@misc{cryptoeprint:2009:448,
author = {Ning Ding and Dawu Gu and Bart Preneel},
title = {Precise Bounded-Concurrent Zero-Knowledge in Almost Constant Rounds},
howpublished = {Cryptology ePrint Archive, Report 2009/448},
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.