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# modarith.h

    00001 #ifndef CRYPTOPP_MODARITH_H
    00002 #define CRYPTOPP_MODARITH_H
    00003
    00004 // implementations are in integer.cpp
    00005
    00006 #include "cryptlib.h"
    00007 #include "misc.h"
    00008 #include "integer.h"
    00009 #include "algebra.h"
    00010
    00011 NAMESPACE_BEGIN(CryptoPP)
    00012
    00013 CRYPTOPP_DLL_TEMPLATE_CLASS AbstractGroup<Integer>;
    00014 CRYPTOPP_DLL_TEMPLATE_CLASS AbstractRing<Integer>;
    00015 CRYPTOPP_DLL_TEMPLATE_CLASS AbstractEuclideanDomain<Integer>;
    00016
    00017 //! ring of congruence classes modulo n
    00018 /*! \note this implementation represents each congruence class as the smallest non-negative integer in that class */
    00019 class CRYPTOPP_DLL ModularArithmetic : public AbstractRing<Integer>
    00020 {
    00021 public:
    00022
    00023         typedef int RandomizationParameter;
    00024         typedef Integer Element;
    00025
    00026         ModularArithmetic(const Integer &modulus = Integer::One())
    00027                 : m_modulus(modulus), m_result((word)0, modulus.reg.size()) {}
    00028
    00029         ModularArithmetic(const ModularArithmetic &ma)
    00030                 : m_modulus(ma.m_modulus), m_result((word)0, m_modulus.reg.size()) {}
    00031
    00032         ModularArithmetic(BufferedTransformation &bt);  // construct from BER encoded parameters
    00033
    00034         virtual ModularArithmetic * Clone() const {return new ModularArithmetic(*this);}
    00035
    00036         void DEREncode(BufferedTransformation &bt) const;
    00037
    00038         void DEREncodeElement(BufferedTransformation &out, const Element &a) const;
    00039         void BERDecodeElement(BufferedTransformation &in, Element &a) const;
    00040
    00041         const Integer& GetModulus() const {return m_modulus;}
    00042         void SetModulus(const Integer &newModulus) {m_modulus = newModulus; m_result.reg.resize(m_modulus.reg.size());}
    00043
    00044         virtual bool IsMontgomeryRepresentation() const {return false;}
    00045
    00046         virtual Integer ConvertIn(const Integer &a) const
    00047                 {return a%m_modulus;}
    00048
    00049         virtual Integer ConvertOut(const Integer &a) const
    00050                 {return a;}
    00051
    00052         const Integer& Half(const Integer &a) const;
    00053
    00054         bool Equal(const Integer &a, const Integer &b) const
    00055                 {return a==b;}
    00056
    00057         const Integer& Identity() const
    00058                 {return Integer::Zero();}
    00059
    00060         const Integer& Add(const Integer &a, const Integer &b) const;
    00061
    00062         Integer& Accumulate(Integer &a, const Integer &b) const;
    00063
    00064         const Integer& Inverse(const Integer &a) const;
    00065
    00066         const Integer& Subtract(const Integer &a, const Integer &b) const;
    00067
    00068         Integer& Reduce(Integer &a, const Integer &b) const;
    00069
    00070         const Integer& Double(const Integer &a) const
    00071                 {return Add(a, a);}
    00072
    00073         const Integer& MultiplicativeIdentity() const
    00074                 {return Integer::One();}
    00075
    00076         const Integer& Multiply(const Integer &a, const Integer &b) const
    00077                 {return m_result1 = a*b%m_modulus;}
    00078
    00079         const Integer& Square(const Integer &a) const
    00080                 {return m_result1 = a.Squared()%m_modulus;}
    00081
    00082         bool IsUnit(const Integer &a) const
    00083                 {return Integer::Gcd(a, m_modulus).IsUnit();}
    00084
    00085         const Integer& MultiplicativeInverse(const Integer &a) const
    00086                 {return m_result1 = a.InverseMod(m_modulus);}
    00087
    00088         const Integer& Divide(const Integer &a, const Integer &b) const
    00089                 {return Multiply(a, MultiplicativeInverse(b));}
    00090
    00091         Integer CascadeExponentiate(const Integer &x, const Integer &e1, const Integer &y, const Integer &e2) const;
    00092
    00093         void SimultaneousExponentiate(Element *results, const Element &base, const Integer *exponents, unsigned int exponentsCount) const;
    00094
    00095         unsigned int MaxElementBitLength() const
    00096                 {return (m_modulus-1).BitCount();}
    00097
    00098         unsigned int MaxElementByteLength() const
    00099                 {return (m_modulus-1).ByteCount();}
    00100
    00101         Element RandomElement( RandomNumberGenerator &rng , const RandomizationParameter &ignore_for_now = 0 ) const
    00102                 // left RandomizationParameter arg as ref in case RandomizationParameter becomes a more complicated struct
    00103         {
    00104                 return Element( rng , Integer( (long) 0) , m_modulus - Integer( (long) 1 )   ) ;
    00105         }
    00106
    00107         bool operator==(const ModularArithmetic &rhs) const
    00108                 {return m_modulus == rhs.m_modulus;}
    00109
    00110         static const RandomizationParameter DefaultRandomizationParameter ;
    00111
    00112 protected:
    00113         Integer m_modulus;
    00114         mutable Integer m_result, m_result1;
    00115
    00116 };
    00117
    00118 // const ModularArithmetic::RandomizationParameter ModularArithmetic::DefaultRandomizationParameter = 0 ;
    00119
    00120 //! do modular arithmetics in Montgomery representation for increased speed
    00121 /*! \note the Montgomery representation represents each congruence class [a] as a*r%n, where r is a convenient power of 2 */
    00122 class CRYPTOPP_DLL MontgomeryRepresentation : public ModularArithmetic
    00123 {
    00124 public:
    00125         MontgomeryRepresentation(const Integer &modulus);       // modulus must be odd
    00126
    00127         virtual ModularArithmetic * Clone() const {return new MontgomeryRepresentation(*this);}
    00128
    00129         bool IsMontgomeryRepresentation() const {return true;}
    00130
    00131         Integer ConvertIn(const Integer &a) const
    00132                 {return (a<<(WORD_BITS*m_modulus.reg.size()))%m_modulus;}
    00133
    00134         Integer ConvertOut(const Integer &a) const;
    00135
    00136         const Integer& MultiplicativeIdentity() const
    00137                 {return m_result1 = Integer::Power2(WORD_BITS*m_modulus.reg.size())%m_modulus;}
    00138
    00139         const Integer& Multiply(const Integer &a, const Integer &b) const;
    00140
    00141         const Integer& Square(const Integer &a) const;
    00142
    00143         const Integer& MultiplicativeInverse(const Integer &a) const;
    00144
    00145         Integer CascadeExponentiate(const Integer &x, const Integer &e1, const Integer &y, const Integer &e2) const
    00146                 {return AbstractRing<Integer>::CascadeExponentiate(x, e1, y, e2);}
    00147
    00148         void SimultaneousExponentiate(Element *results, const Element &base, const Integer *exponents, unsigned int exponentsCount) const
    00149                 {AbstractRing<Integer>::SimultaneousExponentiate(results, base, exponents, exponentsCount);}
    00150
    00151 private:
    00152         Integer m_u;
    00153         mutable SecAlignedWordBlock m_workspace;
    00154 };
    00155
    00156 NAMESPACE_END
    00157
    00158 #endif