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using System;
using Org.BouncyCastle.Math.EC.Multiplier;
namespace Org.BouncyCastle.Math.EC.Endo
{
public abstract class EndoUtilities
{
public static readonly string PRECOMP_NAME = "bc_endo";
public static BigInteger[] DecomposeScalar(ScalarSplitParameters p, BigInteger k)
{
int bits = p.Bits;
BigInteger b1 = CalculateB(k, p.G1, bits);
BigInteger b2 = CalculateB(k, p.G2, bits);
BigInteger a = k.Subtract((b1.Multiply(p.V1A)).Add(b2.Multiply(p.V2A)));
BigInteger b = (b1.Multiply(p.V1B)).Add(b2.Multiply(p.V2B)).Negate();
return new BigInteger[]{ a, b };
}
public static ECPoint MapPoint(ECEndomorphism endomorphism, ECPoint p)
{
EndoPreCompInfo precomp = (EndoPreCompInfo)p.Curve.Precompute(p, PRECOMP_NAME,
new MapPointCallback(endomorphism, p));
return precomp.MappedPoint;
}
private static BigInteger CalculateB(BigInteger k, BigInteger g, int t)
{
bool negative = (g.SignValue < 0);
BigInteger b = k.Multiply(g.Abs());
bool extra = b.TestBit(t - 1);
b = b.ShiftRight(t);
if (extra)
{
b = b.Add(BigInteger.One);
}
return negative ? b.Negate() : b;
}
private class MapPointCallback
: IPreCompCallback
{
private readonly ECEndomorphism m_endomorphism;
private readonly ECPoint m_point;
internal MapPointCallback(ECEndomorphism endomorphism, ECPoint point)
{
this.m_endomorphism = endomorphism;
this.m_point = point;
}
public PreCompInfo Precompute(PreCompInfo existing)
{
EndoPreCompInfo existingEndo = existing as EndoPreCompInfo;
if (CheckExisting(existingEndo, m_endomorphism))
return existingEndo;
ECPoint mappedPoint = m_endomorphism.PointMap.Map(m_point);
EndoPreCompInfo result = new EndoPreCompInfo();
result.Endomorphism = m_endomorphism;
result.MappedPoint = mappedPoint;
return result;
}
private bool CheckExisting(EndoPreCompInfo existingEndo, ECEndomorphism endomorphism)
{
return null != existingEndo
&& existingEndo.Endomorphism == endomorphism
&& existingEndo.MappedPoint != null;
}
}
}
}
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