARC4 byte stream.  A search for "ARC4

	*		discard" should find these papers.  Recommended practice is to drop the first

	*		KDefaultDiscardBytes bytes of the key stream.  

	*

	* @param aKey			The key to use.  aKey must be less than or equal to

	*						KRC4MaxKeySizeBytes.  

	* @param aDiscardBytes	The number of bytes to drop from the beginning of the key

	*						stream.

	* @return				A pointer to the new CARC4 object.

	*  

	* @leave KErrKeyNotWeakEnough	If the key size is larger than that allowed by the

	*								cipher strength restrictions of the crypto library.

	*								See TCrypto::IsSymmetricWeakEnoughL()

	*/

	IMPORT_C static CARC4* NewL(const TDesC8& aKey, 

		TUint aDiscardBytes = KDefaultDiscardBytes);

	/**

	* Constructs an instance of a CARC4 object, and initialises it with a key and

	* (optionally) the number of initial bytes to discard. Defaults to 256. 

	*

	* The number of dropped bytes <b>must</b> be agreed with the other

	* party, with which information is to be exchanged, prior to encipherment.

	*

	* @see CARC4::NewL()

	*

	* @param aKey			The key to use.  aKey must be less than or equal to

	*						KRC4MaxKeySizeBytes.  

	* @param aDiscardBytes	The number of bytes to drop from the beginning of the key

	*						stream.

	* @return				A pointer to the new CARC4 object.

	*  

	* @leave KErrKeyNotWeakEnough	If the key size is larger than that allowed by the

	*								cipher strength restrictions of the crypto library.

	*								See TCrypto::IsSymmetricWeakEnoughL()

	*/

	IMPORT_C static CARC4* NewLC(const TDesC8& aKey, 

		TUint aDiscardBytes = KDefaultDiscardBytes);

public:	

	virtual void Reset(void);

	virtual TInt KeySize(void) const;

protected:

	/**	

	 * Performs an ARC4 encryption or decryption on supplied data.

	 * 

	 * @note ARC4 encryption and decryption are symmetrical.

	 *

	 * @param aData	On input, data to be transformed; 

	 *				on return, transformed data.

	 */

	virtual void DoProcess(TDes8& aData);

private:

	CARC4(const TDesC8& aKey, TUint aDiscardBytes);

	void GenerateSBox();

	inline TUint8 GenerateByte();

	void DiscardBytes(TInt aDiscardBytes);

private:

	TUint8 ix;

	TUint8 iy;

	TInt iDiscardBytes;

	TUint8 iState[KSBoxSize];

	TBuf8<KMaxARC4KeyBytes> iKey;

};

#endif	//	__ARC4_H__