In this paper, we introduce an efficient communication protocol for vehicular ad hoc networks (VANETs) based on conditionally anonymous ring signature scheme to address the issue on anonymous authentication and efficient tracking in case of a dispute. It offers low storage requirements and fast message authentication. In addition, the proposed protocol does not require Road-side Units to aid to authenticate or track. Indeed, the obvious advantage is that our construction does not depend on any fully trusted authority during the tracing phase.