Extended private information retrieval and its application in biometrics authentications

In this paper we generalize the concept of Private Information Retrieval (PIR) by formalizing a new cryptographic primitive, named Extended Private Information Retrieval (EPIR). Instead of enabling a user to retrieve a bit (or a block) from a database as in the case of PIR, an EPIR protocol enables a user to evaluate a function f which takes a string chosen by the user and a block from the database as input. Like PIR, EPIR can also be considered as a special case of the secure two-party computation problem (and more specifically the oblivious function evaluation problem). We propose two EPIR protocols, one for testing equality and the other for computing Hamming distance. As an important application, we show how to construct strong privacy-preserving biometric-based authentication schemes by employing these EPIR protocols.