nRF5340 - LESC OOB pairing

[Gabriele]

Hi,
After successful connection to custom nRF5340 peripheral, among pairing options under nRF Connect For Desktop Bluetooth LE (v4.0.4) I checked this one.

Pasting any random 32 char string I get peripheral printlog

<inf> ble: secure pairing accepted
<err> bt_smp: reason 0x4

and central printlog

Authentication failed with status BLE_GAP_SEC_STATUS_CONFIRM_VALUE

I know Out-Of-Band (OOB) is an association model where Bluetooth radio itself is the "Band" and a secret needs to be exchanged out of it to be secure.

What is meant to be the secure OOB link in this case ?
Can anybody explain this interface and how to use it ?

[Hieu]

Hi Gabriele,

My apology for the late reply.

I will support you with this question. However, I need more time to be sure of the answer.

Unless someone from the community already helped you, I will be back with the answer latest by the end of Mon Jan 16, but likely before that.

Hieu

[Simonr]

Hi

Hieu is out of office for the time being, so I have been assigned this case. I talked to one of the nRF Connect for Desktop app developers, and this is a known issue where there are no planned updates/fixes unfortunately. The OOB feature does not work as expected in the nRF Connect for Desktop BLE app.

Best regards,

Simon

[Gabriele]

Hello,

Ok it doesn't work. I'm still interested in the intended use case.

Maybe I'm wrong, but I've explained it to myself this way. The OOB link is myself reading the Diffie-Hellman long term key pair out of peripheral and typing it by hand in the central (nRF Connect for Desktop).

How to retrieve the keys ?

[Simonr]

Hi

As we don't have a "generic" LESC OOB pairing example project as is, I think the closest we do have is the ble_app_hrs_nfc pairing example in the nRF5 SDK. The file nfc_ble_pair_lib.c shows the API calls used to manage OOB pairing with NFC tags and the peer manager, and it should be totally fine replacing the NFC APIs with the OOB transport of your choice. You can also look at the message sequence chart for LESC OOB bonding in the SoftDevice specification for a better overview of how it's done: https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.s140.api.v7.3.0%2Fgroup___b_l_e___g_a_p___p_e_r_i_p_h___l_e_s_c___b_o_n_d_i_n_g___o_o_b___m_s_c.html 

Best regards,

Simon