Getting rcvd Pairing Failed:Numeric Comparison Failed during pairing process

[prashaanth]

Hi,

I am using a nrf52840 dongle for sniffing the bluetooth connection between 2 devices. These are the wireshark logs secure_pairing_app.pcapng

What I could see is it initiates the pairing with secured connection then key exchange is happening and fails during the comparison. Where exactly can I debug to identify this issue?

I am trying to do justworks pairing, noinputnooutput. Please pour your suggestions here. 

Additional information:
My peripheral is based on ARM platform and it's an embedded device. My Master device is the app which initiates the connection.

[Elfving]

Hi, 

What is running on the embedded device? Have you checked that you can get a working connection with other SW running on it, or with a different app? Is it an nRF?

Regards,

Elfving

[prashaanth]

It is not a nrf I am filtering out for my device mac address in wireshark logs so if you see the slave is my device (which is having bluetooth 4 with bluez 5.55 version) mac address and master is the app so I am trying to sniff the bluetooth layer. When I sniff I see the packets says numeric comparison failure. There is the key exchange happenign but it fails in the numeric comparison of the keys.

What could be the possibility here?

[Elfving]

Make sure that the BlueZ version supports LESC pairing. And you mentioned you're trying to do Just Works pairing with NoInputNoOutput, but if the sniffed packets indicate a numeric comparison failure it might be a mismatch in the pairing methods between the devices.

Are there any error logs with info on any of the devices?

Regards,

Elfving

[prashaanth]

I could observe that when I do a default-agent on bluetoothctl 



How to enable the justworks pairing method?

Then I try to pair the device I don't see the numeric comparison issue and it says Sent pairing DHKey check but later there are no logs regarding the security.

I am using the latest bluez which is 5.78. I am attaching the bt monitor logs for your reference. Attaching my sniffing logs once I made the default-agent to be on without_numeric_key_issue.pcapngbtmon_logs.txt

[Elfving]

prashaanth said:

How to enable the justworks pairing method?

I won't be able to help you regarding getting that working with BlueZ. Try stack overflow or BlueZ directly.

Regards,

Elfving

[prashaanth]

Atleast can you guide me like which approach is being taken here for the pairing process. Is it passkey mechanism or numeric comparison mechanism?

[Elfving]

Elfving said:

Make sure that the BlueZ version supports LESC pairing. And you mentioned you're trying to do Just Works pairing with NoInputNoOutput, but if the sniffed packets indicate a numeric comparison failure it might be a mismatch in the pairing methods between the devices.

This gives the impression of both - ie. different approaches, hence the crash.

Regards,

Elfving