Pairing and Bonding Process#

Bluetooth Low Energy (BLE) security uses pairing to establish encryption keys and bonding to store keys for future connections. The SiWx917 supports multiple pairing methods and secure key exchange.

Pairing Methods#

Just Works:

• No user interaction required

• Suitable for devices without displays/keyboards

• Lower security (no MITM protection)

Numeric Comparison:

• Both devices display 6-digit number

• User confirms numbers match

• Provides MITM protection

Passkey Entry:

• One device displays passkey, other device enters it

• Suitable for device + phone/tablet scenarios

• Provides MITM protection

Out-of-Band (OOB):

• Key exchange through alternative channel (NFC, etc.)

• Not available in the current stack; pairing returns error 0x4B02 (SMP OOB not available)

Pairing Process#

1. Set Pairing Capabilities:

• Use rsi_ble_set_smp_pairing_cap_data() to configure pairing capabilities; the payload is the structure rsi_ble_set_smp_pairing_capabilty_data

• In that structure, specify: IO capability, OOB data flag, authentication requirements, encryption key size, and keys to be exchanged (for example, LTK, IRK, CSRK)

• Key distribution is set separately for initiator (ini_key_distribution) and responder (rsp_key_distribution) with bits for EncKey/LTK, IdKey/IRK, and Sign/CSRK

2. Initiate Pairing:

• Use rsi_ble_smp_pair_request() to initiate pairing

• Or respond to pairing request from peer using rsi_ble_smp_pair_response()

3. Handle Pairing Events:

• Register SMP callbacks using rsi_ble_smp_register_callbacks()

• Handle passkey events: rsi_ble_smp_passkey() for passkey entry

• Handle pairing failure: rsi_ble_smp_pair_failed() for error handling

4. Key Exchange:

• Pairing establishes encryption keys

• Long-Term Key (LTK) used for encryption

• Handle LTK request: rsi_ble_ltk_req_reply() for reconnection

Bonding#

Bonding Process:

• Bonding stores pairing keys for future connections

• Bonded devices can reconnect without re-pairing

• The application is responsible for storing bonding keys (LTK, IRK, etc.); the stack does not persist them automatically.

Bonding Management:

• Bonding occurs automatically after successful pairing

• Bonded device information stored in resolving list

• Use resolving list APIs to manage bonded devices

Security Best Practices#

Pairing Method Selection:

• Use Numeric Comparison or Passkey Entry when possible (better security)

• Use Just Works only when user interaction not possible

• Consider application security requirements

Key Management:

• Store encryption keys securely

• Protect IRKs and LTKs from unauthorized access

• Implement proper key rotation if required

APIs Used in This Section#

SDK: Developing with WiSeConnect SDK, BLE API Reference guide — Overview.