private static final SecretKey MD5_KEY =
      new SecretKeySpec("secret key".getBytes(UTF_8), "HmacMD5");
  private static final SecretKey SHA1_KEY =
      new SecretKeySpec("secret key".getBytes(UTF_8), "HmacSHA1");
  private static final SecretKey SHA256_KEY =
      new SecretKeySpec("secret key".getBytes(UTF_8), "HmacSHA256");
  private static final SecretKey SHA512_KEY =
      new SecretKeySpec("secret key".getBytes(UTF_8), "HmacSHA512");