1 files changed, 22 insertions, 5 deletions
diff --git a/bcprov/src/main/java/org/bouncycastle/crypto/ec/ECFixedTransform.java b/bcprov/src/main/java/org/bouncycastle/crypto/ec/ECFixedTransform.java
index e35e077..2c6a920 100644
--- a/bcprov/src/main/java/org/bouncycastle/crypto/ec/ECFixedTransform.java
+++ b/bcprov/src/main/java/org/bouncycastle/crypto/ec/ECFixedTransform.java
@@ -3,8 +3,11 @@ package org.bouncycastle.crypto.ec;
 import java.math.BigInteger;
 
 import org.bouncycastle.crypto.CipherParameters;
+import org.bouncycastle.crypto.params.ECDomainParameters;
 import org.bouncycastle.crypto.params.ECPublicKeyParameters;
+import org.bouncycastle.math.ec.ECMultiplier;
 import org.bouncycastle.math.ec.ECPoint;
+import org.bouncycastle.math.ec.FixedPointCombMultiplier;
 
 /**
  * this transforms the original randomness used for an ElGamal encryption by a fixed value.
@@ -38,7 +41,7 @@ public class ECFixedTransform
     }
 
     /**
-     * Transform an existing cipher test pair using the ElGamal algorithm. Note: it is assumed this
+     * Transform an existing cipher text pair using the ElGamal algorithm. Note: it is assumed this
      * transform has been initialised with the same public key that was used to create the original
      * cipher text.
      *
@@ -52,11 +55,20 @@ public class ECFixedTransform
             throw new IllegalStateException("ECFixedTransform not initialised");
         }
 
-        ECPoint  g = key.getParameters().getG();
-        ECPoint  gamma = g.multiply(k);
-        ECPoint  phi = key.getQ().multiply(k).add(cipherText.getY());
+        ECDomainParameters ec = key.getParameters();
+        BigInteger n = ec.getN();
 
-        return new ECPair(cipherText.getX().add(gamma).normalize(), phi.normalize());
+        ECMultiplier basePointMultiplier = createBasePointMultiplier();
+        BigInteger k = this.k.mod(n);
+
+        ECPoint[] gamma_phi = new ECPoint[]{
+            basePointMultiplier.multiply(ec.getG(), k).add(cipherText.getX()),
+            key.getQ().multiply(k).add(cipherText.getY())
+        };
+
+        ec.getCurve().normalizeAll(gamma_phi);
+
+        return new ECPair(gamma_phi[0], gamma_phi[1]);
     }
 
     /**
@@ -68,4 +80,9 @@ public class ECFixedTransform
     {
         return k;
     }
+
+    protected ECMultiplier createBasePointMultiplier()
+    {
+        return new FixedPointCombMultiplier();
+    }
 }