Acknowledgements

We would like to thank the anonymous reviewers for their comments and in particular their pointers to the ``blackhat'' literature. Our shepherd, David Wagner, similarly provided input that was very helpful. We would like to thank Geoffrey Voelker, Anand Balachandran, and Daniel Faria for providing feedback on earlier drafts of this paper. Finally, a special thanks goes to the residents of csl-south at UCSD, who were at times unwitting victims of this research. This work was funded by DARPA Grant N66001-01-1-8933 and NIST Grant 60NANB1D0118.