MITM set when using JustWork option, how is this possible?

[jean-marc]

When pairing with nRF Connect and nRF52 I use the Just Work mode. No Keyboard No Display.

In 4.2 (and also 4.0) the MITM cannot be used in this mode.

If I set it on the pairing nRF Connect option, the MITM is set. Is this correct?

According to the specs this should not be. Pls see below the btmon message. I have NoInputNoOutput which is equal to Just Work and we can see the MITM is set.

[Einar Thorsrud]

Hi,

I don't know where this log comes from (it does not look like a log from the nRF5 SDK). What is it? In any case you are right that there cannot be any MITM protection if one of the devices does not have either keyboard or display, so I don't know why this is logged.

As a side note, you could do something with static passkey printed on the device even though it does not have any display or keyboard, provided the other device has a keyboard. In that case you would have to set the I/O capabilities to indicate display though, so there is anyway an error in the log output in your screenshot.

[jean-marc]

Hello, thanks for the reply.

This is not a log, this is btmon (linux bluetooth monitor) it shows on real time what is going on on the Bluetooth in different layers. And the exchange is ACL Request and Response in this case.

[Einar Thorsrud]

OK, I see. nRF Connect for Desktop is a test tool so it is not necessarily a problem, but I agree it seems a bit odd that MITM is supported together with IO capabilities set to "No keyboard, no display". I will check with the developer to get an answer to why this is and update this thread when I do.

Update: It is intentional to not limit the options in nRF Connect to "what makes sense", and sending this combination in the pairing request is not illegal.

[jean-marc]

Thank you... :-)