Tagged: tempest

Tech Minds: Eavesdropping on Video Monitors with TempestSDR

Over on his latest video Tech Minds' explores the use of TempestSDR to eavesdrop on video monitors with his Airspy Mini. TempestSDR is a program that we've posted about several times in the past. With an RTL-SDR or other compatible SDR like a HackRF it allows you to reconstruct an image from a computer monitor or TV just from the radio waves unintentionally emitted by the screen or cable. SDRs with larger bandwidths like the HackRF or Airspy are better at reconstructing the image as they can collect more information.

In his video Tech Minds shows how to download and setup one of the newer branches of TempestSDR which unlike older versions doesn't require much installation work. Using an Airspy Mini he shows that he is able to view what is on his screen via the emitted RF waves.

Eavesdropping Video Monitors With TempestSDR RTL-SDR

A Self-Executable version of TempestSDR is now Available

TempestSDR is an open source tool made by Martin Marinov which allows you to use any SDR that has a supporting ExtIO (such as RTL-SDR, Airspy, SDRplay, HackRF) to receive the unintentional signals radiated from a screen, and turn that signal back into a live image. This can let you view what is on a screen through a wall without using any physical cables.

We first posted a demonstration of TempestSDR back in 2017 when we were finally able to get it to compile. Compiling the software took a fair amount of work for those without experience, and even running it was a chore. However, getting it to work is worth it as you can do some really interesting demonstrations.

However these problems are over and recently Erwin Ried @eried has made a self-executable version of TempestSDR. This means that no compilation, java installs, mingw or extra dlls are required to get the program to work as now it's just an exe that you can run. You will still need the appropriate ExtIO dlls for your SDR. The video in his twitter post shows it working with a HackRF.

GNU Radio TEMPEST Implementation Now Available

TEMPEST refers to a technique that is used to eavesdrop on electronic equipment via their unintentional radio emissions (as well as via sounds and vibrations). All electronics emit some sort of unintentional RF signals, and by capturing and processing those signals some data can be recovered. For example the unintentional signals from a computer screen can be captured, and converted back into a live image of what the screen is displaying.

Until recently we have relied on an open source program by Martin Marinov called TempestSDR which has allowed RTL-SDR and other SDR owners perform interesting TEMPEST experiments with computer and TV monitors. We have a tutorial and demo on  TempestSDR available on a previous post of ours. However, TempestSDR has always been a little difficult to set up and use.

More recently a GNU Radio re-implementation of TempestSDR called gr-tempest has been released. Currently the implementation requires the older GNU Radio 3.7, but they note that a 3.8 compatible version is on the way.

The GNU Radio implementation is a good starting point for further experimentation, and we hope to see more developments in the future. They request that the GitHub repo be starred as it will help them get funding for future work on the project.

The creators have also released a video shown below that demonstrates the code with some recorded data. They have also released the recorded data, with links available on the GitHub. It's not clear which SDR they used, but we assume they used a wide bandwidth SDR as the recovered image is quite clear.

Examples using gr-tempest

GR-TEMPEST: GNU Radio TEMPEST Implementation
GR-TEMPEST: GNU Radio TEMPEST Implementation

Performing a Side Channel TEMPEST Attack on a PC

TEMPEST refers to a technique that is used to eavesdrop on electronic equipment via their unintentional radio emissions (as well as via sounds and vibrations). All electronics emit some sort of unintentional RF signals, and by capturing and processing those signals some data can be recovered. For example the unintentional signals from a computer screen could be captured, and converted back into a live image of what the screen is displaying. We have tutorials on how to do this with a program called TempestSDR available on a previous post of ours.

Recently Mikhail Davidov and Baron Oldenburg from duo.com have uploaded a write up about their TEMPEST experiments. The write up introduces the science behind TEMPEST eavesdropping first, then moves on to topics like software defined radios and antennas.

At the end of their post they perform some experiments like constantly writing data to memory on a PC, and putting the PCs GPU under varying load states. These experiments result in clear RFI bursts and pulsing carriers being visible in the spectrum, indicating that the PC is indeed unintentionally transmitting RF. They note that machine learning could be used to gather some information from these signals.

Their write up reminds us of previous TEMPEST related posts that we've uploaded in the past. One example is where an RTL-SDR was used to successfully attack AES encryption wirelessly via the unintentional RF emitted by an FPGA performing an encryption algorithm. Another interesting post was where we saw how a HackRF was used to obtain the PIN of a cyprocurrency hardware wallet via TEMPEST. Search TEMPEST on our blog for more posts like that.

TEMPEST PC Side Channel Setup: RF pulses from writing to memory and a GPU.
TEMPEST PC Side Channel Setup: RF pulses from writing to memory and a GPU.

