LESC with old phones (e.g. iPhone 4s)

[sam wagner]

Hi,

I just implemented LESC Numeric Match on the NUS service for my peripheral device (based on ble_app_multirole_lesc example). I am able to connect to my device using numeric match confirmation with iPhone 6 and iPhone SE and transfer data.

However, when I use iPhone 4S (which doesn't support Bluetooth 4.2), then I see prompt to manually enter 6 digit key on the phone. With that, the pairing/bonding seems to go fine. However, there is no data transfer.

I am using BLE_GAP_CONN_SEC_MODE_SET_LESC_ENC_WITH_MITM for &cccd_md.write_perm and &attr_md_.read_perm and &attr_md.write_perm in rx_char_add() I am using BLE_GAP_CONN_SEC_MODE_SET_LESC_ENC_WITH_MITM for &attr_ms.read_perm and &attr_md.write_perm in tx_char_add()

Any pointers on what might be going wrong?

Thanks, Sam

[Petter Myhre]

Since LESC isn't supported I guess you are not doing LESC pairing.

Instead you are probably doing Legacy pairing with Passkey Entry. This will not result in security level 4 (BLE_GAP_CONN_SEC_MODE_SET_LESC_ENC_WITH_MITM) but security level 3 (BLE_GAP_CONN_SEC_MODE_SET_ENC_WITH_MITM)

[Petter Myhre]

That is exactly what it means. If you want devices that doesn't support LESC to access your attributes you cannot use BLE_GAP_CONN_SEC_MODE_SET_LESC_ENC_WITH_MITM.

BLE_GAP_CONN_SEC_MODE_SET_LESC_ENC_WITH_MITM is the only option that requires LESC. Use BLE_GAP_CONN_SEC_MODE_SET_ENC_NO_MITM if you want devices that pair with just works to access your attributes, or use BLE_GAP_CONN_SEC_MODE_SET_ENC_WITH_MITM if you only want devices that use passkey entry or OOB to access your devices.