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using System;
using Org.BouncyCastle.Math.EC.Custom.Sec;
using Org.BouncyCastle.Math.Field;
using Org.BouncyCastle.Utilities.Encoders;
namespace Org.BouncyCastle.Math.EC.Custom.Djb
{
internal class Curve25519
: ECCurve
{
public static readonly BigInteger q = Nat256.ToBigInteger(Curve25519Field.P);
private const int Curve25519_DEFAULT_COORDS = COORD_JACOBIAN_MODIFIED;
protected readonly Curve25519Point m_infinity;
public Curve25519()
: base(FiniteFields.GetPrimeField(q))
{
this.m_infinity = new Curve25519Point(this, null, null);
this.m_a = FromBigInteger(new BigInteger(1,
Hex.Decode("2AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA984914A144")));
this.m_b = FromBigInteger(new BigInteger(1,
Hex.Decode("7B425ED097B425ED097B425ED097B425ED097B425ED097B4260B5E9C7710C864")));
this.m_order = new BigInteger(1, Hex.Decode("1000000000000000000000000000000014DEF9DEA2F79CD65812631A5CF5D3ED"));
this.m_cofactor = BigInteger.ValueOf(8);
this.m_coord = Curve25519_DEFAULT_COORDS;
}
protected override ECCurve CloneCurve()
{
return new Curve25519();
}
public override bool SupportsCoordinateSystem(int coord)
{
switch (coord)
{
case COORD_JACOBIAN_MODIFIED:
return true;
default:
return false;
}
}
public virtual BigInteger Q
{
get { return q; }
}
public override ECPoint Infinity
{
get { return m_infinity; }
}
public override int FieldSize
{
get { return q.BitLength; }
}
public override ECFieldElement FromBigInteger(BigInteger x)
{
return new Curve25519FieldElement(x);
}
protected internal override ECPoint CreateRawPoint(ECFieldElement x, ECFieldElement y, bool withCompression)
{
return new Curve25519Point(this, x, y, withCompression);
}
protected internal override ECPoint CreateRawPoint(ECFieldElement x, ECFieldElement y, ECFieldElement[] zs, bool withCompression)
{
return new Curve25519Point(this, x, y, zs, withCompression);
}
protected override ECPoint DecompressPoint(int yTilde, BigInteger X1)
{
ECFieldElement x = FromBigInteger(X1);
ECFieldElement alpha = x.Square().Add(A).Multiply(x).Add(B);
ECFieldElement beta = alpha.Sqrt();
//
// if we can't find a sqrt we haven't got a point on the
// curve - run!
//
if (beta == null)
throw new ArithmeticException("Invalid point compression");
if (beta.TestBitZero() != (yTilde == 1))
{
// Use the other root
beta = beta.Negate();
}
return new Curve25519Point(this, x, beta, true);
}
}
}
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