Design of an Efficient OFDMA-Based Multi-User Key Generation Protocol

Secret key generation exploits the unique random features of wireless channels, hence, it is eminently suitable for the resource constrained Internet of Things applications. However, it has only been involved for single links between a pair of users, whilst there is a paucity of the literature on group and multi-user key generation. This paper proposes an orthogonal frequency-division multiple access (OFDMA) based multi-user key generation protocol to efficiently establish keys in a star topology. The uplink and downlink multi-user access facilitated by OFDMA allows the central node to simultaneously communicate with multiple users, which can significantly reduce the channel probing overhead. In particular, we provide a compelling case study of multi-user secret key generation by designing a prototype based on IEEE 802.11ax, a new Wi-Fi standard to be released. Our simulation results have demonstrated that the OFDMA-based multi-user key generation protocol incurs low interference amongst the users, whilst benefiting from channel reciprocity and generating unique random keys.