@misc{cryptoeprint:2009:385,
author = {Brent Waters},
title = {Dual System Encryption: Realizing Fully Secure IBE and HIBE under Simple Assumptions},
howpublished = {Cryptology ePrint Archive, Report 2009/385},
year = {2009},
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.