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 !!!

[Petter Myhre]

1. There is no LTK in pairing. Only in bonding.

2. In bonding there is only one LTK. This is used in all subsequent connections.

[Giang]

Hi , as I know . In phase 2 of pairing/bonding , has 2 option

1. LE legacy pairing , STK will be created for encrypt connection , then if pairing , STK is sent to LL for create session key . If bonding , LTK is created replace STK , then LTK is sent to LL for create session key
2. if LE secure connection pairing , LTK will be created for encrypt connection and sent to LL

Is it correct ? thank !!!

[Petter Myhre]

1. If you have bonded LTK will be used for subsequent connections. Not the connection when you pair.

2. Correct.

[Giang]

Thank for reply , I have question .

1. If don't pairing or bonding , Is the Link Layer connection encrypt ? Then, Is the PDU package in Link Layer encrypted for send from device A to device B ?
2. What is diffence between Link Layer connection and GAP connection ? or they are one
3. If don't pairing and bonding , LL hasn't STK or LTK , so how LL encrypt by ?

[Petter Myhre]

1. The link can either be encrypted by pairing, or if you have previously bonded, you can encrypt the link with LTK.

2. I'm don't know how to answer this, they are two different layers in the stack. Could you be more specific?

3. Then you need to pair or bond...