Coding Strategies for the Wiretap Channel and for Secure Network Coding

Meeting Time: Nov. 30, 2009, 2:00-2:50pm

Abstract: In this talk we consider two related aspects of information theoretic secrecy which recently have gained some attention in the community: First, we consider transmission over Wyner's wiretap channel where both the main and the wiretapper's channel are binary erasure channels. We show that the recently proposed class of polar codes asymptotically can achieve capacity on a degraded version of this channel, and for finite blocklength compare these codes with a new construction based on bilayer LDPC codes. In the second part we then consider secure network coding over networks with link erasures and unequal link capacities in the presence of a wiretapper that can wiretap any subset of k links. In contrast to the case with equal link capacities, we show that for unequal link capacities, the secrecy capacity is not the same in general when the location of the wiretapped links is known or unknown. An example is given to show that when the location of the wiretapped links is unknown the cut-set bound is not achievable. We give achievable strategies where random keys are canceled at intermediate non-sink nodes or injected at intermediate non-source nodes.