@misc{cryptoeprint:2008:183,
author = {Jean-Philippe Aumasson and Willi Meier and Florian Mendel},
title = {Preimage Attacks on 3-Pass HAVAL and Step-Reduced MD5},
howpublished = {Cryptology ePrint Archive, Report 2008/183},
year = {2008},
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.