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");

  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");

   * SHA-1 (160 hash bits) hash function and a {@link SecretKeySpec} created from the given byte
   * array and the SHA-1 algorithm.
   *
   * @param key the key material of the secret key
   * @since 20.0
   */
  public static HashFunction hmacSha1(byte[] key) {
    return hmacSha1(new SecretKeySpec(checkNotNull(key), "HmacSHA1"));
  }

  /**