  Dedicated short range communication (DSRC) relies on secure distribution to
vehicles of a certificate revocation list (CRL) for enabling security
protocols. CRL distribution utilizing vehicle-to-vehicle (V2V) communications
is preferred to an infrastructure-only approach. One approach to V2V CRL
distribution, using rateless coding at the source and forwarding at vehicle
relays is vulnerable to a pollution attack in which a few malicious vehicles
forward incorrect packets which then spread through the network leading to
denial-of-service. This paper develops a new scheme called Precode-and-Hash
that enables efficient packet verification before forwarding thereby preventing
the pollution attack. In contrast to rateless codes, it utilizes a fixed
low-rate precode and random selection of packets from the set of precoded
packets. The fixed precode admits efficient hash verification of all encoded
packets. Specifically, hashes are computed for all precoded packets and sent
securely using signatures. We analyze the performance of the Precode-and-Hash
scheme for a multi-hop line network and provide simulation results for several
schemes in a more realistic vehicular model.
