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/*
* Elliptic curves over GF(p)
*
* (C) 2007 Martin Doering, Christoph Ludwig, Falko Strenzke
* 2010-2011 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) :
p(p), a(a), b(b)
{
BigInt r(BigInt::Power2, p.sig_words() * BOTAN_MP_WORD_BITS);
p_dash = (((r * inverse_mod(r, p)) - 1) / p).word_at(0);
r2 = (r * r) % p;
a_r = (a * r) % p;
b_r = (b * r) % p;
p_words = p.sig_words();
}
// CurveGFp(const CurveGFp& other) = default;
// CurveGFp& operator=(const CurveGFp& other) = default;
/**
* @return curve coefficient a
*/
const BigInt& get_a() const { return a; }
/**
* @return curve coefficient b
*/
const BigInt& get_b() const { return 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 p; }
/**
* @return Montgomery parameter r^2 % p
*/
const BigInt& get_r2() const { return r2; }
/**
* @return a * r mod p
*/
const BigInt& get_a_r() const { return a_r; }
/**
* @return b * r mod p
*/
const BigInt& get_b_r() const { return b_r; }
/**
* @return Montgomery parameter p-dash
*/
word get_p_dash() const { return p_dash; }
/**
* @return p.sig_words()
*/
size_t get_p_words() const { return 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(p, other.p);
std::swap(a, other.a);
std::swap(b, other.b);
std::swap(a_r, other.a_r);
std::swap(b_r, other.b_r);
std::swap(p_words, other.p_words);
std::swap(r2, other.r2);
std::swap(p_dash, other.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
{
/*
Relies on choice of R, but that is fixed by constructor based
on size of p
*/
return (p == other.p && a_r == other.a_r && b_r == other.b_r);
}
private:
// Curve parameters
BigInt p, a, b;
size_t p_words; // cache of p.sig_words()
// Montgomery parameters
BigInt r2, a_r, b_r;
word 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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