Add NafR2LMultiplier

3 files changed, 56 insertions, 1 deletions

diff --git a/core/src/main/java/org/bouncycastle/math/ec/MixedNafR2LMultiplier.java b/core/src/main/java/org/bouncycastle/math/ec/MixedNafR2LMultiplier.java
index 2b700fbc..294e6b0b 100644
--- a/core/src/main/java/org/bouncycastle/math/ec/MixedNafR2LMultiplier.java
+++ b/core/src/main/java/org/bouncycastle/math/ec/MixedNafR2LMultiplier.java
@@ -2,10 +2,18 @@ package org.bouncycastle.math.ec;
 
 import java.math.BigInteger;
 
+/**
+ * Class implementing the NAF (Non-Adjacent Form) multiplication algorithm (right-to-left) using
+ * mixed coordinates.
+ */
 public class MixedNafR2LMultiplier implements ECMultiplier
 {
     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);
diff --git a/core/src/main/java/org/bouncycastle/math/ec/NafL2RMultiplier.java b/core/src/main/java/org/bouncycastle/math/ec/NafL2RMultiplier.java
index d94d25dc..09c15d7e 100644
--- a/core/src/main/java/org/bouncycastle/math/ec/NafL2RMultiplier.java
+++ b/core/src/main/java/org/bouncycastle/math/ec/NafL2RMultiplier.java
@@ -3,7 +3,7 @@ package org.bouncycastle.math.ec;
 import java.math.BigInteger;
 
 /**
- * Class implementing the NAF (Non-Adjacent Form) multiplication algorithm.
+ * Class implementing the NAF (Non-Adjacent Form) multiplication algorithm (left-to-right).
  */
 public class NafL2RMultiplier implements ECMultiplier
 {
diff --git a/core/src/main/java/org/bouncycastle/math/ec/NafR2LMultiplier.java b/core/src/main/java/org/bouncycastle/math/ec/NafR2LMultiplier.java
new file mode 100644
index 00000000..9d652418
--- /dev/null
+++ b/core/src/main/java/org/bouncycastle/math/ec/NafR2LMultiplier.java
@@ -0,0 +1,47 @@
+package org.bouncycastle.math.ec;
+
+import java.math.BigInteger;
+
+/**
+ * Class implementing the NAF (Non-Adjacent Form) multiplication algorithm (right-to-left).
+ */
+public class NafR2LMultiplier implements ECMultiplier
+{
+    public ECPoint multiply(ECPoint p, BigInteger k, PreCompInfo preCompInfo)
+    {
+        if (k.signum() < 0)
+        {
+            throw new IllegalArgumentException("'k' cannot be negative");
+        }
+        if (k.signum() == 0)
+        {
+            return p.getCurve().getInfinity();
+        }
+
+        p = p.normalize();
+
+        ECPoint R0 = p.getCurve().getInfinity(), R1 = p;
+
+        int[] naf = WNafUtil.generateCompactNaf(k);
+        int zeroes = 0;
+
+        for (int i = 0; i < naf.length; ++i)
+        {
+            int ni = naf[i];
+            int digit = ni >> 16;
+            zeroes += ni & 0xFFFF;
+
+            while (--zeroes >= 0)
+            {
+                R1 = R1.twice();
+            }
+
+            ECPoint r = digit < 0 ? R1.negate() : R1;
+            R0 = R0.add(r);
+
+            zeroes = 1;
+        }
+
+        return R0;
+    }
+}