@misc{cryptoeprint:2002:052,
author = {Stefan Lucks},
title = {A Variant of the Cramer-Shoup Cryptosystem for Groups with Unknwon Order},
howpublished = {Cryptology ePrint Archive, Report 2002/052},
year = {2002},
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.