Attacking a Jammer via the Jammer’s Signal

“Study hard what interests you the most in the most undisciplined, irreverent, and original manner possible.”
-Richard Feynman

This posting is complicated and frustrating because some important steps lack detailed information. Most steps can be easily found through Google search, but the step that says “inject malware” is an exception. You can find tutorials on creating malware, some of which are pretty straightforward. You could create simple malware and a client-server app or script that registers when the malware arrives. For those experienced in this area RF, malware, application development, security professionals, and so on, some of this will be routine except for the aspect of parasitic communications. However, the following text provides enough information for hard-working or talented individuals to come to a reasonable understanding with the ability to make a working prototype.
A short article on how to attack or trick a jammer by using the opposing jammer’s signal is not something you see every day. While there are books on parasitic communications, they are usually written for electrical engineers with extensive experience or graduate degrees (Zhang et al., 2015). This article is both an informative article and a high-level procedural example that, with hard work and study, could be turned into a working prototype. On that point this article is
not to teach nefarious, antisocial, bad guys who do some epic malicious hacking. There are more books that touch on these topics, but even more walk-through-like examples on the Web. This article is not written to enable the bad guys but rather to aim at those who need to be aware of or practice the arts of security. It is designed to be used by Whitehats to understand some possibilities that they currently believe are impossible. It is perhaps also useful for those in areas like C-UAS, autonomous vehicles, and so on. It is hoped that it does help open some minds.
Now for parasitic communications.
In espionage, cyber-attacks, and electronic warfare, parasitic communications refer to using an existing signal or communication channel in a way not intended by the original transmitter. This involves capturing, modifying, and retransmitting signals to exploit the communication system.
This method’s applications include intercepting signals intended for legitimate communication, modifying the intercepted signals to embed new data, commands, or disruptions, and rebroadcasting the modified signals back into the system to achieve specific effects like jamming, misleading, or injecting commands (Knox et al., 2015).

Universal Radio Hacker
In general, if you want to really become proficient and understand the wireless security topics mentioned in the article, you should use tools like a spectrum analyzer and a high-end software-defined radio. In the article, you will be asked to capture signals, analyze them, change them, and so on. If you want a quick way to jump into the concepts here, you need to look no further than the excellent tools of Universal Radio Hacker, which you can obtain here: https://github.com/jopohl/urh. The URH lets you perform more
or less every step in this example using a GUI. From interference analysis to custom signal generation. Furthermore, this tool runs on more or less all major OS’s including Windows. Many tools do not easily run on Windows. One last note though. URH’s ease and sophistication can trick you into not learning the deeper secrets of wireless security, which tend to be command line and or programmed in C.

Signal Analysis:
• Identify key characteristics such as frequency, modulation type, and signal pattern. This step involves recording the jammer’s transmission and using signal processing software to dissect its properties. A reasonably straightforward way to do this is to use GNU Radio and an SDR of your choice. If you don’t have the budget for something like BladeRF SDR, you might try an RTL-SDR, a very low-cost SDR. With these tools, you can capture signals, although the range of signals you can capture may be lower than you might like if you use tools like the RTL-SDR. Here is a good post on the subject by Dan Englender.

Signal Matching:
• Develop a signal that closely matches or slightly modifies the characteristics of the jammer’s signal. This may involve using the same frequency and modulation but embedding specific data or commands designed to interfere with the jammer. Use signal generation tools to craft this modified signal.

Transmission:
• Transmit the crafted signal using an SDR or another type of radio transmitter. Ensure the signal blends with or disrupts the original jammer’s signal. This step involves careful timing and signal alignment to maximize the impact on the jammer.

