Cryptology ePrint Archive: BibTeX Citation of Report 2007/167

@misc{cryptoeprint:2007:167,
    author = {Yi-Ru Liu, Wen-Guey Tzeng},
    title = {Public Key Broadcast Encryption with Low Number of Keys and Constant Decryption Time (Version 2)},
    howpublished = {Cryptology ePrint Archive, Report 2007/167},
    year = {2007},
    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.