@misc{cryptoeprint:2004:165,
author = {D. Page and N.P. Smart and F. Vercauteren},
title = {A comparison of MNT curves and supersingular curves},
howpublished = {Cryptology ePrint Archive, Report 2004/165},
year = {2004},
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.