Recent-secure authentication: enforcing revocation in distributed systems

A general method is described for formally specifying and reasoning about distributed systems with any desired degree of immediacy for revoking authentica-tion. To effect revocation, 'authenticating entities' impose freshness constraints on credentials or authenticated statements made by trusted intermediaries. If fresh statements are not presented, then the authentica-tion is questionable. Freshness constraints are derived from initial policy assumptions and authentic statements made by trusted intermediaries. By adjusting freshness constraints, the delay for certain revocation can be arbitrarily bounded. We illustrate how the inclusion of freshness policies within certificates enables the design of a secure and highly available revocation service. We illustrate the application of the method and new techniques in an example.