SDK config Pairing options explanation

[AndreaF33]

Hi everyone,

I would like a bit more insight and recommendations around the following list of SDK_CONFIG options. The description is not clear enough and I don't understand if the following settings might cause issues when pairing.

#ifndef BLE_NFC_SEC_PARAM_BOND

#define BLE_NFC_SEC_PARAM_BOND 1

#endif

// <q> BLE_NFC_SEC_PARAM_KDIST_OWN_ENC - Enables Long Term Key and Master Identification distribution by device.

#ifndef BLE_NFC_SEC_PARAM_KDIST_OWN_ENC

#define BLE_NFC_SEC_PARAM_KDIST_OWN_ENC 1

#endif

// <q> BLE_NFC_SEC_PARAM_KDIST_OWN_ID - Enables Identity Resolving Key and Identity Address Information distribution by device.

#ifndef BLE_NFC_SEC_PARAM_KDIST_OWN_ID

#define BLE_NFC_SEC_PARAM_KDIST_OWN_ID 1

#endif

// <q> BLE_NFC_SEC_PARAM_KDIST_PEER_ENC - Enables Long Term Key and Master Identification distribution by peer.

#ifndef BLE_NFC_SEC_PARAM_KDIST_PEER_ENC

#define BLE_NFC_SEC_PARAM_KDIST_PEER_ENC 1

#endif

// <q> BLE_NFC_SEC_PARAM_KDIST_PEER_ID - Enables Identity Resolving Key and Identity Address Information distribution by peer.

#ifndef BLE_NFC_SEC_PARAM_KDIST_PEER_ID

#define BLE_NFC_SEC_PARAM_KDIST_PEER_ID 1

#endif

// </e>

// <o> BLE_NFC_SEC_PARAM_MIN_KEY_SIZE - Minimal size of a security key.

// <7=> 7

// <8=> 8

// <9=> 9

// <10=> 10

// <11=> 11

// <12=> 12

// <13=> 13

// <14=> 14

// <15=> 15

// <16=> 16

#ifndef BLE_NFC_SEC_PARAM_MIN_KEY_SIZE

#define BLE_NFC_SEC_PARAM_MIN_KEY_SIZE 7

#endif

// <o> BLE_NFC_SEC_PARAM_MAX_KEY_SIZE - Maximal size of a security key.

// <7=> 7

// <8=> 8

// <9=> 9

// <10=> 10

// <11=> 11

// <12=> 12

// <13=> 13

// <14=> 14

// <15=> 15

// <16=> 16

#ifndef BLE_NFC_SEC_PARAM_MAX_KEY_SIZE

#define BLE_NFC_SEC_PARAM_MAX_KEY_SIZE 16

#endif

We had already a couple of reports were the phone, connected to the device successfully, turns again to pairing and gets locked in such situation. The PeerManager errors are 4352, and then a cascade of 4102.

The only way out was a reset. Due to this, I came across these options and I started wondering if some of these might be causing issues.

SDK: 15.3.0
SoftDevice: S140
API version: 6
APP Nordic pkg: 2.3.0

Thanks in advance!

[Kenneth]

For new development I strongly recommend to check out nRF Connect SDK instead:
Development: https://webinars.nordicsemi.com/introducing-nrf-connect-for-vs-code-5 
(Installation video: https://www.youtube.com/playlist?list=PLx_tBuQ_KSqEt7NK-H7Lu78lT2OijwIMl)
BLE video: https://webinars.nordicsemi.com/developing-bluetooth-low-energy-6)

If you are familiar with the nRF5 SDK and BLE, you may find this useful:
https://devzone.nordicsemi.com/guides/nrf-connect-sdk-guides/b/software/posts/building-a-ble-application-on-ncs-comparing-and-contrasting-to-softdevice-based-ble-applications 

But to answer your error codes:

4352 is in hex 0x1100, so likely from peer_manager_types.h:
#define PM_CONN_SEC_ERROR_DISCONNECT         (PM_CONN_SEC_ERROR_BASE + 0x100) /**< @brief Pairing or encryption did not finish before the link disconnected for an unrelated reason. */

4102 is in hex 0x1006, so likely from peer_manager_types.h:
#define PM_CONN_SEC_ERROR_PIN_OR_KEY_MISSING (PM_CONN_SEC_ERROR_BASE + 0x06)  /**< @brief Encryption failed because the peripheral has lost the LTK for this bond. See also @ref BLE_HCI_STATUS_CODE_PIN_OR_KEY_MISSING and Table 3.7 ("Pairing Failed Reason Codes") in the Bluetooth Core Specification 4.2, section 3.H.3.5.5 (@linkBLEcore).  */

Not sure which example you are looking at, but you may find the hid keyboard or mouse example reference for bonding support if you want to continue with the nRF5 SDK. Also check out documentation for peer manager if you haven't:
https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.1.0/lib_pm_usage.html  

Best regards,
Kenneth