Avoiding Theoretical Optimality to Efficiently and Privately Retrieve Security Updates

This work demonstrates the feasibility of building a PIR system with performance similar to non-PIR systems in real situations. Prior Chor PIR systems have chosen block sizes that are theoretically optimized to minimize communication. This (ironically) reduces the throughput of the resulting system by roughly 50x. We constructed a Chor PIR system called upPIR that is efficient by choosing block sizes that are theoretically suboptimal (from a communications standpoint), but fast and efficient in practice. For example, an upPIR mirror running on a threeyear-old desktop provides security updates from Ubuntu 10.04 (1.4 GB of data) fast enough to saturate a T3 link. Measurements run using mirrors distributed around the Internet demonstrate that a client can download software updates with upPIR about as quickly as with FTP.