But why, when a DVD-R handles most use cases at a cost of < $0.25 each, are reliable and ubiquitous, the hardware is likely already there (unless you are using Apple - caveat emptor) and they close the threat vector posed by read/write USB devices.
Sometimes the simplest solution is the best solution.
I’d argue that read-only CD/DVD has a smaller attack surface than USB, so of the two, it’s preferable. I’d further argue that a CD/DVD (ie, the actual object moved between systems) is easier to inspect than USB devices, to validate the behavior.
Plus, compared to a USB form factor, one imagines it’s harder to sneak in circuitry that could retransmit data by unexpected means.
Also, if you think that the seller is lying to you, can't the drive be opened up and inspected to check for that kind of capability ?
I don't know if people class something connected using a data diode as airgapped or not.
you need to use a file transfer tool intended for unidirectional transfer (e.g. multicast) otherwise you will have failure from lost packets.
If you don't require high speed just use RS232.
It is the responsibility of the host to protect the card. The position [i.e., setting] of the write protect switch is unknown to the internal circuitry of the card
A diode / photosensor can't.