def encrypt(self, data):
    """ encrypt data with convergence encryption.

        Args
            data: str, the plain text to be encrypted
    
        Returns
            key: hash(block), encryption key
            id: hash(hash(block), block ID
            ciphertext: enc(key, block)
    """
    assert(isinstance(data, str))
    key, id = self.__sec_key(data)
    return key, id, aes(key, data)