/src/cryptopp/eprecomp.h

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// eprecomp.h - originally written and placed in the public domain by Wei Dai

/// \file eprecomp.h
/// \brief Classes for precomputation in a group

#ifndef CRYPTOPP_EPRECOMP_H
#define CRYPTOPP_EPRECOMP_H

#include "cryptlib.h"
#include "integer.h"
#include "algebra.h"
#include "stdcpp.h"

NAMESPACE_BEGIN(CryptoPP)

/// \brief DL_GroupPrecomputation interface
/// \tparam T Field element
template <class T>
class DL_GroupPrecomputation
{
public:
  typedef T Element;

  virtual ~DL_GroupPrecomputation() {}

  /// \brief Determines if elements needs conversion
  /// \return true if the element needs conversion, false otherwise
  /// \details NeedConversions determines if an element must convert between representations.
  virtual bool NeedConversions() const {return false;}

  /// \brief Converts an element between representations
  /// \param v element to convert
  /// \return an element converted to an alternate representation for internal use
  /// \details ConvertIn is used when an element must convert between representations.
  virtual Element ConvertIn(const Element &v) const {return v;}

  /// \brief Converts an element between representations
  /// \param v element to convert
  /// \return an element converted from an alternate representation
  virtual Element ConvertOut(const Element &v) const {return v;}

  /// \brief Retrieves AbstractGroup interface
  /// \return GetGroup() returns the AbstractGroup interface
  virtual const AbstractGroup<Element> & GetGroup() const =0;

  /// \brief Decodes element in DER format
  /// \param bt BufferedTransformation object
  /// \return element in the group
  virtual Element BERDecodeElement(BufferedTransformation &bt) const =0;

  /// \brief Encodes element in DER format
  /// \param bt BufferedTransformation object
  /// \param P Element to encode
  virtual void DEREncodeElement(BufferedTransformation &bt, const Element &P) const =0;
};

/// \brief DL_FixedBasePrecomputation interface
/// \tparam T Field element
template <class T>
class DL_FixedBasePrecomputation
{
public:
  typedef T Element;

  virtual ~DL_FixedBasePrecomputation() {}

  /// \brief Determines whether this object is initialized
  /// \return true if this object is initialized, false otherwise
  virtual bool IsInitialized() const =0;

  /// \brief Set the base element
  /// \param group the group
  /// \param base element in the group
  virtual void SetBase(const DL_GroupPrecomputation<Element> &group, const Element &base) =0;

  /// \brief Get the base element
  /// \param group the group
  /// \return base element in the group
  virtual const Element & GetBase(const DL_GroupPrecomputation<Element> &group) const =0;

  /// \brief Perform precomputation
  /// \param group the group
  /// \param maxExpBits used to calculate the exponent base
  /// \param storage the suggested number of objects for the precompute table
  /// \details The exact semantics of Precompute() varies, but it typically means calculate
  ///   a table of n objects that can be used later to speed up computation.
  /// \details If a derived class does not override Precompute(), then the base class throws
  ///   NotImplemented.
  /// \sa SupportsPrecomputation(), LoadPrecomputation(), SavePrecomputation()
  virtual void Precompute(const DL_GroupPrecomputation<Element> &group, unsigned int maxExpBits, unsigned int storage) =0;

  /// \brief Retrieve previously saved precomputation
  /// \param group the group
  /// \param storedPrecomputation BufferedTransformation with the saved precomputation
  /// \throw NotImplemented
  /// \sa SupportsPrecomputation(), Precompute()
  virtual void Load(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &storedPrecomputation) =0;

  /// \brief Save precomputation for later use
  /// \param group the group
  /// \param storedPrecomputation BufferedTransformation to write the precomputation
  /// \throw NotImplemented
  /// \sa SupportsPrecomputation(), Precompute()
  virtual void Save(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &storedPrecomputation) const =0;

  /// \brief Exponentiates an element
  /// \param group the group
  /// \param exponent the exponent
  /// \return the result of the exponentiation
  virtual Element Exponentiate(const DL_GroupPrecomputation<Element> &group, const Integer &exponent) const =0;

  /// \brief Exponentiates an element
  /// \param pc1 the first the group precomputation
  /// \param exponent1 the first exponent
  /// \param pc2 the second the group precomputation
  /// \param exponent2 the first exponent2
  /// \return the public element raised to the exponent
  /// \details CascadeExponentiateBaseAndPublicElement raises the public element to
  ///   the base element and precomputation.
  virtual Element CascadeExponentiate(const DL_GroupPrecomputation<Element> &pc1, const Integer &exponent1, const DL_FixedBasePrecomputation<Element> &pc2, const Integer &exponent2) const =0;
};

/// \brief DL_FixedBasePrecomputation adapter class
/// \tparam T Field element
template <class T>
class DL_FixedBasePrecomputationImpl : public DL_FixedBasePrecomputation<T>
{
public:
  typedef T Element;

  virtual ~DL_FixedBasePrecomputationImpl() {}

  DL_FixedBasePrecomputationImpl() : m_windowSize(0) {}

  // DL_FixedBasePrecomputation
  bool IsInitialized() const
    {return !m_bases.empty();}
  void SetBase(const DL_GroupPrecomputation<Element> &group, const Element &base);
  const Element & GetBase(const DL_GroupPrecomputation<Element> &group) const
    {return group.NeedConversions() ? m_base : m_bases[0];}
  void Precompute(const DL_GroupPrecomputation<Element> &group, unsigned int maxExpBits, unsigned int storage);
  void Load(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &storedPrecomputation);
  void Save(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &storedPrecomputation) const;
  Element Exponentiate(const DL_GroupPrecomputation<Element> &group, const Integer &exponent) const;
  Element CascadeExponentiate(const DL_GroupPrecomputation<Element> &pc1, const Integer &exponent1, const DL_FixedBasePrecomputation<Element> &pc2, const Integer &exponent2) const;

private:
  void PrepareCascade(const DL_GroupPrecomputation<Element> &group, std::vector<BaseAndExponent<Element> > &eb, const Integer &exponent) const;

  Element m_base;
  unsigned int m_windowSize;
  Integer m_exponentBase;     // what base to represent the exponent in
  std::vector<Element> m_bases; // precalculated bases
};

NAMESPACE_END

#ifdef CRYPTOPP_MANUALLY_INSTANTIATE_TEMPLATES
#include "eprecomp.cpp"
#endif

#endif

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Created: 2024-11-21 07:03