Physical Layer Secure Information Exchange Protocol for MIMO Ad hoc Networks Against Passive Attacks

In this paper, we propose a secure transmission protocol for two users exchanging their respective information in an n-hop MIMO Ad hoc network. By exploiting the properties of the transmission medium in the physical layer, three channel models are utilized to provide secure transmission, namely one-way relay channel, two-way untrusted relay channel, and multiple access channel. Using these channel models, we design a basic protocol with a minimized time slot cost, i.e. n + 1. Based on this basic protocol, we show that the attacker, either untrusted relay or external eavesdropper, can only obtain a summed signal in each time slot, and this summed signal cannot be decomposed to recover the individual information from the users. We then present cryptographic analysis for the first time to identify a weakness which is common for all known security schemes based on the summed signal. Thirdly, we introduce an evolutionary protocol proposed with two rounds of interlaced information exchange, which defeats this weakness. Finally, the simulation is performed to demonstrate the theoretical analysis.