As you probably know, radio hacking is at the forefront of cybersecurity. Many devices and systems we rely on every day operate through radio signals, including:
Cellphones
Drones
Wi-Fi
Bluetooth
NFC payment systems
Car key fobs
Home security systems
RFID
Satellite communications
GPS, and much more.
This post is for those who are new to radio technology. If you’re already familiar, consider this a helpful review. The goal is to equip you with the foundational knowledge to dive into the exciting world of radio hacking!
Electromagnetic Radiation
We all interact with radio signals daily, even if we don't realize it. Radio communication is so commonplace that many people forget how remarkable it actually is. When we mention "radio," most people think of the devices that play music in their cars, but radio waves are used for far more than just that. To set the stage, let’s start with some basics.
How does radio work? You likely learned in school that when a voltage is applied to metal plates, an electric field is generated. Similarly, when current flows through a wire, it produces a magnetic field. The interaction between these electric and magnetic fields creates what we call radio waves.
When a current in a wire changes, it alters the magnetic field around it. This, in turn, produces a voltage in nearby wires, creating an electromagnetic wave. These waves share similar properties with light, and in fact, visible light itself is a type of electromagnetic wave. Like light, these waves can be reflected, refracted, diffracted, absorbed, and filtered.
Now that we’ve covered how these waves are generated, let’s move on to understanding some of the key properties of these waves.
Frequency
The figure of an electromagnetic wave often takes the form of a sinusoidal pattern. This describes the regular, wave-like movement of a signal. The frequency of a wave refers to how many times it completes a cycle in a given time period. To imagine it, think of pedaling a bicycle. A complete cycle occurs every time your foot returns to its original position.
Electromagnetic waves travel at the speed of light (about 186,000 miles per second). Their frequency, which is measured in hertz (Hz), defines how many cycles occur in one second. For example, 1 cycle per second equals 1 Hz, 1,000 cycles per second equals 1 kilohertz (kHz), 1 million cycles per second equals 1 megahertz (MHz), and 1 billion cycles per second equals 1 gigahertz (GHz).
For our purposes, we’ll focus on frequencies ranging from about 1 MHz to 6 GHz.
Understanding frequency is crucial because it impacts how radio signals travel and interact with their environment. Lower frequencies, for instance, can bend and diffract around objects more easily than higher frequencies.
Why is Frequency Important?
Range: Lower frequency waves travel farther. For example, AM radio waves, operating between 530-1700 kHz, cover much larger areas than FM radio, which typically operates between 88-108 MHz.
Data Transmission: Higher frequencies can carry more data. This is why modern cellular networks use frequencies in the 1.7-2.2 GHz range, enabling much faster data transmission compared to older systems.
Interaction with Objects: Low-frequency waves can penetrate walls, while higher frequencies tend to reflect or get absorbed. This difference in behavior is why lower-frequency signals are used for applications where signal penetration is critical, like weather forecasting and air traffic control.
Different frequencies are designated for specific purposes. Wi-Fi and Bluetooth, for example, work at around 2.5 GHz (similar to your microwave), while car key fobs in the U.S. operate at 315 MHz. Meanwhile, airplane transponders communicating GPS data work at 1090 MHz.
To hack or manipulate these signals, you'll need the right software-defined radio (SDR) device. Here's a quick rundown of the most common SDR devices and their capabilities:
Flipper Zero: Operates below 1 GHz, so it can’t handle signals like Wi-Fi, Bluetooth, or cellular without modifications.
Ettus and HackRF One: Capable of receiving and transmitting across a wide range of frequencies, making them highly versatile for most hacking purposes.
Lime SDR: Has two transmitters and two receiver channels, ideal for more advanced applications.
Wavelength
The wavelength of a signal refers to the physical distance a wave travels in one complete cycle. It can be calculated by dividing the speed of light by the signal’s frequency.
For instance, a Wi-Fi signal at 2.5 GHz has a wavelength of:
300,000,000 meters/second2,500,000,000 cycles/second=0.12 meters\frac{300,000,000 \text{ meters/second}}{2,500,000,000 \text{ cycles/second}} = 0.12 \text{ meters}2,500,000,000 cycles/second300,000,000 meters/second=0.12 meters
This means that during one cycle, a Wi-Fi signal travels 0.12 meters.
Because the speed of light is constant, any radio signal can be described in terms of either frequency or wavelength. However, radio signals are typically categorized by their frequency in most industries.
Conclusion
To become proficient at radio hacking, understanding the fundamentals is key. In this first part of the series, we've covered the basics of electromagnetic radiation, frequency, and wavelength.
Author: David Freire - Sales Representative and Editor at Black Hat
Editor: Jordan Rodgers - Lead Technologist at Black Hat
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