Rev 12/6/18
Today I did a quick search using the term "air-gap," and found what appears to be a desperate attempt by the NSA to suppress the use of air-gap PC's. The claims that they aren't secure from all possible attacks might apply to systems which are targeted by intelligence agencies, but the average person probably doesn't have to worry about these attacks. For instance, the notion that someone can monitor the power line outside your home and determine what's on your encrypted flash drive is absurd, especially since PC's use regulated power supplies which would prevent any data from getting out to the power line from a PC. (The only way to get a signal out would be to modulate the PC's power consumption to such an extent that it could be detected on the power line, which is possible but would probably require noticeable changes in the PC's behavior. A PC's power consumption is low compared to a lot of other things, which might be turning on and off, and then there's power-line noise, so it would be very difficult to get any data this way.) The claim that there are Windows viruses that copy data to and from flash drives in hopes that they will be plugged into an air gap PC is plausible, but I don't care about Windows since nobody who is security-conscious would use Windows for an air-gap PC. Other, even more exotic techniques are also the stuff of intelligence agents, and not likely to be applied to the average home PC-user who just wants to keep personal data such as shopping lists and correspondence from Big Brother. So don't let these claims frighten you away from using an air-gap PC, which combined with an online mini-PC and a KVM switch provide a very high level of security for a very low cost in terms of time and money.
Revision notes
12/6/18- Added "(The only way to get a signal out....)"
