@misc{cryptoeprint:2004:299,
author = {Zhengjun Cao and Sherman S.M. Chow},
title = {Security Flaws in a Pairing-based Group Signature Scheme},
howpublished = {Cryptology ePrint Archive, Report 2004/299},
year = {2004},
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.