SecureRandom      secureRandom = SecureRandom.getInstance("SHA1PRNG");
Curve25519KeyPair keyPair      = Curve25519.generateKeyPair();

byte[] sharedSecret = Curve25519.calculateAgreement(publicKey, privateKey);

SecureRandom secureRandom = SecureRandom.getInstance("SHA1PRNG");
byte[]       signature    = Curve25519.calculateSignature(secureRandom, privateKey, message);

boolean validSignature = Curve25519.verifySignature(publicKey, message, signature);