Obfuscation Padding Schemes that Minimize Rényi Min-Entropy for Privacy

Cezara Petrui, Carlos Antonio Pinzón, Catuscia Palamidessi

Abstract:

Consider a set of users, each of which is choosing and downloading one
file out of a central pool of public files, and an attacker that observes the
download size for each user to identify the choice of each user. This paper
studies the problem of padding the files to obfuscate the exact file sizes
and minimize the expected accuracy of the attacker, without exceeding
some given padding constraints. We derive the algorithm that finds the
optimal padding scheme, prove its correctness, and compare it with an
existing solution that uses a similar but different attack model. We also
discuss how the two solutions are related in terms of private information
leakage.