MixedNafR2LMultiplier.cs
2.24 KB
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using System;
namespace Org.BouncyCastle.Math.EC.Multiplier
{
/**
* Class implementing the NAF (Non-Adjacent Form) multiplication algorithm (right-to-left) using
* mixed coordinates.
*/
public class MixedNafR2LMultiplier
: AbstractECMultiplier
{
protected readonly int additionCoord, doublingCoord;
/**
* By default, addition will be done in Jacobian coordinates, and doubling will be done in
* Modified Jacobian coordinates (independent of the original coordinate system of each point).
*/
public MixedNafR2LMultiplier()
: this(ECCurve.COORD_JACOBIAN, ECCurve.COORD_JACOBIAN_MODIFIED)
{
}
public MixedNafR2LMultiplier(int additionCoord, int doublingCoord)
{
this.additionCoord = additionCoord;
this.doublingCoord = doublingCoord;
}
protected override ECPoint MultiplyPositive(ECPoint p, BigInteger k)
{
ECCurve curveOrig = p.Curve;
ECCurve curveAdd = ConfigureCurve(curveOrig, additionCoord);
ECCurve curveDouble = ConfigureCurve(curveOrig, doublingCoord);
int[] naf = WNafUtilities.GenerateCompactNaf(k);
ECPoint Ra = curveAdd.Infinity;
ECPoint Td = curveDouble.ImportPoint(p);
int zeroes = 0;
for (int i = 0; i < naf.Length; ++i)
{
int ni = naf[i];
int digit = ni >> 16;
zeroes += ni & 0xFFFF;
Td = Td.TimesPow2(zeroes);
ECPoint Tj = curveAdd.ImportPoint(Td);
if (digit < 0)
{
Tj = Tj.Negate();
}
Ra = Ra.Add(Tj);
zeroes = 1;
}
return curveOrig.ImportPoint(Ra);
}
protected virtual ECCurve ConfigureCurve(ECCurve c, int coord)
{
if (c.CoordinateSystem == coord)
return c;
if (!c.SupportsCoordinateSystem(coord))
throw new ArgumentException("Coordinate system " + coord + " not supported by this curve", "coord");
return c.Configure().SetCoordinateSystem(coord).Create();
}
}
}