High Failure Rate in START ENCRYPTION Sequence: 2 Failures per 10 Trials (Baseband or Link Layer Issue)

[Charles Changhun Han]

Hello Nordic Semiconductor tech support team,

HW : nRF52840 ( Build code : nRF52840-CKAA-F )

SW : ncs 2.6.0

Sample Application :  zephyr/samples/bluetooth/hci_spi sample with SoftDevice Controller

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While verifying our software design, we frequently encounter connection errors. Could you help us identify the possible cause of this issue and suggest a resolution? Right after the enhanced connection is completed, we’re expecting an Encryption Change Event from the SoftDevice Controller. However, instead of an Encryption Change Event, a Disconnect Complete (0x05) occurs with the reason ‘Connection Terminated due to MIC Failure (0x3d).

Device A : Android Mobile Phone (central), (iOS case is also reported)

Device B: nRF52840 (Peripheral) 

Frame 17605: 7 bytes on wire (56 bits), 7 bytes captured (56 bits) on interface Fake IF, Import from Hex Dump, id 0 (inbound)
Bluetooth
Bluetooth HCI H4
Bluetooth HCI Event - Disconnect Complete
Event Code: Disconnect Complete (0x05)
Parameter Total Length: 4
Status: Success (0x00)
Connection Handle: 0x00cd
Reason: Connection Terminated due to MIC Failure (0x3d)

(highlighted marked HCI events)

[Kenneth]

Hello,

I get slight impression that there is some marginally timing here or that the wrong keys ares provided. 

Do you see the same if you relax the SPI clock speed, and in specific if you relax (e.g. >10us for test) for instance the timing between slave select and first clock pulse.

Kenneth

[Charles Changhun Han]

Hello Kenneth, 

Thank you for your prompt response and update. Based on the HCI log from device B (nRF52840 SoftDevice controller), I have ruled out one possible cause: the wrong LTK case. During this test, we consistently used the same LTK.

Could you please investigate this case from another perspective? Specifically, could you identify the scenario in which the SoftDevice Controller sends out the (0x3d) reason during a Disconnection Complete event, in collaboration with your BLE Core development team?

According to our logs, the error occurred when the connection began encrypting immediately after it was created, rather than during heavy traffic to/from the SPI bus.

Thanks,

Charles

[Kenneth]

Hello,

To check if the issue is fixed, look for DRGN-23204 in the CHANGELOG for the v2.8.0 release (when it's released that is):
https://github.com/nrfconnect/sdk-nrfxlib/blob/main/softdevice_controller/CHANGELOG.rst

Kenneth

[Charles Changhun Han]

Hello Kenneth, If the DRGN-23204 information is published, please update this case. Since we’re in the verification stage, may I apply the softdevice_controller change (like softdevice_controller/lib/cortex-m4/soft-float/libsoftdevice_controller_multirole.a) within version 2.6.0 instead of the full v2.8.0 NCS? If so, how can I apply that change only?

Thanks, Charles

[Charles Changhun Han]

Subject: Request for Detailed Information on DRGN-23204

Hi Kenneth,

According to our local AE, NCS v2.8 was frozen on October 3rd. However, I am still unable to find DRGN-23204 in the changelog of the main branch. When the information for DRGN-23204 is published, could we receive more detailed information?

We are observing this issue with iOS 14 as well. If the SoftDevice controller includes a fix, I would like to have more details to close our open quality tickets.

Thank you for your assistance.

Best regards,

Charles

[Kenneth]

Hi Charles,

It might be that they are working on the first release candidate for v2.8.0, but I still have high hopes that this will be fixed before the planned release that is end of October of v2.8.0.

Kenneth

[Kenneth]

Hi Charles,

I can see the first mention of a fix, so I expect this to come into v2.8.0:
https://github.com/nrfconnect/sdk-nrfxlib/pull/1507/files#diff-794dbd2613fe781e716b96b313b0fe1528ab53a619a9bce0472999878c513fcb 

Kenneth

[Charles Changhun Han]

Hello Kenneth, Thank you so much for your update. I will try to cherry-pick the change to verify that it is able to resolve my cases. Thanks, Charles

[Charles Changhun Han]

Hello @Kenneth,

The official version is released, and we have the fix for this issue. Let me close this ticket. Thank you for your support, and Happy New Year.

Thanks,
Charles