Cryptology ePrint Archive: BibTeX Citation of Report 2010/155

@misc{cryptoeprint:2010:155,
    author = {Zhang MeiLing and Liu JingMei and Wang XinMei},
    title = {the upper bounds on differntial characteristics in block cipher SMS4},
    howpublished = {Cryptology ePrint Archive, Report 2010/155},
    year = {2010},
    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.