@misc{cryptoeprint:2011:303,
author = {Dennis Hofheinz and Victor Shoup},
title = {GNUC: A New Universal Composability Framework},
howpublished = {Cryptology ePrint Archive, Report 2011/303},
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.