@misc{cryptoeprint:2012:670,
author = {Joppe W. Bos and Craig Costello and Huseyin Hisil and Kristin Lauter},
title = {Fast Cryptography in Genus 2},
howpublished = {Cryptology ePrint Archive, Report 2012/670},
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.