Cryptology ePrint Archive: BibTeX Citation of Report 2011/648

@misc{cryptoeprint:2011:648,
    author = {Tatsuaki Okamoto and Katsuyuki Takashima},
    title = {Achieving Short Ciphertexts or Short Secret-Keys for Adaptively Secure General Inner-Product Encryption},
    howpublished = {Cryptology ePrint Archive, Report 2011/648},
    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.