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?

[David Edwin]

Erase and Reflash the board running the peripheral to delete the bond and try again. 

For nRF connect , click on the adapter wheel, then click "delete bond information".

I can see that the encrypted packets are being decrypted as "Encryption Information" and "Master Identification" are all encrypted packets.

In the Nordic_CLI device, click on the UART over BLE and then click UART TX. Click on the arrow so that the Nordic CLI will send periodic notifications.

It is possible some packets are not decrypted correctly if they are received incorrectly on the sniffer, but that will not impact the entire connection.

Read the user guide to setup the wireshark profile for the sniffer. (section 2.3.2 and section 2.3.3)

[Acutetech]

I have tried this cycle several times and almost always the decryption fails. I am about to give up with a "broken for me" conclusion. I did get one session in which I successfully bonded and then nRF Sniffer/Wireshark could decrypt each of the (encrypted) notifications from the peripheral, but almost always I get the "packet decrypted incorrectly" messages.

Interestingly, my most recent session (attached) shows bonding at around packet 4401, and some packets correctly decrypted until packet 4444, then failed packets with a few correctly decrypted packets interspersed (e.g. 5540, 5672, 5686). From 4444, the only successfully decrypted packets are sent by the slave - I don't know whether this is significant. Could there be some timing issue? e.g. packets come too fast to be processed?

Probably an unrelated bug/feature: whenever I ask nRF Connect to reconnect to the bonded peripheral I get a "failed to authenticate" dialog, even though the nRF Connect behaviour shows that it has connected correctly. 

ble_app_cli_2.pcapng

[David Edwin]

If you want to re-connect to bonded peripheral, then the "perform bonding" check box must be ticked when in the pairing screen.

Keep the boards close by for the test, maybe a few centimeters apart, with the sniffer in the center.

[Acutetech]

No better. The boards are almost touching. Most (but not all) packets give "packet decrypted incorrectly" messages. There is no sign of packets being lost or corrupted prior to encryption being enabled.

Have you actually tried the identical setup yourself?

[David Edwin]

sniffer_pca10040_mic_recover_v2_18Dec2018.hex

This seems to perform better for MIC failure. can you test this and let me know.

Edit: Updated hex fix