@misc{cryptoeprint:2004:302,
author = {Lifeng Guo},
title = {Security of Wang-Li Threshold Signature Scheme },
howpublished = {Cryptology ePrint Archive, Report 2004/302},
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.