Security and Privacy for Partial Order Time

Partial order time expresses issues central to many problems in asynchronous distributed systems, but suffers from inherent security and privacy risks. Secure partial order clocks provide a general method to develop application protocols that transparently protect against these risks. Our previous Signed Vector Timestamp protocol provides a partial order time service with some security: no one can forge dependence on an honest process. However, that protocol still permits some forgery of dependence, permits all denial of precedence, and leaks private information. This paper uses secure coprocessors to improve the vector protocol: our new Sealed Vector Timestamp protocol detects both the presence and absence of causal paths even in the presense of malicious processes, and protects against some privacy risks as well. By solving these previously open security problems, our new protocol provides a foundation for incorporating security and privacy into distributed application protocols based on partial order time. c 1994 S.W. Smith and J.D. Tygar This research was sponsored in part by the Advanced Research Projects Agency under contract number F19628-93C-0193, IBM, Motorola, the National Science Foundation under Presidential Young Investigator Grant CCR-8858087, TRW, and the U. S. Postal Service. The first author also received support from an ONR Graduate Fellowship. The views and conclusions in this document are those of the authors and do not necessarily represent the official policies or endorsements of any of the research sponsors. Carnegie Mellon University Computer Science technical report CMU-CS-94-135