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Comment by crmd | Hacker News Reader

For any engineer interested in nuclear weapons, I highly recommend this three-part series produced by Sandia National Laboratory on their development of Permissive Action Link, the warhead’s electrical isolation and cryptological module that ensures US nuclear weapons will detonate if any only if authorized by the President.

It’s fascinating how they thought about bad path scenarios like thermal damage causing carbon tracking of PCBs potentially defeating the control system.

It is called “Always/Never: The Quest for Safety, Control, and Survivability”

Part 1: https://youtu.be/DQEB3LJ5psk

Part 2: https://youtu.be/sb2qo5m_hTY

Part 3: https://youtu.be/0a1exo_vU_k

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Small correction: The PAL doesn't handle presidential authentication. It's an extra layer of security to prevent a third party from detonating a warhead should they come into physical possession of one, and is (presumably) a static code which is integral to the operation of the weapon itself. Changing it would require complete reassembly of the warhead. The presidential authentication is handled by the missile crew, and the codes rotate daily. The PAL code is fixed and kept safe in the silo, where it is only accessed and input after the presidential order has been authenticated.

The presidential missile code was "00000000" throughout many years of the cold war.

https://arstechnica.com/tech-policy/2013/12/launch-code-for-...

I thought that was the PAL, not the presidential part.

Basically, engineers added a new layer of security, personnel on the ground promptly found a workaround. Nothing ever changes.

Well, as long as it wasn't stick by the silo entrance on the wall on postit we can call it an improvement, eh? I mean you have to at least remember the number of zeros required

> Basically, engineers added a new layer of security, personnel on the ground promptly found a workaround. Nothing ever changes.

Not quite - the highest levels of government added a new security layer and the generals in charge decided to work around it.

I hate to say it, but that article is inaccurately reported, and I cringe every time I see it linked. It conflates the PAL codes with the presidential launch codes, which are two distinct layers of security. Even if the PAL is hard coded to all zeros, you still need presidential authorization to initiate the launch procedure.

My understanding that this included warheads for bombers, so that maybe a bad actor could exploit it.

... thank you. I didn't know those were floating around. I'd heard of them before, just hadn't had a chance to see them.

You’re most welcome. It’s so cool this level of detail is unclassified and open to all.

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