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]

Yes I have done that.
Mostly the issue looks from the flash size only, not able to write these info without erasing and the main issue is erasing that particular region is not possible.

Flash was defined from 0xf4000 to 0xf5000, I increased this to 0xf7000 ( 0xf4000-0xf7000), but was facing the above issue and when I reverted to the old settings then the bond info started showing but was not able to update those info onto the flash like storing on the address 0xf4050, needs erasing first and then update but erase will clean the complete page and this will delete the device information which is essential.

[Vidar Berg]

The FDS region has to be a minium of 2 flash pages (is 3 by default) as it reserves one page for garbage collection. Therefore, the span must be bigger than 0xf4000 to 0xf5000. 

[Gaurav]

I have made this work now and saving in a memory address which after migration doesnt gets affected and I am able to read from the memory but somehow I am again to the start of the problem, getting "PEER removed pairing info".

Below is the implementations- I have read the memory and found its matching with the info stored.

static void pre_shared_bond_set(void)
{
	int err;
	int bond_num = 0;
	struct bt_keys *pairing_info;

	bt_foreach_bond(BT_ID_DEFAULT, bond_cb, &bond_num);

	if (bond_num) {
		return;
	}

	bt_addr_le_t addr = {
	    .type = BT_ADDR_LE_PUBLIC,
	    .a.val = {0x43,0x82,0x5E,0xC7,0xE8,0xF4}
	};

	struct bt_ltk ltk = {
	    .val = {0xcb, 0xea, 0xd5, 0xea, 0xe1, 0xab, 0x7c, 0x36, 0x91, 0x1b, 0xe7, 0xd3, 0x31, 0xd1, 0xf8, 0xbc},
	    .ediv = {0},
	    .rand = {0}		
	};

	struct bt_irk irk = {
		.val = {0xF7, 0xDD, 0x7E, 0xC0, 0xDD, 0x48, 0x69, 0x41, 0x15, 0xF0, 0x2A, 0x92, 0xA7, 0x1E, 0x27, 0x8A},
		.rpa.val = {0}		
	}; 

  /**Copying the retrieved values from the memory onto the relevant array to pass the pairing infos*/
  memcpy(addr.a.val,keys_addr,6);
  memcpy(irk.val,irk_val,16);
  memcpy(ltk.val,ltk_val,16);
  // memcpy(ltk.ediv,ltk_ediv,2);
  // memcpy(ltk.rand,ltk_rand,8);

	pairing_info = bt_keys_get_addr(0, &addr);
	if (pairing_info == NULL) {
		printk("Failed to get keyslot\n");
	}
  printk("LTK value \n");
  for(uint8_t i=0;i<16;i++)
  {
    printk(" %02x",ltk.val[i]);
  }
	memcpy(&pairing_info->ltk, &ltk, sizeof(pairing_info->ltk));
	memcpy(&pairing_info->irk, &irk, sizeof(pairing_info->irk));

	pairing_info->flags = 16; //SMP_FLAG_SC
	pairing_info->enc_size = 16;
	pairing_info->keys = BT_KEYS_IRK | BT_KEYS_LTK_P256;

	err = bt_keys_store(pairing_info);
    if (err) {
        printk("Failed to store keys (err %d)\n", err);
    } else {
        printk("Keys stored successfully\n");
    }

}

void retrieve_pairing_keys(void)
{
  const volatile uint32_t *ptr = (const volatile uint32_t *)(0xf5100); //Workaround to read back the pairing info from the old SDK
  memcpy(irk_val,((uint8_t*)ptr),16);
  memcpy(keys_addr,((uint8_t*)ptr+16+1),6);
  memcpy(ltk_val,((uint8_t*)ptr+16+6+1),16);
  //memcpy(ltk_ediv,((uint8_t*)ptr+16+6+16+1),2);
  //memcpy(ltk_rand,((uint8_t*)ptr+16+6+16+2+1),8);
  printk("Successfully copied pairing info from the memory\n");
}