Exploitation:
• Utilize the transmitted signal to exploit the jammer’s design vulnerabilities. This might involve overloading its receiver with noise, injecting malicious commands, or causing the jammer to function. The goal is to neutralize or degrade the jammer’s effectiveness.
Conducting a cyber-attack against a jammer by parasitically using the jammer’s signal involves several complex steps. In real life, it requires a deep understanding of the jammer’s operation and usage. You should evaluate what software and hardware you want to use before starting, especially if you are using some of the low-end SDRs. Here are some software and hardware recommendations:
Software: GNU Radio, SDR#, MATLAB, Simulink, USRP (Universal Software Radio Peripheral), Universal Radio Hacker SDRs: BladeRF, LimeSDR, Ettus, and others.

Signal Analysis:
The first step in jamming a jammer involves capturing and analyzing the jammer’s signal using tools like GNU Radio and SDR. This helps identify key characteristics such as frequency, modulation type, and signal patterns.

Set Up Equipment:
• SDR Hardware: Select an appropriate SDR (e.g., Ettus Research USRP, HackRF, RTL-SDR).
• Software: Install GNU Radio on your computer.
• Antenna: Connect a suitable antenna to the SDR for capturing the jammer’s signal.

Capture the Jammer’s Signal:
• Connect SDR: Connect the SDR to your computer and open GNU Radio Companion (GRC).
• Create Flowgraph in GRC:
-Signal Source: Add an SDR source block to capture live signals.
-Frequency Tuning: Set the center frequency to the expected frequency range of the jammer.
-Sampling Rate: Adjust the sampling rate to ensure adequate resolution of the signal.
-Display Blocks: Add a waterfall sink and a fast Fourier transform (FFT) sink to visualize the signal.
• Run the Flowgraph: Execute the flowgraph to capture and display the jammer’s signal in real time.
Analyze the Captured Signal:
• Frequency Analysis: Use the FFT display to identify the exact frequency or frequencies the jammer is operating on.
• Modulation Scheme Identification:
Time Domain Analysis: Observe the time domain waveform to identify any recognizable patterns.
Modulation Type: Use signal processing blocks in GRC to demodulate the signal. This may involve adding AM, FM, PSK, or QAM demodulator blocks based on observed patterns.
• Signal Pattern Recognition:
o Spectrogram Analysis: Utilize the waterfall display to identify repeating patterns or changes over time.
o Correlation Analysis: Perform a cross-correlation with known signal patterns if applicable.
• Record and Store the Signal:
o File Sink: Add a file sink block in GRC to record the captured signal for further analysis.
o File Format: Choose a suitable format (e.g., .wav, .bin) for storing the raw signal data.
Post-Processing and Detailed Analysis:
• Load Recorded Signal: Open the recorded signal file in GNU Radio or MATLAB for detailed post-processing.
• Spectral Analysis: Perform detailed spectral analysis to identify harmonics and sidebands.
• Demodulation: Apply various demodulation techniques to decode any embedded data or identify the modulation scheme accurately.
• Signal Characteristics Extraction: Extract key parameters such as signal bandwidth, power levels, and specific modulation characteristics.

