  We introduce an encryption device based on wave-chaos to enhance the physical
security of wireless wave transmission. The proposed encryption device is
composed of a compact quasi-2D disordered cavity, where transmit signals pass
through to be distorted in time before transmission. On the receiving end, the
signals can only be decrypted when they pass through an identical cavity. In
the absence of a proper decryption device, the signals cannot be properly
decrypted. If a cavity with a different shape is used on the receiving end,
vastly different wave dynamics will prevent the signals from being decrypted,
causing them to appear as noise. We experimentally demonstrate the proposed
concept in an apparatus representing a wireless link.
