University of Waterloo
In this paper, the authors extend Goldberg's multi-server information-theoretic Private Information Retrieval (PIR) with a suite of protocols for privacy preserving e-commerce. Their first protocol adds support for single payee tiered pricing, wherein users purchase database records without revealing the indices or prices of those records. Tiered pricing lets the seller set prices based on each user's status within the system; e.g., non-members may pay full price while members may receive a discounted rate. They then extend tiered pricing to support group-based access control lists with record-level granularity; this allows the servers to set access rights based on users' price tiers.