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Comment by icermann | Hacker News Reader

It's being called a data diode (diodes usually allows current in one direction only).

It can be implemented with a fiber optics cable with only the transmitter on the secure side, a laser+photo cell for real air gap, cutting the rx cable in a rs232 or having a microcontroller with an output pin connected to another controllers input pin. By handling it with hardware instead of software you get a very secure partition between the trusted and untrusted side.

It's used to monitor for example industrial systems and power plants.

Wikipedia calls it unidirectional network: https://en.wikipedia.org/wiki/Unidirectional_network

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Yes, this is exactly the kind of approach I'm referring to when I say it's possible (though not trivial to implement), but it still doesn't prevent attacks. Air France 447 crashed with extraordinary loss of life because the pilots responded incorrectly to reported sensor readings. Any scenario where authorised staff are able to affect changes in a control system is vulnerable. The attack vectors just change to suit the target system.

AF447 wasn't a security breach. You're talking about an entire separate class of human-machine interaction problem that has little relevance to the lack of security around access to OT operational surfaces.

Not OP, but the point seemed clearly to be that if sensor input is wrong, then it can result in catastrophic results even when all control systems are normative. The inference then is if hackers can affect sensor readings then they can still effectively control a system - like putting an ice cube on a non-adjustable thermostat.

If hackers can "affect sensor readings" before they feed into the control system, sure. But that is not read only access to the sensor... The trivially simple example is a webcam streaming the thermostat output. The hacker can watch that stream all day - it's not gonna cause any issues with the refrigerator. Even if the hacker had control of the stream, worst they could do is disrupt any monitoring system that uses the stream (e.g. make it appear that there is a fake issue or mask a real one) - but that is significantly lower risk than having remote access to trigger a semipermanent defrost cycle that spoils all the food.

You'd expect the people reading the data to criticize it and not input any command that will compromise the operational safety.

Or, in other words, you'd expect the managers to be smart enough not to set all the fridges to 50°C, whatever data they read on their screens.

All fancier than a camera pointed at the thermostat readout I’m sure but is the laser & photocell anywhere close to similar in concept?

Realistically you could use fiber networking stuff with only one fiber

just leave TxD open...

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