@misc{cryptoeprint:2008:253,
author = {Yiliang Han, Xiaolin Gui, Xu'an Wang},
title = {Multi-Recipient Signcryption for Secure Wireless Group Communication},
howpublished = {Cryptology ePrint Archive, Report 2008/253},
year = {2008},
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.