Added DHExchange class

src/main/java/Main/DHExchange.java

@@ -0,0 +1,105 @@
+package Main;
+
+import org.apache.log4j.Level;
+import org.apache.log4j.LogManager;
+import org.apache.log4j.Logger;
+
+import javax.crypto.KeyAgreement;
+import javax.crypto.interfaces.DHPublicKey;
+import javax.crypto.spec.DHParameterSpec;
+import javax.crypto.spec.SecretKeySpec;
+import java.security.*;
+import java.security.spec.InvalidKeySpecException;
+import java.security.spec.X509EncodedKeySpec;
+
+public class DHExchange {
+    private static final Logger logger = LogManager.getLogger(App.class);
+    private KeyPair keyPair = null;
+    private KeyAgreement agreement = null;
+    private PublicKey thisPublicKey;
+    private PublicKey otherPublicKey;
+    private final int keySize;
+    private SecretKeySpec secretKey;
+
+
+    public DHExchange(int keySize, boolean isHost) {
+        this.keySize = keySize;
+        if (isHost)
+            createKeyPar();
+    }
+
+    void createKeyPar() {
+        logger.log(Level.INFO, "Generating " + keySize + "-bit key pair...");
+
+        try {
+            KeyPairGenerator kPairGen = KeyPairGenerator.getInstance("DH");
+            kPairGen.initialize(keySize);
+            keyPair = kPairGen.generateKeyPair();
+
+
+            agreement = KeyAgreement.getInstance("DH");
+            agreement.init(keyPair.getPrivate());
+        } catch (NoSuchAlgorithmException | InvalidKeyException e) {
+            e.printStackTrace();
+        }
+        thisPublicKey = keyPair.getPublic();
+    }
+
+    void createKeyParFromPublicKey(byte[] publicKeyBytes) throws Exception {
+        if (keyPair != null)
+            throw new Exception("Key pair alredy exists! Perhaps is was generated before?");
+        try {
+            KeyFactory keyFactory = KeyFactory.getInstance("DH");
+            X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(publicKeyBytes);
+
+            otherPublicKey = keyFactory.generatePublic(x509KeySpec);
+
+            DHParameterSpec dhParam = ((DHPublicKey) otherPublicKey).getParams();
+
+            logger.log(Level.INFO, "Generating " + keySize + "-bit key pair...");
+            KeyPairGenerator kPairGen = KeyPairGenerator.getInstance("DH");
+            kPairGen.initialize(dhParam);
+            keyPair = kPairGen.generateKeyPair();
+
+            agreement = KeyAgreement.getInstance("DH");
+            agreement.init(keyPair.getPrivate());
+
+            thisPublicKey = keyPair.getPublic();
+
+        } catch (NoSuchAlgorithmException | InvalidKeySpecException | InvalidAlgorithmParameterException | InvalidKeyException e) {
+            e.printStackTrace();
+        }
+    }
+
+    void onRecievePubKey(byte[] publicKeyBytes) {
+        try {
+            KeyFactory keyFac = KeyFactory.getInstance("DH");
+
+            X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(publicKeyBytes);
+            otherPublicKey = keyFac.generatePublic(x509KeySpec);
+            logger.log(Level.INFO, "Agreement phase...");
+            agreement.doPhase(otherPublicKey, true);
+
+        } catch (NoSuchAlgorithmException | InvalidKeySpecException | InvalidKeyException e) {
+            e.printStackTrace();
+        }
+    }
+
+    byte[] getThisPublicKeyEncoded() {
+        return thisPublicKey.getEncoded();
+    }
+
+    byte[] getOtherPublicKeyEncoded() {
+        return otherPublicKey.getEncoded();
+    }
+
+    void generateSecret() {
+        byte[] secret = agreement.generateSecret();
+        secretKey = new SecretKeySpec(secret, 0, 16, "AES");
+    }
+
+    public SecretKeySpec getSecretKey() {
+        return secretKey;
+    }
+}
+