@misc{cryptoeprint:2015:220,
author = {Dan Boneh and Kevin Lewi and Hart Montgomery and Ananth Raghunathan},
title = {Key Homomorphic PRFs and Their Applications},
howpublished = {Cryptology ePrint Archive, Report 2015/220},
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.