Qi® 1.3 Wireless Charging Authentication

Microchip expert Todd Slack shares details on the mandated addition of authentication in Qi® 1.3 wireless charging transmitters and how you can leverage Microchip Technology-certified reference designs to get the process started.

The following question and answer comes from our Ask Our Experts | About Secure Elements playlist on YouTube.

Can you explain the role of secure elements in the Qi® 1.3 WirelessCharging Specification for the cell phone market?

The Wireless Power Consortium (WPC) is the organization thatis responsible for the development of global specifications in order to unify specificationssurrounding wireless charging protocols. So, initially, when they released version 1.0,and ultimately 1.1, it supported a power level of up to five watts (W), which is now referredto as the Baseline Power Profile (BPP). With the 5W limitation, the problem is that in some cases the battery can actually continue to drain while receiving a 5W charge. Imagine driving in a car: you place your phone on the wireless charging pad, and you haveseveral apps going like a music app, GPS and a number of other apps. So, eventhough your cell phone is sitting on the charger, you'll see the battery drain down because it may require 7 or 8W to keep up with the power demanded to support all of the running applications.

With thatin mind, in 2015 the WPC introduced version 1.2 of the Qi specification with the Extended Power Profile(EPP) that now goes up to 15W. But, at the time, it did not require any authentication.With no authentication, someone could end up placing a receiver or a cell phone on apoorly designed charger that is claiming to be Qi Compliant but isn't. This can actually causedamage to the cell phone itself. With cell phones costing over $1,000, that's certainly a problem.To take care of that, Qi 1.3 has recently been released and Qi 1.3 nowrequires hardware-based authentication. So now, when you place a cell phone on the charger, itwill initially accept either a 0W charge or a 5W charge, then it will go through anX.509 based authentication and challenge-response, cryptographically proving the source of the power transmitter manufacturer,and that it has been approved by the WPC or their accredited labs. Once yougo through that authentication process, the cell phone would accept up to a 15W chargeat this point, staying well ahead of the curve of what it burns down on its battery when you'reusing all the applications at the same time.

In order to do that, there is also a supplementalspecification, which is the authentication specification, which mandates that you have to selecta high quality secure storage subsystem; some might call that a secure element. In anyevent, you need to prove its security worthiness by submitting to a third party. One of the waysthat you can prove security worthiness is to get a Joint Interpretation Library (JIL) score ofJIL High, which is the highest score available, which our CryptoAuthentication™ devices andCryptoAutomotive™ security ICs have achieved, so we can support the silicon side of secure storage subsystems. The next important point is that you have to be licensed and rooted back to the WPCRoot Certificate Authority with that certificate chain. Provisioning comes into play here, whichis why Microchip Technology has become a licensed WPC Manufacturing Certificate Authority. Thatallows us to submit certificate signing requests on behalf of our customers to the WPC root andallows us to get a root certificate, a unique power transmitter manufacturer certificate,which is the manufacturing certificate. Then ultimately we can create independent andunique product-level certificates, which would mean that every power transmitter on the marketwould have a unique ECC P256 key pair with an associate X.509 certificate that roots all the wayback to the WPC.

We also have a full solutionand one-stop shop, which includes our dsPIC33c series to enable all of the chargingapplications and that comes with the Qi stack. We have the secure storage subsystem itemslike the ECC608, or the Trust Anchor TA100. Also, we have an associated cryptographiclibrary that goes along with those, then provisioning, and ultimately we haveapproved reference designs available to make your life easier when you're designinga Qi 1.3 compliant power transmitter.

Want More?

Make sure to check out our WPC Qi 1.3 Reference Design page. For more information, check out our Ask Our Experts | About Secure Elements playlist on YouTube and ourSecure Elementsweb page.

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