@misc{cryptoeprint:2015:306,
author = {Morris Dworkin and Ray Perlner},
title = {Analysis of VAES3 (FF2)},
howpublished = {Cryptology ePrint Archive, Report 2015/306},
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.