Cryptology ePrint Archive: BibTeX Citation of Report 2003/121

@misc{cryptoeprint:2003:121,
    author = {Michael Backes and Birgit Pfitzmann},
    title = {A Cryptographically Sound Security Proof of the Needham-Schroeder-Lowe Public-Key Protocol},
    howpublished = {Cryptology ePrint Archive, Report 2003/121},
    year = {2003},
    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.