Secure Public Key Regime (SPKR) in vehicular networks

Public Key Regime (PKR) was proposed as an alternative to certificate based PKI in securing Vehicular Networks (VNs). It eliminates the need for vehicles to append their certificate for verification because the Road Side Units (RSUs) serve as Delegated Trusted Authorities (DTAs) to issue up-to-date public keys to vehicles for communications. If a vehicle's private/public key needs to be revoked, the root TA performs real time updates and disseminates the changes to these RSUs in the network. Therefore, PKR does not need to maintain a huge Certificate Revocation List (CRL), avoids complex certificate verification process and minimizes the high latency. However, the PKR scheme is vulnerable to Denial of Service (DoS) and collusion attacks. In this paper, we study these attacks and propose a pre-authentication mechanism to secure the PKR scheme. Our new scheme is called the Secure Public Key Regime (SPKR). It is based on the Schnorr signature scheme that requires vehicles to expend some amount of CPU resources before RSUs issue the requested public keys to them. This helps to alleviate the risk of DoS attacks. Furthermore, our scheme is secure against collusion attacks. Through numerical analysis, we show that SPKR has a lower authentication delay compared with the Elliptic Curve Digital Signature (ECDSA) scheme and other ECDSA based counterparts.

I. Introduction

Public key cryptography is used to secure communications in Vehicular Networks (VNs). It guarantees message authentication, integrity and non-repudiation with digital signatures. The private key is used to generate a digital signature whereas the public key is used for verifying the digital signature. If the hash value of the message matches the hash value of the received signature after decryption, it proves that the message is not altered (integrity property) and that the message was created by a known sender such that the sender cannot deny having send the message (authentication and nonrepudiation property). However, since the public keys are published publicly, it has the problem ascertaining if a public key truly belongs to the purported owner. An attacker can create a private/public key pair and then announces it to the entire network that the public key he publishes belongs to another user, for example, Bob. Therefore, when other nodes sends confidential messages encrypted using Bob's public key, the attacker decrypts and reads the message instead. To solve this issue related to the ownership of public key, Public Key Infrastructure (PKI) is used. In North America, the IEEE Wireless Access in Vehicular Environments (WAVE) standard [1] describes the IEEE standard 1609.2 [2] that specifies that a PKI to be employed to secure WAVE messages. In Europe, European Telecommunications Standards Institutes group for Intelligent Transport Systems (ETSI ITS G5) establishes the ETSI TS 102 940 standard [3] that mandates the use of a PKI for secure communication.