Port of latest EC multipliers from Java

1 files changed, 30 insertions, 0 deletions

diff --git a/crypto/src/math/ec/multiplier/ZSignedDigitR2LMultiplier.cs b/crypto/src/math/ec/multiplier/ZSignedDigitR2LMultiplier.cs
new file mode 100644
index 000000000..91c06cbb8
--- /dev/null
+++ b/crypto/src/math/ec/multiplier/ZSignedDigitR2LMultiplier.cs
@@ -0,0 +1,30 @@
+namespace Org.BouncyCastle.Math.EC.Multiplier
+{
+    public class ZSignedDigitR2LMultiplier 
+        : AbstractECMultiplier
+    {
+        /**
+         * 'Zeroless' Signed Digit Right-to-Left.
+         */
+        protected override ECPoint MultiplyPositive(ECPoint p, BigInteger k)
+        {
+            ECPoint R0 = p.Curve.Infinity, R1 = p;
+
+            int n = k.BitLength;
+            int s = k.GetLowestSetBit();
+
+            R1 = R1.TimesPow2(s);
+
+            int i = s;
+            while (++i < n)
+            {
+                R0 = R0.Add(k.TestBit(i) ? R1 : R1.Negate());
+                R1 = R1.Twice();
+            }
+
+            R0 = R0.Add(R1);
+
+            return R0;
+        }
+    }
+}