Cryptology ePrint Archive: BibTeX Citation of Report 2013/138

@misc{cryptoeprint:2013:138,
    author = {Zhang Wei, Liu Shuguang, Yang Xiaoyuan},
    title = {Multi-bit homomorphic encryption based on  learning with errors over rings},
    howpublished = {Cryptology ePrint Archive, Report 2013/138},
    year = {2013},
    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.