We thank our shepherd Peter Honeyman for his comments and help while revising the paper. We thank Sameer Ajmani, Dan Boneh, Thomer Gil, Eu-Jin Goh, Dave Mazières, Chris Laas, Ethan Miller, Raj Rajagopalan, and Emil Sit for their helpful comments. We also thank Jeff Schiller, Garry Zacheiss, and Nickolai Zeldovich for producing logs of revocations on MIT's AFS protection servers.