//! returns true if NumberOfMessages() > 0
		virtual bool AnyMessages() const;
		//! start retrieving the next message
		/*!
			Returns false if no more messages exist or this message 
			is not completely retrieved.
		*/
		virtual bool GetNextMessage();
		//! skip count number of messages
		virtual unsigned int SkipMessages(unsigned int count=UINT_MAX);
		//!
		unsigned int TransferMessagesTo(BufferedTransformation &target, unsigned int count=UINT_MAX, const std::string &channel=NULL_CHANNEL)
			{TransferMessagesTo2(target, count, channel); return count;}
		//!
		unsigned int CopyMessagesTo(BufferedTransformation &target, unsigned int count=UINT_MAX, const std::string &channel=NULL_CHANNEL) const;

		//!
		virtual void SkipAll();
		//!
		void TransferAllTo(BufferedTransformation &target, const std::string &channel=NULL_CHANNEL)
			{TransferAllTo2(target, channel);}
		//!
		void CopyAllTo(BufferedTransformation &target, const std::string &channel=NULL_CHANNEL) const;

		virtual bool GetNextMessageSeries() {return false;}
		virtual unsigned int NumberOfMessagesInThisSeries() const {return NumberOfMessages();}
		virtual unsigned int NumberOfMessageSeries() const {return 0;}
	//@}

	//!	\name NON-BLOCKING TRANSFER OF OUTPUT
	//@{
		virtual unsigned int TransferTo2(BufferedTransformation &target, unsigned long &byteCount, const std::string &channel=NULL_CHANNEL, bool blocking=true) =0;
		virtual unsigned int CopyRangeTo2(BufferedTransformation &target, unsigned long &begin, unsigned long end=ULONG_MAX, const std::string &channel=NULL_CHANNEL, bool blocking=true) const =0;
		unsigned int TransferMessagesTo2(BufferedTransformation &target, unsigned int &messageCount, const std::string &channel=NULL_CHANNEL, bool blocking=true);
		unsigned int TransferAllTo2(BufferedTransformation &target, const std::string &channel=NULL_CHANNEL, bool blocking=true);
	//@}

	//!	\name CHANNELS
	//@{
		struct NoChannelSupport : public NotImplemented
			{NoChannelSupport() : NotImplemented("BufferedTransformation: this object doesn't support multiple channels") {}};

		unsigned int ChannelPut(const std::string &channel, byte inByte, bool blocking=true)
			{return ChannelPut(channel, &inByte, 1, blocking);}
		unsigned int ChannelPut(const std::string &channel, const byte *inString, unsigned int length, bool blocking=true)
			{return ChannelPut2(channel, inString, length, 0, blocking);}

		unsigned int ChannelPutModifiable(const std::string &channel, byte *inString, unsigned int length, bool blocking=true)
			{return ChannelPutModifiable2(channel, inString, length, 0, blocking);}

		unsigned int ChannelPutWord16(const std::string &channel, word16 value, ByteOrder order=BIG_ENDIAN_ORDER, bool blocking=true);
		unsigned int ChannelPutWord32(const std::string &channel, word32 value, ByteOrder order=BIG_ENDIAN_ORDER, bool blocking=true);

		bool ChannelMessageEnd(const std::string &channel, int propagation=-1, bool blocking=true)
			{return !!ChannelPut2(channel, NULL, 0, propagation < 0 ? -1 : propagation+1, blocking);}
		unsigned int ChannelPutMessageEnd(const std::string &channel, const byte *inString, unsigned int length, int propagation=-1, bool blocking=true)
			{return ChannelPut2(channel, inString, length, propagation < 0 ? -1 : propagation+1, blocking);}

		virtual byte * ChannelCreatePutSpace(const std::string &channel, unsigned int &size);

		virtual unsigned int ChannelPut2(const std::string &channel, const byte *begin, unsigned int length, int messageEnd, bool blocking);
		virtual unsigned int ChannelPutModifiable2(const std::string &channel, byte *begin, unsigned int length, int messageEnd, bool blocking);

		virtual bool ChannelFlush(const std::string &channel, bool hardFlush, int propagation=-1, bool blocking=true);
		virtual bool ChannelMessageSeriesEnd(const std::string &channel, int propagation=-1, bool blocking=true);

