Gatt Read/write and insufficient key size error

[Mahendra Tailor]

Hi

When a GATT Table is created using the softdevice api, how do specify that a service or characteristic shall have a minimum key size of X so that if the current encrytion was done with a key <X size, then it will read with the  BLE_L2CAP_CH_STATUS_CODE_INSUFF_ENC_KEY_SIZE  error.

For that error to result, I would have to specify the minimum key size when a add a characteristic (or service) but I cannot find the relevant api to specify that.

I will be most grateful to any pointers.

Look forward to hearing from you

Kind regards
Mahendra

[Hung Bui]

Hi Mahendra, 

Currently our stack doesn't have an option to set the key size requirement for each attribute. You can set the security level but not the key size, by the stack. 

What you need to do is to handle that by the application.

You can return BLE_GATT_STATUS_ATTERR_INSUF_ENC_KEY_SIZE ( not BLE_L2CAP_CH_STATUS_CODE_INSUFF_ENC_KEY_SIZE as it's for L2CAP channel )  when there is an authorized read request or write request. 

[Mahendra Tailor]

Hi
Thank you for getting back.
The workaround you suggest requires that authorisation be enabled for read/write.

Is that correct?

Regards

Mahendra

[Mahendra Tailor]

Is it planned to add this feature in a future softdevice?

[Hung Bui]

Yes, It's correct. You neeed authorisation be enabled on the characteristic. 

I don't think it will be implemented in near future on the softdevice. Not 100% sure about the Zephyr stack though.