Physical-Layer Key Generation Supported by RECAP Antenna Structures

Physical-layer key generation makes use of the reciprocity of wireless time-division duplex (TDD) channels. Both transmission directions experience the same channel, apart from independent noise and quantization effects. The randomness of a mobile channel ensures a certain regeneration rate of keys. Reconfigurable antennas, so-called RECAPs, offer a possibility to also provide randomness in the extreme case when both transmitter and receiver are not moving, even have a line-ofsight connection. RECAP structures and the steps for obtaining a reliably identical and secure key on both sides are discussed.