Strong Secrecy Capacity of a Class of Wiretap Networks

Abstract: This paper considers a special class of wiretap networks with a single source node and K sink nodes. The source message is encoded into a binary digital sequence of length N, divided into K subsequences, and sent to the K sink nodes respectively through noiseless channels. The legitimate receivers are able to obtain subsequences from arbitrary μ1 = Kα1 sink nodes. Meanwhile, there exist eavesdroppers who are able to observe subsequences from arbitrary μ2 = Kα2 sink nodes, where 0 ≤ α2 < α1 ≤ 1. The goal is to let the receivers be able to recover the source message with a vanishing decoding error probability, and keep the eavesdroppers ignorant about the source message. It is clear that the communication model is an extension of wiretap channel II. Secrecy capacity with respect to the strong secrecy criterion is established. In the proof of the direct part, a codebook is generated by a randomized scheme and partitioned by Csiszár’s almost independent coloring scheme. Unlike the linear network coding schemes, our coding scheme is working on the binary field and hence independent of the scale of the network.