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Electonic contract signing

A protocol which allows two or more parties to exchange signed contracts over an email system usually must make use of a "trusted intermediary". The parties send their signed contracts to each other via the intermediary, who forwards them only after he has received all the signatures. The obvious problem with this scheme is that the intermediary creates a significant bottleneck in the case that many contracts need to be exchanged.

In standard protocols, the part played by the intermediary is crucial to protect the parties: for any attempt to exchange contracts off-line without it could result in one party receiving a signed contract without signing it himself.

But there is an ingenious non-standard approach [MOR] which uses randomisation and bypasses the need for any intermediary, allowing the parties to exchange messages directly after all. Security is provided by the use of a "randomised beacon" which ensures that the signed contracts are properly authenticated with probability low enough so that any cheating is almost certain to be discovered.

The aim of this project is to implement Rabin's probabilistic scheme, for two or more signatories and to analyse the security (what is the probability that one of the signatories can cheat successfully?) and efficiency (what is the expected number of messages required to exchange contracts?) both formally and empirically. The implementation part will involve acquiring an elementary knowledge of programming on networks.

On the basis of the analysis, the scheme could be extended to incorporate a facility that increases security at the cost of decreasing efficiency depending on the importance of the contract.

[MOR] M.O.Rabin Transaction Protection by Beacons, Journal of Computer and System Sciences 27, 256-267 (1983)

If you're interested in doing your honours project in this area or a related area, get in touch with Annabelle McIver, in the first instance.

Electronic Voting

A practical electronic voting scheme must guarantee both anonymity (the preference of a voter for a candidate can only be known with some probability proportional to the outcome) and accountability (each voter knows that his vote has been "counted"). This project aims to explore these security and correctness properties and how they might be formalised and analysed with respect to voting schemes.