Cryptology ePrint Archive: BibTeX Citation of Report 2011/138

@misc{cryptoeprint:2011:138,
    author = {Jeongdae Hong and Jung Woo Kim and Jihye Kim and Kunsoo Park and Jung Hee Cheon},
    title = {Constant-Round Privacy Preserving Multiset Union},
    howpublished = {Cryptology ePrint Archive, Report 2011/138},
    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.