@misc{cryptoeprint:2009:280,
author = {Giuseppe Ateniese and Paolo Gasti},
title = {Universally Anonymous IBE based on the Quadratic Residuosity Assumption},
howpublished = {Cryptology ePrint Archive, Report 2009/280},
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.