Cryptology ePrint Archive: BibTeX Citation of Report 2011/480

@misc{cryptoeprint:2011:480,
    author = {Sanjay Bhattacherjee and Palash Sarkar},
    title = {Complete Tree Subset Difference Broadcast Encryption Scheme and its Analysis},
    howpublished = {Cryptology ePrint Archive, Report 2011/480},
    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.