Add GLVMultiplier and supporting interfaces

3 files changed, 56 insertions, 0 deletions

diff --git a/core/src/main/java/org/bouncycastle/math/ec/ECEndomorphism.java b/core/src/main/java/org/bouncycastle/math/ec/ECEndomorphism.java
new file mode 100644
index 00000000..110bd2ab
--- /dev/null
+++ b/core/src/main/java/org/bouncycastle/math/ec/ECEndomorphism.java
@@ -0,0 +1,8 @@
+package org.bouncycastle.math.ec;
+
+public interface ECEndomorphism
+{
+    ECPointMap getPointMap();
+
+    boolean hasEfficientPointMap();
+}
diff --git a/core/src/main/java/org/bouncycastle/math/ec/GLVEndomorphism.java b/core/src/main/java/org/bouncycastle/math/ec/GLVEndomorphism.java
new file mode 100644
index 00000000..bf576908
--- /dev/null
+++ b/core/src/main/java/org/bouncycastle/math/ec/GLVEndomorphism.java
@@ -0,0 +1,8 @@
+package org.bouncycastle.math.ec;
+
+import java.math.BigInteger;
+
+public interface GLVEndomorphism extends ECEndomorphism
+{
+    BigInteger[] decomposeScalar(BigInteger k);
+}
diff --git a/core/src/main/java/org/bouncycastle/math/ec/GLVMultiplier.java b/core/src/main/java/org/bouncycastle/math/ec/GLVMultiplier.java
new file mode 100644
index 00000000..4a6b2343
--- /dev/null
+++ b/core/src/main/java/org/bouncycastle/math/ec/GLVMultiplier.java
@@ -0,0 +1,40 @@
+package org.bouncycastle.math.ec;
+
+import java.math.BigInteger;
+
+public class GLVMultiplier extends AbstractECMultiplier
+{
+    protected final ECCurve curve;
+    protected final GLVEndomorphism glvEndomorphism;
+
+    public GLVMultiplier(ECCurve curve, GLVEndomorphism glvEndomorphism)
+    {
+        if (curve == null || curve.getOrder() == null)
+        {
+            throw new IllegalArgumentException("Need curve with known group order");
+        }
+
+        this.curve = curve;
+        this.glvEndomorphism = glvEndomorphism;
+    }
+
+    protected ECPoint multiplyPositive(ECPoint p, BigInteger k)
+    {
+        if (!curve.equals(p.getCurve()))
+        {
+            throw new IllegalStateException();
+        }
+
+        BigInteger n = p.getCurve().getOrder();
+        BigInteger[] ab = glvEndomorphism.decomposeScalar(k.mod(n));
+        BigInteger a = ab[0], b = ab[1];
+
+        ECPointMap pointMap = glvEndomorphism.getPointMap();
+        if (glvEndomorphism.hasEfficientPointMap())
+        {
+            return ECAlgorithms.implShamirsTrickWNaf(p, a, pointMap, b);
+        }
+
+        return ECAlgorithms.implShamirsTrickWNaf(p, a, pointMap.map(p), b);
+    }
+}