@misc{cryptoeprint:2006:070,
author = {Sergey Doroshenko and Boris Ryabko},
title = {The experimental distinguishing attack on RC4},
howpublished = {Cryptology ePrint Archive, Report 2006/070},
year = {2006},
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.