Software-Defined Radio for Signal Interception
Overview
Teaching: 50 min
Exercises: 0 minQuestions
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Objectives
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Software-Defined Radio (SDR) for Signal Interception
1. Introduction to Software-Defined Radio (SDR)
🔹 What is SDR?
Software-Defined Radio (SDR) is a flexible radio communication system where traditional hardware components (like mixers, filters, and amplifiers) are implemented via software. This allows for real-time signal processing, interception, and manipulation across a wide range of frequencies.
📡 Key Capabilities:
✔ Intercept and analyze wireless signals (WiFi, Bluetooth, GPS, RFID, cellular, etc.)
✔ Transmit, jam, or spoof radio signals
✔ Perform security assessments of wireless networks
✔ Conduct penetration testing & intelligence gathering
🛑 Cybersecurity Concern: SDR enables passive eavesdropping, active jamming, replay attacks, and RF-based exploits.
2. How SDR Works for Signal Interception
2.1 SDR Components
An SDR system consists of:
| Component | Function |
|---|---|
| Antenna | Captures radio waves from the environment |
| RF Front-End | Converts RF signals into digital form |
| Analog-to-Digital Converter (ADC) | Digitizes analog signals for software processing |
| DSP (Digital Signal Processing) | Extracts, analyzes, or modifies signals |
| Software Interface | Controls frequency tuning, decoding, and demodulation |
2.2 SDR Signal Interception Process
1️⃣ Tuning: The SDR tunes into a specific frequency range (e.g., 2.4 GHz for WiFi, 1090 MHz for aircraft ADS-B).
2️⃣ Capturing: The antenna captures raw RF signals, and the SDR converts them into digital form.
3️⃣ Decoding & Demodulation: Software tools process the signals to extract meaningful data (e.g., decrypting WiFi packets, listening to radio communications).
4️⃣ Analysis: The attacker or researcher analyzes the captured data for vulnerabilities.
3. SDR in Cybersecurity & Signal Interception
3.1 Passive RF Interception (Eavesdropping & Sniffing)
SDRs allow attackers to listen to and decode unencrypted communications, including:
| Targeted Signal | Vulnerability | SDR Tool |
|---|---|---|
| WiFi (802.11) | Capturing unencrypted packets | Aircrack-ng, Kismet |
| Bluetooth | Sniffing unsecured Bluetooth devices | Ubertooth One |
| Cellular (GSM, LTE, 5G) | IMSI catching & call interception | OpenBTS, IMSI-catcher |
| RFID & NFC | Cloning RFID cards & eavesdropping | Proxmark3 |
| GPS Signals | Spoofing GPS navigation | GPS-SDR-SIM |
✅ Defense:
✔ Use end-to-end encryption (TLS, WPA3, AES-256).
✔ Deploy frequency-hopping spread spectrum (FHSS).
3.2 Active SDR Attacks (Jamming, Spoofing & Replay Attacks)
SDRs can transmit malicious signals to disrupt or manipulate wireless communications.
| Attack Type | How It Works | Targeted Systems |
|---|---|---|
| WiFi Jamming | Overloads 2.4 GHz / 5 GHz with interference | WiFi networks |
| GPS Spoofing | Sends fake GPS coordinates | Drones, Vehicles |
| RFID Cloning | Records and replays RFID signals | Access control, key fobs |
| IMSI Catching | Tricks phones into connecting to rogue base stations | Mobile phones, IoT |
📌 Example:
- Using HackRF One to jam WiFi or disrupt IoT devices.
- Using an SDR-based IMSI catcher to track mobile phones.
✅ Defense:
✔ RF anomaly detection & signal authentication.
✔ Use GPS receivers with multi-frequency & anti-spoofing tech.
3.3 Military & Intelligence Applications
SDRs are heavily used in electronic warfare (EW), signals intelligence (SIGINT), and counterintelligence.
| Use Case | Application |
|---|---|
| Electronic Warfare (EW) | Jamming enemy radar & communications |
| Signals Intelligence (SIGINT) | Intercepting military & diplomatic communications |
| Counter-Surveillance | Detecting & neutralizing rogue SDR devices |
4. Popular SDR Hardware & Software
4.1 Common SDR Devices
| SDR Device | Frequency Range | Use Case | Price |
|---|---|---|---|
| RTL-SDR | 500 kHz – 1.75 GHz | Basic RF monitoring, ADS-B, GSM | $20-$50 |
| HackRF One | 1 MHz – 6 GHz | RF hacking, jamming, spoofing | $300 |
| LimeSDR | 100 kHz – 3.8 GHz | Advanced RF experiments | $300-$500 |
| USRP (Ettus Research) | DC – 6 GHz | Professional SIGINT, military use | $1,000+ |
4.2 SDR Software for Cybersecurity & Hacking
| Software | Purpose |
|---|---|
| GNU Radio | Open-source signal processing toolkit |
| SDR# (SDRSharp) | Easy-to-use spectrum analysis tool |
| GQRX | RF spectrum visualization & demodulation |
| Aircrack-ng | WiFi interception & decryption |
| IMSI Catcher | Mobile network sniffing & tracking |
5. Defending Against SDR-Based Threats
🔒 Encryption & Authentication
✔ Use end-to-end encryption (AES-256, WPA3, TLS 1.3).
✔ Deploy frequency-hopping spread spectrum (FHSS) & DSSS.
🔒 RF Anomaly Detection
✔ Monitor for unauthorized RF signals.
✔ Use SDRs for real-time spectrum monitoring.
🔒 Physical Security & RF Shielding
✔ Implement Faraday cages for sensitive environments.
✔ Restrict unauthorized SDR devices in secure locations.
6. Conclusion
Software-Defined Radio (SDR) is a powerful tool for signal interception, cybersecurity research, and electronic warfare. However, it also presents major security risks, as attackers can sniff, jam, spoof, and manipulate wireless communications across a wide range of frequencies.
✅ Key Takeaways:
- SDR enables wideband RF interception & active attacks.
- WiFi, Bluetooth, RFID, GPS, and cellular networks are vulnerable.
- Military, intelligence, and cybersecurity professionals use SDR for signals intelligence (SIGINT) and penetration testing.
- Encryption, authentication, and RF monitoring are critical defenses.
📡 Next Steps: Would you like a detailed guide on setting up an SDR for penetration testing, hands-on tutorials, or real-world case studies? 🚀
Key Points
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