@misc{cryptoeprint:2004:324,
author = {G. Laccetti and G. Schmid},
title = {On a Probabilistic Approach to the Security Analysis of Cryptographic Hash Functions},
howpublished = {Cryptology ePrint Archive, Report 2004/324},
year = {2004},
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.