1 files changed, 120 insertions, 0 deletions
diff --git a/crypto/src/math/ec/multiplier/WTauNafMultiplier.cs b/crypto/src/math/ec/multiplier/WTauNafMultiplier.cs
new file mode 100644
index 000000000..f1a605770
--- /dev/null
+++ b/crypto/src/math/ec/multiplier/WTauNafMultiplier.cs
@@ -0,0 +1,120 @@
+using System;
+
+using Org.BouncyCastle.Math.EC.Abc;
+
+namespace Org.BouncyCastle.Math.EC.Multiplier
+{
+	/**
+	* Class implementing the WTNAF (Window
+	* <code>&#964;</code>-adic Non-Adjacent Form) algorithm.
+	*/
+	internal class WTauNafMultiplier
+		: ECMultiplier
+	{
+		/**
+		* Multiplies a {@link org.bouncycastle.math.ec.F2mPoint F2mPoint}
+		* by <code>k</code> using the reduced <code>&#964;</code>-adic NAF (RTNAF)
+		* method.
+		* @param p The F2mPoint to multiply.
+		* @param k The integer by which to multiply <code>k</code>.
+		* @return <code>p</code> multiplied by <code>k</code>.
+		*/
+		public ECPoint Multiply(ECPoint point, BigInteger k, PreCompInfo preCompInfo)
+		{
+			if (!(point is F2mPoint))
+				throw new ArgumentException("Only F2mPoint can be used in WTauNafMultiplier");
+
+			F2mPoint p = (F2mPoint)point;
+
+			F2mCurve curve = (F2mCurve) p.Curve;
+			int m = curve.M;
+			sbyte a = (sbyte) curve.A.ToBigInteger().IntValue;
+			sbyte mu = curve.GetMu();
+			BigInteger[] s = curve.GetSi();
+
+			ZTauElement rho = Tnaf.PartModReduction(k, m, a, s, mu, (sbyte)10);
+
+			return MultiplyWTnaf(p, rho, preCompInfo, a, mu);
+		}
+
+		/**
+		* Multiplies a {@link org.bouncycastle.math.ec.F2mPoint F2mPoint}
+		* by an element <code>&#955;</code> of <code><b>Z</b>[&#964;]</code> using
+		* the <code>&#964;</code>-adic NAF (TNAF) method.
+		* @param p The F2mPoint to multiply.
+		* @param lambda The element <code>&#955;</code> of
+		* <code><b>Z</b>[&#964;]</code> of which to compute the
+		* <code>[&#964;]</code>-adic NAF.
+		* @return <code>p</code> multiplied by <code>&#955;</code>.
+		*/
+		private F2mPoint MultiplyWTnaf(F2mPoint p, ZTauElement lambda,
+			PreCompInfo preCompInfo, sbyte a, sbyte mu)
+		{
+			ZTauElement[] alpha;
+			if (a == 0)
+			{
+				alpha = Tnaf.Alpha0;
+			}
+			else
+			{
+				// a == 1
+				alpha = Tnaf.Alpha1;
+			}
+
+			BigInteger tw = Tnaf.GetTw(mu, Tnaf.Width);
+
+			sbyte[]u = Tnaf.TauAdicWNaf(mu, lambda, Tnaf.Width,
+				BigInteger.ValueOf(Tnaf.Pow2Width), tw, alpha);
+
+			return MultiplyFromWTnaf(p, u, preCompInfo);
+		}
+	    
+		/**
+		* Multiplies a {@link org.bouncycastle.math.ec.F2mPoint F2mPoint}
+		* by an element <code>&#955;</code> of <code><b>Z</b>[&#964;]</code>
+		* using the window <code>&#964;</code>-adic NAF (TNAF) method, given the
+		* WTNAF of <code>&#955;</code>.
+		* @param p The F2mPoint to multiply.
+		* @param u The the WTNAF of <code>&#955;</code>..
+		* @return <code>&#955; * p</code>
+		*/
+		private static F2mPoint MultiplyFromWTnaf(F2mPoint p, sbyte[] u,
+			PreCompInfo preCompInfo)
+		{
+			F2mCurve curve = (F2mCurve)p.Curve;
+			sbyte a = (sbyte) curve.A.ToBigInteger().IntValue;
+
+			F2mPoint[] pu;
+			if ((preCompInfo == null) || !(preCompInfo is WTauNafPreCompInfo))
+			{
+				pu = Tnaf.GetPreComp(p, a);
+				p.SetPreCompInfo(new WTauNafPreCompInfo(pu));
+			}
+			else
+			{
+				pu = ((WTauNafPreCompInfo)preCompInfo).GetPreComp();
+			}
+
+			// q = infinity
+			F2mPoint q = (F2mPoint) p.Curve.Infinity;
+			for (int i = u.Length - 1; i >= 0; i--)
+			{
+				q = Tnaf.Tau(q);
+				if (u[i] != 0)
+				{
+					if (u[i] > 0)
+					{
+						q = q.AddSimple(pu[u[i]]);
+					}
+					else
+					{
+						// u[i] < 0
+						q = q.SubtractSimple(pu[-u[i]]);
+					}
+				}
+			}
+
+			return q;
+		}
+	}
+}