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/*
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* Copyright (c) 2002-2009 Nokia Corporation and/or its subsidiary(-ies).
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* All rights reserved.
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* This component and the accompanying materials are made available
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* under the terms of the License "Eclipse Public License v1.0"
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* which accompanies this distribution, and is available
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* at the URL "http://www.eclipse.org/legal/epl-v10.html".
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*
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* Initial Contributors:
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* Nokia Corporation - initial contribution.
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*
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* Contributors:
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*
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* Description:
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* ** IMPORTANT ** PublishedPartner API's in this file are published to 3rd party developers via the
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* Symbian website. Changes to these API's should be treated as PublishedAll API changes and the Security TA should be consulted.
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* RC4 implementation
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*
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*/
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/**
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@file
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@publishedPartner
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@released
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*/
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#ifndef __ARC4_H__
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#define __ARC4_H__
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#include "streamcipher.h"
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/** The size of the substitution box (i.e. lookup table) in bytes. */
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const TInt KSBoxSize = 256;
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/** Maximum ARC4 key size in bytes. */
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const TInt KMaxARC4KeyBytes = 256; //2048 bits
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/** Number of bytes to discard by default from an ARC4 key stream. */
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const TUint KDefaultDiscardBytes = 768;
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/**
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* Implements an RC4-compatible stream cipher that outputs a pseudorandom stream
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* of bits, having been initialised with a key.
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*
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*/
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class CARC4 : public CStreamCipher
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{
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public:
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/**
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* Constructs an instance of a CARC4 object, and initialises it with a key and
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* (optionally) the number of initial bytes to discard. Defaults to 256.
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*
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* The number of dropped bytes <b>must</b> be agreed with the other
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* party, with which information is to be exchanged, prior to encipherment.
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*
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* @note Several papers have been published indicating that there are weaknesses
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* in the first bytes of an ARC4 byte stream. A search for "ARC4
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* discard" should find these papers. Recommended practice is to drop the first
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* KDefaultDiscardBytes bytes of the key stream.
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*
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* @param aKey The key to use. aKey must be less than or equal to
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* KRC4MaxKeySizeBytes.
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* @param aDiscardBytes The number of bytes to drop from the beginning of the key
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* stream.
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* @return A pointer to the new CARC4 object.
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*
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* @leave KErrKeyNotWeakEnough If the key size is larger than that allowed by the
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* cipher strength restrictions of the crypto library.
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* See TCrypto::IsSymmetricWeakEnoughL()
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*/
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IMPORT_C static CARC4* NewL(const TDesC8& aKey,
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TUint aDiscardBytes = KDefaultDiscardBytes);
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/**
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* Constructs an instance of a CARC4 object, and initialises it with a key and
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* (optionally) the number of initial bytes to discard. Defaults to 256.
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*
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* The number of dropped bytes <b>must</b> be agreed with the other
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* party, with which information is to be exchanged, prior to encipherment.
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*
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* @see CARC4::NewL()
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*
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* @param aKey The key to use. aKey must be less than or equal to
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* KRC4MaxKeySizeBytes.
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* @param aDiscardBytes The number of bytes to drop from the beginning of the key
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* stream.
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* @return A pointer to the new CARC4 object.
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*
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* @leave KErrKeyNotWeakEnough If the key size is larger than that allowed by the
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* cipher strength restrictions of the crypto library.
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* See TCrypto::IsSymmetricWeakEnoughL()
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*/
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IMPORT_C static CARC4* NewLC(const TDesC8& aKey,
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TUint aDiscardBytes = KDefaultDiscardBytes);
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public:
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virtual void Reset(void);
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virtual TInt KeySize(void) const;
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protected:
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/**
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* Performs an ARC4 encryption or decryption on supplied data.
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*
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* @note ARC4 encryption and decryption are symmetrical.
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*
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* @param aData On input, data to be transformed;
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* on return, transformed data.
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*/
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virtual void DoProcess(TDes8& aData);
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private:
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CARC4(const TDesC8& aKey, TUint aDiscardBytes);
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void GenerateSBox();
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inline TUint8 GenerateByte();
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void DiscardBytes(TInt aDiscardBytes);
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private:
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TUint8 ix;
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TUint8 iy;
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TInt iDiscardBytes;
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TUint8 iState[KSBoxSize];
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TBuf8<KMaxARC4KeyBytes> iKey;
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};
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#endif // __ARC4_H__
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