1 /*

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

     3 * All rights reserved.

     4 * This component and the accompanying materials are made available

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

     6 * which accompanies this distribution, and is available

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

     8 *

     9 * Initial Contributors:

    10 * Nokia Corporation - initial contribution.

    11 *

    12 * Contributors:

    13 *

    14 * Description: 

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

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

    17 * RC4 implementation

    18 *

    19 */

    20 

    21 

    22 

    23 

    24 /**

    25  @file 

    26  @internalAll

    27 */

    28  

    29 #ifndef __ARC4_H__

    30 #define __ARC4_H__

    31 

    32 #include "streamcipher.h"

    33 

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

    35 const TInt KSBoxSize = 256;

    36 

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

    38 const TInt KMaxARC4KeyBytes = 256; //2048 bits

    39 

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

    41 const TUint KDefaultDiscardBytes = 768;

    42 

    43 /**

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

    45 * of bits, having been initialised with a key. 

    46 *

    47 * @publishedPartner

    48 * @released 

    49 */

    50 class CARC4 : public CStreamCipher

    51 {

    52 public:

    53 	/**

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

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

    56 	*

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

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

    59 	*

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

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

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

    63 	*		KDefaultDiscardBytes bytes of the key stream.  

    64 	*

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

    66 	*						KRC4MaxKeySizeBytes.  

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

    68 	*						stream.

    69 	* @return				A pointer to the new CARC4 object.

    70 	*  

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

    72 	*								cipher strength restrictions of the crypto library.

    73 	*								See TCrypto::IsSymmetricWeakEnoughL()

    74 	*/

    75 	IMPORT_C static CARC4* NewL(const TDesC8& aKey, 

    76 		TUint aDiscardBytes = KDefaultDiscardBytes);

    77 

    78 	/**

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

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

    81 	*

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

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

    84 	*

    85 	* @see CARC4::NewL()

    86 	*

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

    88 	*						KRC4MaxKeySizeBytes.  

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

    90 	*						stream.

    91 	* @return				A pointer to the new CARC4 object.

    92 	*  

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

    94 	*								cipher strength restrictions of the crypto library.

    95 	*								See TCrypto::IsSymmetricWeakEnoughL()

    96 	*/

    97 	IMPORT_C static CARC4* NewLC(const TDesC8& aKey, 

    98 		TUint aDiscardBytes = KDefaultDiscardBytes);

    99 public:	

   100 	virtual void Reset(void);

   101 	virtual TInt KeySize(void) const;

   102 protected:

   103 	/**	

   104 	 * Performs an ARC4 encryption or decryption on supplied data.

   105 	 * 

   106 	 * @note ARC4 encryption and decryption are symmetrical.

   107 	 *

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

   109 	 *				on return, transformed data.

   110 	 */

   111 	virtual void DoProcess(TDes8& aData);

   112 private:

   113 	CARC4(const TDesC8& aKey, TUint aDiscardBytes);

   114 	void GenerateSBox();

   115 	inline TUint8 GenerateByte();

   116 	void DiscardBytes(TInt aDiscardBytes);

   117 private:

   118 	TUint8 ix;

   119 	TUint8 iy;

   120 	TInt iDiscardBytes;

   121 	TUint8 iState[KSBoxSize];

   122 	TBuf8<KMaxARC4KeyBytes> iKey;

   123 };

   124 

   125 #endif	//	__ARC4_H__