def DeregisterDecrypter(cls, decrypter):
    """Deregisters a decrypter for a specific encryption method.

    Args:
      decrypter (type): decrypter class.

    Raises:
      KeyError: if the corresponding decrypter is not set.
    """
    encryption_method = decrypter.ENCRYPTION_METHOD.lower()
    if encryption_method not in cls._decrypters:
      raise KeyError(
          'Decrypter for encryption method: {0:s} not set.'.format(
              decrypter.ENCRYPTION_METHOD))

    del cls._decrypters[encryption_method]
Deregisters a decrypter for a specific encryption method.

    Args:
      decrypter (type): decrypter class.

    Raises:
      KeyError: if the corresponding decrypter is not set.