		virtual void SetRetrievalChannel(const std::string &channel);
	//@}

	//!	\name ATTACHMENT
	/*! Some BufferedTransformation objects (e.g. Filter objects)
		allow other BufferedTransformation objects to be attached. When
		this is done, the first object instead of buffering its output,
		sents that output to the attached object as input. The entire
		attachment chain is deleted when the anchor object is destructed.
	*/
	//@{
		//! returns whether this object allows attachment
		virtual bool Attachable() {return false;}
		//! returns the object immediately attached to this object or NULL for no attachment
		virtual BufferedTransformation *AttachedTransformation() {assert(!Attachable()); return 0;}
		//!
		virtual const BufferedTransformation *AttachedTransformation() const
			{return const_cast<BufferedTransformation *>(this)->AttachedTransformation();}
		//! delete the current attachment chain and replace it with newAttachment
		virtual void Detach(BufferedTransformation *newAttachment = 0)
			{assert(!Attachable()); throw NotImplemented("BufferedTransformation: this object is not attachable");}
		//! add newAttachment to the end of attachment chain
		virtual void Attach(BufferedTransformation *newAttachment);
	//@}

protected:
	static int DecrementPropagation(int propagation)
		{return propagation != 0 ? propagation - 1 : 0;}
};

//! returns a reference to a BufferedTransformation object that discards all input
BufferedTransformation & TheBitBucket();

//! interface for crypto material, such as public and private keys, and crypto parameters

class CRYPTOPP_DLL CRYPTOPP_NO_VTABLE CryptoMaterial : public NameValuePairs
{
public:
	//! exception thrown when invalid crypto material is detected
	class CRYPTOPP_DLL InvalidMaterial : public InvalidDataFormat
	{
	public:
		explicit InvalidMaterial(const std::string &s) : InvalidDataFormat(s) {}
	};

	//! assign values from source to this object
	/*! \note This function can be used to create a public key from a private key. */
	virtual void AssignFrom(const NameValuePairs &source) =0;

	//! check this object for errors
	/*! \param level denotes the level of thoroughness:
		0 - using this object won't cause a crash or exception (rng is ignored)
		1 - this object will probably function (encrypt, sign, etc.) correctly (but may not check for weak keys and such)
		2 - make sure this object will function correctly, and do reasonable security checks
		3 - do checks that may take a long time
		\return true if the tests pass */
	virtual bool Validate(RandomNumberGenerator &rng, unsigned int level) const =0;

	//! throws InvalidMaterial if this object fails Validate() test
	virtual void ThrowIfInvalid(RandomNumberGenerator &rng, unsigned int level) const
		{if (!Validate(rng, level)) throw InvalidMaterial("CryptoMaterial: this object contains invalid values");}

//	virtual std::vector<std::string> GetSupportedFormats(bool includeSaveOnly=false, bool includeLoadOnly=false);

	//! save key into a BufferedTransformation
	virtual void Save(BufferedTransformation &bt) const
		{throw NotImplemented("CryptoMaterial: this object does not support saving");}

	//! load key from a BufferedTransformation
	/*! \throws KeyingErr if decode fails
		\note Generally does not check that the key is valid.
			Call ValidateKey() or ThrowIfInvalidKey() to check that. */
	virtual void Load(BufferedTransformation &bt)
		{throw NotImplemented("CryptoMaterial: this object does not support loading");}

	//! \return whether this object supports precomputation
	virtual bool SupportsPrecomputation() const {return false;}
	//! do precomputation
	/*! The exact semantics of Precompute() is varies, but
		typically it means calculate a table of n objects
		that can be used later to speed up computation. */
	virtual void Precompute(unsigned int n)
		{assert(!SupportsPrecomputation()); throw NotImplemented("CryptoMaterial: this object does not support precomputation");}
	//! retrieve previously saved precomputation
	virtual void LoadPrecomputation(BufferedTransformation &storedPrecomputation)
		{assert(!SupportsPrecomputation()); throw NotImplemented("CryptoMaterial: this object does not support precomputation");}
	//! save precomputation for later use
	virtual void SavePrecomputation(BufferedTransformation &storedPrecomputation) const
		{assert(!SupportsPrecomputation()); throw NotImplemented("CryptoMaterial: this object does not support precomputation");}

	// for internal library use
	void DoQuickSanityCheck() const	{ThrowIfInvalid(NullRNG(), 0);}
};

//! interface for generatable crypto material, such as private keys and crypto parameters

class CRYPTOPP_DLL CRYPTOPP_NO_VTABLE GeneratableCryptoMaterial : virtual public CryptoMaterial
{
public:
	//! generate a random key or crypto parameters
	/*! \throws KeyingErr if algorithm parameters are invalid, or if a key can't be generated
		(e.g., if this is a public key object) */
	virtual void GenerateRandom(RandomNumberGenerator &rng, const NameValuePairs &params = g_nullNameValuePairs)
		{throw NotImplemented("GeneratableCryptoMaterial: this object does not support key/parameter generation");}

	//! calls the above function with a NameValuePairs object that just specifies "KeySize"
	void GenerateRandomWithKeySize(RandomNumberGenerator &rng, unsigned int keySize);
};

