Cryptology ePrint Archive: BibTeX Citation of Report 2011/208

@misc{cryptoeprint:2011:208,
    author = {Jian Weng and Yunlei Zhao},
    title = {Direct Constructions of Bidirectional  Proxy Re-Encryption with Alleviated Trust in Proxy},
    howpublished = {Cryptology ePrint Archive, Report 2011/208},
    year = {2011},
    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.