Signal Matching:
Many of the techniques that are discussed in the article are common to a large number of EW operations. Often the article will explicitly or implicitly discuss generic jamming, cyber-attacks and so on but it, and the basic level, is all the same. This next step is a good example in that it’s a very common action and should learned and understood if you want to dig deeper into these topics.
This step in the process is crucial as it focuses on developing a matching signal that contains embedded data specifically designed to interfere with and disrupt the jammer. This step begins with the capture of the jammer’s signal, which is essential for understanding the nature and behavior of the interference. Once the signal is captured, a thorough analysis examines its characteristics, such as frequency, amplitude, and modulation patterns. This analysis provides the necessary insights to create a matching signal to counteract the jammer effectively. The creation of this matching signal involves embedding data that can disrupt the jammer’s operations, thereby neutralizing its impact.
Replicate the Jammer’s Signal:
• Capture the Signal:
o Use a software-defined radio (SDR) like Ettus Research USRP, HackRF, or RTL-SDR.
o Capture the jammer’s signal using URH, GNU Radio or similar software.
• Frequency Analysis:
o Identify the operating frequency of the jammer.
• Modulation Scheme:
o Determine the modulation type (AM, FM, PSK, QAM) the jammer uses.
• Signal Characteristics:
o Note other characteristics such as bandwidth, power levels, and repetitive patterns.
Set Up Signal Generation Tools:
• Software Tools:
o Use GNU Radio, MATLAB, URH, or other signal generation tools.
• Hardware:
o Ensure you have a capable SDR for signal transmission Ettus, USRP, HackRF).
Create the Signal:
• GNU Radio Flowgraph:
o Create a flowgraph in GNU Radio to replicate the jammer’s signal. The images below are GNU Radio FlowGraphs. In GNU Radio, you can use the GUI to create FlowBlocks. The definition of FlowBlocks
“A flowgraph is an acyclic directional graph that defines how data samples flow through a series of signal-processing blocks” (GNU Radio, n.d.).
Image 3: The GNU Radio FlowGraph.
• Signal Source Block:
o Set the frequency to match the jammer’s frequency.
o Use the same modulation scheme identified in the analysis.
• Additional Blocks:
o Add any necessary filters and amplifiers to match the signal characteristics.
• Test the Replication:
o Transmit the signal and use a second SDR to capture and compare it to the original jammer’s signal.
Embed Specific Data or Commands:
• Data Embedding:
o Decide what data or commands you want to embed in the signal.
o Modify the flowgraph to embed this data. This can involve altering the signal’s phase, amplitude, or frequency at certain intervals.
• GNU Radio Blocks:
o Add appropriate blocks (e.g., modulator, encoder) to embed the data.
o Use tools like MATLAB for more complex data embedding if needed.
• Test the Modified Signal:
o Simulation Environment:
 Set up a controlled environment to test the modified signal against a similar jammer.
o Evaluate Interference:
 Observe how the modified signal interacts with and interferes with the jammer.
 Adjust the embedded data or commands as necessary to maximize interference.
Deploy the Modified Signal:
• Transmit the Signal:
o Use the SDR to broadcast the modified signal in the presence of the jammer.

Transmission:
The third step involves transmitting the custom-made signal using a Software-Defined Radio (SDR) to blend with or disrupt the original jammer’s signal. This process requires precise calibration of the SDR to ensure that the transmitted signal effectively interferes with the jammer, and you may or may not have issues at this step if you are using a low-end SDR. Assuming your SDR meets requirements, you need to program the SDR to generate a signal that matches the frequency and modulation of the jammer’s signal. By doing so, the custom signal can either mask the jammer’s signal, making it difficult for the jammer to achieve its intended effect, or it can introduce noise and distortions that degrade the jammer’s performance. This technique is commonly used in electronic warfare and signal intelligence operations to counteract and neutralize hostile jamming efforts. Proper execution of this step is crucial for the success of the overall signal disruption strategy.
Set Up Signal Generation Tools:
• Software Tools:
o Use GNU Radio, MATLAB, or other signal generation tools.
• Hardware:
o Ensure you have a capable SDR for signal transmission (Ettus Radio., USRP, HackRF).
Replicate the Jammer’s Signal:
• GNU Radio Flowgraph:
o Create a flowgraph in GNU Radio to replicate the jammer’s signal.
• Signal Source Block:
o Set the frequency to match the jammer’s frequency.
o Use the same modulation scheme identified in the analysis.
• Additional Blocks:
o Add any necessary filters and amplifiers to match the signal characteristics.
• Test the Replication:
o Transmit the signal and use a second SDR to capture and compare it to the original jammer’s signal.
Embed Specific Data or Commands:
• Data Embedding:
o Decide what data or commands you want to embed in the signal.
o Modify the flowgraph to embed this data. This can involve altering the signal’s phase, amplitude, or frequency at certain intervals.
• GNU Radio Blocks:
o Add appropriate blocks (e.g., modulator, encoder) to embed the data.
o Use tools like MATLAB for more complex data embedding if needed.
• Test the Modified Signal:
o Simulation Environment:
 Set up a controlled environment to test the modified signal against a similar jammer.
o Evaluate Interference:
 Observe how the modified signal interacts with and interferes with the jammer.
 Adjust the embedded data or commands as necessary to maximize interference.
Transmit the Signal:
• Transmit the Signal:
o Use the SDR to broadcast the modified signal in the presence of the jammer.
o Ensure the signal blends with or disrupts the original jammer’s signal.
Image 4: Simple illustration showing a representation of using parasitic communications to hack a jammer by capturing, modifying, and retransmitting its signal.