YouTube Tutorial: Spying on Computer Monitors with TempestSDR

Over on YouTube SignalsEverywhere (aka Corrosive) has uploaded a tutorial video showing how to use TempestSDR with an Airspy SDR. Back in November 2017 we posted about how we were able to get TempestSDR to run with an RTL-SDR, Airspy and SDRplay, and showed some results. Since then several people have managed to repeat our results, but many have also had trouble understanding how to make TempestSDR work and what all the settings are for.

TempestSDR is an open source tool that allows you to use any SDR that has a supporting ExtIO (such as RTL-SDR, Airspy, SDRplay, HackRF) to receive the unintentional signal radiation from a screen, and turn that signal back into a live image. This can let you view what is on a screen without any physical connections.

Corrosive's tutorial video shows us how to tune the signal in the TempestSDR software in order to receive a clear image as well as showing the software in action.

How to Spy on Computer Monitors | TempestSDR Tutorial (with an Airspy)

Transmitting RF Music Directly From the System Bus on your PC

Recently we've come into knowledge of a program on GitHub called "System Bus Radio" which lets you transmit RF directly from your computer, laptop or phone without any transmitting hardware at all. It works on the principle of manipulating the unintentional RF radiation produced by a computers system bus by sending instructions that can produce different AM tones. An SDR like the RTL-SDR V3 or RTL-SDR with upconverter, or any portable AM radio that can tune down to 1580 kHz can be used to receive the tones. To run the software don't even need to download or compile anything, as there is now a web based app that you can instantly run which will play a simple song.

However, the RF emissions don't seem to occur on every PC, or are perhaps at another frequency. We tested a Windows desktop and Dell laptop and found that no were signals produced. A list of field reports indicates that it is mostly MacBook Pro and Air computers that produce the signal, with some transmitting signals strong enough to be received from a few centimeters to up to 2m away. This could obviously be a security risk if a sophisticated attacker was able to sniff these tones and recover data.

This program runs instructions on the computer that cause electromagnetic radiation. The emissions are of a broad frequency range. To be accepted by the radio, those frequencies must:

  • Be emitted by the computer processor and other subsystems
  • Escape the computer shielding
  • Pass through the air or other obstructions
  • Be accepted by the antenna
  • Be selected by the receiver

By trial and error, the above frequency was found to be ideal for that equipment. If somebody would like to send me a SDR that is capable of receiving 100 kHz and up then I could test other frequencies.

There is also an interesting related piece of software based on System Bus Radio called 'musicplayer', which takes a .wav file and allows you to transmit the modulated music directly via the system bus.

If you're interested in unintentionally emitted signals from PCs, have a look at this previous post showing how to recover images from the unintentional signals emitted by computer monitors. This is also similar to RPiTX which is a similar concept for Raspberry Pi's.

System Bus Radio web app
System Bus Radio web app

TempestSDR: An SDR tool for Eavesdropping on Computer Screens via Unintentionally Radiated RF

Thanks to RTL-SDR.com reader 'flatflyfish' for submitting information on how to get Martin Marinov's TempestSDR up and running on a Windows system. If you didn't already know by definition "TEMPEST" refers to techniques used by some spy agencies to eavesdrop on electronic equipment via their unintentional radio emissions (as well as via sounds and vibrations). All electronics emit some sort of unintentional RF signals, and by capturing and processing those signals some data can be recovered. For example the unintentional signals from a computer screen could be captured, and converted back into a live image of what the screen is displaying.

TempestSDR is an open source tool that allows you to use any SDR that has a supporting ExtIO (such as RTL-SDR, Airspy, SDRplay, HackRF) to receive the unintentional signal radiation from a screen, and turn that signal back into a live image. This can let you view what is on a screen without any physical connections. If a high gain directional antenna is used then it may be possible to receive images from several meters away as well.

TempestSDR showing what's on the screen via unintentional RF radiation from the monitor.
TempestSDR showing what's on the screen via unintentional RF radiation from the monitor.

Although TempestSDR has been released now for a number of years it hasn't worked properly in Windows with ExtIO interfaces. In his email flatflyfish showed us how to compile a new version that does work.

1. You need to install a 32-bit version of the Java runtime. The 64-bit version won't work with extio's possibly because they are all 32-bit. Also install the JDK.

2. You need to install MingW32 and MSYS and put their bin folders in your Windows PATH.

3. Then when compiling I was seeing a lot of CC command unknown errors. To fix that I just added CC=gcc to the top of all makefiles. I also removed the Mirics compilation line from the JavaGUI makefile to make things easier as we're not using that sdr.

4. Originally my JDK folder was in Program Files. The makefile didn't like the spaces in the folder, so I moved it to a folder without spaces and it fixed the errors.

