OOB Pairing question

Hello.

1. Obviously unauthenticated connections have to be allowed so that the connection can become authenticated and bonded.  However you can set the GAPBOND_BOND_FAIL_ACTION to GAPBOND_FAIL_TERMINATE_LINK using the GAPBondMgr_SetParameter function. This will cause the connection to drop if your pairing parameters are not met. You can set the various pairing parameters such as GAPBOND_MITM_PROTECTION (authentication) using this function.

2.  If you pass callback functions from the application to the bond manager when registering, the application will be notified of the bond manager's various state changes. An example of this in the glucosesensor project where the following callbacks are defined:

// Bond Manager Callbacks
static const gapBondCBs_t glucoseBondCB =
{
  glucosePasscodeCB,
  glucosePairStateCB
};

The glucosePairStateCB will notify you of gap bond manager state changes.

Another option is the linkDB_Authen() funciton which will return the following:

 * @return      SUCCESS if link is authenticated.
 *              bleNotConnected - connection handle is invalid
 *              LINKDB_ERR_INSUFFICIENT_AUTHEN - link is not encrypted
 *              LINBDB_ERR_INSUFFICIENT_KEYSIZE - key size encrypted is not large enough
 *              LINKDB_ERR_INSUFFICIENT_ENCRYPTION - link is encrypted, but not authenticated

There is no function to check which type of authentication is used. You would have to modify the bond manager to accomplish this. Perhaps, set a global variable here:

  // Is bond manager setup for OOB data?
  if ( gapBond_OOBDataFlag )
  {
    VOID osal_memcpy( params.secReqs.oob, gapBond_OOBData, KEYLEN );
  }

Hi Tim

Thank you very much for your detailed answer, I really appreciate it.

I'll try to use GAPBOND_FAIL_TERMINATE_LINK and set only the OOB-flag (no MITM). Then the OOB-pairing should be used. Then in the bond manager callback PairStateCb I check linkDB_Authen(): if it returns LINKDB_ERR_INSUFFICIENT_ENCRYPTION, obviously Just Works was used and I terminate the link. Otherwise, OOB was sucessfully used.

I will try this solution and will respond again if this was not working well

Thanks again

Hi Tim

I guess it works: the connection is terminated automatically after a simple pairing by the peripheral.

But on the other hand, the OOB pairing does still not work properly: the peripheral receives a key (16 byte TK according to the standard) which is stored in the GAP-Bond-Manager as OOB_DATA:

GAPBondMgr_SetParameter( GAPBOND_OOB_DATA, sizeof ( uint8 ), &uartTxBuffer[1] );

Apparently, the TK is not updated by this function: during the pairing a SMP Error Confirm value failed (0x04) appear, the wrong keys are used for STK. If a OOB-Key of 16 bytes of '0' is used it works. But the connection is terminated because this is "just works". Because the key initialisation is 16 times 0 I assume the function I use does not properly update the key.

Could you provide an idea to update the TK which I can use to store the key received by OOB, other than the function above?

Thank you in advance

Matthias