@misc{cryptoeprint:2008:155,
author = {David Freeman},
title = {A Generalized Brezing-Weng Algorithm for Constructing Pairing-Friendly Ordinary Abelian Varieties},
howpublished = {Cryptology ePrint Archive, Report 2008/155},
year = {2008},
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.