A Novel Algorithm for Secret Key Generation in Passive Backscatter Communication Systems Mohammad Hossein Chinaei † , Diethelm Ostry ⋆ , Vijay Sivaraman † † University of New South Wales, Sydney, Australia ⋆ Data61, CSIRO m.chinaei@unsw.edu.au, diet.ostry@data61.csiro.au, vijay@unsw.edu.au Abstract. The extreme asymmetry of passive backscatter communica- tions systems such as passive Wi-Fi, while allowing significant reduction of node power consumption for communications, imposes severe resource limitations on implementing secure communications. Target applications for this technology are typically driven by the promise of low power con- sumption, up to four orders of magnitude lower than commercial Wi-Fi chipsets. Industry standard security approaches using encryption tech- nology are problematic in this power regime, particularly as the poten- tial low complexity and size of passive nodes will encourage application to high-density networks of very small, energy-poor devices. Generation of shared symmetric keys through reciprocal channel measurements, for example of received signal strength (RSS), is a natural approach in this situation. However previous work in this area has focused on the sym- metric case where base station and nodes communicate at the same radio frequency. Backscatter communications uses two frequencies, typically a pilot beacon transmitted by a base station on one frequency, and re- sponse on a shifted frequency. This paper describes a protocol for RSS- based shared key generation for this architecture and reports the results of an experimental implementation using software radio emulation of backscatter communication. Keywords: Physical layer security · Secret key generation · Passive sen- sors · Backscatter communication 1 Introduction Power consumption remains a key limiting constraint in achieving long-lived net- works of wireless sensor nodes, and communications is typically a major compo- nent of their power budget. The appearance of many applications requiring small low-power sensors in areas such as the Internet of Things (IoT), wearable devices, and implantable medical sensors, has attracted a great deal of research interest in techniques able to achieve low-power communications. The most extreme ap- proaches to date employ backscatter technologies which can reduce power con- sumption by orders of magnitude through transfering as much as possible of the power-consuming transmitter functionality of the wireless communications