BLE pairing authentication fail after migrating to ncs3.0.2

[ziv123]

Hi Nordic

i am working with nrf52832 and nrf52840

After migration from ncs2.9.2 to 3.0.2 my device (end point) has an issue with pairing to one of the gateways (the gateways are not ncs/zephyr based).

In the end point device logs i see this pair fail reason “BT_SECURITY_ERR_AUTH_REQUIREMENT”

I had this call “bt_conn_set_security(conn, BT_SECURITY_LX);” in the pairing_complete() callback.

i tried putting it in the connected() callback, thinking maybe it was a timing issue but it did not help

i am working with SoftDevice controller (CONFIG_BT_LL_SW_SPLIT=n) 

the strange thing for me is that it worked fine in 2.9.2 with the same gateway so what changed ?? , and how can i solve this issue ?

(I intend to use a sniffer to try and catch what the gateway (central) requests in terms of security and see if there is a diff between the gateway that manages to pair and the one that gets failing (may need help with that as well later on))

Hope to read you soon

Best regards

Ziv

[Susheel Nuguru]

Hi Ziv, 

The migration notes for NCSv3.0.0 seems to have stated

 The :kconfig:option:`CONFIG_BT_SMP_SC_PAIR_ONLY` Kconfig option is enabled by default in Zephyr.

If you want the same behavior as before, then maybe you can try setting CONFIG_BT_SMP_SC_PAIR_ONLY=n in your prj.conf to override this new default and see if you get the behavior similar to what you saw with NCSv2.9.0. Test and let me know.

[ziv123]

seems like it is related to this config  "CONFIG_BT_SMP_SC_PAIR_ONLY"

which in ncs2.9.2 is not set but in ncs3.0.2 is by default =y .. which means the device expects the gateway to communicate in secure pairing only, and there is no tolerance for gateways which practice legacy pairing (here is the explanation about the diff between the two - https://academy.nordicsemi.com/courses/bluetooth-low-energy-fundamentals/lessons/lesson-5-bluetooth-le-security-fundamentals/topic/legacy-pairing-vs-le-secure-connections/ )

this is mentioned in zephyr 4.1 migration guide  https://docs.zephyrproject.org/latest/releases/migration-guide-4.1.html#bluetooth-host:~:text=set%20to%200.-,LE%20legacy%20pairing,-is%20no%20longer

(... i wonder why we must go over migration guides of 4.0, 4.1 and ncs instead of just the ncs for that but that's just me) 

changing the config to  =y solved the issue and all gateways can connect and pair with the devices now

best regards

Ziv