@classmethod
def GetDecrypter(cls, encryption_method, **kwargs):
    """Retrieves the decrypter object for a specific encryption method.

    Args:
      encryption_method (str): encryption method identifier.
      kwargs (dict): keyword arguments depending on the decrypter.

    Returns:
      Decrypter: decrypter or None if the encryption method does not exists.

    Raises:
      CredentialError: if the necessary credentials are missing.
    """
    encryption_method = encryption_method.lower()
    decrypter = cls._decrypters.get(encryption_method, None)
    if not decrypter:
        return None
    return decrypter(**kwargs)
