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]

Thank for reply , I also want to ask about STK and LTK . As I understand , STK is used to encrypt the connection , which will be used for distribute LTK , EDIV , Rand , IRK , CSRK , public Address between Host of Master and Host of Slave . Then , host send LTK to Link layer for create session key , session key is used to encrypt all PDUs in Link Layer . I understand that is correct ? Pls help me , thank !!!