Cryptology ePrint Archive: BibTeX Citation of Report 2015/471

@misc{cryptoeprint:2015:471,
    author = {Yansong Gao, Damith C. Ranasinghe, Gefei Li, Said F. Al-Sarawi, Omid Kavehei, and Derek Abbott},
    title = {A Challenge Obfuscation Method for Thwarting Model Building Attacks on PUFs},
    howpublished = {Cryptology ePrint Archive, Report 2015/471},
    year = {2015},
    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.