A Flexible Framework for Secret Handshakes

In the society increasingly concerned with the erosion of privacy, privacy-preserving techniques are becoming very important. This motivates research in cryptographic techniques offering built-in privacy. A secret handshake is a protocol whereby participants establish a secure, anonymous and unobservable communication channel only if they are members of the same group. This type of “private” authentication is a valuable tool in the arsenal of privacy-preserving cryptographic techniques. Prior research focused on 2-party secret handshakes with onetime credentials. This paper breaks new ground on two accounts: (1) it shows how to obtain secure and efficient secret handshakes with reusable credentials, and (2) it represents the first treatment of group (or multi-party) secret handshakes, thus providing a natural extension to the secret handshake technology. An interesting new issue encountered in multi-party secret handshakes is the need to ensure that all parties are indeed distinct. (This is a real challenge since the parties cannot expose their identities.) We tackle this and other challenging issues in constructing GCD – a flexible framework for secret handshakes. The proposed GCD framework lends itself to many practical instantiations and offers several novel and appealing features such as self-distinction and strong anonymity with reusable credentials. In addition to describing the motivation and stepby-step construction of the framework, this paper provides a thorough security analysis and illustrates two concrete framework instantiations.