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.