@misc{cryptoeprint:2004:276,
author = {C. Carlet},
title = {Improving the algebraic immunity of resilient and nonlinear functions and constructing bent functions},
howpublished = {Cryptology ePrint Archive, Report 2004/276},
year = {2004},
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.