A Distance-Sensitive Attribute Based Cryptosystem for Privacy-Preserving Querying

We propose an attribute-based cryptosystem in which decryption is conditional on the distance between attributes. Alice constructs a cipher text that consists of an encrypted message and a hidden attribute vector. Bob is able to decrypt Alice´s message if and only if his attribute vector is within a specified maximum distance from Alice´s attribute vector. We provide constructions for Euclidean and Hamming distances. The cryptosystem has advantages for privacy preserving querying. In particular, all parties can broadcast their respective cipher texts or store them on a database server. Then, a client -- not necessarily belonging to the original set of parties -- can independently and privately query the database server for cipher texts whose attributes are within some small distance from its own attribute. We describe an application of this cryptosystem in which a customer obtains recommendations from other customers of a movie rental company in a privacy-preserving manner.