Cryptology ePrint Archive: BibTeX Citation of Report 2015/151

@misc{cryptoeprint:2015:151,
    author = {Daniel J. Bernstein and Andreas Hülsing and Tanja Lange and Ruben Niederhagen},
    title = {Bad directions in cryptographic hash functions},
    howpublished = {Cryptology ePrint Archive, Report 2015/151},
    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.