@misc{cryptoeprint:2005:311,
author = {Cecile Canovas and Jessy Clediere},
title = {What do S-boxes Say in Differential Side Channel Attacks?},
howpublished = {Cryptology ePrint Archive, Report 2005/311},
year = {2005},
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.