@misc{cryptoeprint:2003:200,
author = {Zheng Dong , Shengli Liu & kefei Chen},
title = {Cryptanalysis of B.Lee-S.Kim-K.Kim Proxy Signature},
howpublished = {Cryptology ePrint Archive, Report 2003/200},
year = {2003},
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.