Cryptology ePrint Archive: BibTeX Citation of Report 2012/248

@misc{cryptoeprint:2012:248,
    author = {Ghassan O. Karame and Elli Androulaki and Srdjan Capkun},
    title = {Two Bitcoins at the Price of One? Double-Spending Attacks on Fast Payments in Bitcoin},
    howpublished = {Cryptology ePrint Archive, Report 2012/248},
    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.