@misc{cryptoeprint:2012:167,
author = {Sorina Ionica},
title = {Pairing-based methods for genus 2 jacobians with maximal endomorphism ring},
howpublished = {Cryptology ePrint Archive, Report 2012/167},
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.