Achievable strategies for general secure network coding

This paper considers secure network coding over networks with restricted wiretapping sets and unequal link capacities in the presence of a wiretapper that can wiretap any subset of k links. In particular, we consider networks with point-to-point erasure channels. Existing results for wireline networks show that for the case of both unrestricted wiretapping sets and equal (unit) link capacities, the secrecy capacity is given by the cut-set bound, whether or not the location of the wiretapped links is known, and can be achieved by injecting k random keys at the source which are decoded at the sink along with the message. In contrast, for restricted wiretapping sets and unequal link capacities we show that this global key strategy is suboptimal. In particular, we propose achievable strategies where random keys are canceled at intermediate non-sink nodes, injected at intermediate non-source nodes, or a combination of both strategies is considered.