BLE - passkey

[Roei]

Hi,

I have a question regarding BLE connection with passkey.

When starting connection and bonding process, a device can display a passkey so the other side will send this passkey in order to establish connection.

My question is - what's happening in the background while waiting for this passkey to be sent? Does other procedures (diffie-hellman etc) are freeze until passkey is sent?

Do you have any flow chart which can explain the steps?

Thanks!

[Simonr]

Hi

The passkey is printed over UART. By default this will be printed to the COM port that a DK is connected to, so that you can see the passkey on a terminal like PuTTY, or an interface of your choice connected to UART pins on your device.

Not everything happens "out of band" but this is the entire process of an Out of Band bonding process.

Best regards,

Simon

[Roei]

Hi,

Can you please help me to undestand what exactly the passkey blocks? What will happen when the user sends the passkey, which didn't happen before? They were already connected, didn't they?

Regarding out of band - where can I see a list of actions which occur out of band?

Thanks!

[Simonr]

Hi again

Indeed, they are already connected, these methods you are looking at are methods of pairing the two devices. Pairing in BLE is a concept where devices that are initially connected can exchange encryption keys and encrypt the link. When they have, the link is secure and the devices are "paired". Then when they're paired you can also bond the devices, which means they store the encryption keys that have been exchanged so that they are paired already the next time they connect.

The OOB actions are the pairing and bonding process itself. So it will connect as usual, but the exchange of keys and encryption will be handled OOB.

Best regards,

Simon

[Roei]

Thanks!

Regarding the first topic - I'm familiar with that stuff, but how does it related to passkey? Is it part of pairing or bonding?

[Simonr]

The passkey is an optional way to pair. You can use a passkey to make sure that you are pairing to a device you know and intend to pair with.

Best regards,

Simon

[Roei]

But what will happen to the keys if I've already connected, and than I'll send a wrong passkey? They will not be stored and connection will be lost?

Thanks!

[Simonr]

Hi

Check out the Pairing failure sections of the documentation. If the pairing is unsuccessful (like if you enter the incorrect passkey, the central will return a Pairing Failed message and send an error message to the peripheral saying so (and why if you are logging debugging).

Best regards,

Simon