@misc{cryptoeprint:2013:233,
author = {Yiyuan Luo and Xuejia Lai},
title = {Attacks on JH, Gr{\o}stl and SMASH Hash Functions},
howpublished = {Cryptology ePrint Archive, Report 2013/233},
year = {2013},
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.