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 java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PublicKey;
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);
}
String generateSecret() {
byte[] secret = agreement.generateSecret();
return HexFormat.of().formatHex(secret);
}
}
void main() 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:
IO.println("Alice: " + alice.generateSecret());
IO.println("Bob: " + bob.generateSecret());
}
}
This snippet at GitHub