Executive Summary

TEMPEST studies and mitigates unintended electromagnetic emissions from devices to prevent interception and extraction of sensitive information. First identified in the 1950s, these vulnerabilities led to the development of classified security standards to protect military and government communications. While modern technology may have reduced the risks, the rise of sophisticated cyber threats and the widespread use of electronic devices continue to make electromagnetic security a relevant concern.

Images Sourced From: EEP

1 What is TEMPEST?

The U.S. government used the codename TEMPEST to describe both investigating unintended electromagnetic emissions from electronic devices and implementing countermeasures to prevent their use. It involves researching, detecting, and shielding electronic devices to prevent adversaries from intercepting confidential information via electromagnetic leakage.

“The examination and control of electromagnetic energy emissions from electrical or electronic devices”

While TEMPEST focuses specifically on detecting and preventing unintended electromagnetic emissions from devices, EMS (Electromagnetic Spectrum) refers to the entire range of electromagnetic frequencies, which people can actively manipulate for various purposes, such as communication or signal extraction. [source]

2 Understanding TEMPEST

Every electronic device—whether a computer, monitor, keyboard, printer, or even a simple circuit—emits electromagnetic radiation as it operates, regardless of whether it was designed to transmit signals. The electromagnetic radiation created by devices is capable of interfering with other electronic systems; for instance, holding a walkie-talkie next to a radio can cause an audible distortion. 

The emanations, which can be electromagnetic, vibrational, or acoustic, have the potential to travel through walls, ceilings, and floors.In addition to causing interference with nearby devices, these emissions can allow interception and analysis. With the right equipment, an attacker can analyse these signals and reconstruct the original data, such as:

• Text/images displayed on a screen (by capturing emissions from a monitor);
• Keystrokes entered on a keyboard (by detecting the signals from presses of a key);
• Audio from a physical phone line (by detecting vibrations felt outside of the wire);
• Audio from a room (by detecting vibrations on surfaces, such as glass). [source]

If attackers intercept and record these emissions, they can analyse them and recover the intelligence processed by the source device. [source]

3 Historical Background

The concept of TEMPEST dates back to the 1950s, when U.S. intelligence agencies discovered that computers, teleprinters, and communication devices emitted electromagnetic signals that could be intercepted and reconstructed. During a routine test, it was revealed that plaintext messages being encrypted by a teleprinter could be reconstructed from intercepted emissions.

These emissions, referred to as “compromising emanations,” posed a serious security risk, as attackers could extract sensitive information without physical access to the targeted system.

In response, the U.S. established classified standards—a comprehensive effort to secure electronic communications against electromagnetic espionage. While this alarming discovery led to early countermeasures, the phenomenon remained largely unaddressed and classified for years. [source]

It is thought that the term “TEMPEST” itself was first used as a codename for this study. Although this isn’t an official term, it has been proposed over time to stand for “Telecommunications Electronics Material Protected from Emanating Spurious Transmissions.” According to others, it also stands for “Transient Electromagnetic Pulse Emanation Standard.” Regardless, TEMPEST is now a crucial component of information security regulations all over the world. 

4 Standards and Regulation

As societies become more reliant on information systems, cyber warfare elements often focus on attacking them. Without EMS protection against both intended and unintended emissions, devices in cyberspace are vulnerable to cyberwarfare and terrorist threats. Recognising the security risks posed by TEMPEST-related vulnerabilities and broader electromagnetic spectrum concerns, governments and military organisations have developed strict standards to regulate and mitigate these threats. Some of the most notable include:

• NACSIM 5100A (USA): A classified U.S. government document detailing TEMPEST security requirements.
• NSA TEMPEST Endorsement Program (USA): Certifies equipment that meets strict electromagnetic shielding requirements.
• AMSG 720B (NATO) The NATO equivalent of the U.S. TEMPEST standards.
• European and German TEMPEST Programmes: European nations, including Germany and the UK, have their own classification and shielding standards.

The purpose of these standards is to limit the unintentional transmission of sensitive data through electromagnetic emissions and to ensure that organisations handling classified information use properly shielded equipment.

Although proper design minimises the unintentional signals given off by a device, some unintentional signals will always be present. When a device processes information such as printed text or voice, it is vulnerable to “leaking” through unintentional signals. [source]

5 TEMPEST Attack Methods

TEMPEST attacks are a form of side-channel attack, meaning adversaries are able to extract information by analysing indirect signals rather than directly accessing a system. One well-known example is Van Eck phreaking, a technique demonstrated in 1985 by Dutch scientist Wim van Eck, who intercepted the emissions from a computer monitor and displayed the retrieved images on a TV screen. In order to collect this information, a typical TEMPEST attack may follow these steps:

• Strategic Positioning: The attacker places a radio receiver, or active directional antenna, at an optimal distance to the target device (e.g., in a nearby parking lot or building) to capture the leaked signals.
• Data Interception: Using these antennas and radio equipment, the attacker records the device’s electromagnetic emissions.
• Signal Processing: Advanced signal analysis tools reconstruct all, or substantial portions of the intercepted emissions into readable data, such as keystrokes, screen images, or cryptographic keys. 

Variables such as external electromagnetic interference, signal weakness over distances, and partial transmissions often corrupt the data picked up. However, advanced algorithms can help to provide a more complete picture of the original data.

5.1 TEMPEST Equipment

TEMPEST monitoring equipment includes various kinds of sensitive receivers, which can monitor a wide range of frequencies, and a combination of hardware and software that is capable of processing the received signals into the original data. The U.S. government forbids the sale of TEMPEST monitoring devices to the public. However, unapproved organizations can still obtain or construct the technology easily.

