@misc{cryptoeprint:2011:680,
author = {Craig Gentry and Shai Halevi and Nigel P. Smart},
title = {Better Bootstrapping in Fully Homomorphic Encryption},
howpublished = {Cryptology ePrint Archive, Report 2011/680},
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.