Coded Caching for Wiretap Broadcast Channels

The paper studies the wiretap erasure broadcast channel (BC) with an external eavesdropper when the legitimate receivers have cache memories. Various secure coding schemes are proposed for a scenario where K-w weak receivers have same erasure probabilities and K-s strong receivers have same erasure probabilities. The coding schemes achieve the cache-aided secrecy capacity when only weak receivers have cache memories and this cache memory is either small or large. They also allow to conclude the following: 1) Under a total cache budget it is often beneficial to assign the cache memories unequally between strong and weak receivers. 2.) Joint cache-channel coding is necessary to attain the optimal performance. 3.) The secrecy capacity can be positive even when the eavesdropper is stronger than the legitimate receivers.