@misc{cryptoeprint:2003:086,
author = {Paulo S. L. M. Barreto and Ben Lynn and Michael Scott},
title = {On the Selection of Pairing-Friendly Groups},
howpublished = {Cryptology ePrint Archive, Report 2003/086},
year = {2003},
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.