@misc{cryptoeprint:2008:254,
author = {Zhenchao ZHU and Yuqing ZHANG and FengjiaoWANG},
title = {An Efficient Identity-based Ring Signcryption Scheme},
howpublished = {Cryptology ePrint Archive, Report 2008/254},
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.