121 lines
3.1 KiB
C#
121 lines
3.1 KiB
C#
using System;
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using Org.BouncyCastle.Math.EC.Abc;
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namespace Org.BouncyCastle.Math.EC.Multiplier
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{
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/**
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* Class implementing the WTNAF (Window
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* <code>τ</code>-adic Non-Adjacent Form) algorithm.
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*/
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internal class WTauNafMultiplier
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: ECMultiplier
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{
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/**
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* Multiplies a {@link org.bouncycastle.math.ec.F2mPoint F2mPoint}
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* by <code>k</code> using the reduced <code>τ</code>-adic NAF (RTNAF)
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* method.
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* @param p The F2mPoint to multiply.
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* @param k The integer by which to multiply <code>k</code>.
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* @return <code>p</code> multiplied by <code>k</code>.
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*/
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public ECPoint Multiply(ECPoint point, BigInteger k, PreCompInfo preCompInfo)
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{
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if (!(point is F2mPoint))
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throw new ArgumentException("Only F2mPoint can be used in WTauNafMultiplier");
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F2mPoint p = (F2mPoint)point;
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F2mCurve curve = (F2mCurve) p.Curve;
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int m = curve.M;
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sbyte a = (sbyte) curve.A.ToBigInteger().IntValue;
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sbyte mu = curve.GetMu();
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BigInteger[] s = curve.GetSi();
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ZTauElement rho = Tnaf.PartModReduction(k, m, a, s, mu, (sbyte)10);
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return MultiplyWTnaf(p, rho, preCompInfo, a, mu);
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}
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/**
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* Multiplies a {@link org.bouncycastle.math.ec.F2mPoint F2mPoint}
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* by an element <code>λ</code> of <code><b>Z</b>[τ]</code> using
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* the <code>τ</code>-adic NAF (TNAF) method.
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* @param p The F2mPoint to multiply.
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* @param lambda The element <code>λ</code> of
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* <code><b>Z</b>[τ]</code> of which to compute the
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* <code>[τ]</code>-adic NAF.
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* @return <code>p</code> multiplied by <code>λ</code>.
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*/
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private F2mPoint MultiplyWTnaf(F2mPoint p, ZTauElement lambda,
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PreCompInfo preCompInfo, sbyte a, sbyte mu)
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{
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ZTauElement[] alpha;
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if (a == 0)
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{
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alpha = Tnaf.Alpha0;
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}
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else
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{
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// a == 1
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alpha = Tnaf.Alpha1;
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}
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BigInteger tw = Tnaf.GetTw(mu, Tnaf.Width);
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sbyte[]u = Tnaf.TauAdicWNaf(mu, lambda, Tnaf.Width,
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BigInteger.ValueOf(Tnaf.Pow2Width), tw, alpha);
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return MultiplyFromWTnaf(p, u, preCompInfo);
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}
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/**
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* Multiplies a {@link org.bouncycastle.math.ec.F2mPoint F2mPoint}
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* by an element <code>λ</code> of <code><b>Z</b>[τ]</code>
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* using the window <code>τ</code>-adic NAF (TNAF) method, given the
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* WTNAF of <code>λ</code>.
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* @param p The F2mPoint to multiply.
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* @param u The the WTNAF of <code>λ</code>..
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* @return <code>λ * p</code>
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*/
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private static F2mPoint MultiplyFromWTnaf(F2mPoint p, sbyte[] u,
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PreCompInfo preCompInfo)
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{
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F2mCurve curve = (F2mCurve)p.Curve;
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sbyte a = (sbyte) curve.A.ToBigInteger().IntValue;
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F2mPoint[] pu;
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if ((preCompInfo == null) || !(preCompInfo is WTauNafPreCompInfo))
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{
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pu = Tnaf.GetPreComp(p, a);
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p.SetPreCompInfo(new WTauNafPreCompInfo(pu));
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}
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else
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{
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pu = ((WTauNafPreCompInfo)preCompInfo).GetPreComp();
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}
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// q = infinity
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F2mPoint q = (F2mPoint) p.Curve.Infinity;
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for (int i = u.Length - 1; i >= 0; i--)
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{
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q = Tnaf.Tau(q);
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if (u[i] != 0)
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{
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if (u[i] > 0)
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{
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q = q.AddSimple(pu[u[i]]);
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}
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else
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{
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// u[i] < 0
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q = q.SubtractSimple(pu[-u[i]]);
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}
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}
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}
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return q;
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}
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}
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}
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