Because wireless signals travel in free space, they can be picked up by any device in range equipped with a suitable radio receiver. This has implications for the security of data on a wireless network, as it could be accessed by outside devices. Both WiFi and Bluetooth are equipped to address this problem by a combination of authentication and encryption. Authentication is a method of controlling access to the network so that only recognised devices are accepted. This can be done using a password or the MAC address of the device. Encryption involves scrambling the data in such a way that it becomes extremely difficult for any unauthenticated device to unscramble it. When properly implemented, Bluetooth and the 802.11g WiFi standard provide good, but not perfect, data security.