Ask Our Experts (AOE): What Is Qi 1.3 Wireless Charging Authentication?

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 Wireless Charging Specification for the cell phone market?

The Wireless Power Consortium (WPC) is the organization that is responsible for the development of global specifications in order to unify specifications surrounding 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 referred to 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 have several apps going like a music app, GPS and a number of other apps. So, even though 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 that in 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 a poorly designed charger that is claiming to be Qi Compliant but isn't. This can actually cause damage 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 now requires hardware-based authentication. So now, when you place a cell phone on the charger, it will initially accept either a 0W charge or a 5W charge, then it will go through an X.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 you go through that authentication process, the cell phone would accept up to a 15W charge at this point, staying well ahead of the curve of what it burns down on its battery when you're using all the applications at the same time.

In order to do that, there is also a supplemental specification, which is the authentication specification, which mandates that you have to select a high quality secure storage subsystem; some might call that a secure element. In any event, you need to prove its security worthiness by submitting to a third party. One of the ways that you can prove security worthiness is to get a Joint Interpretation Library (JIL) score of JIL High, which is the highest score available, which our CryptoAuthentication™ devices and CryptoAutomotive™ 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 WPC Root Certificate Authority with that certificate chain. Provisioning comes into play here, which is why Microchip Technology has become a licensed WPC Manufacturing Certificate Authority. That allows us to submit certificate signing requests on behalf of our customers to the WPC root and allows us to get a root certificate, a unique power transmitter manufacturer certificate, which is the manufacturing certificate. Then ultimately we can create independent and unique product-level certificates, which would mean that every power transmitter on the market would have a unique ECC P256 key pair with an associate X.509 certificate that roots all the way back to the WPC.

We also have a full solution and one-stop shop, which includes our dsPIC33c series to enable all of the charging applications and that comes with the Qi stack. We have the secure storage subsystem items like the ECC608, or the Trust Anchor TA100. Also, we have an associated cryptographic library that goes along with those, then provisioning, and ultimately we have approved reference designs available to make your life easier when you're designing a 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 our Secure Elements web page.