6 TEMPEST Countermeasures

6.1 Filtering

Radiofrequency filtering reduces or prevents contamination at the source device. Filtering allows necessary signals to pass through a conductor while blocking unwanted electromagnetic emissions to prevent leakage. Various protective materials, such as TEMPEST paint, shielding fabrics, window films, tents, and power filters, further enhance security by limiting electromagnetic exposure. 

6.2 Shielding

The most advanced devices use specially designed advanced micro-components to reduce TEMPEST emanations. Shielding is one of the most effective countermeasures and typically entails enclosing the gadget in a Faraday cage that prevents stray emissions, in addition to specific alterations to the power supply. Typically, a thick metal case encases the object.

In order to prevent information from escaping, TEMPEST shielding also includes considerations like room layout and equipment placement. Additionally, with sufficient building space and appropriate structural support, there is no limit to the potential size of an electromagnetically shielded enclosure. However, a more practical solution is a Sensitive Compartmented Information Facility (SCIF), the U.S. designation for a secure room. SCIFs are commonly found in buildings that regularly host sensitive discussions, with the White House Situation Room being one of the most well-known examples. Many SCIFs are designed to be semi-portable, allowing them to be relocated or assembled in different locations as needed.

Another important shielding measure is red/black separation, which involves segregating classified (red) and unclassified (black) data-processing channels. This ensures that signals from classified systems do not unintentionally leak into unclassified systems.

6.3 Noise Generation and Disruption

An active countermeasure could be to introduce noise into electromagnetic waves. This technique introduces interference in the signals, making them difficult to interpret. By distorting the emissions, attackers find it much harder to extract usable data.

One specific approach involves using specialised fonts designed to reduce distinguishable electromagnetic emissions. Fonts without distinctive elements produce similar emissions over time, making it difficult for attackers to extract meaningful data. While an attacker may still be able to reconstruct the screen image using intercepted signals, the lack of unique character details ensures that the retrieved content remains unreadable.

The strategic placement of devices also plays a role in reducing vulnerabilities. For example, computer monitors should not face windows, as this allows emissions to escape and potentially be intercepted. Moreover, keeping devices away from metal cabinets, radiators, and pipes is crucial, as these materials can amplify and conduct electromagnetic waves.

7 Legacy and Threat

Ultimately, TEMPEST attacks from emanation vulnerabilities threaten the security of confidential or proprietary information, requiring effective countermeasures. Unauthorised parties can intercept unintentional emissions from electronic devices and reconstruct them into readable intelligence. If the compromised device is handling sensitive data, the interference and disclosure of this information could have negative repercussions.

There is ongoing debate about the true threat of TEMPEST attacks. Some experts see TEMPEST monitoring as a concern, while others believe modern devices make exploiting signal leaks harder, reducing risk. For the general public, TEMPEST is unlikely to be a major issue. However, for intelligence agencies, spies, and those handling classified information, it remains a valid security concern. While it may not be as prominent a topic as it once was, it is still relevant in high-security environments.

8 Future Threat

TEMPEST’s prominence as a threat may have diminished for the general public over time. However, the potential for information leaks from electronic devices remains, particularly for those handling classified information. In our opinion, several factors contribute to the growing concern about these attacks in the coming years:

• Increased Awareness and Research: With more attention being paid to TEMPEST vulnerabilities, researchers are uncovering new and previously unknown risks. As technology evolves, so do the methods for exploiting these vulnerabilities, making it increasingly important to remain vigilant.
• Sophisticated Hackers: Cybercriminals continue to develop more advanced techniques to exploit vulnerabilities. TEMPEST attacks are a sophisticated data theft method, and as hackers improve, the risks of electromagnetic espionage continue to grow.
• The Proliferation of Electronic Devices: In the modern era, nearly every household and office is filled with interconnected devices—computers, smartphones, smart home technology, and more. Each device presents a potential risk for electromagnetic leakage, making the task of safeguarding sensitive information more complex. The sheer number of devices means that the likelihood of interception also rises.
• High-Value Targets: Organisations handling sensitive or classified information, such as government agencies, military bodies, and large corporations, remain prime targets for TEMPEST-style attacks. The stakes are higher, and the potential for espionage and data theft could have severe consequences for national security, corporate privacy, and personal safety. 

Regular audits and assessments of electromagnetic emissions may help organisations identify vulnerabilities before they become serious risks. Consider it a routine system check—identifying small issues early helps prevent larger problems and enhances long-term security and performance. Staying ahead of potential threats also means continuously investing in research and developing better countermeasures.

On the human side, training and awareness are just as important as technical defences. Employees don’t need to be TEMPEST experts, but should understand how unintentional leaks can expose sensitive data and compromise security. A little awareness goes a long way in strengthening an organisation’s overall security. [source]

9 Conclusion

TEMPEST has evolved from a classified intelligence issue to a well-known security threat, with countermeasures now incorporated into contemporary cybersecurity and defence plans. Even though the danger of electromagnetic interception has decreased as technology has advanced, it is still a concern as adversaries create increasingly complex cyber espionage techniques. Additionally, vulnerabilities related to sound and vibration remain very real, posing significant risks for secure communications and sensitive environments. The growing use of commercial and networked devices brings new vulnerabilities, necessitating ongoing innovation, regulation, and monitoring.

As information warfare and surveillance grow, electromagnetic security will stay crucial for national defense and corporate cybersecurity, requiring constant vigilance. Organisations should balance practical security measures with evolving threats, ensuring that sensitive data remains protected against both known and emerging TEMPEST risks.