The Java Version Almanac
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Diffie-Hellman Key Agreement

With key agreement algorithms two parties can agree on a shared secret by exchanging information over public channels only.

Since Java 1.4

import; import; import; import java.util.HexFormat; import javax.crypto.KeyAgreement; public class DiffieHellmanKeyAgreement { static class Party { private KeyPair key; private KeyAgreement agreement; Party() throws Exception { key = KeyPairGenerator.getInstance("DiffieHellman").generateKeyPair(); agreement = KeyAgreement.getInstance("DiffieHellman"); agreement.init(key.getPrivate()); } PublicKey getPublicKey() { return key.getPublic(); } void retrieveOtherPublicKey(PublicKey key) throws Exception { agreement.doPhase(key, true); } void printSecret() { byte[] secret = agreement.generateSecret(); System.out.println(HexFormat.of().formatHex(secret)); } } public static void main(String[] args) throws Exception { var alice = new Party(); var bob = new Party(); // Alice and Bob exchange their public keys alice.retrieveOtherPublicKey(bob.getPublicKey()); bob.retrieveOtherPublicKey(alice.getPublicKey()); // Now both parties can calculate a shared secret: alice.printSecret(); bob.printSecret(); } }

This snippet at GitHub