@misc{cryptoeprint:2013:176,
author = {Jing Lv and Bin Zhang and Dongdai Lin},
title = {Distinguishing Attacks on RC4 and A New Improvement of the Cipher},
howpublished = {Cryptology ePrint Archive, Report 2013/176},
year = {2013},
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.