MITM protection implementation for BLE pairing

[Kaveh.M]

I have two Adafruit feather with nRF52832 on them, using one as central and the other as peripheral. 

I have created some codes based on ble_app_uart from Nordic SDK and combine peer manager with it for security.

They work fine, but when I set "#define SEC_PARAM_MITM              1" on both, they stop connecting to each other. 

How can I include MITM protection to my connection? 

Thanks

[ovrebekk]

Hi

Did you check the log on the peripheral and central side to see if there is any indication there why they won't connect?

Have you checked that they both successfully start advertising and scanning?

Best regards
Torbjørn

[Kaveh.M]

Thanks Torbjorn. This is the error I get from debugging central device. 

<info> app_timer: RTC: initialized.
<error> app: ERROR 7 [NRF_ERROR_INVALID_PARAM] \nRF5_SDK_17.0.2_d674dde\examples\My Projects\uart_central_wpmg_5\main.c:829
PC at: 0x00035077
<error> app: End of error report

For MITM protection using nrf52832, do I need to take one of these paths: Display a code, NFC, or UART OOB.

If that is the case may be I can not have MITM protection because I have two Adafruit feather communicating but sitting far apart from each other.

[ovrebekk]

Hi 

As mentioned by fhfs above you need some IO capabilities in order to authenticate the link and get MITM protection. 

The following matrix shows which IO capabilities you need on each side of the link in order to get authenticated pairing:

For instance, you can uses MITM pairing if you support keyboard on one side and display on the other. 

Either you have to connect buttons and a display to the Arduino feather directly, but if using UART is an option you can also implement simple keyboard and display functionality through the UART terminal:
Simply display the passkey in the UART terminal on one side, and have the user enter the same passkey in the terminal for the other side. 

Best regards
Torbjørn

[Kaveh.M]

Thanks Torbjorn. This is the error I get from debugging central device. 

<info> app_timer: RTC: initialized.
<error> app: ERROR 7 [NRF_ERROR_INVALID_PARAM] \nRF5_SDK_17.0.2_d674dde\examples\My Projects\uart_central_wpmg_5\main.c:829
PC at: 0x00035077
<error> app: End of error report

For MITM protection using nrf52832, do I need to take one of these paths: Display a code, NFC, or UART OOB.

If that is the case may be I can not have MITM protection because I have two Adafruit feather communicating but sitting far apart from each other.

[ovrebekk]

Hi 

This error happens because you are trying to enable MITM protection without any IO capabilities. This is not possible, and leads to an INVALID PARAM error. 

If you want MITM protection you need to find some way to add IO capabilities to your Adafruit feather boards. 

Best regards
Torbjørn