@misc{cryptoeprint:2015:781,
author = {Daniel J. Bernstein and Chitchanok Chuengsatiansup and David Kohel and Tanja Lange},
title = {Twisted Hessian curves},
howpublished = {Cryptology ePrint Archive, Report 2015/781},
year = {2015},
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.