Mitigation of insider and outsider DoS attack against signature based authentication in VANETs

Authentication is an essential framework for safe and secure communication of messages in VANETs. For authenticating messages the IEEE 1609.2 standard uses ECDSA as the standard digital signature algorithm. But the verification time for an ECDSA signature is very high. As a result an inside or an outside attacker could use a fraction of bandwidth and flood the network with invalid signatures resulting in Denial of Service (DoS) attack. Thus in this work a two phase scheme is proposed to mitigate inside and outside DoS attackers in VANETs. In the first phase HMAC signatures computed from private and public key pair are used for authenticating the communicating entity. As only authentic users can compute the HMAC signature, DoS attack due to outside attackers is mitigated. If the entity is authentic and subjects other vehicle to DoS attack, the second phase is designed to detect the insider attackers. In this phase based on the number of invalid signatures flooded by the attacker, it is compared against a threshold value to identify the inside attacker. Hence DoS attack is mitigated due to inside as well as outside attackers. Experimental results show that the proposed scheme not only alleviates DoS attack but also performs better with negligible computational overhead.