ABSTRACT: The Automatic Identification System (AIS) is a maritime situational awareness system, designed as a collision avoidance tool to increase security at sea. Widely accepted, its data is now used for various applications, from maritime traffic predictions to the environmental effects of noise pollution. However, the AIS has been designed without security in mind and does not embed any authentication strategy. Research has shown how this lack of authentication could lead to disastrous consequences. Authentication AIS is thus an active research field, but the constraints imposed by the AIS network require subtle protocol design and careful use of new cryptographic technologies. This work proposes an authentication scheme for the AIS using the advantages of certificateless cryptography. The scheme is backward-compatible with standard AIS versions. We evaluate the performance and security of our proposed scheme through simulations and theoretical analysis. Our results show that our scheme provides strong security guarantees and efficient performance, making it a promising candidate for authenticating AIS signals in practice.