@misc{cryptoeprint:2007:261,
author = {Subhamoy Maitra and Goutam Paul},
title = {New Form of Permutation Bias and Secret Key Leakage in Keystream Bytes of RC4},
howpublished = {Cryptology ePrint Archive, Report 2007/261},
year = {2007},
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.