@misc{cryptoeprint:2008:524,
author = {Li Hongda and Feng dengguo and Li Bao and Xue Haixia},
title = {Round-Optimal Zero-Knowledge Proofs of Knowledge for NP},
howpublished = {Cryptology ePrint Archive, Report 2008/524},
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.