@misc{cryptoeprint:2015:943,
author = {Tung Chou},
title = {Sandy2x: New Curve25519 Speed Records},
howpublished = {Cryptology ePrint Archive, Report 2015/943},
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.