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Zhang, Yuexin, Xiang, Yang, Huang, Xinyi.  2017.  A Cross-Layer Key Establishment Model for Wireless Devices in Cyber-Physical Systems. Proceedings of the 3rd ACM Workshop on Cyber-Physical System Security. :43–53.

Wireless communications in Cyber-Physical Systems (CPS) are vulnerable to many adversarial attacks such as eavesdropping. To secure the communications, secret session keys need to be established between wireless devices. In existing symmetric key establishment protocols, it is assumed that devices are pre-loaded with secrets. In the CPS, however, wireless devices are produced by different companies. It is not practical to assume that the devices are pre-loaded with certain secrets when they leave companies. As a consequence, existing symmetric key establishment protocols cannot be directly implemented in the CPS. Motivated by these observations, this paper presents a cross-layer key establishment model for heterogeneous wireless devices in the CPS. Specifically, by implementing our model, wireless devices extract master keys (shared with the system authority) at the physical layer using ambient wireless signals. Then, the system authority distributes secrets for devices (according to an existing symmetric key establishment protocol) by making use of the extracted master keys. Completing these operations, wireless devices can establish secret session keys at higher layers by calling the employed key establishment protocol. Additionally, we prove the security of the proposed model. We analyse the performance of the new model by implementing it and converting existing symmetric key establishment protocols into cross-layer key establishment protocols.

Zhang, Yuexin, Xiang, Yang, Huang, Xinyi.  2016.  Password-Authenticated Group Key Exchange: A Cross-Layer Design. ACM Trans. Internet Technol.. 16:24:1–24:20.
Two-party password-authenticated key exchange (2PAKE) protocols provide a natural mechanism for secret key establishment in distributed applications, and they have been extensively studied in past decades. However, only a few efforts have been made so far to design password-authenticated group key exchange (GPAKE) protocols. In a 2PAKE or GPAKE protocol, it is assumed that short passwords are preshared among users. This assumption, however, would be impractical in certain applications. Motivated by this observation, this article presents a GPAKE protocol without the password sharing assumption. To obtain the passwords, wireless devices, such as smart phones, tablets, and laptops, are used to extract short secrets at the physical layer. Using the extracted secrets, users in our protocol can establish a group key at higher layers with light computation consumptions. Thus, our GPAKE protocol is a cross-layer design. Additionally, our protocol is a compiler, that is, our protocol can transform any provably secure 2PAKE protocol into a GPAKE protocol with only one more round of communications. Besides, the proposed protocol is proved secure in the standard model.