An Analysis of Bluetooth Security

Team A:Padmaja SriramanPadmapriya GudipatiSreenivasulu Lekkala

Introduction

Short range radio technology which utilizes wireless protocol.

Can transmit data up to 100 meters. Composed of 8 active devices which

share a master – slave relationship. Developed by Bluetooth Special

Interest Group (SIG).

LINK KEY

SEMI TRANSPARENT TEMPORARY KEY

UNIT KEY COMBINATION KEY INITIALIZATION MASTER

CIPHERING KEY

ENCRYPTION KEY CONSTRAINED ENCRYPTION KEY PAYLOAD KEY

Types of keys

Security Architecture Generation of initialization key Authentication Generation of link key Link key exchange Generation of encryption key

Key Pairing Generation of initialization key: A method similar

to SAFER+ Block Cipher is used. The input to this method is the public address of the bluetooth unit, PIN, length of the pin and a random number

Authentication: This process involves a challenge-response scheme.

Link key generation: Any one type of the key is generated.

Link key exchange: The generated key is exchanged.

Generation of encryption key: Uses Cipher Keys for encryption of data

Modes of Operation Mode 1 – No Security. Authentication and

encryption are bypassed. Mode2 –Service level security. Used after

the link connection is established. Mode3 – Link level security. Uses the link

keys. Mode4 – Similar to Mode2 but with

enhanced security techniques

Eavesdropping

Attacker can see and change the payload

Easy when it is not encrypted One solution is frequency hopping

technology 2.4 GHZ ISM band which is license free Hops between frequencies in pseudo-

random order Difficult to pick up the signal

Impersonation

Receivers want to be sure that they receive from original sending party Attacker impersonates the sending unit

• Needs to give correct response to the challenge• Not easy, No attack on SAFER+ known

Changes the payload data• Easy if no encryption, manipulate CRC• Since CRC calculation is a linear task • Attacker can compute how to modify CRC according

to modification to encrypted data

K= current link keyKAB = Combination key

Combination key generation

Pairing

Can be prone to attack if it is done in public places

The current link key used to generate the combination key, KAB, is derived as

KINT=E22(BD_ADDR_A, IN_RAND,PKEY)

PKEY is the secret pass key If an attacker can guess PKEY, he can

calculate combination key If PKEY is short, it becomes easy to

guess it

Authentication(Challenge-Response)

BD_ADDRB

AU_RAND

ClaimantVerifier

SRESCalculates SRES’

Success if SRES’==SRES

SRES=E1(KAB,AU_RAND,BD_ADDRB) If PKEY is small, attacker can try possible

value to get a match between SRES’ and SRES Short passkey values should be avoided

Improper key storage Disclosure of keys

Malicious USB plugs, Viruses, Trojan horses Device should be paired with hosts it is allowed

on Host should communicate only with trusted

parties Adding link key to the database without

pairing Device assumes that valid bonding exists Restrict the access Encrypt the database

Contd… Denial of service

Delete or corrupt the link keys in the database

Change the CRC along with the keys Authentication fails repeatedly, waiting

time increases Solution is to request new pairing Need to provide good integrity

protection to the database

Location Tracking Tracking users movements by tracking

bluetooth device Bluetooth access codes CAC, LAC, IAC are

derived from the device address These codes help in tracking To prevent this devices operate in

anonymity mode updating their device address randomly

Implementation flaws Key database management, user

interaction, memory protection Snarf attack – Set up connection without

consent or alerting Backdoor attack – Erase link from list of

paired devices but not from database of the victim. Attacker attacks the target

Bluejacking – Sending unsolicited messages to bluetooth devices

Security for Bluetooth Applications

• Bluetooth security will depend on the application exactly how one should use.• Some applications need more security design than other applications because some applications are more security sensitive.• Here we discuss the security mechanisms for three different

bluetooth applications.1. Headset.2. Network Access.3. SIM Access.

Headset The Bluetooth headset profile is used for headset

connections to mobile phones and laptops. The security association is used to authenticate

and encrypt all communication between two Bluetooth wireless devices.

Bluetooth pass-key usage can prevent illegal use of stolen headset.

A typical headset configuration consists of two devices a headset (HS) and audio gateway (AG).

AG is typically a cellular phone , laptop , PC. The communication between HS and AG is

protected by the authentication and encryption mechanisms.

Headset (contd..) The HS and AG need to store the pass-

keys and link-keys for secure connections. HS usually does not have the user

interface , AG will control some of the basic settings of HS (e.g volume setting, changing the passkey).

The pairing will only succeed if only the AG knows the correct pass-key of HS.

If the HS is stolen , the thief will not know the pass-key and will not succeed to connect to the HS with another AG.

Network Access Network access to an IP network in Bluetooth is

provided through PAN profile. Network access points (NAcP) connected to LAN

through wired network in one side and the other side Bluetooth wireless devices will be connected.

NAcPs can be accessed by anybody because it is open , but service will be restricted by service provider , only authorized persons will be allowed to access the network.

Suggested security architecture is built around common access key (CAK) concept .

SIM Access The SIM (subscription identity module)

access application is provided by a Bluetooth profile.

A SIM card is an integrated circuit used in GSM mobile telephone system. It is used to hold the subscriber information.

The Bluetooth SIM access profile defines procedures and protocols for access to a remote SIM over a Bluetooth connection.

The SIM is used for security critical services. The card holds secret keys and subscriber information.

Conclusion Bluetooth is a widely used

technology for short distance wireless communication

Still has security loopholes and research is going on to improve security

References

[1] Christian Gehrmann, Joakim Persson, Ben Smeets, Bluetooth Security, Artech House, 2004 [2] http://www.cs.utk.edu/~tyang/wireless/blue.htm [3] http://www.cs.utk.edu/~dasgupta/bluetooth/ [4] http://en.wikipedia.org/wiki/Bluetooth [5]. http://www.bluetooth.com/Bluetooth/Technology