  One of the biggest problems of vehicular ad-hoc networks is revocation. The
efficient management of such issue has become one of the major paradigms in
this area of research. A solution proposed here is based on the use of
authenticated data structures like revocation trees to replace the classical
and inefficient certificate revocation lists. In particular, the idea of this
paper is to propose the use of k-ary hash trees, Huffman coding and a duplex
version of the SHA-3 hash function, to optimize insertions and searches in the
revocation structure. Thus, the inclusion of a new certificate revoked in the
tree, only implies a new iteration of the duplex construction of the hash
function, avoiding recalculating the entire hashes and the entire tree.
Furthermore, a k-ary Huffman tree is used to insert leaf nodes at different
levels so that those revoked nodes that are more queried, are located closer to
the root node position, so the revocation proof is smaller for those vehicles
that spend more time on the roads. This paper details a method to calculate the
optimum value $k$ for the k-ary tree in order to optimize the revocation proof
size. Therefore, the proposal described here improves both the insertion of new
revoked certificates in the revocation structure and the search of revoked
certificates in the revocation structure. This paper is part of a work in
progress, so that we plan to implement the scheme in real scenarios to get
ideal values of the parameters and comparisons with other schemes.
