@misc{cryptoeprint:2011:374,
author = {Ethan Heilman},
title = {Restoring the Differential Resistance of MD6 },
howpublished = {Cryptology ePrint Archive, Report 2011/374},
year = {2011},
note = {\url{http://eprint.iacr.org/}},
}
You will need the url.sty package (comes with most LaTeX installations) for the last line. Otherwise, remove the \url command.