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/*
* Elliptic curves over GF(p)
*
* (C) 2007 Martin Doering, Christoph Ludwig, Falko Strenzke
* 2010-2011,2012 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#ifndef BOTAN_GFP_CURVE_H__
#define BOTAN_GFP_CURVE_H__
#include <botan/numthry.h>
namespace Botan {
/**
* This class represents an elliptic curve over GF(p)
*/
class BOTAN_DLL CurveGFp
{
public:
/**
* Create an uninitialized CurveGFp
*/
CurveGFp() {}
/**
* Construct the elliptic curve E: y^2 = x^3 + ax + b over GF(p)
* @param p prime number of the field
* @param a first coefficient
* @param b second coefficient
*/
CurveGFp(const BigInt& p, const BigInt& a, const BigInt& b) :
m_p(p),
m_a(a),
m_b(b),
m_p_words(m_p.sig_words()),
m_p_dash(monty_inverse(m_p.word_at(0)))
{
const BigInt r = BigInt::power_of_2(m_p_words * BOTAN_MP_WORD_BITS);
m_r2 = (r * r) % p;
m_a_r = (a * r) % p;
m_b_r = (b * r) % p;
}
CurveGFp(const CurveGFp&) = default;
CurveGFp& operator=(const CurveGFp&) = default;
/**
* @return curve coefficient a
*/
const BigInt& get_a() const { return m_a; }
/**
* @return curve coefficient b
*/
const BigInt& get_b() const { return m_b; }
/**
* Get prime modulus of the field of the curve
* @return prime modulus of the field of the curve
*/
const BigInt& get_p() const { return m_p; }
/**
* @return Montgomery parameter r^2 % p
*/
const BigInt& get_r2() const { return m_r2; }
/**
* @return a * r mod p
*/
const BigInt& get_a_r() const { return m_a_r; }
/**
* @return b * r mod p
*/
const BigInt& get_b_r() const { return m_b_r; }
/**
* @return Montgomery parameter p-dash
*/
word get_p_dash() const { return m_p_dash; }
/**
* @return p.sig_words()
*/
size_t get_p_words() const { return m_p_words; }
/**
* swaps the states of *this and other, does not throw
* @param other curve to swap values with
*/
void swap(CurveGFp& other)
{
std::swap(m_p, other.m_p);
std::swap(m_a, other.m_a);
std::swap(m_b, other.m_b);
std::swap(m_a_r, other.m_a_r);
std::swap(m_b_r, other.m_b_r);
std::swap(m_p_words, other.m_p_words);
std::swap(m_r2, other.m_r2);
std::swap(m_p_dash, other.m_p_dash);
}
/**
* Equality operator
* @param other curve to compare with
* @return true iff this is the same curve as other
*/
bool operator==(const CurveGFp& other) const
{
return (m_p == other.m_p &&
m_a == other.m_a &&
m_b == other.m_b);
}
private:
// Curve parameters
BigInt m_p, m_a, m_b;
size_t m_p_words; // cache of m_p.sig_words()
// Montgomery parameters
BigInt m_r2, m_a_r, m_b_r;
word m_p_dash;
};
/**
* Equality operator
* @param lhs a curve
* @param rhs a curve
* @return true iff lhs is not the same as rhs
*/
inline bool operator!=(const CurveGFp& lhs, const CurveGFp& rhs)
{
return !(lhs == rhs);
}
}
namespace std {
template<> inline
void swap<Botan::CurveGFp>(Botan::CurveGFp& curve1,
Botan::CurveGFp& curve2)
{
curve1.swap(curve2);
}
} // namespace std
#endif
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