1 files changed, 44 insertions, 0 deletions
diff --git a/core/src/main/java/org/spongycastle/crypto/generators/ElGamalKeyPairGenerator.java b/core/src/main/java/org/spongycastle/crypto/generators/ElGamalKeyPairGenerator.java
new file mode 100644
index 00000000..cb0a9fcf
--- /dev/null
+++ b/core/src/main/java/org/spongycastle/crypto/generators/ElGamalKeyPairGenerator.java
@@ -0,0 +1,44 @@
+package org.spongycastle.crypto.generators;
+
+import java.math.BigInteger;
+
+import org.spongycastle.crypto.AsymmetricCipherKeyPair;
+import org.spongycastle.crypto.AsymmetricCipherKeyPairGenerator;
+import org.spongycastle.crypto.KeyGenerationParameters;
+import org.spongycastle.crypto.params.DHParameters;
+import org.spongycastle.crypto.params.ElGamalKeyGenerationParameters;
+import org.spongycastle.crypto.params.ElGamalParameters;
+import org.spongycastle.crypto.params.ElGamalPrivateKeyParameters;
+import org.spongycastle.crypto.params.ElGamalPublicKeyParameters;
+
+/**
+ * a ElGamal key pair generator.
+ * <p>
+ * This generates keys consistent for use with ElGamal as described in
+ * page 164 of "Handbook of Applied Cryptography".
+ */
+public class ElGamalKeyPairGenerator
+    implements AsymmetricCipherKeyPairGenerator
+{
+    private ElGamalKeyGenerationParameters param;
+
+    public void init(
+        KeyGenerationParameters param)
+    {
+        this.param = (ElGamalKeyGenerationParameters)param;
+    }
+
+    public AsymmetricCipherKeyPair generateKeyPair()
+    {
+        DHKeyGeneratorHelper helper = DHKeyGeneratorHelper.INSTANCE;
+        ElGamalParameters egp = param.getParameters();
+        DHParameters dhp = new DHParameters(egp.getP(), egp.getG(), null, egp.getL());  
+
+        BigInteger x = helper.calculatePrivate(dhp, param.getRandom()); 
+        BigInteger y = helper.calculatePublic(dhp, x);
+
+        return new AsymmetricCipherKeyPair(
+            new ElGamalPublicKeyParameters(y, egp),
+            new ElGamalPrivateKeyParameters(x, egp));
+    }
+}