Insider Impersonation Attack on a Tripartite ID-Based Authenticated Key Agreement Protocol with Bilinear Pairings

A key agreement protocol is designed for two or more entities to agree upon a shared secret key, which can subsequently be used to preserve confidentiality and data integrity over an open network. Since Joux has pioneered the notion of pairing-based tripartite key agreement protocol, various group key agreement schemes have been proposed after then. In 2003, Liu et al. proposed a tripartite identity-based authenticated key agreement protocol using bilinear pairings. Although the scheme is claimed to be efficient and secure, we discover that it is in fact breakable. In this paper, we highlight the flaw by demonstrating an insider impersonation attack on the scheme and suggest a few enhancements to conquer the defect.