Cryptology ePrint Archive: BibTeX Citation of Report 2012/223

@misc{cryptoeprint:2012:223,
    author = {Enrico Thomae},
    title = {A Generalization of the Rainbow Band Separation Attack and its Applications to Multivariate Schemes},
    howpublished = {Cryptology ePrint Archive, Report 2012/223},
    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.