Posets and protocols - picking the right three-party protocol.

In this paper we introduce a framework in which we can investigate the
possibility of adapting a security protocol in order to obtain optimal
efficiency according to the communication channels available. This
method is based on the observation that there is a partial order
imposed upon the actions of the various parties involved in a
protocol. We define operations permitted on the partially ordered set
associated with the protocol and obtain transformations of the
original protocol while preserving the security properties.
Performing these operations on the protocol we enumerate the options
available to a system.