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I'm looking to understand what security is necessary to fully protect a computer with VERY sensitive information. Let's say we are using a firewall to protect users from the external network, all users have anti-virus software on their computers. Would you need anti-keylogging software or anything else? Also I've heard of the program "TEMPEST" to protect the user from radiation emissions from the screen being reconstructed elsewhere maliciously. What is the essentials for protection please?


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TEMPEST is an entire field of study - In recent years I've heard mention of attempts to do similar analysis on keyboard emissions. – Michael Kohne Aug 6 '10 at 18:59
@Michael Kohne your right the paper is entitled "Sniffing Keystrokes With Lasers and Voltmeters", its a good read i posted a link to it in my post. – Rook Aug 6 '10 at 21:12
Once again SO has used SF as a dumping ground for a question that doesn't fit. This is no more an SF subject than it is an SO subject. – John Gardeniers Aug 8 '10 at 0:07
The best SE site for this would be Information Security. I would strongly advice the poster to search the site first; these topics have been discussed in detail there. – Jenny D Sep 28 at 9:24

8 Answers 8

No security is perfect, but if I was to have to protect uber sensitive data I would start with the basics you have already but add:

  • No NIC of any kind even in the computer.
  • Full Disk encryption with boot password
  • Automatic power down after xx mins of inactivity
  • Secure room dedicated for the machine(s) containing the data
    • Electromagnet around the door frame of said room, that can only be deactivated off site
    • Room is a Faraday Cage
  • All un-needed ports superglued and have the connectors snipped internally
  • weld the case shut

All in all, the only truly secure machine is one that has been unplugged from everything, put into a cement brick, then a safe then dropped to the bottom of the ocean.


TEMPEST is not a software program. TEMPEST is a United States Department of Defense (U.S. DoD) standard for the protection of secure, classified information systems.

TEMPEST standard ensures that the computers do not radiate electromagnetic, optical, audio, or any other signal which would reveal the operations of the computer. For example, in a particular TEMPEST-certified data center, electricity to the computers is provided via a mechanism that cannot transmit high-frequency information back to the power line. The power line does not reach inside the room. Rather, outside the room, the power drives a massive motor. The motor spins a plastic shaft that goes into the TEMPEST room. Inside the TEMPEST room, a generator returns the spinning mechanical power to electrical power. An automatic clutch system ensures that the power load as seen from outside the room does not vary -- the attacker can't determine if people are working inside based on the amount of electrical power consumed. Inside this room, people were working on some Important Stuff.

As you can imagine, TEMPEST contermeasures are probably beyond what you need. In fact, the U.S. GAO thinks it is beyond what most government agencies need.

With regard to keystoke logging, there are historical cases of this being accomplished by:

  1. Using a microphone (perhaps a nearby hacked desk phone?) to analyze the typing sounds and recreate that which was typed.
  2. With antennae, intercept the electromagnetic signals of the keyboard (most keyboards raster scan a keyswitch matrix...) and reproduce the typed keys.
  3. By installing a physical device on the keyboard cable which traps the keys. (These can be installed inside the keyboard.)
  4. With key-logging software, as you described.

If you want the kind of security that protects against items 1-3, you need to find someone who has expertise in TSCM (Technical Surveillance Counter-Measures). These people are very expensive.

You haven't really given us enough details to decide what you need, though.

BTW, TEMPEST-level attacks are able to function just fine against LCDs. Also, if you transmit the data through an Ethernet switch, you have to be careful because the link activity LED is rebroadcasting your packets at a level which can be detected and decoded through your glass windows -- for real. Of course, no TEMPEST facility has normal glass windows, anyway. In the 1980's TEMPEST windows allowed only a rosy pink-orange color through, and they weren't that commonly found. I'm not sure such a thing as a TEMPEST window still exists today -- the interception technology has advanced to the point that the shielding has to be improved.