//! interface for public keys

class CRYPTOPP_DLL CRYPTOPP_NO_VTABLE PublicKey : virtual public CryptoMaterial
{
};

//! interface for private keys

class CRYPTOPP_DLL CRYPTOPP_NO_VTABLE PrivateKey : public GeneratableCryptoMaterial
{
};

//! interface for crypto prameters

class CRYPTOPP_DLL CRYPTOPP_NO_VTABLE CryptoParameters : public GeneratableCryptoMaterial
{
};

//! interface for asymmetric algorithms

class CRYPTOPP_DLL CRYPTOPP_NO_VTABLE AsymmetricAlgorithm : public Algorithm
{
public:
	//! returns a reference to the crypto material used by this object
	virtual CryptoMaterial & AccessMaterial() =0;
	//! returns a const reference to the crypto material used by this object
	virtual const CryptoMaterial & GetMaterial() const =0;

	//! for backwards compatibility, calls AccessMaterial().Load(bt)
	void BERDecode(BufferedTransformation &bt)
		{AccessMaterial().Load(bt);}
	//! for backwards compatibility, calls GetMaterial().Save(bt)
	void DEREncode(BufferedTransformation &bt) const
		{GetMaterial().Save(bt);}
};

//! interface for asymmetric algorithms using public keys

class CRYPTOPP_DLL CRYPTOPP_NO_VTABLE PublicKeyAlgorithm : public AsymmetricAlgorithm
{
public:
	// VC60 workaround: no co-variant return type
	CryptoMaterial & AccessMaterial() {return AccessPublicKey();}
	const CryptoMaterial & GetMaterial() const {return GetPublicKey();}

	virtual PublicKey & AccessPublicKey() =0;
	virtual const PublicKey & GetPublicKey() const {return const_cast<PublicKeyAlgorithm *>(this)->AccessPublicKey();}
};

//! interface for asymmetric algorithms using private keys

class CRYPTOPP_DLL CRYPTOPP_NO_VTABLE PrivateKeyAlgorithm : public AsymmetricAlgorithm
{
public:
	CryptoMaterial & AccessMaterial() {return AccessPrivateKey();}
	const CryptoMaterial & GetMaterial() const {return GetPrivateKey();}

	virtual PrivateKey & AccessPrivateKey() =0;
	virtual const PrivateKey & GetPrivateKey() const {return const_cast<PrivateKeyAlgorithm *>(this)->AccessPrivateKey();}
};

//! interface for key agreement algorithms

class CRYPTOPP_DLL CRYPTOPP_NO_VTABLE KeyAgreementAlgorithm : public AsymmetricAlgorithm
{
public:
	CryptoMaterial & AccessMaterial() {return AccessCryptoParameters();}
	const CryptoMaterial & GetMaterial() const {return GetCryptoParameters();}

	virtual CryptoParameters & AccessCryptoParameters() =0;
	virtual const CryptoParameters & GetCryptoParameters() const {return const_cast<KeyAgreementAlgorithm *>(this)->AccessCryptoParameters();}
};

//! interface for public-key encryptors and decryptors

/*! This class provides an interface common to encryptors and decryptors
	for querying their plaintext and ciphertext lengths.
*/
class CRYPTOPP_DLL CRYPTOPP_NO_VTABLE PK_CryptoSystem
{
public:
	virtual ~PK_CryptoSystem() {}

	//! maximum length of plaintext for a given ciphertext length
	/*! \note This function returns 0 if ciphertextLength is not valid (too long or too short). */
	virtual unsigned int MaxPlaintextLength(unsigned int ciphertextLength) const =0;

	//! calculate length of ciphertext given length of plaintext
	/*! \note This function returns 0 if plaintextLength is not valid (too long). */
	virtual unsigned int CiphertextLength(unsigned int plaintextLength) const =0;

	//! this object supports the use of the parameter with the given name
	/*! some possible parameter names: EncodingParameters, KeyDerivationParameters */
	virtual bool ParameterSupported(const char *name) const =0;

	//! return fixed ciphertext length, if one exists, otherwise return 0
	/*! \note "Fixed" here means length of ciphertext does not depend on length of plaintext.
		It usually does depend on the key length. */
	virtual unsigned int FixedCiphertextLength() const {return 0;}

	//! return maximum plaintext length given the fixed ciphertext length, if one exists, otherwise return 0
	virtual unsigned int FixedMaxPlaintextLength() const {return 0;}

#ifdef CRYPTOPP_MAINTAIN_BACKWARDS_COMPATIBILITY
	unsigned int MaxPlainTextLength(unsigned int cipherTextLength) const {return MaxPlaintextLength(cipherTextLength);}
	unsigned int CipherTextLength(unsigned int plainTextLength) const {return CiphertextLength(plainTextLength);}
#endif
};

//! interface for public-key encryptors