1. Motivation Some previous privacy preserving authentication (PPA) schemes for vehicular ad-hoc network (VANET) are able to secure vehicle-to-vehicle (V2V) communication, and trace a vehicle conditionally. However due to centralized key management center (KMC), few could jump out scope of asymmetric key mechanism, thus corresponding cost is too high to suit broadcasting scenarios especially with high vehicle density. Plus, the tracing can’t reach a single one of many biological drivers of one vehicle. So we consider an improved solution based on two ideas: 1) Decentralizing KMC by giving its duties to tamper-proof device (TPD); 2) Utilizing two-factor authentication (2FA) to integrate biological identifiers of drivers into messages. Overview is shown in Figure 1. The objective is to both authenticate anonymous drivers faster and provide enough evidences to trace any biological anonym driver.