What else would you exfiltrate/steal besides passphrases and private keys? Serial numbers/IPs/hostnames of any discovered devices on the air-gapped network?
Send to the airgapped computer(s) software updates and new commands to run? 20 bytes per second is enough for that, or is it bits? A shellcode is about 40bytes or less.
I guess if you want to guard against this the reasonable thing to do would be to physically take out the mic and speakers of any to-be-secure-computers. Or have one computer listen in on these high frequencies on the perimeter or whatever. Would be interesting to discover chats.
Send to the airgapped computer(s) software updates and new commands to run? 20 bytes per second is enough for that, or is it bits? A shellcode is about 40bytes or less.
I guess if you want to guard against this the reasonable thing to do would be to physically take out the mic and speakers of any to-be-secure-computers. Or have one computer listen in on these high frequencies on the perimeter or whatever. Would be interesting to discover chats.