Pairing passkey , cancel pairing on android side still give access to characteristic

[Olfox]

Hi ,

I'm working on nrf52833, s113. 

I have trouble to secure my system. It has no kayboard or screen, and with 6digit fixd pathkey( no other choice).

That's mean it advertise once wake up with accelerometre. 

I want to protect access to my 4 characteristics. So i enable bounding and  MITM. to have the passkey popup on android. Without MITM, i don't have passkey pop up. But then the strange stuff appar:

My program is based on hrs example + dfu merging.

I was thinking that, by using pairing protection with 6 digit fixed pathkey( no other choice cause no IO), i would not be able to read/write my characteriqtics. But with nrfConnect, if you are fast enough, when bounding window pops up , and you click cancel and really fast after, you are able to click on the row to read a characteristics, the connexion is maintained and you have access to all , without been securly paired !!! Note that here, my charac are in OPEN. I juste relly on the fact that the passkey will avoid to go next step...

I know i can protect each caracteristic by using : BLE_GAP_CONN_SEC_MODE_SET_ENC_NO_MITM , what i did. 

But a side effect appears: after first pairing on the phone by writing the 6 digit passkey, the same windows pops up FOR EACH characteristic you read ( only the first time) ... so it s a bit anoying because you have the feeling to have paired at connexion step , but in fact it has absolutely no impact on security.

If you click cancel you are still connected and if fast enough you can even have access to all. If you paired successfully, you will have to enter this same path key for each characteristic you have protected, what give a strange effect to the final user, he has the feeling that first pairing didn't worked.

What i need is :First, ask pairng after connect. If yes 6digit ok , no more asked user to enter pathkey. If no or cancel, close connexion or retry but doesn't give access. Only paired device should have access.

Hope to have been clear :)

[Amanda Hsieh]

Hi Florian, 

Olfox said:

Hm so it is "normal" .

That is not normal. It is a known issue on our app. 

Olfox said:

A.

- use a read autorization on characteristic that should generate BLE_GATTS_EVT_RW_AUTHORIZE_REQUEST event in ble_on_ble_evt function, for each trial of reading. I will clear a timeout timer in this event. If timeout timer occurs, i force disconnection.

I think it's a good solution. You could add a timeout in your application to check if you get some activity specific to the app you are using (read or writes to a specific characteristic etc). See my colleague Susheel's answer in this post for the timeout implement. 

Olfox said:

B.

Rely on the NRF_BLE_CONN_PARAMS_MAX_SUPERVISION_TIMEOUT_DEVIATION that, if i understood should expire after a certain time of inactivity, what is not the case in my application it is set to 65535 so around 11minutes but it never generate any ble event or force disconnect. Do i understand correctly its purpose ? Is there some code to add to manage it ?

 All BLE connections have a supervision timeout. If there are no packets within the supervision timeout, the connection will end with the disconnect reason being "timeout". However, the BLE connection will not end, as long as the BLE stack on the phone still works. From your log, the master (phone) still sent the ack. Therefore, it would not disconnect after a supervision timeout.

 -Amanda H. 

[Olfox]

Ok issue of fast connect /disconnect happens with your app, but also with mine, so may be it is linked to Android ?

I have implemented the reste to check for disconnexion and it works fine :).

We are very busy now with pairing in our app. Do you know if NrfConnect i sable to get from IOs and Android the list of paired devices ?

Because we scan and try to connect to a list of paired succesfully devices saved into our app when we launch it. But imagine user has unpaired with android menu. we try to connect something unpaired. So in running mode , the pop up pairing keys happens to enter 6 digit. But It is on top of our app and we have no way to give the good code to enter to the user...