Logs-

00> Watchdog is getting fed here : adv 0 and conn 1
00> Connected
00> [00:00:35.289,337] <dbg> bt_smp: smp_send_security_req: 
00> [00:00:35.289,520] <dbg> bt_keys: bt_keys_get_addr: F4:E8:C7:5E:82:43 (public)
00> [00:00:35.289,703] <dbg> bt_smp: smp_init: prnd 8ea5292745f0b134613f0187006f8a2e
00> [00:00:35.457,733] <dbg> bt_smp: bt_smp_encrypt_change: chan 0x200042b0 conn 0x20003e58 handle 0 encrypt 0x00 hci status 0x06
00> Security failed: F4:E8:C7:5E:82:43 (public) level 1 err 2
00> [00:00:35.577,758] <dbg> bt_smp: bt_smp_disconnected: chan 0x200042b0 cid 0x0006
00> MTU exchange failed (err 14)[00:00:35.578,125] <dbg> bt_keys: bt_keys_find_addr: F4:E8:C7:5E:82:43 (public)
00> [00:00:35.578,308] <dbg> bt_keys: bt_keys_find_addr: F4:E8:C7:5E:82:43 (public)
00> Disconnected (reason 0x13)

This is the memory region of the flash-

[Gaurav]

Getting this in the HCI log-

00> Bluetooth initialized
00> [00:00:00.042,877] <dbg> bt_id: set_random_address: D3:C4:88:DC:F4:8D
00> [00:00:00.042,877] <dbg> bt_hci_core: bt_hci_cmd_create: opcode 0x2005 param_len 6
00> [00:00:00.042,907] <dbg> bt_hci_core: bt_hci_cmd_create: buf 0x20034930
00> [00:00:00.042,938] <dbg> bt_hci_core: bt_hci
00> [00:00:13.049,743] <dbg> bt_sdc_hci_driver: event_packet_process: LE Meta Event (0x0a), len (31)
00> [00:00:13.049,774] <dbg> bt_hci_core: bt_recv: buf 0x200344e4 len 33
00> [00:00:13.049,896] <dbg> bt_hci_core: rx_work_handler: Getting net_buf from queue
00> [00:00:13.049,926] <dbg> bt_hci_core: rx_work_handler: buf 0x200344e4 type 1 len 33
00> [00:00:13.049,926] <dbg> bt_hci_core: hci_event: event 0x3e
00> [00:00:13.049,957] <dbg> bt_hci_core: hci_le_meta_event: subevent 0x0a
00> [00:00:13.050,323] <dbg> bt_hci_core: bt_hci_le_enh_conn_complete: status 0x00 handle 0 role 1 peer F4:E8:C7:5E:82:43 (public-id) peer RPA 6A:42:04:06:EF:A4
00> [00:00:13.050,567] <dbg> bt_hci_core: bt_hci_le_enh_conn_complete: local RPA 00:00:00:00:00:00
00> [00:00:13.050,598] <dbg> bt_adv: bt_le_adv_resume: Host cannot resume connectable advertising (-12)
00> [00:00:13.050,659] <dbg> bt_smp: bt_smp_accept: conn 0x20003e58 handle 0
00> [00:00:13.050,689] <dbg> bt_smp: bt_smp_connected: chan 0x200042b0 cid 0x0006
00> [00:00:13.050,964] <dbg> bt_keys: bt_keys_find_addr: F4:E8:C7:5E:82:43 (public)
00> Watchdog is getting fed here : adv 0 and conn 1
00> Connected
00> [00:00:13.051,788] <dbg> bt_smp: smp_send_security_req: 
00> [00:00:13.051,971] <dbg> bt_keys: bt_keys_get_addr: F4:E8:C7:5E:82:43 (public)
00> [00:00:13.052,185] <dbg> bt_smp: smp_init: prnd e41b32de696c8ba9106144bf66704065
00> [00:00:13.052,215] <dbg> bt_hci_core: bt_hci_cmd_create: opcode 0x2016 param_len 2
00> [00:00:13.052,246] <dbg> bt_hci_core: bt_hci_cmd_create: buf 0x20034930
00> [00:00:13.052,276] <dbg> bt_hci_core: bt_hci_cmd_send_sync: buf 0x20034930 opcode 0x2016 len 5
00> [00:00:13.052,307] <dbg> bt_hci_core: process_events: count 2
00> [00:00:13.052,337] <dbg> bt_hci_core: process_events: ev->state 4
00> [00:00:13.052,337] <dbg> bt_hci_core: send_cmd: calling net_buf_get
00> [00:00:13.052,337] <dbg> bt_hci_core: send_cmd: calling sem_take_wait
00> [00:00:13.052,368] <dbg> bt_hci_core: send_cmd: Sending command 0x2016 (buf 0x20034930) to driver
00> [00:00:13.052,368] <dbg> bt_hci_core: bt_send: buf 0x20034930 len 5 type 0
00> [00:00:13.052,398] <dbg> bt_sdc_hci_driver: hci_driver_send: 
00> [00:00:13.052,398] <dbg> bt_sdc_hci_driver: cmd_handle: 
00> [00:00:13.052,459] <dbg> bt_sdc_hci_driver: hci_driver_send: Exit: 0
00> [00:00:13.052,459] <dbg> bt_hci_core: process_events: ev->state 1
00> [00:00:13.052,490] <dbg> bt_sdc_hci_driver: event_packet_process: Command Status (0x2016) status: 0x00
00> [00:00:13.052,520] <dbg> bt_hci_core: bt_recv: buf 0x20034930 len 6
00> [00:00:13.052,551] <dbg> bt_hci_core: hci_cmd_status: opcode 0x2016
00> [00:00:13.052,551] <dbg> bt_hci_core: hci_cmd_done: opcode 0x2016 status 0x00 buf 0x20034930

[Vidar Berg]

Did the existing bond have the LESC bit set?

[Gaurav]

I just reversed to the old state of ours where things actually worked and stopped the new bonding from populating in the structure and strangely that part is also not working now.

Gaurav said:

It worked Vidar. Reversing the IRK,LTK was the main culprit.

This part here.

Vidar Berg said:

Did the existing bond have the LESC bit set?

this is the config used-

//BLE_SEC
#define SEC_PARAM_BOND                      1                                       /**< Perform bonding. */
#define SEC_PARAM_MITM                      0                                       /**< Man In The Middle protection not required. */
#define SEC_PARAM_LESC                      0                                       /**< LE Secure Connections not enabled. */
#define SEC_PARAM_KEYPRESS                  0                                       /**< Keypress notifications not enabled. */
#define SEC_PARAM_IO_CAPABILITIES           BLE_GAP_IO_CAPS_NONE                    /**< No I/O capabilities. */
#define SEC_PARAM_OOB                       0                                       /**< Out Of Band data not available. */
#define SEC_PARAM_MIN_KEY_SIZE              7                                       /**< Minimum encryption key size. */
#define SEC_PARAM_MAX_KEY_SIZE              16                                      /**< Maximum encryption key size. */

[Gaurav]

SO In the previous build where it was connecting, I made the phone to rebond and saved the LTK in the structure that you have shared and after this it started connecting. I think LTK changes with every paired connection and this was causing the issue for the connection to not go through in the old setup.

Need to check for the setup I am taking the keys from memory shared from the nRF5 SDK.
Do share if you get some insight from the above shared logs.

[Vidar Berg]

The LTK changes if you re-pair, but it does not change across connections. 

Gaurav said:

this is the config used-

You were previously testing with LESC bonding. As mentioned earlier, you should not set the SC bit in NCS if you use legacy pairing. I also believe you need to store the EDIV and Rand.

[Gaurav]

So what should be the flag value and config for security in my applciation?

[Gaurav]

I have changed the flag to SMP_FLAG_SC for pairing_info->flags = 5 and also copied EDIV and RAND values to the structures now, but still same issue.

Vidar Berg said:

You were previously testing with LESC bonding. As mentioned earlier, you should not set the SC bit in NCS if you use legacy pairing. I also believe you need to store the EDIV and Rand.

Should I enable CONFIG_BT_SMP_SC_PAIR_ONLY and remove bt_conn_set_security(conn, BT_SECURITY_L2) for my connection?