Cryptology ePrint Archive: BibTeX Citation of Report 2012/686

@misc{cryptoeprint:2012:686,
    author = {Jian Zou and Wenling Wu and Shuang Wu and Le Dong},
    title = {Improved (Pseudo) Preimage Attack and Second Preimage Attack on Round-Reduced Gr{\o}stl},
    howpublished = {Cryptology ePrint Archive, Report 2012/686},
    year = {2012},
    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.