@misc{cryptoeprint:2009:502,
author = {Ruchi Gode, Sugata Gangopadhyay},
title = {On second order nonlinearities of cubic monomial Boolean functions},
howpublished = {Cryptology ePrint Archive, Report 2009/502},
year = {2009},
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.