Cryptology ePrint Archive: BibTeX Citation of Report 2007/251

@misc{cryptoeprint:2007:251,
    author = {V{\'e}ronique Cortier and  Ralf Kuesters and Bogdan Warinschi},
    title = {A Cryptographic Model for Branching Time Security Properties -- the Case of Contract Signing Protocols},
    howpublished = {Cryptology ePrint Archive, Report 2007/251},
    year = {2007},
    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.