Issues with Zephyr Peripheral NFC Pairing Example

[andreribeiro423]

Hi! Following my last post, I continue having problems with Zephyr Peripheral NFC Pairing Example on verifying the packets exchanged since as soon as I touch the NFC antenna with my smartphone I cannot see any Security Manager Protocol (SMP) packet exchanged in Wireshark. I needed to visualize these packets to ensure that Pairing Feature Exchange and next pairing steps (key exchange) are occurring as intended (LE Secure Connections OOB pairing).
I checked out the Sniffing the pairing procedure of a connection in the nRF Sniffer user guide. Since I am using LE Secure Connections I had to enable Secure Connections Debug Mode on the device. So, for that I added the CONFIG_BT_USE_DEBUG_KEYS=y on the prj.conf. However, after this I continued not to see any Security Manager Protocol (SMP) packet exchanged in Wireshark during the pairing procedure. I also checked out the menuconfig for exploring the available Kconfig options and ensure that the Secure Connections Debug Mode option is enabled.
Thank you for your help!

[Simonr]

Hi

I think the reason you're not seeing this data on Wireshark is because the OOB pairing share encryption keys/authentication data over the "alternative" communication channel, in this case being NFC.

Wireshark won't be able to sniff any data transferred over NFC as it's a completely different protocol and frequency than BLE.

Best regards,

Simon

[andreribeiro423]

But if I enable Security Manager Debug Mode, the connection uses the debug keys specified in the Bluetooth Core Specification Vol. 3, Part H, 2.3.5.6.1 and anyone is able to decipher encrypted air traffic. So, the sniffer should be able to join in on the OOB pairing because uses the same keys to decrypt the encrypted packets (debug private/public key pair described in Core Specification Vol. 3, Part H, 2.3.5.6.1).

[Simonr]

But the Security Manager Debug mode is something completely different that transmits the keys over BLE. Have you followed the "Sniffing the pairing procedure" guide that tells you to enter the private key into the input field of Wireshark in a big-endian, hexadecimal format with a leading "0x" on your end? If so you will see BLE packets on the sniffer trace. What nRF device are you using for sniffing by the way?

Best regards,

Simon

[andreribeiro423]

Hi! I already understood what my problem was. Thanks for all the help!

[Simonr]

You're welcome to share your solution here so that DevZone users with the same issue in the future might find it helpful.

Glad you figured it out!

-Simon

[andreribeiro423]

Sure! The problem was that as advertising is only performed after touching the NFC antenna, the intended device does not appear in the Wireshark device list during the first pairing. As the exchange of SMP packets takes place before advertising starts, if the device is not selected in the list of devices in Wireshark, the SMP packets do not appear. Thus, in the following pairings, the device is already displayed in the device list and if it is selected, the SMP packets are already displayed.