public byte getNext() {
        int i = this.i;
        int j = this.j;
        byte tmp;
        //CfbNX̃Zbg
        i = (i + 1) & 0xff;
        j = (j + key[i]) & 0xff;
        this.i = i;
        this.j = j;
        //ւ
        tmp = key[i];
        key[i] = key[j];
        key[j] = tmp;
        return key[(key[i] + key[j]) & 0xff];
    }