On the Secrecy Capacity of 3-Receiver Broadcast Channel With Causal States and Conferencing

We investigate the secrecy capacity region of 2-receiver, 1-eavesdropper Broadcast Channel (BC) with two causal states and conferencing decoders. The encoder sends two messages, one of them for both legitimate receivers and the other one for the first legitimate receiver. It keeps these messages secret from the eavesdropper. Each state is causally available at the corresponding receiver, while both states are known causally at the encoder. Each receiver wishes to send the state which is not available at the other receiver, through a noiseless link with limited capacity. We find an inner bound on the secrecy capacity region of this channel. The achievability scheme employs block Markov coding and Shannon strategy for channels with state. In each block, we make use of the states to generate two keys which will be used in the next block. The idea is to utilize the cooperation of both receivers to recover both keys at each receiver while ensuring secrecy. We also establish an outer bound on the secrecy capacity region of the 2-rec., 1-eav. BC with Causal Channel State Information (CCSI) and conferencing. We prove that the proposed bounds coincide for a special case.