ec2n.h

Go to the documentation of this file.

// ec2n.h - originally written and placed in the public domain by Wei Dai

/// \file ec2n.h
/// \brief Classes for Elliptic Curves over binary fields


#ifndef CRYPTOPP_EC2N_H
#define CRYPTOPP_EC2N_H

#include "cryptlib.h"
#include "gf2n.h"
#include "integer.h"
#include "algebra.h"
#include "ecpoint.h"
#include "eprecomp.h"
#include "smartptr.h"
#include "pubkey.h"

#if CRYPTOPP_MSC_VERSION
# pragma warning(push)
# pragma warning(disable: 4231 4275)
#endif

NAMESPACE_BEGIN(CryptoPP)

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

    virtual ~EC2N() {}

    /// \brief Construct an EC2N
    EC2N() {}

    /// \brief Construct an EC2N
    /// \param field Field, GF2NP derived class
    /// \param a Field::Element
    /// \param b Field::Element
    EC2N(const Field &field, const Field::Element &a, const Field::Element &b)
        : m_field(field), m_a(a), m_b(b) {}

    /// \brief Construct an EC2N from BER encoded parameters
    /// \param bt BufferedTransformation derived object
    /// \details This constructor will decode and extract the the fields fieldID and curve of the sequence ECParameters
    EC2N(BufferedTransformation &bt);

    /// \brief Encode the fields fieldID and curve of the sequence ECParameters
    /// \param bt BufferedTransformation derived object
    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>;

/// \brief Elliptic Curve precomputation
/// \tparam EC elliptic curve field
template <class EC> class EcPrecomputation;

/// \brief EC2N precomputation specialization
/// \details Implementation of <tt>DL_GroupPrecomputation<EC2N::Point></tt>
/// \sa DL_GroupPrecomputation
template<> class EcPrecomputation<EC2N> : public DL_GroupPrecomputation<EC2N::Point>
{
public:
    typedef EC2N EllipticCurve;

    virtual ~EcPrecomputation() {}

    // 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);}

    /// \brief Set the elliptic curve
    /// \param ec ECP derived class
    /// \details SetCurve() is not inherited
    void SetCurve(const EC2N &ec) {m_ec = ec;}

    /// \brief Get the elliptic curve
    /// \returns EC2N curve
    /// \details GetCurve() is not inherited
    const EC2N & GetCurve() const {return m_ec;}

private:
    EC2N m_ec;
};

NAMESPACE_END

#if CRYPTOPP_MSC_VERSION
# pragma warning(pop)
#endif

#endif