The difference between security in low energy Bluetooth and BR / EDR

Question

This is a basic task, but I cannot recognize it. I read the spec, but still I don't know. My question is that in low energy bluetooth we use short and long term keys in security. What are the differences between them? and also please tell me, are these keys used in BR / EDR too? Thanks in advance.

Answer 1

Short-term key (STK) is used as the first step for encryption (immediately after pairing). After encrypting the link, a Long Term Key (LTK) is generated.

In principle, if the master does not have LTK generated against the slave, and the same slave tries to connect to the master again, the master assumes that the slave is not authenticated and, therefore, tries to reconnect with the slave. If LTK is present, the wizard realizes that this device is already authenticated and continues to encrypt the session.

Answer 2

To know the difference between them, you should understand the pairing phases in BLE: Phase 1: two devices exchange information about the device, for example, capabilities, etc. Step 2: A short-term key (STK) is created based on a specific procedure according to the BLE specification. Phase 3: Long Term Key (LTK), Signature Enable Key (CSRK) and Identity Key (IRK) are encrypted using STK and exchanged between the two devices.

After step 3, the STK will no longer be used. Instead, LTK is used to encrypt the channel level, and CSRK is used to encrypt the AAT level, depending on the security mode.

In short, STK is used during pairing to encrypt LTK and other information between devices, LTK is subsequently used in normal data transfer.

Answer 3

It is too late, but for the information of others.

1. What is the difference between STK and LTK?

FROM SAFETY GUIDE :

A LE connection starts with two devices that are compatible with a temporary key (TK), the value of which depends on the pairing method used. Then the devices exchange random values ​​and generate a short-term key (STK) based on these values ​​and TK. The communication is then encrypted using STK, which allows secure key distribution for LTK, IRK and CSRK.

2. Are these keys also used in BR / EDR?

No, LTK and STK are not used in BR / EDR. The basic pairing process is different in BR / EDR and BLE. BR / EDR uses key agreement, while BLE uses key transfer for pairing. In BR / EDR, the link key is equivalent to LTK in BLE.