Cryptology ePrint Archive: BibTeX Citation of Report 2012/420

@misc{cryptoeprint:2012:420,
    author = {Denise Demirel and Jeroen van de Graaf},
    title = {A Publicly-Veriable Mix-net with Everlasting Privacy Towards Observers},
    howpublished = {Cryptology ePrint Archive, Report 2012/420},
    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.