@misc{cryptoeprint:2012:323,
author = {Thore Graepel and Kristin Lauter and Michael Naehrig},
title = {ML Confidential: Machine Learning on Encrypted Data},
howpublished = {Cryptology ePrint Archive, Report 2012/323},
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.