def apply(config, val):
    """ Pseudonymize using format preserving encryption.
    Example config:
    {
        'func': 'fpe',
        'key': 'some-secret-key',
        'alphabet': string.ascii_letters
    }
    """
    validate_func_params(config, MANDATORY_CONFIG_PARAMS)
    try:
        alphabet = config.get('alphabet', string.printable)
        e = pyffx.String(config['key'].encode("utf-8"), alphabet, length=len(val))
        return e.encrypt(val)
    except ValueError:
        raise PseudoFuncError("Could not pseudonymize '{0}'. Check alphabet compatibility ({1})".format(val, alphabet))