@misc{cryptoeprint:2009:592,
author = {Ivan Damgård and Martin Geisler and Jesper Buus Nielsen},
title = {From Passive to Covert Security at Low Cost},
howpublished = {Cryptology ePrint Archive, Report 2009/592},
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.