nRF Sniffer decryption is not working after entering passkey

[Acutetech]

I am a newbie with nRF Sniffer, which I have installed on one PCA10040 board. I am sniffing communications between a Samsung phone running nRF Connect and a second PCA10040 running the glucose sample app.

I believe I am following the instructions in the User Guide section 5.5: when the glucose app prints the 6-digit passkey I enter this into Wireshark and type enter, then I enter it into the phone. The phone and peripheral then bond and work, but Wireshark starts printing "Encrypted packet decrypted incorrectly (Bad MIC)" . When I click on Log I see this:

INFO: Setting Passkey: 691295

INFO: Sent key value to sniffer: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 140, 95]

A screenshot is here:

/resized-image/__size/640x480/__key/support-attachments/beef5d1b77644c448dabff31668f3a47-e588f28969f94ee0a39b08c9e8afde0d/Screenshot-2018_2D00_11_2D00_19-10.57.32.png

Q1: Are my results expected? What should I do differently?

Q2: Assuming I am able to get beyond this problem, is it possible to sniff subsequent connections? The Central and Peripheral will be bonded and the peripheral will not print a passkey. Can nRF Sniffer decrypt the second session based on keys it has saved?

[bill.diken]

Acutetech I'm having an identical issue with Wireshark 3.0.1 with the latest nrf sniffer nrfsniffer200beta312oct20181c2a221 with the nRF52840 DK board. I can't seem to get decryption to work reliably, I do sometimes see correct value at the attribute even with the MIC error message but it only works for the first few transmissions before it't completely broken. Were you ever able to resolve this issue?

[Acutetech]

I could not resolve the problem and gave up.

This is pure speculation: I had another problem with notification data being corrupted, which was later fixed by a library update, or similar (I think to BLE Library 2.0.4). I wonder if there could be a connection? For this other problem see devzone.nordicsemi.com/.../167037

[David Edwin]

There is a new release being worked on to fix encryption issues and seems to perform better.nrf_sniffer_2.0.0-temp_beta-4_2May2019_47b3f5f.zip

You can try this and let me know if this works better. Unfortunately this snapshot that I uploaded here has not yet been tested for passkey but has been tested for Justworks pairing.

Edited: The sniffing of encrypted link  is improved only for the nRF52xxx based development kits, the performance of the nRF51 based development kits when used as sniffer remains the same as the previous release.

[bill.diken]

David, I used the file you provided, although I had to change the contents of the nrf_sniffer.bat file to get Wireshark to recognize the devboard.

@echo off
python "%~dp0nrf_sniffer.py"  %*

The bad MIC error is still there, it seems that it decrypts the first few transactions correctly and then starts to fail and doesn't recover. What seems to work better is the disconnect/reconnect detection, in the previous build I could never get packets when there was a disconnect and the strap started advertising or when it tried to establish a new connection.

[David Edwin]

Can you share your pcap file ?

<<Reminder>> : Can you share your pcap file

Additional comment:

Make sure that the sniffer board is between the central and peripheral.
Keep a minimum separation of about 10cm between the sniffer and the other boards.
(the sniffer's ability to decrypt is still sensitive to packet loss)