Pervasive computing leads to an increased integration between the real world and the computational world, and many applications in pervasive computing adapt to the user's context, such as the location of the user, to meet a user's continuously changing requirements. We consider a class of applications that wish to consider a user's context when deciding whether to authorize a user's access to physical or information resources.

Existing context-sensitive authorization systems have a central server that collects context information, and evaluates policies to make authorization decisions on behalf of a resource owner. A centralized solution assumes that all resource owners trust the server to make correct decisions, and all users trust the server not to disclose private context information. In many realistic applications of pervasive computing, however, the resources, users, and sources of context information are inherently distributed among many organizations that do not necessarily trust each other.

In this talk, we present a secure distributed proof system for context-sensitive authorization. Our system enables multiple hosts to evaluate an authorization query in a peer-to-peer way, while preserving the confidentiality and integrity policies of mutually untrusted principals running those hosts. We also develop a novel caching and revocation mechanism to support policies that refer to dynamic context information in different administrative domains. Our experimental results show that the amortized performance of our system scales to a large proof that spans across dozens of servers.

--- An Institute for Security Technology Studies project at Dartmouth College.  This project is supported by Award number 2000-DT-CX-K001 from the U.S. Department of Homeland Security and by Grant number 2005-DD-BX-1091 awarded by the Bureau of Justice Assistance. Points of view in this presentation are those of the author and do not necessarily represent the official position of the U.S. Department of Homeland Security or the U.S. Department of Justice.---