Abstract: We show the method of expanding the order of the finite field. As the order becomes bigger and bigger, the more powerful security code comes out, since, the encrypting code becomes the more and more difficult to decript. This is because the number of the occurring cases is exponentially increasing as the order of the primitive equation of the finite field is increasing. In this study, we show the method to expand the finite field length. Especially, the zero crossing detector is designed and designing method is precisely described.