How to control nuclear weapons and make our world safer?

Today, the entire mankind is living under the shadow of nuclear war. The stocks of nuclear weapons in US and Russia at present are more than enough to destroy all major cities in our world. How can we protect human from this nuclear threat? As a first step of nuclear armament control, we propose to revise the Treaty on the Non-Proliferation of Nuclear Weapons to add a new article, which specifies that all existing and future nuclear weapons will have two sets of launching codes. The first set of launching code will be controlled by the government owning those nuclear weapons, just like what is practiced today. The second set of launching code will be controlled by a new international body established by the United Nation. The launch of the nuclear weapon will require both sets of codes. That means, no government can launch any nuclear weapon unilaterally without the approval of the international body. This will be greatly helpful to prevent accidental nuclear war or nuclear blackmail.
Technically, this system is not difficult to setup. But of course, politically, it will face tremendous challenges. However, the difficulty of implementing this proposal could be less than the ban of all nuclear weapons.