Cooperative Key Agreement for Wireless Networking: Key Rates and Practical Protocol Design

In this paper, we investigate the design of a practical information-theoretically secure secret key agreement protocol for a cooperative wireless network employing standard modulation. Assuming relay selection has been completed, the key agreement problem is studied in a three-node cooperative wireless communication system over block-fading channels. Passive attacks from an eavesdropper collocated with the relay are considered. We derive upper and lower bounds on the secret key rate of this cooperative wireless system. The difference between the bounds is shown to be small for practical communication scenarios, which indicates they are tight. We then propose a practical secret key agreement protocol for this system with both the communicants and the honest relay participating in the public discussion. The tradeoff between security and protocol efficiency is considered in the joint design of advantage distillation, information reconciliation, and privacy amplification. The protocol parameters are optimized to achieve the tight bound on the secret key rate.