@misc{cryptoeprint:2010:457,
author = {Thomaz Oliveira and Julio López},
title = {Improving the performance of Luffa Hash Algorithm},
howpublished = {Cryptology ePrint Archive, Report 2010/457},
year = {2010},
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.