Generate keys:
KeyPairGenerator kpg = KeyPairGenerator.getInstance("EC");
kpg.initialize(new ECGenParameterSpec("secp521r1"), new SecureRandom());
KeyPair keyPair = kpg.generateKeyPair();
ECPrivateKey privateKey = (ECPrivateKey) keyPair.getPrivate();
ECPublicKey publicKey = (ECPublicKey) keyPair.getPublic();
byte[] privateKeyS = privateKey.getS().toByteArray();
byte[] publicKeyX = publicKey.getW().getAffineX().toByteArray();
byte[] publicKeyY = publicKey.getW().getAffineY().toByteArray();
