Searching for the Light: Adventures with OpticSpy

Conference:  Defcon 26



The presentation discusses the use of various devices and techniques for transmitting and receiving data in a secure manner.
  • The speaker demonstrates the use of a hackable badge with an infrared LED to transmit data
  • The speaker also showcases a device called Tomu, which can be used to control LEDs through a computer
  • The presentation also covers the use of logic analyzers and oscilloscopes to decode signals
  • The speaker emphasizes the importance of setting threshold voltages and using comparators to ensure accurate signal decoding
The speaker uses a parallax electronic badge to demonstrate the transmission of data through an infrared LED. The badge has no visual indication of data transmission, but the speaker is able to capture and verify the message using a photodiode. This method was used during production to test the badges.


In the counter-future where we, the dissidents and hackers, have control of technology, sending secret messages through blinkenlights can let us exchange information without being detected by dystopian leaders. By modulating light in a way that the human eye cannot see, this simple, yet clever, covert channel lets us hide in plain sight. To decode such transmissions, we must employ some sort of optical receiver. Enter OpticSpy, an open source hardware module that captures, amplifies, and converts an optical signal from a visible or infrared light source into a digital form that can be analyzed or decoded with a computer. This presentation provides a brief history of covert channels and optical communications, explores the development process and operational details of OpticSpy, and gives a variety of demonstrations of the unit in action.



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