text: // dmac.h - written and placed in the public domain by Wei Dai
  
  //! \file
  //! \headerfile dmac.h
  //! \brief Classes for DMAC message authentication code
  
  #ifndef CRYPTOPP_DMAC_H
  #define CRYPTOPP_DMAC_H
  
  #include "cbcmac.h"
  
  NAMESPACE_BEGIN(CryptoPP)
  
  //! \class DMAC_Base
  //! \brief DMAC message authentication code base class
  //! \tparam T class derived from BlockCipherDocumentation
  template <class T>
  class CRYPTOPP_NO_VTABLE DMAC_Base : public SameKeyLengthAs<T>, public MessageAuthenticationCode
  {
  public:
  	static std::string StaticAlgorithmName() {return std::string("DMAC(") + T::StaticAlgorithmName() + ")";}
  
  	CRYPTOPP_CONSTANT(DIGESTSIZE=T::BLOCKSIZE)
  
  	DMAC_Base() : m_subkeylength(0), m_counter(0) {}
  
  	void UncheckedSetKey(const byte *key, unsigned int length, const NameValuePairs &params);
  	void Update(const byte *input, size_t length);
  	void TruncatedFinal(byte *mac, size_t size);
  	unsigned int DigestSize() const {return DIGESTSIZE;}
  
  private:
  	byte *GenerateSubKeys(const byte *key, size_t keylength);
  
  	size_t m_subkeylength;
  	SecByteBlock m_subkeys;
  	CBC_MAC<T> m_mac1;
  	typename T::Encryption m_f2;
  	unsigned int m_counter;
  };
  
  //! \class DMAC
  //! \brief DMAC message authentication code
  //! \tparam T class derived from BlockCipherDocumentation
  //! \sa <A HREF="https://eprint.iacr.org/1997/010">CBC MAC for Real-Time Data Sources (08.15.1997)</A>
  //!   by Erez Petrank and Charles Rackoff
  template <class T>
  class DMAC : public MessageAuthenticationCodeFinal<DMAC_Base<T> >
  {
  public:
  	//! \brief Construct a DMAC
  	DMAC() {}
  
  	//! \brief Construct a DMAC
  	//! \param key a byte array used to key the cipher
  	//! \param length the size of the byte array, in bytes
  	DMAC(const byte *key, size_t length=DMAC_Base<T>::DEFAULT_KEYLENGTH)
  		{this->SetKey(key, length);}
  };
  
  template <class T>
  void DMAC_Base<T>::UncheckedSetKey(const byte *key, unsigned int length, const NameValuePairs &params)
  {
  	m_subkeylength = T::StaticGetValidKeyLength(T::BLOCKSIZE);
  	m_subkeys.resize(2*UnsignedMin((unsigned int)T::BLOCKSIZE, m_subkeylength));
  	m_mac1.SetKey(GenerateSubKeys(key, length), m_subkeylength, params);
  	m_f2.SetKey(m_subkeys+m_subkeys.size()/2, m_subkeylength, params);
  	m_counter = 0;
  	m_subkeys.resize(0);
  }
  
  template <class T>
  void DMAC_Base<T>::Update(const byte *input, size_t length)
  {
  	m_mac1.Update(input, length);
  	m_counter = (unsigned int)((m_counter + length) % T::BLOCKSIZE);
  }
  
  template <class T>
  void DMAC_Base<T>::TruncatedFinal(byte *mac, size_t size)
  {
  	ThrowIfInvalidTruncatedSize(size);
  
  	byte pad[T::BLOCKSIZE];
  	byte padByte = byte(T::BLOCKSIZE-m_counter);
  	memset(pad, padByte, padByte);
  	m_mac1.Update(pad, padByte);
  	m_mac1.TruncatedFinal(mac, size);
  	m_f2.ProcessBlock(mac);
  
  	m_counter = 0;	// reset for next message
  }
  
  template <class T>
  byte *DMAC_Base<T>::GenerateSubKeys(const byte *key, size_t keylength)
  {
  	typename T::Encryption cipher(key, keylength);
  	memset(m_subkeys, 0, m_subkeys.size());
  	cipher.ProcessBlock(m_subkeys);
  	m_subkeys[m_subkeys.size()/2 + T::BLOCKSIZE - 1] = 1;
  	cipher.ProcessBlock(m_subkeys+m_subkeys.size()/2);
  	return m_subkeys;
  }
  
  NAMESPACE_END
  
  #endif
  