@misc{cryptoeprint:2013:068,
    author = {Allison Lewko and Brent Waters},
    title = {Why Proving HIBE Systems Secure is Difficult},
    howpublished = {Cryptology ePrint Archive, Report 2013/068},
    year = {2013},
    url = {http://eprint.iacr.org/2013/068},
}