1. “I don’t have to be careful, I’ve got a gun.”
security
Bluetooth
Lauri Mikkola
“I don’t have to be careful, I’ve got a gun.”
-Homer Simpson

2. About Bluetooth
Developed by a group called Bluetooth Special Interest Group (SIG), formed in may 1998
Founding members were Ericsson, Nokia, Intel, IBM and Toshiba
Bluetooth connects different wireless devises, like laptops, mobile phones, PDAs, refrigerators etc.
Bluetooth is intended to distances about 10 meters (piconet)

3. Bluetooth details Utilizes the 2.45Ghz ISM-band
Uses fast frequency-hopping spread spectrum (FHSS) technique between 79 frequencies 1600/s
Can give bit rates up to 1 Mbps
Piconet consist of max 8 nodes
Low cost ( ~5€ ) and small size

4. Bluetooth components Radio unit Baseband unit
TDD and FHSS
Baseband unit
Voice to data conversion, packet segmentation, master/slave communication, identification of parties, control authorization
Link Management Protocol (LMP)
Set up connections and implement security features like key exchanges and encryption
Logical Link Control and Adaptation Protocol (L2CAP)
Multiplexing, packer segmentation/reassemly, QoS
Service Discovery Protocol (SDP)
Queries a Bluetooth devise and checks what services it supports

5. Bluetooth protocol Architecture

6. Bluetooth security features
The Bluetooth specification include security features at the link level
Supports authorization, authentication and encryption
Based on a secret link key that is shared by a pair of devices
Link key generated by a pairing procedure when two devices communicate for the first time

7. Security modes of Bluetooth(1)
No security, for testing only. Allows other Bluetooth devices initiate connections with it, PUSH messages
Security mode 2
A device does not initiate security procedures before establishment of the link between the devices at the L2CAP level.
Trusted and untrusted devices
Security polices can flexible impose different trust levels: authentication, authorisation and encyrption

8. Security modes of Bluetooth (2)
Security at the Baseband level
Security manager imposes security policies
LMP makes encryption and key exchanges

9. Key Management (1) Link keys
All keys are 128bit random numbers and are either temporary or semi-permanent
Unit key KA , unique long-term private key of a device
Combination key KAB derived from units A and B. Generated for each pair of devices
Master key Kmaster ,used when master device wants to transmit to several devices at once
Initialization key Kinit ,used in the initialization process.

10. Key Management (2) Encryption key PIN Code
Derived from the current link key. Each time encryption is needed the encryption key will be automatically changed
Separated from authentication key
PIN Code
Fixed or selected by the user
Usually 4 digits, can be 8 to 128 bits
Shared secret

11. Establishment of Initialization Key (Pairing)

12. Verification of Initialization Key (Pairing)

13. Establishment of Link Key (1) (Pairing)
Link key of devices A and B = unit key KA of device A

14. Establishment of Link Key (2) (Pairing)
Link key of devices A and B = combination key KAB

15. Authentication and Encryption
Authentication by issuing a challenge to another device
The other device replies to challenge with a message based on the challenge, the Device address and the shared link key.
The device that issued the challenge verifies the response and authenticates if the response is equals to it’s own calculations.
Encryption is based on the 4 LFSR algorithm

16. Bluetooth security weaknesses (1)
Unlike in b WLAN, the security algorithms of Bluetooth are considered strong. However there are some attack possibilities
PIN weakness
Initial authentication is based on a PIN that can be anywhere between bits.
If poorly chosen can be easy to guess
Impersonation
A hacker can scan the MIN and ESN and pretend to be someone else
Stealing the Unit Key
Only the device is authenticated, not the user
Replay attacks
A hacker can record Bluetooth transmissions in all 79 frequencies and then in some way figure out frequency hopping sequence and then replay the whole transmission.

17. Bluetooth security weaknesses (2)
Man in the middle
Bluetooth authentication is not based on public key certificates. It is possible to play man in the middle
Location attack
A Bluetooth device has (globally) a unique identification number, therefore it is possible to identify and locate users position
Denial-of-Service attack
Jamming the whole ISM band, takes lot of energy
Put so many Bluetooth devices that the band is consumed
Try to connect, authentication fails, but a legal client will not get through either

18. How to avoid being attacked
Paring is the most critical moment of a attack
Paring should be performed in a most secure place
Long PIN numbers are strongly encouraged
Avoid using unit keys. Use combination keys
To check default settings of device
Chose to respond only to inquiries of known devices
Do not save PIN permanently in memory

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