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  • Case ID: 260565
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Pairing always fail with nRF52/Raspberry Pi 4/Win10 and an Omron BPM.

fabocode

Hello! I will try to make this as simple as possible with the details regarding this issue

What I have

  • nRF52840 DK (pca10056) (As BLE sniffer)
  • nRF52 (pca10040) (Used in the nRF Connect win10 application)
  • Raspberry Pi 4 
  • OMRON BP7350 BPM
  • Hope (just kidding)

One thing to have in mind

Whenever I test this with my phone in the nRF Connect for mobile or in the native OMRON Connect US application this process works perfectly, I am able to connect, pair and read blood pressure data from the sensor.

Description

I am working with an OMRON BP7350 BPM Sensor trying to read blood pressure data from it and I have problems with pairing process using the nRF Connect v3.6.0 - Bluetooth Low Energy application, but basically in order to get data from the BPM is required to connect to it and pair to be able to access to their blood pressure service/characteristics. At this point I have tested a lot of different use cases without success. 

My main purpose is to get it to work in the Raspberry Pi 4 but this issue happens also in the nRF52 (PCA10040) and nRF52840 (PCA10056) (I tried backwards) so I think that this might lead me to solve the issue in the raspberry pi (perhaps?). 

In the Pi I have bluez v5.50, in the nRF BLE application tool the version is v2.4.2.

And whenever I tried pairing in the Pi 4 or in the nRF52 board BLE application I have this:

> ACL Data RX: Handle 64 flags 0x02 dlen 6                                                         #20 [hci0] 26.420475
      SMP: Pairing Failed (0x05) len 1
        Reason: Unspecified reason (0x08)


This also happens with another devices like in WIN10 with virtual machines with Debian with bluez, Fedora linux OS, all of them testing with bluetoothctl
which is the same tool that I use in the Pi 4.


What I have tried

For debugging I used the nRF Connect for Mobile application and there I am able to bond/pair to the device successfully with my android and do whatever I want, I am also able to sniff this communication process using wireshark and nRF52 board that I have.

First the request from nRF Connect in my android device to "bond"

And here is the response from BPM

BUT when I do the pairing process with my raspberry pi 4 (And the nRF52) the connection fails with an "Unspecified Reason"

The Response from the BPM

I used sudo btmon to monitor the behavior inside the Raspberry Pi

> ACL Data RX: Handle 64 flags 0x02 dlen 6                                                         #17 [hci0] 26.323537
      SMP: Security Request (0x0b) len 1
        Authentication requirement: Bonding, No MITM, Legacy, No Keypresses (0x01)
< ACL Data TX: Handle 64 flags 0x00 dlen 11                                                        #18 [hci0] 26.323661
      SMP: Pairing Request (0x01) len 6
        IO capability: NoInputNoOutput (0x03)
        OOB data: Authentication data not present (0x00)
        Authentication requirement: Bonding, No MITM, Legacy, No Keypresses (0x01)
        Max encryption key size: 16
        Initiator key distribution: EncKey Sign (0x05)
        Responder key distribution: EncKey IdKey Sign (0x07)
> HCI Event: Number of Completed Packets (0x13) plen 5                                             #19 [hci0] 26.371976
        Num handles: 1
        Handle: 64
        Count: 2
> ACL Data RX: Handle 64 flags 0x02 dlen 6                                                         #20 [hci0] 26.420475
      SMP: Pairing Failed (0x05) len 1
        Reason: Unspecified reason (0x08)

I also tested to pair with the GUI tool and gatttool, no success.

-----------------------------------------------------------------------------------------------

And of course, this is the response from the nRF BLE application everytime I tried to pair: 

Authentication failed with status BLE_GAP_SEC_STATUS_UNSPECIFIED

I also tried to reproduce the same requirements as the android appears to share with the BPM in terms of: 

- IO Capability: Keyboard, Display (0x04)

- AuthReq: 0x05, MITM Flag, Boding Flags: Bonding 

This with always a pairing failed response... 

