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