@misc{cryptoeprint:2011:647,
    author = {Fanbao Liu and Tao Xie and Changxiang Shen},
    title = {Breaking $H^2$-MAC Using Birthday Paradox},
    howpublished = {Cryptology ePrint Archive, Report 2011/647},
    year = {2011},
    url = {http://eprint.iacr.org/2011/647},
}