@misc{cryptoeprint:2014:110,
author = {Sourav Das},
title = {Halka: A Lightweight, Software Friendly Block Cipher Using Ultra-lightweight 8-bit S-box},
howpublished = {Cryptology ePrint Archive, Report 2014/110},
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.