Key agreement algorithms in Java JCE

21 Sep 2023

security

Key agreement algorithms, also known as key exchange algorithms, play a crucial role in secure communications. In Java, the Java Cryptography Extension (JCE) provides a robust set of key agreement algorithms that can be used to establish secure connections and exchange cryptographic keys between parties.

In this blog post, we will explore some of the key agreement algorithms available in Java JCE and learn how to use them in your Java applications.

1. Diffie-Hellman (DH)

The Diffie-Hellman key agreement algorithm is one of the oldest and most widely used algorithms for secure key exchange. It allows two parties to agree upon a shared secret key over an insecure communication channel. The Java JCE provides a KeyAgreement class to implement the Diffie-Hellman algorithm.

Here’s an example of how to use the Diffie-Hellman algorithm in Java:

import javax.crypto.KeyAgreement;
import javax.crypto.spec.DHParameterSpec;
import javax.crypto.spec.DHPublicKeySpec;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PublicKey;
import java.security.spec.X509EncodedKeySpec;

public class DiffieHellmanExample {
    public static void main(String[] args) throws Exception {
        // Generate Alice's key pair
        KeyPairGenerator aliceKpg = KeyPairGenerator.getInstance("DiffieHellman");
        KeyPair aliceKp = aliceKpg.generateKeyPair();

        // Generate Bob's key pair
        KeyPairGenerator bobKpg = KeyPairGenerator.getInstance("DiffieHellman");
        KeyPair bobKp = bobKpg.generateKeyPair();

        // Alice's public key
        PublicKey alicePublicKey = aliceKp.getPublic();
        byte[] aliceEncodedPublicKey = alicePublicKey.getEncoded();

        // Bob's public key
        PublicKey bobPublicKey = bobKp.getPublic();
        byte[] bobEncodedPublicKey = bobPublicKey.getEncoded();

        // Initialize key agreement with Alice's private key
        KeyFactory keyFactory = KeyFactory.getInstance("DiffieHellman");
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(bobEncodedPublicKey);
        PublicKey bobPublicKeyRecovered = keyFactory.generatePublic(x509KeySpec);
        KeyAgreement aliceKeyAgreement = KeyAgreement.getInstance("DiffieHellman");
        aliceKeyAgreement.init(aliceKp.getPrivate());
        aliceKeyAgreement.doPhase(bobPublicKeyRecovered, true);

        // Alice's shared secret key
        byte[] aliceSharedSecret = aliceKeyAgreement.generateSecret();

        // Initialize key agreement with Bob's private key
        keyFactory = KeyFactory.getInstance("DiffieHellman");
        x509KeySpec = new X509EncodedKeySpec(aliceEncodedPublicKey);
        PublicKey alicePublicKeyRecovered = keyFactory.generatePublic(x509KeySpec);
        KeyAgreement bobKeyAgreement = KeyAgreement.getInstance("DiffieHellman");
        bobKeyAgreement.init(bobKp.getPrivate());
        bobKeyAgreement.doPhase(alicePublicKeyRecovered, true);

        // Bob's shared secret key
        byte[] bobSharedSecret = bobKeyAgreement.generateSecret();

        // Check if the shared secret keys match
        if (Arrays.equals(aliceSharedSecret, bobSharedSecret)) {
            System.out.println("Shared secret keys match!");
        } else {
            System.out.println("Shared secret keys do not match!");
        }
    }
}

2. Elliptic Curve Diffie-Hellman (ECDH)

Elliptic Curve Diffie-Hellman (ECDH) is a variant of the Diffie-Hellman key agreement algorithm that utilizes elliptic curve cryptography. It offers similar security with shorter key lengths, making it more efficient and suitable for resource-constrained environments. The Java JCE provides an EllipticCurve class to implement ECDH.

Here’s an example of how to use the ECDH algorithm in Java:

import javax.crypto.KeyAgreement;
import java.security.*;
import java.security.spec.ECGenParameterSpec;

public class ECDHExample {
    public static void main(String[] args) throws Exception {
        // Generate Alice's key pair
        KeyPairGenerator aliceKpg = KeyPairGenerator.getInstance("EC");
        aliceKpg.initialize(new ECGenParameterSpec("secp256r1"));
        KeyPair aliceKp = aliceKpg.generateKeyPair();

        // Generate Bob's key pair
        KeyPairGenerator bobKpg = KeyPairGenerator.getInstance("EC");
        bobKpg.initialize(new ECGenParameterSpec("secp256r1"));
        KeyPair bobKp = bobKpg.generateKeyPair();

        // Initialize key agreement with Alice's private key
        KeyAgreement aliceKeyAgreement = KeyAgreement.getInstance("ECDH");
        aliceKeyAgreement.init(aliceKp.getPrivate());
        aliceKeyAgreement.doPhase(bobKp.getPublic(), true);

        // Alice's shared secret key
        byte[] aliceSharedSecret = aliceKeyAgreement.generateSecret();

        // Initialize key agreement with Bob's private key
        KeyAgreement bobKeyAgreement = KeyAgreement.getInstance("ECDH");
        bobKeyAgreement.init(bobKp.getPrivate());
        bobKeyAgreement.doPhase(aliceKp.getPublic(), true);

        // Bob's shared secret key
        byte[] bobSharedSecret = bobKeyAgreement.generateSecret();

        // Check if the shared secret keys match
        if (Arrays.equals(aliceSharedSecret, bobSharedSecret)) {
            System.out.println("Shared secret keys match!");
        } else {
            System.out.println("Shared secret keys do not match!");
        }
    }
}

These examples demonstrate how to use the Diffie-Hellman and Elliptic Curve Diffie-Hellman key agreement algorithms in Java JCE. By leveraging these algorithms, you can securely exchange cryptographic keys in your Java applications, ensuring secure communication between parties.

#java #security