The Art of Pairing

It's an old chestnut the pairing conundrum, how to make it safe and secure yet so simple people aren't left confused and frustrated whilst trying to pair products. Bluetooth Smart currently has 3 pairing options:

• Passkey entry
• Just Works
• OOB

Passkey entry has long been the mainstay for keyboards, suited as it is to displaying a code on the PC screen that the user enters on the keyboard to securely pair. Products with no means for user entry and no display, such as Bluetooth headsets have relied on Just Works with its limited security. The third option, Out Of Band (OOB) pairing, over NFC, represents the most secure option available by completing the pairing process and encryption key exchange entirely Out of Band (OOB) at 13.56MHz where NFC operates. The very limited range that is inherent to NFC, typically mm to a few cm, means it is next to impossible to eavesdrop without becoming apparent to the user.

nRF52832 on-chip NFC-A Tag Support

The nRF52832 is the world's first Bluetooth Smart SoC with on-chip NFC support. Nordic took the decision to implement this in the nRF52 series as we see NFC playing a major role for Bluetooth Smart pairing in the future. NFC-A Tag is standard to the nRF52832.

A rather nice feature is the wake-on-field on the nRF52832. This allows the device to be in SENSE mode, with all other peripherals in OFF mode, consuming only 100nA, thus using minimal energy. On detection of the NFC field in close proximity the nRF52832 wakes up and is read for work.

The NFC peripheral operates in a read-only mode, suitable for touch to pair, so it exposes information for pairing but doesn't read information out of the smartphone per se.

Hardware implementation takes care of the RF and baseband logic and handles collision resolution. As an nRF52832 peripheral the NFC has full PPI access to engage with other peripherals directly and is hooked up to EasyDMA allowing read/write directly to memory. The NFC driver libraries take care of the rest, this largely software implementation means there's lots of future scope for additional libraries as new use cases and possibilities arise, and we will be right on top of that as they happen.

fig 1.The pairing process with NFC for Bluetooth Smart

Give it a spin

If you’re interested in exploring NFC touch to pair possibilities, then we’ve added an antenna port on the nRF52 development kit. We’ve even been kind enough to ship the nRF52 DK with an NFC antenna to get you started.

As NFC’s working at 13.56MHz, much lower down than the 2.4GHz where Bluetooth does its stuff there’s none of the usual high frequency matching headaches some of you will know when working at the gigahertz level. No, just plug the antenna into the board and you can get experimenting with NFC.

The supporting nRF52 SDK contains examples for implementing touch to pair in your applications.

Simplifying Wearables, IoT and more

It seems to us that the complimentary nature of NFC and Bluetooth Smart is something of a slam-dunk. Bluetooth Smart's got the low power comm's down pat, NFC with its inherent range limitations plays perfectly into that first use scenario, the pairing bit.

Wearables will obviously benefit as the smartphone is the yin to their yang. But look a little further and more interesting cases appear.

All this IoT stuff that we are told that we are all about to start buying or using at home, at work, at play, at sleep etc. Well if you think about most of those 'things', they are likely to mostly be sexily designed boxes, though many will be pretty ugly too, with little more than an LED or two for our viewing pleasure.

Not much chance of passkey pairing there, no, definitely a shoe-in for NFC pairing we think. Further scenarios start to flood in when you give this a bit of thought. IoT will see its biggest overall impact in the smart city concept, largely in new build installations. Electricians and installers will be tasked with a lot more than running in cables and terminating, there could be tens or hundreds of installs happening in the same time frame and it could prove a hellish mess to attempt that with pairing scheme that has meters of range as opposed to centimeters of range. Tap to pair, job done!

NFC gaining momentum

Success, as with any technological standard, requires a certain level of critical mass to spawn innovative usage of the technology. NFC has been around for a while but the last couple of years have seen a steady inclusion into smartphones and tablets. The smartphone as payment device is the major driver but it is already generating new NFC use cases, touch to pair will surely be a big one of these.

OS Dependencies and the entry of Apple

The current libraries in nRF52 SDK support a simple NFC pairing mechanism which is followed by ‘Just Works’ pairing for Bluetooth Smart. There’s a good reason for this however. Right now the major phone vendors aren’t offering native OOB pairing for Bluetooth Smart it is expected many will come with the adoption of Bluetooth’s Simple Secure Pairing but for now it’s possible to tap to pair over NFC which triggers the Just Works pairing mechanism, which is still a much simpler user experience than performing standard Bluetooth Smart pairing from the often lengthy and confusing devices list in the Bluetooth menu on your phone. You can currently try out NFC pairing on the nRF52832 with a Nexus 7 and Samsung Galaxy S5/S6 models.

Apple had until recently decided to abstain from NFC in its iOS product line. However this all changed with the arrival of the iPhone 6, where NFC hardware is now present. Just this month it was announced that Apple had joined the board of NFC Forum, possibly a significant development for the future looks bright for touch to pair for Bluetooth Smart but we can only wait and see.

Check out our video showing the straightforward simplicity of touch to pair for Bluetooth Smart

nRF52 development kits are available from our distribution network now, for more details go to: www.nordicsemi.com

Learn more about The nRF52 Series for Bluetooth Smart

https://www.nordicsemi.com/Products/nRF52-Series-SoC