Windows Automatically Reading 0xFCD3 characteristic ID at pairing.

[Kurt Jorgensen]

We have a device that we are trying to implement an encrypted data transfer on.  We wanted to lock down all the characteristics until we write  a passkey on our security characteristic.  This works on andriod systems and ios but when working with windows the OS pairing process tries to read from  0xFCD3 characteristic ID  and it is causing or security to fail.  I dont know why windows is doing this, nor what we can do to stop it.  It seems like windows is polling the devices for characteristic id's through certain ranges.   Any help would be greatly appreciated.  

[Kenneth]

I think a sniffer log would be helpful to understand the problem in more details. But if I remember correctly there are some differences between the OS's in how and when the secure the link, my impression is that Windows will always try to secure the link, while iOS will only secure the link if characteristics require it. 

You should also look into whether you may be violating the iOS guidelines:
https://developer.apple.com/accessories/Accessory-Design-Guidelines.pdf

"The accessory should not request pairing until an ATT request is rejected using the Insufficient Authentication error code. See the Bluetooth 4.0 specification, Volume 3, Part F, Section 4 for details"

Best regards,
Kenneth

[Kurt Jorgensen]

Hi Kenneth,  Thanks for the response.  We do have a wireshark capture.   I couldnt figure out how to attach so if you would give me an email I could send it.   We are having the problem with windows and not IOS.  The problom occurs around line no 142 ,  I think when it is reading the characteristic 0xFCD3.  

See image below: 

The full trace is like this : 

[Kenneth]

I don't think there is any direct relation with what you are observing around line 142 and your problem. I do believe Windows (oppose to iOS) will secure the link with the highest common security level supported by the peer and host in any case. I do believe the  security procedures occurs prior to line 142.

But to be able to look into this in more details I need an on-air sniffer log (iOS and Windows for comparison):
https://www.nordicsemi.com/Products/Development-tools/nRF-Sniffer-for-Bluetooth-LE

I can make this case private/confidential if you don't want to share the on-air sniffer logs public.

Kenneth