Secret Key Generation for Ambient Backscatter Communication

Research output: ThesisDoctoral ThesisCollection of Articles


The interest in wireless Internet of Things (IoT) devices and Ambient Intelligence has increased significantly in recent years. The security of IoT devices has become a concern, as IoT has made it possible for things and people to interact with each other anytime and any place. Therefore, sufficient protection against active eavesdropping or confusing devices with other users' devices is an essential requirement. Due to the embedded nature of these devices, they are often limited in their computational, communication and power resources. Ambient backscatter communication (AmBC) is seen as a viable solution for resource limited devices, as the wireless nodes are communicating without any active RF components. However, the interference from the ambient transmitter remains a major challenge, as the ambient signal is present at the receiver together with the backscattered signal. This thesis contributes to secure IoT device communication in an AmBC setting. The contributions are a two-way secret key agreement protocol and a backscatter device design. We developed a novel secret key agreement protocol that uses an advantage distillation method to collect secret key from error corrected parity bits. Our protocol provides complementary performance compared to protocols known in the literature. We have analysed the performance of the key agreement protocol in two different operating scenarios, in a quantum key distribution setting and in a satellite setting. The second contribution is a backscatter device design that introduces polarization conversion between the direct and scattered path signals and exploits that at the dual polarization receiver antenna to substantially decrease the interference from the ambient transmitter. We showed that in an anechoic RF chamber, our proposed set-up could achieve more than 25 dB isolation between the backscattered component, and the ambient component for narrowband signals. In this thesis, we analyse secret key generation between ambient backscatter devices where the channel between an ambient transmitter and the backscatter devices is used as a source of randomness. We show that even in non-line-of-sight channels the distance from legitimate users to an eavesdropper being larger than a few wavelengths is not alone a sufficient security guarantee. This is in contrast with previous secret key generation methods where the distance is assumed to prevent the eavesdropper from having any information about the key prior to error correction. Our simulations show that a distance based approach is too optimistic, and there is a possibility that the eavesdropper still knows a substantial part of the final key. A working solution is based on a two-way key agreement protocol, and assuming that the eavesdropper's error rates are k times that of the legitimate users, with k < 1. This method gives the legitimate users the freedom to trade off between achievable key rate and the eavesdropper's knowledge of the final key.
Translated title of the contributionSecret Key Generation for Ambient Backscatter Communication
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Tirkkonen, Olav, Supervising Professor
  • Vehkalahti, Roope, Thesis Advisor
Print ISBNs978-952-64-1296-2
Electronic ISBNs978-952-64-1297-9
Publication statusPublished - 2023
MoE publication typeG5 Doctoral dissertation (article)


  • fyysisen kerroksen tietoturva
  • IoT
  • polarisaatiomuunnos
  • salausavaimen kehittäminen
  • takaisinheijastukseen perustuva kommunikaatio
  • ambient backscatter
  • physical layer security
  • polarization conversion
  • secret key generation


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