Private handshakes with optional accountability

Nowadays, users are increasingly concerned about individual privacy in cyberspace and Internet. In this paper, we propose the concept of private handshakes with optional accountability, which allows the two users in handshaking to decide real time whether or not to make their interactions accountable. Such optionally accountable private handshaking protocols are a more flexible privacy-preserving authentication primitive than unlink-able secret handshakes and private handshakes. We formulate a formal definition for optionally accountable private handshakes, and propose a concrete scheme based on bilinear pairings.