Cryptology ePrint Archive: BibTeX Citation of Report 2004/156

@misc{cryptoeprint:2004:156,
    author = {Kenneth G. Paterson and Fred Piper and Ruediger Schack},
    title = {Quantum cryptography: a practical information security perspective},
    howpublished = {Cryptology ePrint Archive, Report 2004/156},
    year = {2004},
    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.