As for how to avoid keystroke logging software; use a VT102 terminal?

i think the OP is mistaken, i don't see how TEMPEST relates to this question at all. Although props on knowing a lot about this. – Rook Aug 6 '10 at 20:01
I think the OP is mistaken, also, but I thought I would share with him a notion of how so. ;) Thanks for the props. – Heath Hunnicutt Aug 6 '10 at 21:58

How about antivirus and try using a virtual keyboard for supersensitive info. The most secure system is the one without the network,


Military systems with truly confidential information are located in windowless rooms without network connectivity. Entry is physical only, through a single point with varying levels of security. These systems are generally considered secure.

Having a network connection would be the primary vector for information escape. How would the key logger make its way to the system? Are users downloading software that may contain a key logger? Does it really matter if there is a key logger (what kind of uber secure info are users inputting to the machine that the attacker couldn't use a backdoor to access)?

Also note that HW key loggers are a threat. They usually manifest as a small dongle that plugs between the keyboard and the machine, but they can also be implanted in the keyboard for increased sneakiness. As far as I know, these are undetectable without physical investigation of the PC and peripherals.

Intercepting the signal from the monitor is fairly advanced. I've never heard of it being used in an actual attack scenario, and it becomes even more difficult when considering non-CRT monitors, since the voltages are much lower. Much more common is some way to get visual access to the monitor (say a window-telescopes can see a long way).


Don't forget power attacks. If the computer is still using a PS/2 keyboard, the ground from an outlet a fair distance away (30m maybe? I don't know for sure and don't have any references right now) can be monitored for minute voltages which can then be turned into keystrokes.


I'm looking to understand what security is necessary to fully protect a computer with VERY sensitive information. Let's say we are using a firewall to protect users from the external network, all users have anti-virus software on their computers.

  • Question 1: What are you protecting it from?

Presumably "exposure to non company personnel"

  • Question 2: What are the restrictions on what you can do to protect the data?

Also presumably you can't turn the computer off, put it in a safe, encase the safe in cement, and drop it down a deep sea trench. Identify the things that you MUST be able to do for the information to do you any good. Some of the other answers are probably going to impinge on your ability to do the things you need to because you didn't answer this question for their authors.

If you can identify the things you must do, and the most likely ways the information can be exposed, you can identify the risks and act to prevent or mitigate them as appropriate (as an example, if people other than you have to have access to the information, and you are concerned that those people might leak the information, that is a risk you must mitigate, and cannot prevent.)

If the computer is only going to (for example) host a certificate authority used to sign internal SSL certificates, then it might be that you can follow all or most of the rules above. You might even be able to store the computer in a safe when it isn't in use.

If instead you are storing data that your company needs for processing on a daily basis, then you'll probably have to resort to approaches that are aimed more at mitigation of risk than absolute security. Antivirus software is a tool for this.


There was an awesome defcon talk entitled Sniffing Keystrokes With Lasers and Voltmeters. This attack is a lot like intercepting Van Eck Phreaking but for keyboards instead of CRTs. This process is error prone and a highly uncommon attack. However "workarounds" are discussed in that paper.

Also there is no such thing as anti-keylogging software. If someone has hacked your machine and is able to install keylogging software then its game over.

The Wikipedia article you link to says something very different than "the TEMPEST project is very old and is about intercepting the radio waves produced by CRT's, if you use an LCD monitor then then you don't have to worry about this exotic attack." – Bill Weiss Aug 6 '10 at 19:28
@Bill Weiss Okay fine, "Van Eck Phreaking", which has absolutely nothing to do with this question. – Rook Aug 6 '10 at 20:32

Unfortunately, there's no way you can make a computer secure. Even if there's no network at all, what if someone comes into your building with a weapon and simply takes the computer? What kind of data are you hiding on there after all?

Also, TEMPEST is not only ridiculous but totally irrelevant if you're using an LCD.

Actually no, I just found out that van eck phreaking does work with LCD ( – Rook Aug 6 '10 at 21:11