how to add authenticity/MITM for a device without any IO capabilities?

[madblue]

Hi,

My device does not have IO capabilities so i have used LE secure connection with just works for pairing. since it does not offer any authenticity, i wish to add some level of pass key options to authenticate it. ie i want to use a static pass key to authenticate the connection in addition to what just works offers.

please note: i don't want to replace the random seed value used in just works with a static key.

What i want to do is sent a random value or static key to the client and it should generate a key and send it back based on pre decided algorithm only known to my client and server. once it is authenticated, it should perform LE secure connection with just works.

how can i add this? is there some other better options?

I want only my application to connect to the device, Is there any better way to discard other clients. I do not want to use whitelisting for this.

i know MITM protection cannot be achieved for devices without io but can we achieve something similar?

[Marjeris Romero]

Hi,

Have you considered using OOB pairing with NFC? Or is this not a possibility?

Best Regards,

Marjeris

[madblue]

Hi Msromero,

Thanks for the suggestion.

I have considered the NFC option but many mid range android phones does not have NFC. so decided not to go with NFC.

At least is there any way to add a hard coded key which should be entered to start the pairing process ?

my server has an rgb LED, so i am looking at the possibility of generating some patterns and entering that in the android phone. but i am not sure how to proceed 

[madblue]

Hi,

i have found the gls example in sdk15.2 and it uses mitm by displaying the key through UART. it looks interesting , since it is done in a different way compared to my sdk14.0.

How can i modify that to make the a constant key ? I  know the security level will be same as just works but it will at least prevent some generic apps from connecting to my server.

can i port that code to from sdk15.2 to sdk 14.0, i am using s132 v5 ?

in the multi connect example on sdk14, if the key matches we have to give the input on ble server where as in the gls example it is sent from client side. how can i implement the same logic to my sdk 14 based appliaction?

is there any other examples in sdk14 for lesc?

[Marjeris Romero]

Hi madblue,

Just a quick answer before leaving the office here. If you take a look here I think you can reply to sd_ble_gap_auth_key_reply with a hardcoded key after receiving the BLE_GAP_EVT_AUTH_KEY_REQUEST, but I haven't tried this myself.

You should also take a look at this answer here: https://devzone.nordicsemi.com/f/nordic-q-a/26759/lesc-confusion/105193#105193

You could blink the LED on your device a given number of times and input this on the phone application. But you will not get any MITM protection from this.

We also have a gls example in sdk14.0 you can take a look at, see <InstallFolder>\examples\ble_peripheral\ble_app_gls

Best Regards,

Marjeris

[madblue]

Thank  you Marjeris for your kind response.

if the passkey used in each time is random to some extend ie.  rgb can represent 3 diff numbers and 4/5 fields will give a decent randomness to the key. so i think this gives some level of protection against MITM attacks

[madblue]

Hi Marjeris,

There seems to be a bug in the gls example, if i remove the bonding information(delete the bonding) from the android app it cannot pair with the device. it can only after erasing the bonding information from the nrf device.

i have tried with the example on sdk14 and 15.2.

Is it bug or should i have to write some code to take care of it?

[Marjeris Romero]

Hi madblue,

It is suppose to work like this. If you delete the bonding information on one of the devices then you need to rebond.

-Marjeris