@misc{cryptoeprint:2014:817,
author = {Hwajeong Seo, Zhe Liu, Jongseok Choi, Howon Kim},
title = {Optimized Karatsuba Squaring on 8-bit AVR Processors},
howpublished = {Cryptology ePrint Archive, Report 2014/817},
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.