The broadcast nature of wireless communication makes it inherently vulnerable to eavesdropping by an adversary. However, the destination and eavesdropper can have different ‘views’ of the transmission through distinct channels. We have examined how to exploit this distinction along with relay (helper) nodes to ensure information-theoretic (unconditional) secrecy. We have demonstrated that cooperative network secrecy can be achieved for arbitrary wireless relay networks by utilizing the signal interactions to carry secure information forward cooperatively. We have shown an achievable trade-off between the reliable transmission rate from the source to the legitimate destination and the amount of information leaked to a class of eavesdroppers over an arbitrary wireless relay network. Roughly speaking, the trade-off is related to the information-theoretic min-cuts between the source-destination and source-eavesdropper pairs. For example, one extreme point of the trade-off is where we can ensure perfect secrecy (zero rate of information leakage to the eavesdropper) for an information rate of (approximately) the `difference’ between these two min-cut values. However, this ‘separable’ scheme where the relay network is operated as before, but the secrecy is induced end-to-end is not necessarily the best scheme. We have shown that one can use ‘friendly’ jamming by inserting junk/noise messages into the network by helpful relays can significantly improve the secrecy rate. This has been shown also for arbitrary noisy networks. A short summary of these results can be found here.
In wireless sensor networks, nodes observe correlated physical processes. We have examined how to generate information-theoretic secure keys using access to these correlated processes in combination with the broadcast channel. In particular, we have shown that functionally the two sources of secrecy are additive, though operationally we need to intricately code them jointly in order to generate secrecy. We have also characterized the secrecy rate when an additionally public discussion channel is available, and one can interactively generate the secret key.