Cryptology ePrint Archive: BibTeX Citation of Report 2011/557

@misc{cryptoeprint:2011:557,
    author = {Chen Cai-Sen, Wang Tao, Chen  Xiao-Cen and Zhou Ping},
    title = {An Improved Trace Driven Instruction Cache Timing Attack on RSA},
    howpublished = {Cryptology ePrint Archive, Report 2011/557},
    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.