Cryptology ePrint Archive: BibTeX Citation of Report 2009/189

@misc{cryptoeprint:2009:189,
    author = {Sherman S.M. Chow and Jian Weng and Yanjiang Yang and Robert H. Deng},
    title = {Efficient Unidirectional Proxy Re-Encryption},
    howpublished = {Cryptology ePrint Archive, Report 2009/189},
    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.