5. Lastly to compile it you need to specify the ARCHNAME as x86 eg "make all JAVA_HOME=F:/Java/jdk1.7.0_45 ARCHNAME=X86"

After doing all that it compiled and I had a working JAR file. The extio's that are used normally with HDSDR work fine now and I get some images from my test monitor with an rtlsdr.

We tested compilation ourselves and were successful at getting a working program. To help others we've just uploaded a fork of the code with the makefile changes done, as well as a precompiled release ZIP available on the releases page so no compilation should be required to just use it. Note that to use the precompiled JAR you still need to install MingW32, and also don't forget to install the MingW /bin and msys /1.0/bin folders into the Windows PATH. You also do need to have the 32-bit Java runtime installed as the 64-bit version doesn't seem to work. On at least one Win 10 machine we also had to manually add a 'Prefs' folder to the Java path in the registry.

We've tested the software with the ExtIO for RTL-SDRs (available on the HDSDR downloads page) and confirmed that it works. Images from one of our older DELL monitors using DVI are received nicely, although they are a bit blurry. We also tried using an Airspy or SDRplay unit and this significantly improved the quality of the images a lot due to the larger bandwidth. The quality was good enough to make out large text on the screens. ExtIO's for the Airspy are available on this page, and for the SDRplay on the official SDRplay website. Note that for the SDRplay we were unable to go above 6 MHz, and on the RTL-SDR 2.8 MHz was the limit - anything higher on these SDRs did not produce an image possibly due to dropped samples.

To use the software you should ideally know the resolution and refresh rate of your target monitor. But if you don't there are auto-correlation graphs which actually help to predict the detected resolution and frame rate. Just click on the peaks. Also, you will need to know the frequency that your monitor unintentionally emits at. If you don't know you can browse around in SDR# looking for interference peaks that change depending on what the image of the screen is showing. For example in the image below we show what the interference might look like. A tip to improving images is to increase the "Lpass" option and to watch that the auto FPS search doesn't deviate too far from your expected frame rate. If it goes too far, reset it by re-selecting your screen resolution.

Unintentionally radiated RF signal from computer screen shown in SDR#
Unintentionally radiated RF signal from computer screen shown in SDR#

The best results were had with the Airspy listening to an older 19" DELL monitor connected via DVI. A newer Phillips 1080p monitor connected via HDMI had much weaker unintentional signals but images were still able to be recovered. A third AOC 1080p monitor produced no emissions that we could find.

Clear images were obtained with an antenna used in the same room as the monitor. In a neighboring room the images on the DELL monitor could still be received, but they were too blurry to make anything out. Possibly a higher gain directional antenna could improve that.

An example set up with RTL-SDR antenna and monitors
An example set up with RTL-SDR antenna and monitors

Below we've uploaded a video to YouTube showing our results with TempestSDR.

TempestSDR - Remotely Eavesdropping on Monitors via Unintentionally Radiated RF

If you want to learn more about TEMPEST and TempestSDR Martin Marinovs dissertation on this software might be a good read (pdf).

Using an RTL-SDR and TEMPEST to attack AES

All electronic devices emit some sort of unintentional RF signals which can be received by an eavesdropping radio. These unintentional signals are sometimes referred to as TEMPEST, after the NSA and NATO specification which aims to ensure that electronic devices containing sensitive information cannot be spied upon through unintentional radio emissions, sounds or vibrations. TEMPEST can also refers to the opposite, which is spying on unsecured electronic devices by these means.

Recently the team at Fox-IT, a cybersecurity specialist company has released a paper showing how an RTL-SDR can be used as a TEMPEST attack device to help recover AES-256 encryption keys (pdf) from a distance by utilizing unintentional RF emissions. AES is an encryption standard commonly used in computing with protocols like HTTPS (e.g. with online banking) and for securing WiFi networks.

In their experiments they set up an AES implementation on an FPGA, and used a simple wire loop antenna and RTL-SDR to measure and record the RF emissions. By then doing some analysis on the recorded signal they are able to fairly easily extract the AES encryption key, thus defeating the encryption.

Further testing in an anechoic chamber showed that with a discone antenna they were able to recover the keys from up to a meter away. A directional antenna could probably reach even further distances.

In the past we’ve seen a similar attack using a Funcube dongle, which is an SDR similar to the RTL-SDR. In that attack they were able to remotely recover encryption keys from a laptop running GnuPC. Also, somewhat related is Disney’s EM Sense which uses an RTL-SDR to identify electronic devices by their RF emissions.

[Also seen on Hackaday]

Fictional scenario involving a hacker recording RFI from a remote PC.
Fictional scenario involving a hacker recording RFI from a remote PC.