Optionally Identifiable Private Handshakes

It is now a trend that Internet users are increasingly concerned about individual privacy, and as a result numerous privacy-preserving authentication techniques have been proposed. In this paper, we propose the concept of private handshakes with optional identifiability, which allows the two users in a handshake deciding real time to either proceed their interaction as secret handshake or as private handshake. Such optionally identifiable private handshakes are a more flexible privacy-preserving authentication primitive than secret handshakes and private handshakes. We formulate a formal definition for optionally identifiable private handshakes, as well as a set of security definitions. We then propose a concrete scheme, which is provably secure with respect to the formulated security definitions under the Bilinear Diffie-Hellman (BDH) assumption. We implement a proof-ofconcept prototype of the proposed scheme, on top of the widely used TLS protocol.