Cryptology ePrint Archive: BibTeX Citation of Report 2009/595

@misc{cryptoeprint:2009:595,
    author = {Endre Bangerter and Jan Camenisch and Stephan Krenn},
    title = {Efficiency Limitations for $\Sigma$-Protocols for Group Homomorphisms},
    howpublished = {Cryptology ePrint Archive, Report 2009/595},
    year = {2009},
    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.