@misc{cryptoeprint:2007:373,
author = {Markku-Juhani O. Saarinen},
title = {A Meet-in-the-Middle Collision Attack Against the New FORK-256},
howpublished = {Cryptology ePrint Archive, Report 2007/373},
year = {2007},
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.