@misc{cryptoeprint:2015:065,
author = {Andrey Dmukh and Denis Dygin and Grigory Marshalko},
title = {A lightweight-friendly modifcation of GOST block cipher},
howpublished = {Cryptology ePrint Archive, Report 2015/065},
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.