1 files changed, 58 insertions, 0 deletions
diff --git a/core/src/main/java/org/spongycastle/math/ec/endo/GLVTypeBEndomorphism.java b/core/src/main/java/org/spongycastle/math/ec/endo/GLVTypeBEndomorphism.java
new file mode 100644
index 00000000..884cbf53
--- /dev/null
+++ b/core/src/main/java/org/spongycastle/math/ec/endo/GLVTypeBEndomorphism.java
@@ -0,0 +1,58 @@
+package org.spongycastle.math.ec.endo;
+
+import java.math.BigInteger;
+
+import org.spongycastle.math.ec.ECConstants;
+import org.spongycastle.math.ec.ECCurve;
+import org.spongycastle.math.ec.ECPointMap;
+import org.spongycastle.math.ec.ScaleXPointMap;
+
+public class GLVTypeBEndomorphism implements GLVEndomorphism
+{
+    protected final ECCurve curve;
+    protected final GLVTypeBParameters parameters;
+    protected final ECPointMap pointMap;
+
+    public GLVTypeBEndomorphism(ECCurve curve, GLVTypeBParameters parameters)
+    {
+        this.curve = curve;
+        this.parameters = parameters;
+        this.pointMap = new ScaleXPointMap(curve.fromBigInteger(parameters.getBeta()));
+    }
+
+    public BigInteger[] decomposeScalar(BigInteger k)
+    {
+        int bits = parameters.getBits();
+        BigInteger b1 = calculateB(k, parameters.getG1(), bits);
+        BigInteger b2 = calculateB(k, parameters.getG2(), bits);
+
+        BigInteger[] v1 = parameters.getV1(), v2 = parameters.getV2();
+        BigInteger a = k.subtract((b1.multiply(v1[0])).add(b2.multiply(v2[0])));
+        BigInteger b = (b1.multiply(v1[1])).add(b2.multiply(v2[1])).negate();
+
+        return new BigInteger[]{ a, b };
+    }
+
+    public ECPointMap getPointMap()
+    {
+        return pointMap;
+    }
+
+    public boolean hasEfficientPointMap()
+    {
+        return true;
+    }
+
+    protected BigInteger calculateB(BigInteger k, BigInteger g, int t)
+    {
+        boolean negative = (g.signum() < 0);
+        BigInteger b = k.multiply(g.abs());
+        boolean extra = b.testBit(t - 1);
+        b = b.shiftRight(t);
+        if (extra)
+        {
+            b = b.add(ECConstants.ONE);
+        }
+        return negative ? b.negate() : b;
+    }
+}