TEMPEST: Attack that Listen Radio Signals

At some point, we all are interested in knowing about others’ life and action as observance is a human tendency, but cyber criminals have taken this tendency in a bit more serious manner and come up with a technique called TEMPEST attack. It really works in a furtive way without awareness of organizations or individuals. Even your local TV antenna and other gadgets in electronic stores can help hackers to spy on neighbors TV. During the cold war, the USA has applied a technique to spy on the Soviets, which are known as TEMPEST by government agencies and defense contractors.

What is TEMPEST?

It is a snooping attack that use remote radio signals to monitor your computers and cell phones. In technical outlook, TEMPEST is a contraction of Telecommunications Electronics Material Protected from Emanating Spurious Transmissions – the name of a technology that involves the observing (and harboring) of devices that let out electromagnetic radiation (EMR) in a way that can be accustomed to rebuild comprehensible data. A Dutch scientist Wim van Eck in 1985 discovered that it is possible to catch computer monitor emission and display them on a TV monitor therefore, this attack is referred to ‘Van Eck Phreaking’.

NSA Role in TEMPEST Technology:

Due to the severity of this attack, the National Communications Security Committee has formulated standards for TEMPEST certification in NSA TEMPEST Endorsement Program in the USA. The program is designed to test the TEMPEST equipments manufacturing, development and sales, which are used by the US and NATO nations, Government agencies, and Government contractors. NSA and NATO run TEMPEST program in two stages: TEMPEST Manufacturer Program and TEMPEST Test Services Program. While other countries like Germany, the National Telecom Board handles such program and in the UK, GCHQ (Government Communication Headquarter) runs their own program.

The three levels set by NATO and the USA for TEMPEST equipments are NATO SDIP-27 Level A, Level B, and Level C. The first level-A is very secure and used only by US governments and contractors, while the second level-B is less secure compared to Level-A and requires government approval before its practice. The third Level-C is for general commercial usage.

How Does TEMPEST Attack Work?

It is obvious that electronic device produces electromagnetic signals or emanations. For example, electronic shaver, transistor radios produces the signals, which can be easily identifiable or accessible by attackers. These unwanted signals also impart in the form of sound, so when an electronic device works on some information, it produces such unnecessary signals and there is a potential risk in showing up of such information through such signals. For example, a crosstalk on telephone lines, you may hear the other person’s voice on another line. Phone lines, computer cables, electronic grounded system help to transfer magnetic signals at other unwanted places.

Another example is of electron gun – an electronic component used in old televisions, computer displays, which was popular as CRTs (cathode ray tubes). Computer monitors display the information via an electron gun that generates pixel on the screen. An electron gun produces electron pulses that move across the entire screen appearing pixels. The high and low of pixels depends on its formation (light or dark). The electric current turns into voltage and this process produces electromagnetic pulses that successively emit invisible electromagnetic radio waves carrying a great distance.

Even hard disk stores data in binary form (1s and 0s) that causes pulses and EMR (Electronic Magnetic Radiation). The most interesting thing is that each radio wave output seems different, even after they are coming from the same model of computer due to a minute difference in its manufacturing. With a proper technique, an attacker can reconstruct all or part of data received from EMR.

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Mitigate TEMPEST Attack:

The business environments have many electronic devices that emit signals, which could put personal, customer, and financial information at risk. Organizations can take below precautions to mitigate TEMPEST attack that is as under.

  • Always use TEMPEST proof fonts that are slightly blurred so it helps to prevent the conversion of the signals into fonts.
  • Keep an updated virus scanner on your PC because many TEMPEST viruses are out there that helps attacker to reconstruct the image and manipulate processor and hard disk.
  • Close all open slots of your computer with metal plates to prevent emissions.
  • Keep a good quality cable used for monitor, printer and make them short. Also, keep them away from telephone and network lines.
  • Keep Tempest-proof tents that can stop radiation range between 10 KHz and 2 KHz.
  • Organizations can block signals by putting filters in power cables, which is useful also for telephone lines.


From the rarely discussed topic, we can ensure that TEMPEST is the study of the weaknesses of exposing emanations from communications and other electrical apparatus that hold data. Still, there are many communication engineers disagree with TEMPEST attack and believes it as hoax instead of threat while other data security people consider it as an eavesdropping attack on computer displays. Due to emerging software and hardware market, eavesdropping apparatus for compromising emanations are nearly accessible at low cost to consumers.


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