Concerns for VANET participants will be the reliability and trustworthiness of received messages and the privacy in the use of the VANET to prevent vehicle tracking. To address these concerns, public key certificates have been standardized for VANETS; however, with the use of public key certificates comes additional concerns, especially how to ensure that received certificates are valid. To achieve this aim, timely distribution of certificate revocation lists (CRLs) to VANET participants will be essential. Depending on the policies for the number of pseudonyms carried by vehicles and the triggers for revoking certificates, the size of the CRL may grow very quickly. This paper investigates the parameters that determine the sizes of CRLs in an attempt to quantify the scope of CRL distribution challenges. We also propose adding a "valid after" field to the WAVE Certificate in the IEEE Trial-Use Standard 1609.2 to reduce some of the large CRL sizes we discovered.
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