Conclusion

So I honestly would like to know what do you think I might need to do to be able to pair successfully the raspberry pi with this BPM device. Do you know what exactly means the "Unspecified reason (0x08)" or what is required to change when you have a Pairing Failed (0x05) in the SMP?

I honestly do not understand how the Initiator Key(s) / Responder Key(s) works and how are able to be changed in order to make work this communication process as I need in the nRF52 with the BLE application, is this something more "device specific"? 

From my point of view, there is something in the security layer that is not ending to be completed to achieve a completed pairing process... But I don't know what is it yet

Any suggestion will be helpful on issue. Thank you for your time.

  

  • 0 in reply to Hung Bui

    Hi Hung and thank you for your suggestions. 

    I realized that I made two terrible mistakes and 1 step was also required to make this to work:

    1. This BPM device has a button to enable a "Pairing Mode" which I thought this was something that was activated after pairing with the mobile device, after re-checking the user guide I realized about this and then I was able to pair to it successfully with my nRF52 DK board and Raspberry Pi.
    2. The problem in the raspberry pi is that I was using bluetoothctl tool to pair and then I was trying to request indications with the gatttool, apparently working with both systems creates a conflict and leads to this kind of problems where in gatttool you may find the 
      fabocode said:
      Status: PIN or Key Missing (0x06
      But once you try to work only with gatttool everything else is much easier 

    Another tip to have in consideration is that gatttool can enable pairing by setting the security level (sec-level) to "medium", if you set it to "high" it will enable MITM and there the connection was not successfull in my side becuase of "authentication failure". 

    Now both devices, my nRF52 DK and my Raspberry Pi 4 are able to request data to the Omron BPM easily. Thank you very much for your tips.

  • 0

    Hi Fabian,

    I am working on a similar personal project (ultimately connecting a pi to Omron BPM, using nrf52dk to sniff and help figure it out) and was wondering if you have have references on how to properly set the security parameters on the pi to pair in order to read the BPM data?  I also saw on stack overflow you were using python on the pi, which BLE library did you use and is that public or are there references to that?

    Unfortunately I only have 1 nrf52dk so I am using it to sniff between the pi or phone and BPM device.  Hopefully I can get another sniffer to sniff the nrf52dk.

    Currently this is where I am:

    Successful pair from manufacturer app:

    BP7450_success_pair_from_manufacture_app.pcapng

    NRF app on iPhone:

    - can read blood pressure data after pairing through manufacturer app.  However when connecting via nrf phone app then trying to read BP measurement (which you need to be paired) it tries to pair and fails.

    BP7450_pair_from_nrf_phone_app.pcapng

    Pi:

    - using gatttool, security-level = low, cleared BPM paired data, BPM in pairing mode (hold down bluetooth button) -> can connect, read device info etc.  But when I try to read BPM data it fails with "Passkey entry failed".  This is what is seen sniffing the BPM:

    and this is what btmon reads on the pi:

    - Now same thing but with security-level= medium -> btmon shows the pi connected but then pairing failed with same reason

    nrf52DK as Central trying to pair through BLE tool in nrf connect for desktop:

    note: can't sniff this atm, only have one nrf device

    - can connect but when trying to pair with params [No keyboard/no display, no secure connection, no MITM, no OOB, no keypress, bonding yes] I receive this error

    15:35:43.967	Error when calling replySecParams: Error: Error occured when replying sec params. Errorcode: Unknown value (0x8005)
15:35:43.970	Received status with code 4 Unknown value, message: 'Error sending packet to target. Code: 0x802a'

    Additionally is there reference code for the nrf52dk for connecting and pairing to a peripheral, so that I can mess with security params and don't have to start from scratch?

    I believe I just need to set the security parameters properly as the models I have are supposed to be able to pair without a pin, but unsure how to do so.  I believe it is Bonding, no SC, no MITM, no OOB.  

    Any help is much appreciated.

  • 0 in reply to eblas

    Hello , this is an inactive case. Please create a new ticket for your question.

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