Cryptology ePrint Archive: BibTeX Citation of Report 2015/150

@misc{cryptoeprint:2015:150,
    author = {Tobias Pulls and Roel Peeters},
    title = {Insynd: Privacy-Preserving Transparency Logging Using Balloons},
    howpublished = {Cryptology ePrint Archive, Report 2015/150},
    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.