How to get past "link secure failed! error: PM_CONN_SEC_ERROR_DISCONNECT

RE: How to get past "link secure failed! error: PM_CONN_SEC_ERROR_DISCONNECT

Pierre Landau — Tue, 05 Apr 2016 22:17:37 GMT

With the help of your FAE (Audun), we were able to work around this by (a) changing SEC_PARAM_MITM to 0, SEC_PARAM_IO_CAPABILITIES to BLE_GAP_IO_CAPS_NONE, and then editing pm_evt_handler to remove the check for MITM.

Nowhere near clear why this manifested in the way it did, but at least we can now move forward.

RE: How to get past "link secure failed! error: PM_CONN_SEC_ERROR_DISCONNECT

Pierre Landau — Mon, 04 Apr 2016 20:17:17 GMT

Several seconds after these, I see: Rcvd Connection Parameter Update Request Rcvd Connection Parameter Update Reesponse (Accepted) but nothing relevant to pairing, and eventually the phone shows "not bonded" while RTT shows "link secure failed! error: PM_CONN_SEC_ERROR_DISCONNECT", which is not particularly informative

RE: How to get past "link secure failed! error: PM_CONN_SEC_ERROR_DISCONNECT

Pierre Landau — Mon, 04 Apr 2016 19:26:54 GMT

I had previously deleted the bonding on the phone; this time I also deleted the bonding tables on the nRF51 before running the sniffing session.

Unfortunately, I only see two apparently relevant packets: Master-->Slave, SMP, Rcvd Pairing Request: Bonding, MITM, Initiator Key(s): LTK IRK CSRK, Responder Key(s): LTK IRK CSRK. and Slave-->Master, Rcvd Pairing Response: Bonding, MITM, Initiator Key(s): LTK IRK, Responder Key(s) LTK IRK.

This is followed by a minute or so of empty data PDU's but no further packets that appear relevant to pairing.

RE: How to get past "link secure failed! error: PM_CONN_SEC_ERROR_DISCONNECT

FormerMember — Mon, 04 Apr 2016 08:52:07 GMT

The sniffer can catch the key exchange process. In order to do so, you have to make sure that the sniffer is present when the two devices exchange encryption keys, not just when the devices are re-connecting. You can upload the file in the original question, not in the comments.

Could you delete the bonding information on both the phone and the nRF51/52 device before using sniffer to capture the bonding process?

RE: How to get past "link secure failed! error: PM_CONN_SEC_ERROR_DISCONNECT

Pierre Landau — Sat, 02 Apr 2016 00:39:42 GMT

Sorry about that - apparently the pairing still did not succeed. I see "received pairing request (packet 1307). This shows: AuthReq: Bonding, MITM Max encryption size 16 Initiator key distribution: LTK IRK CSRK Responder Key Distribution: LTK IRK CSRK

Then Rcvd pairing response: Bonding, Initiator keys: LTK IRK, Responder keys LTK IRK (packet 1310) , followed by more than a minute of empty data PDUs until the remote disconnects.

RE: How to get past "link secure failed! error: PM_CONN_SEC_ERROR_DISCONNECT

Pierre Landau — Fri, 01 Apr 2016 22:46:04 GMT

So I got the sniffer set up. It basically didn't catch much of anything in the repeated pairing attempts until the pairing magically worked and it started capturing lots of traffic. No idea why the pairing was failing previously (in BT Classic you got to sniff the key exchange process but seemingly not so much here). I also wonder whether one of the newer Wireshark versions (I used 1.10 per instructions) might actually be able to decode Glucose Profile or Battery Level packets? I saved the file just in case it contains some hidden data on the pairing mess, but this page does not seem to have an easy "upload here" button.

RE: How to get past "link secure failed! error: PM_CONN_SEC_ERROR_DISCONNECT

FormerMember — Fri, 01 Apr 2016 07:44:31 GMT

It would be very useful to check what is being transferred over the air. Do you have an extra nRF51-DK or a nRF51-Dongle? If so, could you use the sniffer to track what is being transferred over the air? And upload the sniffer trace here?

The sniffer should be used with Wireshark, and it works best with version 1.10, not one of the newer versions. Wireshark can be downloaded here: