Two open problems related to the complexity of multiplicative LSSSs are considered in this paper.
The first one deals with strongly multiplicative LSSSs. As opposed to the case of multiplicative LSSSs, it is not known whether there is an efficient method to transform an LSSS into a strongly multiplicative LSSS for the same access structure with a polynomial increase of the complexity. We prove a property of strongly multiplicative LSSSs that could be useful in solving this problem. Namely, using a suitable generalization of the well-known Berlekamp-Welch decoder, we show that all strongly multiplicative LSSSs enable efficient reconstruction of a shared secret in the presence of malicious faults.
The second one is to characterize the access structures of ideal multiplicative LSSSs. Specifically, we wonder whether all self-dual vector space access structures are in this situation. By the aforementioned connection, this in fact constitutes an open problem about matroid theory, since it can be re-stated in terms of representability of identically self-dual matroids by self-dual codes. We introduce a new concept, the flat-partition, that provides a useful classification of identically self-dual matroids. Uniform identically self-dual matroids, which are known to be representable by self-dual codes, form one of the classes. We prove that this property also holds for the family of matroids that, in a natural way, is the next class in the above classification: the identically self-dual bipartite matroids.
Category / Keywords: cryptographic protocols / multi-party computation, multiplicative linear secret sharing schemes, identically self-dual matroids, self-dual codes, efficient error correction Publication Info: This is the full version of the paper that appeared in Crypto 2005 Date: received 22 Sep 2004, last revised 26 Jan 2007 Contact author: matcpl at mat upc es Available formats: PDF | BibTeX Citation Note: 23 Sep 2004: Authors' affiliations have been updated. 5 Jan 2007: Publication Info updated. 26 Jan 2007: a new version with major revisions has been uploaded. Version: 20070126:171645 (All versions of this report) Discussion forum: Show discussion | Start new discussion