Cryptology ePrint Archive: BibTeX Citation of Report 2015/589

@misc{cryptoeprint:2015:589,
    author = {A.-M. Leventi-Peetz and J.-V. Peetz},
    title = {Generating S-Box Multivariate Quadratic Equation Systems And Estimating   Algebraic Attack Resistance Aided By SageMath},
    howpublished = {Cryptology ePrint Archive, Report 2015/589},
    year = {2015},
    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.