@misc{cryptoeprint:2005:089,
author = {Hans Dobbertin and Gregor Leander},
title = {Cryptographer's Toolkit for Construction of $8$-Bit Bent Functions},
howpublished = {Cryptology ePrint Archive, Report 2005/089},
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.