Stuxnet:
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Nuclear enrichment:
	As noted before:  Proportion of U235 and U238 affects reactivity
		More U235 = more reactive
		More U238 = less reactive
		Yes, this seems backwards!
	So you want the lighter particles

Centrifuges:
	Spin to get the heavy particles to the outside
	Simpler example:  Adding used motor oil for diesel fuel
	Problem:  Uranium is solid!
	Solution:  Make it a gas
		There's a long and complicated procedure
		Ends up with flourine bonded to each uranium atom
		Definition of fluorine...
	Gas centrifuges have to spin really fast

Long spinning things tend to flex at certain speeds
	Resonant frequency is bad
	There'll be a stable frequency, usually higher
	There's also a limit to how high the frequency should be
	Finally, the walls usually aren't all that thick

Making them not work anymore without bombing:
	Too slow could hit resonant frequencies
	Too fast will exceed mechanical limits
	Too high of gas pressure will also exceed mechanical limits
	The shape is really pretty important, a little off won't work well
	The operators might notice unless we keep gauge readings correct

This kind of system uses Programmable Logic Controllers (PLC)
	If you want one, look for an arduino
	These can have network connectivity
		But they don't have to, and maybe you don't want it
		Air-gapped
		Helps avoid viruses

Stuxnet worm, working backwards

Step7 and programming PLCs:
	Usually you plug a laptop into the PLC to program it
		Maybe keep that laptop offline
	So if we've got control of the software that programs it...
	In this case, Siemens controllers
	Dynamic Link Library replacement
	Carefully make sure it's the right hardware

Spreading via USB:
	Hid in a few files
	Used a previously unknown Windows bug to execute a special shortcut
	If a laptop isn't online, bringing files to it by USB can be common
	The virus deletes itself if it's in the wrong spot

Worm mode:  Just spread everywhere without doing much of anything
	This has been done a lot of times, but stuxnet was a little unusual
	4 separate zero-day exploits used
	Besides USB device, it'll use remote procedure calls

Did it work?
	Iran dismantled and removed 984 centrifuges
	No more than 2 years worth of setback
		Maybe less, kinda unclear exactly how well it worked

How do we tell if enrichment is for electricity or weapons?
	Weapons generally require a higher level of enrichment
	Same enrichment process either way
	Highly enriched uranium from scrapped weapons can be fuel
		Have to control it more carefully!
	Nuclear power is usually kind of expensive
		Especially if you have other energy sources