Write Characteristic only when Paired

[Joao Dullius]

NCS 2.1.0 / nRF52840-DK

Hello,

I have a single write characteristic on my service:

BT_GATT_SERVICE_DEFINE( custom_srv,

                        BT_GATT_PRIMARY_SERVICE(BT_UUID_CUSTOM_SERVICE),

                        BT_GATT_CHARACTERISTIC( BT_UUID_ADV_PERIOD_CHRC,

                                                BT_GATT_CHRC_WRITE_WITHOUT_RESP,

                                                BT_GATT_PERM_WRITE,

                                                NULL, on_write, NULL),

                        );

How do I set that this characteristic can be only written if there is an active pairing with the device?

In other words, I want user to only be able to write characteristic if security level is 3 or above.

[Hung Bui]

Hi Joao, 

It's not possible to do the exact feature as you mentioned that the service/characteristic only visible to paired device. 
But you can either do what you did to require permission or you can add the service/characteristic after you know that the link has been encrypted. 
You can have a look at my example here on how to add a service/characteristic after connected: https://devzone.nordicsemi.com/support-private/support/290356#permalink=769225