Security is a critical issue in wireless communication. When using Bluetooth Low Energy (BLE), Simple Secure Pairing is used when two devices wish to communicate securely. This process establishes a secret link key to correctly authenticate devices. However, in most cases the pairing process itself is carried out on the same exposed wireless medium and is therefore still vulnerable to interceptions and attacks. To enhance security during the pairing process, Laird developed a unique approach called Whisper Mode.
While pairing is in progress, the transmission power is significantly decreased. This ensures that pairing is not completed unless the devices are within a relatively close proximity to each other. This proximity-enhanced security adds the extra level of trust that can be used to authenticate BLE devices. An additional benefit of Whisper Mode is that end users of products that are implementing Laird’s BL600 Series can be certain they are connecting to the correct, intended remote device by simply bringing them into close proximity. Finally, Laird’s Whisper Mode may decrease footprint and bill of materials (BOM) costs for OEMs by removing requirements for additional wireless technologies, such as Near Field Communications (NFC); it provides similar attributes from within the BL600 module.
Whisper Mode pairing is achieved with the function BleTxPwrWhilePairing(). This function, called once at startup, sets the transmit power of all packets that are transmitted while pairing is in progress. Radial measurements have shown that setting the pairing transmit power to -55 creates a ‘bubble’ with a radius of about 30 cm, outside which pairing will not succeed. This should be decreased even further if the BL600 Series module is covered by the final product enclosures which affect the radio’s overall RF performance.
Learn more about how to configure, load, and test Whisper Mode Pairing in the Whisper Mode Application Note.