How To Air Gap a Computer

The highest level of security for a computer is for it to be air-gapped. It’s the only way to reduce the chance of the computer being hacked to as close to zero as possible. Anything less and a dedicated hacker will get into it somehow.

Why Would I Want To Air Gap a Computer?

The average person doesn’t need to air gap a computer. This is mostly the domain of corporations and governments. For a government, it could be a sensitive database, project, or maybe controlling a weapons system. For a corporation, it could house trade secrets, financial information, or running an industrial process. Activist groups might also do this to prevent having their work shut down.

You’re probably not worried about those things if you’re only running a home computer. Still, implementing just one or two of these measures will increase your security dramatically.

What’s An Air Gap?

When you air gap a computer there’s nothing between the computer and the rest of the world but air. Of course, since WiFi came along it has changed to mean no connection to the outside world at all. Nothing that isn’t already on the computer should be able to get on it. Nothing on the computer should be able to be taken off of it.

How Do I Air Gap My Computer?

Air gapping a computer is not as simple as just unplugging the network cable and disabling the wifi. Remember, this is a high-value target for criminal hackers and Nation-State Actors (NSAs) who work for foreign governments. They’ve got money and time. Plus they love a challenge, so going after an air-gapped computer is enticing to them.

Let’s start from the outside of the computer and work our way inside:

1. Operational security (OpSec) is important. OpSec can be oversimplified as being on a need-to-know basis. No one needs to know what’s in the room, let alone what the computer is for or who is authorized to operate it. Treat it as if it didn’t exist. If unauthorized people know about it, they’re susceptible to social engineering attacks. 

2. Make sure it’s in a secure room. The room should have just one entrance and it must be locked at all times. If you go inside to work, lock the door behind you. Only authorized operators of the PC should have access. How you do this is up to you. Physical and electronic smart locks each have their pros and cons.
   
   Be cautious of drop ceilings. If an attacker can pop out a ceiling tile and go over the wall, the locked door means nothing. No windows, either. The room’s sole purpose should be to house that computer. If you’re storing stuff in there, then there’s an opportunity to sneak in and hide a web camera, microphone, or RF listening device.

3. Make sure it’s a safe room. Safe for the computer, that is. The room should provide the ideal climate for the computer so that it lasts as long as possible. Anytime an airgap computer breaks down and there’s disposal, there’s a chance to get information off the discarded computer.
   
   You’ll need computer-safe fire suppression as well. Something using inert gases or halocarbon compounds is appropriate. It has to be non-destructive to the computer, or the hacker may try to destroy the computer by turning on the sprinklers if they can.

4. Keep all other unnecessary electronic devices out of the room. No printers, cellphones, tablets, USB flash drives, or key fobs. If it has a battery in it or uses electricity it doesn’t go in that room. Are we being paranoid? No. Check out the air-gap research Dr. Mordechai Guri is doing and see what’s possible. 

5. Speaking of USB, plug or remove any unnecessary USB ports. You might need a USB port or two for the keyboard and mouse. Those devices should be locked in place and not removable. Any other USB port should be removed or blocked using something like a USB port blocker. Better yet, use a USB to PS/2 keyboard and mouse converter adapter, with a PS/2 keyboard and mouse. Then you don’t need any external USB ports at all.

6. Eliminate all methods of networking possible. Remove the WiFi, Ethernet, and Bluetooth hardware or start with a computer that doesn’t have any of that. Just disabling those devices isn’t enough. Any necessary network cable needs to be shielded. It might be a controller for an industrial process so some cables may be necessary.

7. Disable all common network ports on the computer. This means the ports like 80 for HTTP, 21 for FTP, and other virtual ports. If the hacker somehow gets physically connected to the computer, at least these ports won’t be sitting there ready and waiting.

8. Encrypt the hard drive. If the hacker still gets to the computer, at least the data is encrypted and useless to them.

9. Shut the computer down whenever it isn’t needed. Unplug it, even.

Is My Computer Safe Now?

Get used to the terms acceptable risk and reasonably secure. As long as there are hackers, both white hat and black hat, new ways to jump the air gap will continue to be developed. There’s only so much you can do, but when you air gap your computer it’s at least a good start.