@misc{cryptoeprint:2013:669,
author = {Dan Boneh and Valeria Nikolaenko and Gil Segev},
title = {Attribute-Based Encryption for Arithmetic Circuits},
howpublished = {Cryptology ePrint Archive, Report 2013/669},
year = {2013},
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.