@misc{cryptoeprint:2005:116,
author = {Nigel Smart and Frederik Vercauteren},
title = {On Computable Isomorphisms in Efficient Asymmetric Pairing Based Systems},
howpublished = {Cryptology ePrint Archive, Report 2005/116},
year = {2005},
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.