A Privacy Attack on Coded Caching by Colluding Users

Coded caching is beneficial due to its ability to leverage the multicast property of a wireless channel. Under specific network settings, the coded caching scheme has been shown to reveal the user file requests. In prior work, a privacy attack by a single attacker on coded caching was presented. In this letter, we focus on a relatively secure setting whereby only the intended users access the files. Nevertheless, we show that, even in this setting, privacy is compromised if the users are colluding. The time complexity of the attack on a network with N files, K users, and l <= K colluding users is shown to be in the order of root ln(N(K - l))N(K- l)/2 steps.