@misc{cryptoeprint:2011:083,
author = {Natalia Tokareva},
title = {On the number of bent functions from iterative constructions: lower bounds and hypotheses},
howpublished = {Cryptology ePrint Archive, Report 2011/083},
year = {2011},
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.