Robust information-theoretic private information retrieval

An information-theoretic private information retrieval (PIR) protocol allows a user to retrieve a data item of its choice from a database replicated amongst several servers, such that each server gains absolutely no information on the identity of the item being retrieved. One problem with this approach is that current systems do not guarantee availability of servers at all times for many reasons, e.g., crash of server or communication problems. In this work we design robust PIR protocols, i.e., protocols which still work correctly even if only some servers are available during the protocol's operation. We present various robust PIR protocols giving different tradeoffs between the different parameters. We first present a generic transformation from regular PIR protocols to robust PIR protocols. We then present two constructions of specific robust PIR protocols. Finally, we construct robust PIR protocols which can tolerate Byzantine servers, i.e., robust PIR protocols which still work in the presence of malicious servers or servers with a corrupted or obsolete database.