ec2n.h

#ifndef CRYPTOPP_EC2N_H
#define CRYPTOPP_EC2N_H

#include "gf2n.h"
#include "eprecomp.h"
#include "smartptr.h"
#include "pubkey.h"

NAMESPACE_BEGIN(CryptoPP)

//! Elliptic Curve Point
struct CRYPTOPP_DLL EC2NPoint
{
        EC2NPoint() : identity(true) {}
        EC2NPoint(const PolynomialMod2 &x, const PolynomialMod2 &y)
                : identity(false), x(x), y(y) {}

        bool operator==(const EC2NPoint &t) const
                {return (identity && t.identity) || (!identity && !t.identity && x==t.x && y==t.y);}
        bool operator< (const EC2NPoint &t) const
                {return identity ? !t.identity : (!t.identity && (x<t.x || (x==t.x && y<t.y)));}

        bool identity;
        PolynomialMod2 x, y;
};

CRYPTOPP_DLL_TEMPLATE_CLASS AbstractGroup<EC2NPoint>;

//! Elliptic Curve over GF(2^n)
class CRYPTOPP_DLL EC2N : public AbstractGroup<EC2NPoint>
{
public:
        typedef GF2NP Field;
        typedef Field::Element FieldElement;
        typedef EC2NPoint Point;

        EC2N() {}
        EC2N(const Field &field, const Field::Element &a, const Field::Element &b)
                : m_field(field), m_a(a), m_b(b) {}
        // construct from BER encoded parameters
        // this constructor will decode and extract the the fields fieldID and curve of the sequence ECParameters
        EC2N(BufferedTransformation &bt);

        // encode the fields fieldID and curve of the sequence ECParameters
        void DEREncode(BufferedTransformation &bt) const;

        bool Equal(const Point &P, const Point &Q) const;
        const Point& Identity() const;
        const Point& Inverse(const Point &P) const;
        bool InversionIsFast() const {return true;}
        const Point& Add(const Point &P, const Point &Q) const;
        const Point& Double(const Point &P) const;

        Point Multiply(const Integer &k, const Point &P) const
                {return ScalarMultiply(P, k);}
        Point CascadeMultiply(const Integer &k1, const Point &P, const Integer &k2, const Point &Q) const
                {return CascadeScalarMultiply(P, k1, Q, k2);}

        bool ValidateParameters(RandomNumberGenerator &rng, unsigned int level=3) const;
        bool VerifyPoint(const Point &P) const;

        unsigned int EncodedPointSize(bool compressed = false) const
                {return 1 + (compressed?1:2)*m_field->MaxElementByteLength();}
        // returns false if point is compressed and not valid (doesn't check if uncompressed)
        bool DecodePoint(Point &P, BufferedTransformation &bt, size_t len) const;
        bool DecodePoint(Point &P, const byte *encodedPoint, size_t len) const;
        void EncodePoint(byte *encodedPoint, const Point &P, bool compressed) const;
        void EncodePoint(BufferedTransformation &bt, const Point &P, bool compressed) const;

        Point BERDecodePoint(BufferedTransformation &bt) const;
        void DEREncodePoint(BufferedTransformation &bt, const Point &P, bool compressed) const;

        Integer FieldSize() const {return Integer::Power2(m_field->MaxElementBitLength());}
        const Field & GetField() const {return *m_field;}
        const FieldElement & GetA() const {return m_a;}
        const FieldElement & GetB() const {return m_b;}

        bool operator==(const EC2N &rhs) const
                {return GetField() == rhs.GetField() && m_a == rhs.m_a && m_b == rhs.m_b;}

private:
        clonable_ptr<Field> m_field;
        FieldElement m_a, m_b;
        mutable Point m_R;
};

CRYPTOPP_DLL_TEMPLATE_CLASS DL_FixedBasePrecomputationImpl<EC2N::Point>;
CRYPTOPP_DLL_TEMPLATE_CLASS DL_GroupPrecomputation<EC2N::Point>;

template <class T> class EcPrecomputation;

//! EC2N precomputation
template<> class EcPrecomputation<EC2N> : public DL_GroupPrecomputation<EC2N::Point>
{
public:
        typedef EC2N EllipticCurve;

        // DL_GroupPrecomputation
        const AbstractGroup<Element> & GetGroup() const {return m_ec;}
        Element BERDecodeElement(BufferedTransformation &bt) const {return m_ec.BERDecodePoint(bt);}
        void DEREncodeElement(BufferedTransformation &bt, const Element &v) const {m_ec.DEREncodePoint(bt, v, false);}

        // non-inherited
        void SetCurve(const EC2N &ec) {m_ec = ec;}
        const EC2N & GetCurve() const {return m_ec;}

private:
        EC2N m_ec;
};

NAMESPACE_END

#endif

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