| Dynamic update of shared control systems |
| This
was a one-year EPSRC funded project that ran from November 2002 to
November 2003, although work related to it has continued beyond that
date. This project essentially looked at the issues surrounding
updating the parameters of a secret sharing scheme after deployment. The project involved:
|
| Research papers |
| S.G.
Barwick, W.-A. Jackson and K.M. Martin, Updating the parameters of a
threshold scheme by minimal broadcast, IEEE Transactions
Information Theory, Vol. 51 (2) (2005) 620—633. Threshold schemes allow secret data to be protected amongst a set of participants in such a way that only a pre-specified threshold of participants can reconstruct the secret from private information (shares) distributed to them on system setup using secure channels. We consider the general problem of designing unconditionally secure threshold schemes whose defining parameters (the threshold and the number of participants) can later be changed by using only public channel broadcast messages. In this paper we are interested in the efficiency of such threshold schemes, and seek to minimise storage costs (size of shares) as well as optimise performance in low bandwidth environments by minimising the size of necessary broadcast messages. We prove a number of lower bounds on the smallest size of broadcast message necessary to make general changes to the parameters of a threshold scheme in which each participant already holds shares of minimal size. We establish the tightness of these bounds by demonstrating optimal schemes. |
| S.G. Barwick, W.-A. Jackson, K.M. Martin and C.M.
O’Keefe, Optimal updating of ideal
threshold schemes, Australasian Journal of
Combinatorics, Vol. 36 (2006) 123-132. We consider the problem of updating the parameters of a threshold scheme using broadcast messages when the dealer knows that some parameter update may be required when the scheme is initially set up, but not the precise parameters of the update. In order to optimise performance in low bandwidth environments we determine the smallest broadcast necessary to update the parameters when each participant holds shares of minimal size. |
| K.M. Martin, Dynamic access policies for
unconditionally secure secret sharing schemes, Proceedings
of IEEE Information Theory Workshop (ITW 05), Awaji Island, Japan
(2005). Secret sharing schemes are cryptographic primitives that can be employed in any situation where it is desirable to distribute information relating to secret data amongst a number of entities. Following a secure initialization process a secret sharing scheme normally has a fixed access policy (specified by an access structure). However in dynamic environments it is likely that access policies will be subject to change: for example entities may wish to join the scheme, entities may be expelled from the scheme or security thresholds may change. Rather than undergo a costly re-initialization process, there have been several different proposals for designing secret sharing schemes that permit dynamic access policies. We will review various existing models and proposals, and identify several open problems. |
| G. Chaddoud and K.M. Martin, Distributed Certificate Authority in cluster-based ad hoc networks, Proceedings of 3rd International Conference on Mobile Computing and Ubiquitous Networking (2006). |
| Presentations |
| Dynamic access policies for
unconditionally secure secret sharing schemes. IEEE Workshop, Awaji Island, Japan (2005). |
| Keith's Electronic Domicile |