Vehicular Ad-hoc NETworks (VANETs) have become an attractive research field following the development of wireless communication technologies. They can be used to enhance driver's safety and comfort by offering a vehicular communication system. VANETs are typically composed of On-Board Units (OBUs), Road Side Units (RSUs) and a Trusted Authority (TA). In VANETs, each vehicle (i.e., OBU) has to broadcast a safety message every 100 - 300 ms to nearby vehicles and RSUs to share information such as traffic data (speed, acceleration, and deceleration), GPS (Global Positioning System) data, and accident notification. The mobility and self-organization of network construction are also main features of VANETs. However, the flexible wireless environment and periodical broadcast messages of VANETs can be threatened by an adversary because various attacks such as malicious data injection attacks, data replay attacks, and location tracking can be launched. To thwart these attacks, many communication protocols ensuring security and privacy have been introduced. In this thesis, the existing protocols are analyzed and novel anonymous authentication protocols for VANETs are proposed. Specifically, three components are designed and evaluated as follows.
• An anonymous roaming protocol which can be used among heterogeneous networks is proposed. Security of the proposed protocol was proved in a CK model, which is a security model for key exchange protocols
• An anonymous message authentication for vehicular communications is proposed. The performance of the proposed protocol was evaluated using a network simulator and a cryptographic library.
• A key management architecture for efficient revocation is proposed. The proposed architecture distributes not revocation lists but a group key to un-revoked vehicles. Thus, the vehicles do not need to consider management of revocation lists.