@misc{cryptoeprint:2010:020,
author = {Rongquan Feng, Hongfeng Wu},
title = {Number of Jacobi quartic curves over finite fields},
howpublished = {Cryptology ePrint Archive, Report 2010/020},
year = {2010},
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.