Enabling BLE security mode 4 only on BLE and not on BLE-Mesh

Question

Hello, 
 
 I wanted to enable L4 security on my BLE connection, 
 
 /** Level 4: Authenticated Secure Connections and 128-bit key. */ 
 BT_SECURITY_L4 , 
 Hence added the param in my prj.conf as : 
 CONFIG_BT_SMP_SC_ONLY=y 
 
 But now as an unintended result the L4 security is also enabled for my BLE-Mesh models, and it is prompting me to enter key while provisioning. 
 
 Is this a bug..? How can I enable L4 security only for BLE and not for BLE-Mesh..? 
 
 Thanks,

tesc · Accepted Answer

Hi, 
 After some investigation, it turns out centrals waits until after a failed read/write before pairing. In other words, if the only service actually being used is the Mesh Proxy Service, then pairing should not be required, and therefore should not be triggered by the central. 
 Therefore it should be possible to set a higher security level on one service, and no security on another service, and as long as you only use the no security service you should get no pairing requests. There might however be other apps or OS functions reading or writing on certain characteristics, triggering the pair request. 
 In other words: By setting no security on the Mesh Proxy Service, it should be possible to use PB-GATT and only get the OOB for mesh, not the OOB for BLE pairing. 
 The CONFIG_BT_SMP_SC_ONLY=y should only affect services with security, so the behavior in terms of triggering pairing should not rely on it being n or y. 
 In order to figure out why you still get BLE pairing, I need more information about your setup. What kind of device is your central, and what other BLE services do you have on the device? 
 Regards, Terje

Enabling BLE security mode 4 only on BLE and not on BLE-Mesh

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