Cryptology ePrint Archive: BibTeX Citation of Report 2013/656

@misc{cryptoeprint:2013:656,
    author = {Robbert van den Berg and Boris Skoric and Vincent van der Leest},
    title = {Bias-based modeling and entropy analysis of PUFs},
    howpublished = {Cryptology ePrint Archive, Report 2013/656},
    year = {2013},
    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.