A basic primer
All digital electronic device use electrical signals to work. These signals are manipulated and in case of digital ones, between two voltage levels, they oscillate. These eletrical signals are carried through by conductors which generate small EM signals as well as a side-effect. Now, communication today uses such varying EM signals (modulated signals) for the process. Thus with sufficient effort, one can, in theory, use these stray EM signals to transmit data which can then be picked up by an attacker. Imagine a confidential document sent to print and the printer silently transmitting all the contents to an attacker. Scary!
Diving into the details...
Cui, with about 4 lines of code, injected to the embedded firmware of the printer, can program it so that it can transmit data using these stray EM signals. But there range is so short that it is almost useless. This is where the cleverness comes in – in order to generate waves which can transmit information, they need to be sufficiently powerful and this is done by switching the states of the digital electronic circuitry at variable frequencies to generate the carrier waves which can then carry the modulated signal which has the actual information. Though Cui’s current demonstration can only beam the information to a few metres, he predicts that the range can be increased to more than 30m and the signals can even penetrate reinforced concrete walls.
The possible ramifications
With the age of Internet-of-Things dawning upon us, such an easy hack could prove to be a tremendous security hole which can be hard to plug. Since the medium of transport is not something monitored (its not WiFi or over wires), The trick performed was on a cheap laser printer and thus implies that anything with an embedded computer can be used in this attack renndering all the connected devices to emit information to attacker at will. This calls for stricter rules and better electronic components. Such leakage can be stopped but will come at a price hike. EM sheilding can be done with metal cages but may not be feasible always and might need better methods.
The funtenna experiment by Cui demonstrates basically that with persistence and ingineuity, almost all digital electronic device can be used to transmit information in secret without being detected. With the IoT age upon us, we need to significantly step up our security game or it maybe too late...