System Bus Radio is a software tool that transmits AM radio signals from computers without radio transmitting hardware.
The tool addresses a specific security research problem: extracting data from air-gapped computers that have been intentionally isolated by removing internet, wireless, Bluetooth, USB, and audio capabilities. It works by executing CPU instructions that cause electromagnetic radiation across a broad frequency range. The specific instruction used, `_mm_stream_si128`, writes through to memory addresses in a way that generates emissions. By trial and error, certain frequencies can be tuned to escape the computer's shielding, propagate through air or obstacles, and be received by a standard AM radio receiver. The approach is grounded in documented electromagnetic exfiltration techniques referenced in TEMPEST guidelines from the US National Security Agency and Department of Defense.
This tool is intended for security researchers and those studying air-gap vulnerabilities rather than general developers. It suits projects involving security analysis, penetration testing of isolated systems, and electromagnetic side-channel research. The tool has been demonstrated to work on a 2015 MacBook Air transmitting to a Sony STR-K670P radio receiver tuned to 1580 kHz, achieving clear transmission over two meters in open air or one meter through drywall. Results vary significantly based on hardware, antenna placement, and receiver equipment. The project actively solicits test results from users with different hardware configurations, particularly embedded systems like Raspberry Pi, to map frequency response across diverse platforms.
Development activity shows ongoing engagement with the research community. The project maintains a test data file documenting results across different equipment configurations and invites community contributions through pull requests. The tool includes a browser-based demonstration interface for experimentation without requiring compilation. Documentation includes a guide for receiving signals using RTL SDR hardware, expanding the project's utility for those studying the phenomenon.
