Cryptology ePrint Archive: BibTeX Citation of Report 2013/231

@misc{cryptoeprint:2013:231,
    author = {Guido Bertoni and Joan Daemen and Michael Peeters and Gilles Van Assche},
    title = {Sakura: a flexible coding for tree hashing},
    howpublished = {Cryptology ePrint Archive, Report 2013/231},
    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.