@misc{cryptoeprint:2012:565,
author = {Zvika Brakerski and Craig Gentry and Shai Halevi},
title = {Packed Ciphertexts in LWE-based Homomorphic Encryption},
howpublished = {Cryptology ePrint Archive, Report 2012/565},
year = {2012},
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.