Security Analysis and Improvement of Certificateless Aggregate Signature Scheme for Vehicular Ad Hoc Networks

In 2018, Wang Daxing and Teng Jikai proposed a certificateless aggregate signature scheme for vehicular ad-hoc networks, and proved that their scheme was existentially unforgeable in the random oracle model. To analyze the security of this scheme, three types of forgery attacks are given: "honest-but-curious" KGC attacks, malicious KGC and RSU coalition attacks, and internal signers' coalition attacks. The analysis results show that the certificateless aggregate signature scheme designed by Wang Daxing and Teng Jikai is insecure against these three types of attacks. To resist these attacks, an improved certificateless aggregate signature scheme is further proposed. The new scheme not only satisfies existential unforgeability under adaptive chosen-message attacks, but also resists effectively coalition attacks.