Cryptology ePrint Archive: BibTeX Citation of Report 2005/200

@misc{cryptoeprint:2005:200,
    author = {Johannes Buchmann and Andrei Pychkine and Ralf-Philipp Weinmann},
    title = {Block ciphers sensitive to Groebner Basis Attacks },
    howpublished = {Cryptology ePrint Archive, Report 2005/200},
    year = {2005},
    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.