Cryptanalysis of a paacp: A portable privacy-preserving authentication and access control protocol in vehicular ad hoc networks

Vehicular ad hoc networks (VANETs) are emerging to improve road safety and traffic management. Privacy and security are very important in VANETs. Existing authentication protocols to secure VANETs raise challenges such as certificate distribution and reduction of the strong reliance on tamper-proof devices. Recently, Yeh et al. proposed a portable privacy-preserving authentication and access control protocol in vehicular ad hoc networks (PAACP). However, PAACP in the authorization phase is breakable and cannot keep privacy in VANETs. In this paper, we present a cryptanalysis of an attachable blind signature and show that the PAACP's Authorized Credential (AC) is not secure and private even the AC secretly stored in a tamper-proof device. Our analysis showed that in PAACP, an eavesdropper can construct the AC from an intercepted blind document. As a result, PAACP in the authorization phase is breakable, and as any outsider can know who has which access privileges to access which service, the user's privacy in VANETs is jeopardized.