@misc{cryptoeprint:2011:490,
author = {Allison Lewko},
title = {Tools for Simulating Features of Composite Order Bilinear Groups in the Prime Order Setting},
howpublished = {Cryptology ePrint Archive, Report 2011/490},
year = {2011},
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.