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163 lines
6.6 KiB
163 lines
6.6 KiB
![]()
4 years ago
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// eprecomp.h - originally written and placed in the public domain by Wei Dai
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/// \file eprecomp.h
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/// \brief Classes for precomputation in a group
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#ifndef CRYPTOPP_EPRECOMP_H
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#define CRYPTOPP_EPRECOMP_H
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#include "cryptlib.h"
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#include "integer.h"
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#include "algebra.h"
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#include "stdcpp.h"
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NAMESPACE_BEGIN(CryptoPP)
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/// \brief DL_GroupPrecomputation interface
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/// \tparam T Field element
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template <class T>
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class DL_GroupPrecomputation
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{
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public:
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typedef T Element;
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virtual ~DL_GroupPrecomputation() {}
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/// \brief Determines if elements needs conversion
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/// \returns true if the element needs conversion, false otherwise
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/// \details NeedConversions determines if an element must convert between representations.
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virtual bool NeedConversions() const {return false;}
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/// \brief Converts an element between representations
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/// \param v element to convert
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/// \returns an element converted to an alternate representation for internal use
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/// \details ConvertIn is used when an element must convert between representations.
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virtual Element ConvertIn(const Element &v) const {return v;}
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/// \brief Converts an element between representations
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/// \param v element to convert
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/// \returns an element converted from an alternate representation
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virtual Element ConvertOut(const Element &v) const {return v;}
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/// \brief Retrieves AbstractGroup interface
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/// \returns GetGroup() returns the AbstractGroup interface
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virtual const AbstractGroup<Element> & GetGroup() const =0;
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/// \brief Decodes element in DER format
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/// \param bt BufferedTransformation object
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/// \returns element in the group
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virtual Element BERDecodeElement(BufferedTransformation &bt) const =0;
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/// \brief Encodes element in DER format
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/// \param bt BufferedTransformation object
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/// \param P Element to encode
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virtual void DEREncodeElement(BufferedTransformation &bt, const Element &P) const =0;
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};
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/// \brief DL_FixedBasePrecomputation interface
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/// \tparam T Field element
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template <class T>
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class DL_FixedBasePrecomputation
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{
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public:
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typedef T Element;
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virtual ~DL_FixedBasePrecomputation() {}
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/// \brief Determines whether this object is initialized
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/// \returns true if this object is initialized, false otherwise
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virtual bool IsInitialized() const =0;
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/// \brief Set the base element
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/// \param group the group
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/// \param base element in the group
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virtual void SetBase(const DL_GroupPrecomputation<Element> &group, const Element &base) =0;
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/// \brief Get the base element
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/// \param group the group
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/// \returns base element in the group
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virtual const Element & GetBase(const DL_GroupPrecomputation<Element> &group) const =0;
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/// \brief Perform precomputation
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/// \param group the group
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/// \param maxExpBits used to calculate the exponent base
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/// \param storage the suggested number of objects for the precompute table
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/// \details The exact semantics of Precompute() varies, but it typically means calculate
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/// a table of n objects that can be used later to speed up computation.
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/// \details If a derived class does not override Precompute(), then the base class throws
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/// NotImplemented.
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/// \sa SupportsPrecomputation(), LoadPrecomputation(), SavePrecomputation()
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virtual void Precompute(const DL_GroupPrecomputation<Element> &group, unsigned int maxExpBits, unsigned int storage) =0;
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/// \brief Retrieve previously saved precomputation
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/// \param group the the group
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/// \param storedPrecomputation BufferedTransformation with the saved precomputation
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/// \throws NotImplemented
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/// \sa SupportsPrecomputation(), Precompute()
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virtual void Load(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &storedPrecomputation) =0;
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/// \brief Save precomputation for later use
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/// \param group the the group
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/// \param storedPrecomputation BufferedTransformation to write the precomputation
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/// \throws NotImplemented
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/// \sa SupportsPrecomputation(), Precompute()
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virtual void Save(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &storedPrecomputation) const =0;
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/// \brief Exponentiates an element
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/// \param group the group
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/// \param exponent the exponent
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/// \return the result of the exponentiation
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virtual Element Exponentiate(const DL_GroupPrecomputation<Element> &group, const Integer &exponent) const =0;
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/// \brief Exponentiates an element
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/// \param pc1 the first the group precomputation
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/// \param exponent1 the first exponent
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/// \param pc2 the second the group precomputation
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/// \param exponent2 the first exponent2
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/// \returns the public element raised to the exponent
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/// \details CascadeExponentiateBaseAndPublicElement raises the public element to
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/// the base element and precomputation.
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virtual Element CascadeExponentiate(const DL_GroupPrecomputation<Element> &pc1, const Integer &exponent1, const DL_FixedBasePrecomputation<Element> &pc2, const Integer &exponent2) const =0;
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};
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/// \brief DL_FixedBasePrecomputation adapter class
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/// \tparam T Field element
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template <class T>
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class DL_FixedBasePrecomputationImpl : public DL_FixedBasePrecomputation<T>
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{
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public:
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typedef T Element;
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virtual ~DL_FixedBasePrecomputationImpl() {}
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DL_FixedBasePrecomputationImpl() : m_windowSize(0) {}
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// DL_FixedBasePrecomputation
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bool IsInitialized() const
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{return !m_bases.empty();}
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void SetBase(const DL_GroupPrecomputation<Element> &group, const Element &base);
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const Element & GetBase(const DL_GroupPrecomputation<Element> &group) const
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{return group.NeedConversions() ? m_base : m_bases[0];}
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void Precompute(const DL_GroupPrecomputation<Element> &group, unsigned int maxExpBits, unsigned int storage);
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void Load(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &storedPrecomputation);
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void Save(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &storedPrecomputation) const;
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Element Exponentiate(const DL_GroupPrecomputation<Element> &group, const Integer &exponent) const;
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Element CascadeExponentiate(const DL_GroupPrecomputation<Element> &pc1, const Integer &exponent1, const DL_FixedBasePrecomputation<Element> &pc2, const Integer &exponent2) const;
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private:
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void PrepareCascade(const DL_GroupPrecomputation<Element> &group, std::vector<BaseAndExponent<Element> > &eb, const Integer &exponent) const;
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Element m_base;
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unsigned int m_windowSize;
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Integer m_exponentBase; // what base to represent the exponent in
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std::vector<Element> m_bases; // precalculated bases
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};
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NAMESPACE_END
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#ifdef CRYPTOPP_MANUALLY_INSTANTIATE_TEMPLATES
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#include "eprecomp.cpp"
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#endif
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#endif
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