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

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

bjorn-spockeli — Fri, 14 Jul 2017 14:07:53 GMT

Hi Sam, its not possible to modify the GATT table after you have added the services/characteristics/descriptors on the fly. in order to change the properties of the CCCD you'll have to disable the Softdevice, re-enable it and then re-add the services/characteristics/descriptors with the different configuration. I think the better option is to set the security mode to BLE_GAP_CONN_SEC_MODE_SET_ENC_WITH_MITM to ensure that you can access the attributes with phones that does not support LESC. If the phones support LESC then you can upgrade the security mode by using pm_conn_secure with force_repairing set to true.

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

sam wagner — Wed, 12 Jul 2017 20:23:33 GMT

Thanks, Petter.

Is there any way to change the security mode on the fly (to BLE_GAP_CONN_SEC_MODE_SET_ENC_WITH_MITM) to allow connection and data exchange with BLE4.1 central devices (like iPhone 4s) and keep the default setting to BLE_GAP_CONN_SEC_MODE_SET_LESC_ENC_WITH_MITM for BLE4.2 central devices?

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

Petter Myhre — Wed, 12 Jul 2017 07:26:36 GMT

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.

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

sam wagner — Tue, 11 Jul 2017 17:51:05 GMT

Hi Petter,

I am using BLE_GAP_CONN_SEC_MODE_SET_LESC_ENC_WITH_MITM for attributes and CCCDs in the tx_char_add and rx_char_add functions in ble_nus.c. If the central (iPhone 4s) does not support lesc pairing, then does it mean that we will not be able to do data transfer with that central?

What is the provision for backward compatibility then? I do see that the iPhone 4s prompts the user to enter the 6 digit code displayed on the peripheral device (nRF52) and then show the peripheral as connected.

What should be the settings in rx_char_add and tx_char_add of ble_nus.c to guarantee backward compatibility with phones that do not support BLE 4.2?

thanks, Sam

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

Petter Myhre — Fri, 09 Jun 2017 14:46:06 GMT

Even if it shows successful (legacy) pairing you have characteristic values and CCCDs that require the connection to be in security level 4 (LESC pairing with MITM) before they read or written.

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

sam wagner — Thu, 08 Jun 2017 20:18:02 GMT

HI Petter, Yes, I suppose it is legacy pairing. What I am not able to understand is that while both FW and the phone show that pairing is successful, the datapath is not working. The app is not able to enable notifications on device's characteristics. Is there any particular setting that is needed to ensure that LESC falls back correctly to BLE 4.1 method of display and passkey entry? thanks, Sam

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

Petter Myhre — Wed, 07 Jun 2017 08:39:53 GMT

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)