@misc{cryptoeprint:2011:471,
author = {P. Scholl and N.P. Smart},
title = {Improved Key Generation For Gentry's Fully Homomorphic Encryption Scheme},
howpublished = {Cryptology ePrint Archive, Report 2011/471},
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.