diff --git a/Crypto/src/math/ec/ECAlgorithms.cs b/Crypto/src/math/ec/ECAlgorithms.cs
new file mode 100644
index 000000000..be4fd1b14
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+++ b/Crypto/src/math/ec/ECAlgorithms.cs
@@ -0,0 +1,93 @@
+using System;
+
+using Org.BouncyCastle.Math;
+
+namespace Org.BouncyCastle.Math.EC
+{
+ public class ECAlgorithms
+ {
+ public static ECPoint SumOfTwoMultiplies(ECPoint P, BigInteger a,
+ ECPoint Q, BigInteger b)
+ {
+ ECCurve c = P.Curve;
+ if (!c.Equals(Q.Curve))
+ throw new ArgumentException("P and Q must be on same curve");
+
+ // Point multiplication for Koblitz curves (using WTNAF) beats Shamir's trick
+ if (c is F2mCurve)
+ {
+ F2mCurve f2mCurve = (F2mCurve) c;
+ if (f2mCurve.IsKoblitz)
+ {
+ return P.Multiply(a).Add(Q.Multiply(b));
+ }
+ }
+
+ return ImplShamirsTrick(P, a, Q, b);
+ }
+
+ /*
+ * "Shamir's Trick", originally due to E. G. Straus
+ * (Addition chains of vectors. American Mathematical Monthly,
+ * 71(7):806-808, Aug./Sept. 1964)
+ *
+ * Input: The points P, Q, scalar k = (km?, ... , k1, k0)
+ * and scalar l = (lm?, ... , l1, l0).
+ * Output: R = k * P + l * Q.
+ * 1: Z <- P + Q
+ * 2: R <- O
+ * 3: for i from m-1 down to 0 do
+ * 4: R <- R + R {point doubling}
+ * 5: if (ki = 1) and (li = 0) then R <- R + P end if
+ * 6: if (ki = 0) and (li = 1) then R <- R + Q end if
+ * 7: if (ki = 1) and (li = 1) then R <- R + Z end if
+ * 8: end for
+ * 9: return R
+ */
+ public static ECPoint ShamirsTrick(
+ ECPoint P,
+ BigInteger k,
+ ECPoint Q,
+ BigInteger l)
+ {
+ if (!P.Curve.Equals(Q.Curve))
+ throw new ArgumentException("P and Q must be on same curve");
+
+ return ImplShamirsTrick(P, k, Q, l);
+ }
+
+ private static ECPoint ImplShamirsTrick(ECPoint P, BigInteger k,
+ ECPoint Q, BigInteger l)
+ {
+ int m = System.Math.Max(k.BitLength, l.BitLength);
+ ECPoint Z = P.Add(Q);
+ ECPoint R = P.Curve.Infinity;
+
+ for (int i = m - 1; i >= 0; --i)
+ {
+ R = R.Twice();
+
+ if (k.TestBit(i))
+ {
+ if (l.TestBit(i))
+ {
+ R = R.Add(Z);
+ }
+ else
+ {
+ R = R.Add(P);
+ }
+ }
+ else
+ {
+ if (l.TestBit(i))
+ {
+ R = R.Add(Q);
+ }
+ }
+ }
+
+ return R;
+ }
+ }
+}
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