For more information on a MAC, see RFC 2104. See also e467 Listing All Available Message Authentication Code (MAC) Key Generators. 
    try {
        // Generate a key for the HMAC-MD5 keyed-hashing algorithm
        KeyGenerator keyGen = KeyGenerator.getInstance("HmacMD5");
        SecretKey key = keyGen.generateKey();
    
        // Generate a key for the HMAC-SHA1 keyed-hashing algorithm
        keyGen = KeyGenerator.getInstance("HmacSHA1");
        key = keyGen.generateKey();
    } catch (java.security.NoSuchAlgorithmException e) {
    }