MacTest.java

package ot.security;

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.Key;
import java.security.SecureRandom;
import java.util.Base64;
import java.util.Base64.Encoder;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

public class MacTest {

	public static void main(String[] args) throws Exception {
		Path macKey = Paths.get("/tmp/crypt/mac.key");

		if (Files.notExists(macKey)) {
			final byte[] keybytes0 = new byte[512];
			new SecureRandom().nextBytes(keybytes0);

			Files.write(macKey, keybytes0);
		}

		final Encoder encoder = Base64.getEncoder();
		final byte[] keybytes = Files.readAllBytes(macKey);

		Key key = new SecretKeySpec(keybytes, "HMACSHA512");
		Mac mac = Mac.getInstance("HMACSHA512");
		mac.init(key);
		System.out.println(mac.getMacLength());

		byte[] hashValue = mac.doFinal("the lazy dog jumps over the quick brown fox".getBytes());

		System.out.println(encoder.encodeToString(hashValue));
		System.out.println(encoder.encodeToString(key.getEncoded()));
	}
}