@misc{cryptoeprint:2013:692,
author = {Craig Costello and Huseyin Hisil and Benjamin Smith},
title = {Faster Compact Diffie-Hellman: Endomorphisms on the x-line},
howpublished = {Cryptology ePrint Archive, Report 2013/692},
year = {2013},
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.