1 files changed, 77 insertions, 0 deletions
diff --git a/libraries/spongycastle/core/src/main/java/org/spongycastle/math/ec/MixedNafR2LMultiplier.java b/libraries/spongycastle/core/src/main/java/org/spongycastle/math/ec/MixedNafR2LMultiplier.java
new file mode 100644
index 000000000..e626103ae
--- /dev/null
+++ b/libraries/spongycastle/core/src/main/java/org/spongycastle/math/ec/MixedNafR2LMultiplier.java
@@ -0,0 +1,77 @@
+package org.spongycastle.math.ec;
+
+import java.math.BigInteger;
+
+/**
+ * Class implementing the NAF (Non-Adjacent Form) multiplication algorithm (right-to-left) using
+ * mixed coordinates.
+ */
+public class MixedNafR2LMultiplier extends AbstractECMultiplier
+{
+    protected int additionCoord, doublingCoord;
+
+    /**
+     * By default, addition will be done in Jacobian coordinates, and doubling will be done in
+     * Modified Jacobian coordinates (independent of the original coordinate system of each point).
+     */
+    public MixedNafR2LMultiplier()
+    {
+        this(ECCurve.COORD_JACOBIAN, ECCurve.COORD_JACOBIAN_MODIFIED);
+    }
+
+    public MixedNafR2LMultiplier(int additionCoord, int doublingCoord)
+    {
+        this.additionCoord = additionCoord;
+        this.doublingCoord = doublingCoord;
+    }
+
+    protected ECPoint multiplyPositive(ECPoint p, BigInteger k)
+    {
+        ECCurve curveOrig = p.getCurve();
+
+        ECCurve curveAdd = configureCurve(curveOrig, additionCoord);
+        ECCurve curveDouble = configureCurve(curveOrig, doublingCoord);
+
+        int[] naf = WNafUtil.generateCompactNaf(k);
+
+        ECPoint Ra = curveAdd.getInfinity();
+        ECPoint Td = curveDouble.importPoint(p);
+
+        int zeroes = 0;
+        for (int i = 0; i < naf.length; ++i)
+        {
+            int ni = naf[i];
+            int digit = ni >> 16;
+            zeroes += ni & 0xFFFF;
+
+            Td = Td.timesPow2(zeroes);
+
+            ECPoint Tj = curveAdd.importPoint(Td);
+            if (digit < 0)
+            {
+                Tj = Tj.negate();
+            }
+
+            Ra = Ra.add(Tj);
+
+            zeroes = 1;
+        }
+
+        return curveOrig.importPoint(Ra);
+    }
+
+    protected ECCurve configureCurve(ECCurve c, int coord)
+    {
+        if (c.getCoordinateSystem() == coord)
+        {
+            return c;
+        }
+
+        if (!c.supportsCoordinateSystem(coord))
+        {
+            throw new IllegalArgumentException("Coordinate system " + coord + " not supported by this curve");
+        }
+
+        return c.configure().setCoordinateSystem(coord).create();
+    }
+}