MIT researchers have built a new chip that blocks attempts to wirelessly charge a device’s battery unless the charger provides the required cryptographic authentication.
According to the researchers from MIT’s Microsystems Technology Laboratories, this could help contain the problem of counterfeit wireless chargers causing power surges that fry a device’s circuitry.
The same technology also solves another problem with wireless chargers. When two devices share a single charger, if they are different distances from the charger’s electrical coil, their charging rates can vary enormously, to the extent that one device might charge fully while the other remains virtually uncharged.
In the same way that the researchers’ chip can block power transfer from an unauthorized charger, it can slow the power transfer to a device nearer the charging coil, ensuring more equitable charge rates.
“Security is one of the most critical issues in the ‘internet of things,’” says Professor Anantha Chandrakasan, referring to the popular idea that vehicles, appliances, civil-engineering structures, manufacturing equipment, and even livestock will soon have sensors that report information directly to networked servers. “We will see security functionality embedded into virtually every function and component of an IoT node.”
In a wireless charging system, both the charger and the target device contain metal coils. The device’s coil must be “tuned” to the transmission frequency in order to receive power.
The MIT researchers’ chief innovation is a more compact and efficient circuit for tuning the frequency of the receiving coil. A standard tuning circuit connects the coil to a series of capacitors, electronic components that can store charge. Between each pair of capacitors is a switch, and switching capacitors on and off changes the receiver’s frequency.
Instead of a single coil attached to a bank of capacitors, the MIT researchers’ design uses a pair of coils attached to one capacitor each — no switches required.
The chip uses an authentication technique called elliptic curve cryptography, which is a “public-key” cryptographic technique. Using publicly available information, the chip can generate – and verify the response to – a question that only a charger with valid private information can answer.
The chip doesn’t need to store a secret key of its own. Moreover, the researchers have found a way to simplify the encryption circuit so that it takes up less space on the chip and consumes less power.
Image credits:Christine Daniloff/MIT