Software Engineering

Access control and privacy policy relations tend to
focus on decision outcomes and are very sensitive to defined
terms and state. Small changes or updates to a policy language
or vocabulary may make two similar policies incomparable. To
address this we develop two flexible policy relations derived from
bisimulation in process calculi. Strong licensing compares the
outcome of two policies strictly, similar to strong bisimulation.
Weak licensing compares the outcome of policies more flexibly
by ignoring irrelevant (non-conflicting) differences between outcomes,
similar to weak bisimulation. We illustrate the relations
using examples from P3P.

Access control and privacy policy relations tend to focus on decision outcomes and are very sensitive
to defined terms and state. Small changes or updates to a policy language or vocabulary may make
two similar policies incomparable. To address this we develop two flexible policy relations derived from
bisimulation in process calculi. Strong licensing compares the outcome of two policies strictly, similar to
strong bisimulation. Weak licensing compares the outcome of policies more flexibly by ignoring irrelevant
(non-conflicting) differences between outcomes, similar to weak bisimulation. We illustrate the relations
using examples from P3P and EPAL.

Web services offer an opportunity to redesign a variety of older systems to exploit the advantages of a flexible, extensible, secure set of standards. In this work we revisit WSEmail, a system proposed over ten years ago to improve email by redesigning it as a family of web services. WSEmail offers an alternative vision of how instant messaging and email services could have evolved, offering security, extensi-bility, and openness in a distributed environment instead of the hardened walled gardens that today's rich messaging systems have become. WSEmail's architecture , especially its automatic plug-in download feature allows for rich extensions without changing the base protocol or libraries. We demonstrate WSEmail's flexibility using three business use cases: secure channel instant messaging, business workflows with routed forms, and on-demand attachments. Since increased flexibility often mitigates against security and performance, we designed WSEmail with security in mind and formally proved the security of one of its core protocols (on-demand attachments) using the TulaFale and ProVerif automated proof tools. We provide performance measurements for WSEmail functions in a prototype we implemented using .NET. Our experiments show a latency of about a quarter of a second per transaction under load.