nRF5 SDK 17.1.0: Numeric Comparison pairing dialog on phone fails to dismiss after peripheral rejects pairing

RE: nRF5 SDK 17.1.0: Numeric Comparison pairing dialog on phone fails to dismiss after peripheral rejects pairing

David Duan — Thu, 24 Sep 2026 01:41:36 GMT

Thank you so much for the detailed explanation.

RE: nRF5 SDK 17.1.0: Numeric Comparison pairing dialog on phone fails to dismiss after peripheral rejects pairing

tesc — Mon, 21 Sep 2026 16:11:17 GMT

Hi,

We can conclude then, that the reason for the missing SMP Pairing Failed packet from the peripheral, is the missing DHKey Check packet from the central. From what we can tell, this implementation of the peripheral is allowed by the Bluetooth Specification.

The behavior seems to have changed for the SoftDevice Controller of nRF Connect SDK, which in turn has led to better interoperability with central devices not sending DHKey Check packets. The change will not be backported to the SoftDevices of nRF5 SDK. This means when they see this issue, the workaround is to close the pairing dialog manually at the central end or wait for a central side timeout.

Regards,
Terje

RE: nRF5 SDK 17.1.0: Numeric Comparison pairing dialog on phone fails to dismiss after peripheral rejects pairing

David Duan — Sun, 20 Sep 2026 05:32:12 GMT

HI Terje

1. sd_ble_gap_auth_key_reply returns NRF_SUCCESS without any error messages, until the pairing response times out.

2.I have attached the Ellisys packet capture log above, and there is no DHKey Check packet.

RE: nRF5 SDK 17.1.0: Numeric Comparison pairing dialog on phone fails to dismiss after peripheral rejects pairing

tesc — Fri, 18 Sep 2026 13:50:16 GMT

Hi,

We have investigated the issue, but here we see the peripheral sends a Pairing Failed (0x05) with reason Numeric Comparison Failed (0x0c), in response to a Pairing DHKey Check sent from the central. That Pairing DHKey Check is missing from the MSC, but that packet is essentially what the peripheral responds to. From what we can tell, this way of handing it is allowed by the Bluetooth specification.

Therefore:
1. Can we confirm the return value from sd_ble_gap_auth_key_reply(BLE_GAP_AUTH_KEY_TYPE_NONE, NULL)? (Should be NRF_SUCCESS. If something else, that error code would be important for figuring out what happens.)
2. When we see the issue (dialogue on central does not go away), does the central send a Pairing DHKey Check packet?

Regards,
Terje

RE: nRF5 SDK 17.1.0: Numeric Comparison pairing dialog on phone fails to dismiss after peripheral rejects pairing

David Duan — Mon, 14 Sep 2026 03:22:25 GMT

HI Tesc

any update on this

RE: nRF5 SDK 17.1.0: Numeric Comparison pairing dialog on phone fails to dismiss after peripheral rejects pairing

David Duan — Thu, 10 Sep 2026 01:39:57 GMT

HI Tesc

my result is same customer,we both use ellisys to capture the data, we can't see the sd_ble_gap_auth_key_reply()

below it is my snifer result.

ellisys sniffer result:

devzone.nordicsemi.com/.../sniffer_5F00_result.btt

if you use my project with NRF52 DK, this can be easy to reproduce by any smart phone with nrf connect.

RE: nRF5 SDK 17.1.0: Numeric Comparison pairing dialog on phone fails to dismiss after peripheral rejects pairing

tesc — Wed, 09 Sep 2026 13:42:17 GMT

Hi,

[quote user=""]Question:
I would like to confirm whether the nRF5 SDK SoftDevice itself inherently does not support sending this SMP Pairing Failed command in this scenario?[/quote]

The SoftDevice should send the SMP Pairing failed command. The code that you shared looks correct. Setting key_type = BLE_GAP_AUTH_KEY_TYPE_NONE and sending that value in sd_ble_gap_auth_key_reply() should lead to the SoftDevice sending SMP Pairing failed, as per the Bonding: Numeric Comparison Message Sequence Chart.

I see from the logs that the error code returned by the SoftDevice from the call to sd_ble_gap_auth_key_reply() is NRF_SUCCESS, so if there is no SMP Pairing failed command sent then this looks like an issue with the SoftDevice. However I do not find any similar prior reports, and nRF5 SDK is several years old at this point. Are you able to confirm there is indeed no SMP Pairing failed command sent, by using a sniffer (such as for instance the nRF Sniffer)?

Regards,
Terje