@misc{cryptoeprint:2005:248,
author = {Michael Szydlo and Yiqun Lisa Yin},
title = {Collision-Resistant usage of MD5 and SHA-1 via Message Preprocessing},
howpublished = {Cryptology ePrint Archive, Report 2005/248},
year = {2005},
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.