@misc{cryptoeprint:2015:906,
author = {Adnan Baysal and Suhap Sahin},
title = {RoadRunneR: A Small And Fast Bitslice Block Cipher For Low Cost 8-bit Processors},
howpublished = {Cryptology ePrint Archive, Report 2015/906},
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.