@misc{cryptoeprint:2015:417,
author = {Mark Bun and Mark Zhandry},
title = {Order-Revealing Encryption and the Hardness of Private Learning},
howpublished = {Cryptology ePrint Archive, Report 2015/417},
year = {2015},
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.