modarith.h

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// modarith.h - originally written and placed in the public domain by Wei Dai
 
 
#ifndef CRYPTOPP_MODARITH_H
#define CRYPTOPP_MODARITH_H
 
// implementations are in integer.cpp
 
#include "cryptlib.h"
#include "integer.h"
#include "algebra.h"
#include "secblock.h"
#include "misc.h"
 
#if CRYPTOPP_MSC_VERSION
# pragma warning(push)
# pragma warning(disable: 4231 4275)
#endif
 
NAMESPACE_BEGIN(CryptoPP)
 
CRYPTOPP_DLL_TEMPLATE_CLASS AbstractGroup<Integer>;
CRYPTOPP_DLL_TEMPLATE_CLASS AbstractRing<Integer>;
CRYPTOPP_DLL_TEMPLATE_CLASS AbstractEuclideanDomain<Integer>;
 
class CRYPTOPP_DLL ModularArithmetic : public AbstractRing<Integer>
{
public:
 
        typedef int RandomizationParameter;
        typedef Integer Element;
 
        virtual ~ModularArithmetic() {}
 
        ModularArithmetic(const Integer &modulus = Integer::One())
                : m_modulus(modulus), m_result(static_cast<word>(0), modulus.reg.size()) {}
 
        ModularArithmetic(const ModularArithmetic &ma)
                : AbstractRing<Integer>(ma), m_modulus(ma.m_modulus), m_result(static_cast<word>(0), m_modulus.reg.size()) {}
 
        ModularArithmetic& operator=(const ModularArithmetic &ma) {
                if (this != &ma)
                {
                        m_modulus = ma.m_modulus;
                        m_result = Integer(static_cast<word>(0), m_modulus.reg.size());
                }
                return *this;
        }
 
        ModularArithmetic(BufferedTransformation &bt);  // construct from BER encoded parameters
 
        virtual ModularArithmetic * Clone() const {return new ModularArithmetic(*this);}
 
        void DEREncode(BufferedTransformation &bt) const;
 
        void DEREncodeElement(BufferedTransformation &out, const Element &a) const;
 
        void BERDecodeElement(BufferedTransformation &in, Element &a) const;
 
        const Integer& GetModulus() const {return m_modulus;}
 
        void SetModulus(const Integer &newModulus)
                {m_modulus = newModulus; m_result.reg.resize(m_modulus.reg.size());}
 
        virtual bool IsMontgomeryRepresentation() const {return false;}
 
        virtual Integer ConvertIn(const Integer &a) const
                {return a%m_modulus;}
 
        virtual Integer ConvertOut(const Integer &a) const
                {return a;}
 
        const Integer& Half(const Integer &a) const;
 
        bool Equal(const Integer &a, const Integer &b) const
                {return a==b;}
 
        const Integer& Identity() const
                {return Integer::Zero();}
 
        const Integer& Add(const Integer &a, const Integer &b) const;
 
        Integer& Accumulate(Integer &a, const Integer &b) const;
 
        const Integer& Inverse(const Integer &a) const;
 
        const Integer& Subtract(const Integer &a, const Integer &b) const;
 
        Integer& Reduce(Integer &a, const Integer &b) const;
 
        const Integer& Double(const Integer &a) const
                {return Add(a, a);}
 
        const Integer& MultiplicativeIdentity() const
                {return Integer::One();}
 
        const Integer& Multiply(const Integer &a, const Integer &b) const
                {return m_result1 = a*b%m_modulus;}
 
        const Integer& Square(const Integer &a) const
                {return m_result1 = a.Squared()%m_modulus;}
 
        bool IsUnit(const Integer &a) const
                {return Integer::Gcd(a, m_modulus).IsUnit();}
 
        const Integer& MultiplicativeInverse(const Integer &a) const
                {return m_result1 = a.InverseMod(m_modulus);}
 
        const Integer& Divide(const Integer &a, const Integer &b) const
                {return Multiply(a, MultiplicativeInverse(b));}
 
        Integer CascadeExponentiate(const Integer &x, const Integer &e1, const Integer &y, const Integer &e2) const;
 
        void SimultaneousExponentiate(Element *results, const Element &base, const Integer *exponents, unsigned int exponentsCount) const;
 
        unsigned int MaxElementBitLength() const
                {return (m_modulus-1).BitCount();}
 
        unsigned int MaxElementByteLength() const
                {return (m_modulus-1).ByteCount();}
 
        Element RandomElement(RandomNumberGenerator &rng, const RandomizationParameter &ignore_for_now = 0) const
                // left RandomizationParameter arg as ref in case RandomizationParameter becomes a more complicated struct
        {
                CRYPTOPP_UNUSED(ignore_for_now);
                return Element(rng, Integer::Zero(), m_modulus - Integer::One()) ;
        }
 
        bool operator==(const ModularArithmetic &rhs) const
                {return m_modulus == rhs.m_modulus;}
 
        static const RandomizationParameter DefaultRandomizationParameter;
 
private:
        // TODO: Clang on OS X needs a real operator=.
        // Squash warning on missing assignment operator.
        // ModularArithmetic& operator=(const ModularArithmetic &ma);
 
protected:
        Integer m_modulus;
        mutable Integer m_result, m_result1;
};
 
// const ModularArithmetic::RandomizationParameter ModularArithmetic::DefaultRandomizationParameter = 0 ;
 
class CRYPTOPP_DLL MontgomeryRepresentation : public ModularArithmetic
{
public:
        virtual ~MontgomeryRepresentation() {}
 
        MontgomeryRepresentation(const Integer &modulus);
 
        virtual ModularArithmetic * Clone() const {return new MontgomeryRepresentation(*this);}
 
        bool IsMontgomeryRepresentation() const {return true;}
 
        Integer ConvertIn(const Integer &a) const
                {return (a<<(WORD_BITS*m_modulus.reg.size()))%m_modulus;}
 
        Integer ConvertOut(const Integer &a) const;
 
        const Integer& MultiplicativeIdentity() const
                {return m_result1 = Integer::Power2(WORD_BITS*m_modulus.reg.size())%m_modulus;}
 
        const Integer& Multiply(const Integer &a, const Integer &b) const;
 
        const Integer& Square(const Integer &a) const;
 
        const Integer& MultiplicativeInverse(const Integer &a) const;
 
        Integer CascadeExponentiate(const Integer &x, const Integer &e1, const Integer &y, const Integer &e2) const
                {return AbstractRing<Integer>::CascadeExponentiate(x, e1, y, e2);}
 
        void SimultaneousExponentiate(Element *results, const Element &base, const Integer *exponents, unsigned int exponentsCount) const
                {AbstractRing<Integer>::SimultaneousExponentiate(results, base, exponents, exponentsCount);}
 
private:
        Integer m_u;
        mutable IntegerSecBlock m_workspace;
};
 
NAMESPACE_END
 
#if CRYPTOPP_MSC_VERSION
# pragma warning(pop)
#endif
 
#endif