code: public SecretKey unwrapSecretKey(String wrappedKey) {
  
          return (SecretKey) unwrap(wrappedKey, Keys.SYMMETRIC_ALGORITHM,
                  Cipher.SECRET_KEY, WRAP_ALGORITHM_SYMMETRIC);
      }
docs: Unwraps the given encoded {@link SecretKey}, using
  WRAP_ALGORITHM_SYMMETRIC.
  
  @param wrappedKey The wrapped key, base-64 encoded, as returned by
  {@link #wrapSecretKey(SecretKey)} .
  @return The unwrapped {@link SecretKey}.