Connection using old pairing information saved

[Gaurav]

I am running an experiment to use a static keys for pairing information without breaking the existing flow of pairing/bonding.
What I am doing is I am storing the pairing info of my central device and storing it into a structure and then erasing the flash to remove those information, and after reset I am retrieving those bonding information and connecting again using the same central devices but I am getting "Peer removed bonding info" response on my phone.

void store_ltk_in_zephyr(void)
{
    int id, err;
    struct bt_keys pairing_info = {
    .addr = {
        .type = BT_ADDR_LE_PUBLIC,
        .a.val = {0x43,0x82,0x5E,0xC7,0xE8,0xF4,0xFD}
    },
    .irk = {0x8A, 0x27, 0x1E, 0xA7, 0x92, 0x2A, 0xF0, 0x15, 0x41, 0x69, 0x48, 0xDD, 0xC0, 0x7E, 0xDD, 0xF7},
    .ltk = {
        .val = {0xc0, 0xe6, 0x9a, 0x0a, 0xf7, 0x4b, 0xdc, 0xb7, 0x7d, 0x23, 0xf4, 0xb4, 0x89, 0x8d, 0x96, 0x02},
        .ediv = {0x00,0x00},
        .rand = {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00},
      }
    };

    // Store the keys using the settings API
    err = bt_keys_store(&pairing_info);
    if (err) {
        printk("Failed to store keys (err %d)\n", err);
    } else {
        printk("Keys stored successfully\n");
    }
}

In main, I am calling like this to load the info onto the flash- 

  settings_subsys_init();
  //smp_bt_register();
	bt_conn_auth_cb_register(&auth_cb_display);
  bt_conn_auth_info_cb_register(&conn_auth_info_callbacks);
	err = bt_enable(NULL);
	if (err) {
		printk("Bluetooth init failed (err %d)\n", err);
    k_sleep(K_MSEC(100));
		err = bt_enable(NULL);                                      //Trying one more time after this system reset
    if(err) NVIC_SystemReset();
	}
  store_ltk_in_zephyr();
  if (IS_ENABLED(CONFIG_SETTINGS)) {
    settings_load();
  }

And on connect I am using like this-

  bt_conn_set_security(conn, BT_SECURITY_L1|BT_SECURITY_FORCE_PAIR);

Do let me know, how can I connect with the same bonding info which I have made a copy of from the same bonding structure.

[Vidar Berg]

Hello,

To troubleshoot this, I recommend you start by enabling CONFIG_BT_LOG_SNIFFER_INFO to have the keys printed on boot. This would help confirm us confirm if they keys were successfully stored or not.

Best regards,

Vidar

[Gaurav]

I am reading the pairing info using nrfjprog --memrd 0xfe000 -n 1024, as I know its taking the info from the settings page and the address of the page is this -

Not getting any logs related to bonding on boot using CONFIG_BT_LOG_SNIFFER_INFO.

[Gaurav]

Vidar Berg Anything on this?

[Gaurav]

Its failing here in comparing EDIV and RAND values with the key`s one so that the LTK can be copied and connection can be passed on-

[Vidar Berg]

I can't see the EDIV or RAND values. I suggest you print out both.

[Gaurav]

00> RAND from key : 17829121634713032291
00> RAND from HCI buf: 13934090300794250199
00> EDIV from key : 34889
00> EDIV from HCI buf : 61501

These are the values printed for EDIV and RAND.

[Gaurav]

Used this flow for printing the logs-

#if !defined(CONFIG_BT_SMP_SC_PAIR_ONLY)
	LOG_DBG("Its inside this loop now %d\n",conn->le.keys->keys);
    uint64_t value = 0;
    for (int i = 0; i < 8; i++) {
        value |= ((uint64_t)conn->le.keys->periph_ltk.rand[i]) << (i * 8);
    }
	printk("RAND from key : %llu\n",value);
	printk("RAND from HCI buf: %llu\n",rand);
	printk("EDIV from key : %d\n",(conn->le.keys->periph_ltk.ediv[0]<<8)|conn->le.keys->periph_ltk.ediv[1]);	
	printk("EDIV from HCI buf : %d\n",ediv);		
	if (conn->le.keys && (conn->le.keys->keys & BT_KEYS_PERIPH_LTK) &&
	    !memcmp(conn->le.keys->periph_ltk.rand, &rand, 8) &&
	    !memcmp(conn->le.keys->periph_ltk.ediv, &ediv, 2)) {
		enc_size = conn->le.keys->enc_size;

		memcpy(ltk, conn->le.keys->periph_ltk.val, enc_size);
		if (enc_size < BT_SMP_MAX_ENC_KEY_SIZE) {
			(void)memset(ltk + enc_size, 0,
				     BT_SMP_MAX_ENC_KEY_SIZE - enc_size);
		}

		atomic_set_bit(smp->flags, SMP_FLAG_ENC_PENDING);
		return true;
	}
#endif /* !CONFIG_BT_SMP_SC_PAIR_ONLY */

[Gaurav]

Vidar Berg Anything on the above.

[Vidar Berg]

For legacy pairing, the EDIV/RAND is used to identify which LTK to use for encryption for a particular bond. So the question is why the EDIV and RAND stored on your device do not match the EDIV and RAND seemingly sent by your central. The mismatch suggests that your central and peripheral device does not have the same LTK.

[Gaurav]

Then how do we proceed then, I have tried to directly copy the values in the structure and tried that but still didn`t worked.

Can you try once on your end if in legacy pairing it works?

[Vidar Berg]

The EDIV/RAND mismatch indicates that the bond on your central does not match the bond you have on your peripheral. I suggest you delete the bonds on both sides, then repeat the pairing with your nRF5 SDK based app to exchange new keys. 

[Gaurav]

Vidar Berg said:

I suggest you delete the bonds on both sides, then repeat the pairing with your nRF5 SDK based app to exchange new keys. 

Took out a new phone which was never bonded and did a "nrfjprog --recover" on peripheral side but the issue still remains.

00> RAND from key : 8706050920731000218
00> RAND from HCI buf: 12730499317999264668
00> EDIV from key : 17407
00> EDIV from HCI buf : 47649