@misc{cryptoeprint:2008:410,
author = {Xu an Wang and Xiaoyuan Yang and Fagen Li},
title = {On the Role of PKG for Proxy Re-encryption in Identity Based Setting},
howpublished = {Cryptology ePrint Archive, Report 2008/410},
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.