what is different between pairing vs bonding , STK vs LTK

[Giang]

hi all , I am looking out theory about SM layer in BLE . I read CoreV5.0 but I do not understand much about pairing , bonding , STK , LTK . Can you give me some document about that ? Thank !!!

[shibshab]

Pairing: Select a key, use this key to encrypt data between these devices. When the devices are disconnected, everything is forgotten and it is if the devices never knew each other. The next time you want to talk secretly to the same device, everything has to be done all over again.

Bonding: First, do Pairing to have a secure link, then exchange keys for the next time we meet, so that we don't need to perform Pairing again to have a secure link.

By doing bonding, the user will (for example) not have to enter the 6 digit passkey every time the smartwatch is connected to the phone.

[Giang]

Hi Emil Lenngren , I want to ask some question .

1. In pairing , keys don't distribute , so each re-connect secure , we will re-pairing , so the new STK and LTK is created , so have we changed ?
2. In bonding , LTK is stored . So each reconnect , old - LTK will be used . So , when the new LTK is created ?
3. Can you discribe for me the process phase 3 performance between master and slave and how the LTK is used in Link layer ?

Thank !!!