Cryptology ePrint Archive: BibTeX Citation of Report 2011/421

@misc{cryptoeprint:2011:421,
    author = {Ivan Damg{\aa}rd and Jakob Funder and  Jesper Buus Nielsen and Louis Salvail},
    title = {Superposition Attacks on Cryptographic Protocols},
    howpublished = {Cryptology ePrint Archive, Report 2011/421},
    year = {2011},
    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.