security
Lauri Mikkola
“I don’t have to be careful, I’ve got a gun.”
-Homer Simpson
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)
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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
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Bluetooth components
•
Radio 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)
–
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Queries a Bluetooth devise and checks what services it supports
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Bluetooth protocol Architecture
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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
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Security modes of Bluetooth(1)
• Security mode 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
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Security modes of Bluetooth (2)
• Security mode 3
– Security at the Baseband level
– Security manager imposes security policies
– LMP makes encryption and key exchanges
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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.
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Key Management (2)
• Encryption key
– 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
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Establishment of Initialization Key
(Pairing)
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Verification of Initialization Key
(Pairing)
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Establishment of Link Key (1)
(Pairing)
• Link key of devices A and B = unit key KA of device A
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Establishment of Link Key (2)
(Pairing)
• Link key of devices A and B = combination key KAB
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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
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Bluetooth security weaknesses (1)
• Unlike in 802.11b 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 8-128 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.
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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
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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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For the paranoid
• MobileCloak
• Cloaktec Shied (fabric)
– Blocks 10Mhz to 20Ghz
signal
• Nylon Shell
• Lightweight
• Only $34
•
- mCloak r5TM for Bluetooth
www.mobliecloak.com
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