Pakistan's nukes - how secure?

However, one core would not be enough to ensure a true nuclear explosion. Pakistan's weapons likely have about 12-15kg of uranium metal in the fissile core. This could be in the form of a sphere or hemispheres. Terrorists would need at the least about 50-60kg of uranium, in other words about 4-5 cores worth, for gun-assembly. That requires some heist. I don't think even George Clooney and Brad Pitt would be able to pull it off.

The stolen cores would need to be fabricated and machined in a manner suitable for gun assembly. This is not as trivial a task as often claimed. It would require both advanced theoretical and experimental knowledge.

In short, there is a possible theft scenario but it does require a lot of ifs and buts for it to be pulled off in the real world.

One of the ironies of PALs is that the better designed they are the more confidence military and political leaders have in the security of nuclear postures even at high alert levels. High alert increases the probability of accidental nuclear war. A terrorist attack against India could lead to a nuclear detonation not in spite of PALs but because of PALs.

These are the sorts of dilemmas that nuclear weapons pose.

The highly regarded Pakistani dissident physicist, Pervez Hoodbhoy, makes a very important point about PALs. He argues, correctly, that they are only as reliable as the people who use them. If the military commanders themselves become radicalised or the state is politically taken over then PALs, even futuristic PALs based on the in principle unbreakable quantum cryptography, would be useless.

But that's a political, not technical, matter.