Bluetooth Long Range and encryption

[Grzegorz Blach]

I am using NRF Connect SDK on NRF52840 Dongle and I have written two programs. First acts as bluetooth peripherial device, second acts as bluetooth centeral devices. I have implemented my own service and characteristics. For that characteristics I set permission bit = BT_GATT_PERM_READ_ENCRYPT or BT_GATT_PERM_WRITE_ENCRYPT, it works fine.

Recently I tried to upgrade my programs to support Bluetooth Long Range based on following examples:

https://github.com/nrfconnect/sdk-nrf/tree/master/samples/bluetooth/peripheral_hr_coded

https://github.com/nrfconnect/sdk-nrf/tree/master/samples/bluetooth/central_hr_coded

It works only when permission bit is set to BT_GATT_PERM_READ or BT_GATT_PERM_WRITE, but when I set BT_GATT_PERM_READ_ENCRYPT or BT_GATT_PERM_WRITE_ENCRYPT flag it hands on characteristic read/write.

So, is it possible to use encryption in Long Range mode?

If yes, could you provide any working example?

[Vidar Berg]

Hi,

Encryption should be supported. Do you have any logging enabled to see if it reports any errors? Also, how is it not working, is it that it can't establish a connection?

Best regards,

Vidar

[Grzegorz Blach]

I've published a stripped down versions of my programs at https://github.com/gblach/bluetooth_demos

In both programs I've enabled logging via USB serial. Demo_central program reports err == 5 (BT_ATT_ERR_AUTHENTICATION) in demo_central/src/main.c:33

This programs works correctly in two situations:

1) When I change BT_GATT_PERM_READ_ENCRYPT to BT_GATT_PERM_READ in demo_peripherial/src/main.c:41

2) When I keep encryption enabled, but disable long range mode and extended advertising by commenting out two lines: demo_peripherial/src/main.c:10 and demo_peripherial/prj.conf:9

[Vidar Berg]

Thanks for making the code available . It seems like you have forgotten to integrate pairing support in your main. I suggest you take a look at the Bluetooth LBS sample to see what callbacks are added when the CONFIG_BT_LBS_SECURITY_ENABLED option is enabled.

Ref.

https://github.com/nrfconnect/sdk-nrf/blob/master/samples/bluetooth/peripheral_lbs/src/main.c

[Grzegorz Blach]

Today I spent some time and played with bt_conn_auth_cb callbacks, but with no success. bt_conn_auth_pairing_confirm() in pairing_confirm() return 0 (no error), but then pairing_failed() reports bt_security_err = 1 (BT_SECURITY_ERR_AUTH_FAIL) and security_changed() reports the same error.

[Vidar Berg]

I forgot that the LBS sample was configured to support passkey pairing/bonding by default. The BT_SECURITY_ERR_AUTH_FAIL  error is probably a result of the central not inserting the passkey displayed by the peripheral. Unless you have you implemented support for passkey entry? Anyway, it's easier implement support for "just works" which does not require any user input.

I tested "just works" bonding now by modifiying the hr_coded samples available in NCS SDK (tested with v1.4.0-rc2), and it worked.

hr coded central+peripheral with bonding

0245.coded_phy_and_bonding.zip

[Grzegorz Blach]

It works! Thank you very much!

[Vidar Berg]

No problem, thanks for the update!