@misc{cryptoeprint:2009:073,
author = {GU Chun-Xiang, Guang Yan, ZHU Yue-Fei},
title = {Automatic Approach of Provable Security and its Application for OAEP+},
howpublished = {Cryptology ePrint Archive, Report 2009/073},
year = {2009},
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.