@misc{cryptoeprint:2014:526,
author = {Daniel J. Bernstein and Chitchanok Chuengsatiansup and Tanja Lange},
title = {Curve41417: Karatsuba revisited},
howpublished = {Cryptology ePrint Archive, Report 2014/526},
year = {2014},
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.