Cryptology ePrint Archive: BibTeX Citation of Report 2011/554

@misc{cryptoeprint:2011:554,
    author = {Yu-Chi Chen and Gwoboa Horng},
    title = {On the security models for certificateless signature schemes  achieving level 3 security},
    howpublished = {Cryptology ePrint Archive, Report 2011/554},
    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.