Secret key generation from static channels with untrusted relays

Mohammadreza Keshavarzi, Hadi Zayyani, Ali Kuhestani +1 more

Hao Wei, Baoyu Zheng, Xiaoyun Hou +1 more

Chan Dai Truyen Thai, Jemin Lee, Cheng Chi +1 more

In this paper, we propose a physical-layer secret key generation scheme for multi-antenna legitimate nodes with the help from multiple untrusted relays with single antenna. The relays' actions conform to the rules but they passively eavesdrop the information. Different from most previous key generation schemes, where a key is generated based on a channel coefficient, in the proposed scheme, we use the linear combination of channel coefficients to generate a key. Simulation results show that the rate leaked to the untrusted relays is low and the secret key rate is therefore high. We also point out that the relay communication can achieve higher secret key rate than the direct communication in several distance ranges.

Chan Dai Truyen Thai, Jemin Lee, Tony Q. S. Quek

In this paper, we propose a physical-layer secret key generation scheme for multiantenna legitimate nodes with the help of multiple untrusted relays, equipped with multiple antennas. The untrusted relays conform to the relaying transmission protocol of legitimate nodes, but they also eavesdrop the confidential information of an legitimate transmitter. The key generation scheme is designed with zero forcing (ZF) and minimum mean square error (MMSE) channel estimators for non-, partially, and fully colluding modes of untrusted relays. Furthermore, we propose a scheme adaptive to channel coherence time. Specifically, to achieve a higher secret key rate (SKR) within the channel coherence time, the number of relay and legitimate nodes' antennas are optimally determined and the most suitable antennas are selected for the key generation. Our results show that the proposed scheme achieves a higher SKR than a prior work, and non- and partially colluding modes provide a higher SKR than the fully colluding mode through the proposed scheme. We also verify that exploiting more antennas of untrusted relays does not always enhance the SKR by showing the existence of the optimal number of antennas of the relays participating in the scheme.

Tijana Radojević

René Guillaume, Stephan Ludwig, Andréas Müller +1 more

The generation of symmetric cryptographic keys based on reciprocal channel properties has evolved as a promising approach in recent years, especially for devices with only little computational power. Different schemes individually addressing constraints from special setups have been proposed, but most schemes generally suffer from bad performance in case of (nearly) static scenarios. Addressing this dilemma, we present a novel approach for physical layer based key generation with two static users supported by a third party. In contrast to other solutions, this approach does not rely on special hardware like multiple antennas and does not let the third party know anything about the secret key, as the helper is potentially not fully trusted. The scheme does not evade to other diversity domains, but still exploits temporal and spatial diversity. We present thorough performance and security analysis, also taking a passive attacker into account.