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231e468e19
git-subtree-dir: erigon-lib git-subtree-mainline:3c8cbda809git-subtree-split:93d9c9d9fe
80 lines
2.3 KiB
C++
80 lines
2.3 KiB
C++
#ifndef STARKWARE_ALGEBRA_ELLIPTIC_CURVE_H_
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#define STARKWARE_ALGEBRA_ELLIPTIC_CURVE_H_
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#include <cstddef>
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#include <optional>
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#include <utility>
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#include <vector>
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#include "gsl-lite.hpp"
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#include "big_int.h"
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namespace starkware {
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using std::size_t;
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/*
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Represents a point on an elliptic curve of the form: y^2 = x^3 + alpha*x + beta.
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*/
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template <typename FieldElementT>
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class EcPoint {
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public:
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constexpr EcPoint(const FieldElementT& x, const FieldElementT& y) : x(x), y(y) {}
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bool operator==(const EcPoint& rhs) const { return x == rhs.x && y == rhs.y; }
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bool operator!=(const EcPoint& rhs) const { return !(*this == rhs); }
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/*
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Computes the point added to itself.
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*/
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EcPoint Double(const FieldElementT& alpha) const;
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/*
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Returns the sum of two points. The added point must be different than both the original point
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and its negation.
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*/
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EcPoint operator+(const EcPoint& rhs) const;
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EcPoint operator-() const { return EcPoint(x, -y); }
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EcPoint operator-(const EcPoint& rhs) const { return (*this) + (-rhs); }
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/*
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Returns a random point on the curve: y^2 = x^3 + alpha*x + beta.
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*/
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static EcPoint Random(const FieldElementT& alpha, const FieldElementT& beta, Prng* prng);
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/*
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Returns one of the two points with the given x coordinate or nullopt if there is no such point.
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*/
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static std::optional<EcPoint> GetPointFromX(
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const FieldElementT& x, const FieldElementT& alpha, const FieldElementT& beta);
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template <typename OtherFieldElementT>
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EcPoint<OtherFieldElementT> ConvertTo() const;
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/*
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Given the bool vector representing a scalar, and the alpha of the elliptic curve
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"y^2 = x^3 + alpha * x + beta" the point is on, returns scalar*point.
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*/
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template <size_t N>
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EcPoint<FieldElementT> MultiplyByScalar(
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const BigInt<N>& scalar, const FieldElementT& alpha) const;
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FieldElementT x;
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FieldElementT y;
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private:
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/*
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Returns the sum of this point with a point in the form of std::optional, where std::nullopt
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represents the curve's zero element.
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*/
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std::optional<EcPoint<FieldElementT>> AddOptionalPoint(
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const std::optional<EcPoint<FieldElementT>>& point, const FieldElementT& alpha) const;
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};
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} // namespace starkware
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#include "elliptic_curve.inl"
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#endif // STARKWARE_ALGEBRA_ELLIPTIC_CURVE_H_
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