Exploitation:
The fourth step involves utilizing the transmitted custom signal you made that you could use to overload the jammer’s receiver, inject malicious commands, or cause malfunction. This step is crucial in ensuring that the jammer’s receiver is overwhelmed by the transmitted signal, which can lead to various outcomes. One possible outcome is the injection of malicious commands into the jammer’s system, which can disrupt its normal operations and cause it to malfunction. Another potential outcome is the complete overload of the jammer’s receiver, rendering it incapable of functioning correctly. By carefully executing this step, it is possible to neutralize the jammer and achieve your objectives objectives.
Identify Potential Vulnerabilities:
• Signal Analysis:
o Perform a detailed analysis of the jammer’s signal to identify potential vulnerabilities.
o Consider signal processing algorithms, synchronization methods, and receiver sensitivity.
• Research:
o Investigate known vulnerabilities in similar jamming systems.
Craft the Exploitation Signal:
• Noise Overloading:
o Design a high-power noise signal to overload the jammer’s receiver.
o Use GNU Radio to create a wideband noise source and configure the power levels appropriately.
• Malicious Commands:
o Embed commands in the signal that could exploit flaws in the jammer’s processing logic.
o Utilize signal processing techniques to craft commands that may cause the jammer to execute unintended actions.
• Signal Manipulation:
o Manipulate the signal timing, phase, or frequency to disrupt the jammer’s normal operation.
Set Up the SDR Transmitter:
• Select SDR Hardware:
o Use an SDR device like Ettus Research USRP, HackRF, or similar.
• Connect Transmitting Antenna:
o Attach a suitable antenna for transmitting the custom signal.
• Load the Signal:
o Open the GNU Radio flowgraph containing the custom signal.
o Verify the parameters to ensure they match the intended exploitation technique.
Transmit the Exploitation Signal:
• Begin Transmission:
o Start transmitting the custom-crafted signal using the SDR.
o Monitor the transmission to ensure stable and continuous output.
• Adjust Power Levels:
o Set the transmission power to a level that effectively interacts with the jammer without causing unintended interference to other systems.
Evaluate the Impact:
• Monitor Jammer Response:
o Use a second SDR or spectrum analyzer to observe the jammer’s response to the exploitation signal.
o Look for signs of overload, command execution, or malfunction.
• Adjustments:
o Make real-time adjustments to the signal characteristics as necessary to enhance the impact on the jammer.
Testing:
• Controlled Environment:
o Conduct initial tests in a controlled environment to fine-tune the exploitation signal.
• Real-World Testing:
o Deploy the signal in real-world scenarios to assess its effectiveness in degrading or neutralizing the jammer.
Refinement and Optimization:
• Iterative Improvements:
o Based on test results, continuously refine and optimize the exploitation signal.
References
 GNU Radio. (n.d.). Your first flowgraph. Retrieved July 30, 2024, from https://wiki.gnuradio.org/index.php?title=Your_First_Flowgraph
 Knox, J., Zaman, M. U., & Doufexi, A. (2015). Full-duplex communications with the use of parasitic array radiators. IEEE Communications Letters, 20(1), 7-10. https://www.researchgate.net/publication/283097164_Full-duplex_communications_with_the_use_of_parasitic_array_radiators
 Zhang, X., Chai, Y., Yu, G., & He, C. (2015). Full-duplex wireless communications: Challenges, solutions, and future research directions. IEEE Wireless Communications, 22(6), 108-116. https://doi.org/10.1109/MWC.2015.7117271

Authored by The Living Legend

Robi Sen