1. Mobile and Wireless Network Security
Design Fundamentals
ET-IDA-082
Lecture-22
Mobile and Wireless Network Security
GSM, UMTS,802.11,Bluetooth
, v11
Prof. W. Adi

2. Outlines Wireless Network Security 802.11 Bluetooth Security
2G, 3G Mobile Security
(see early lecture contents)
Wireless Network Security
Bluetooth Security

3. Through Modern Communication
Mobile Environment
Open Global Market
Through Modern Communication
Global Information
Short-Circuit
(AAA Scenario)
Light
Heating
Kitchen
Garage
Door
Gates
...
Remote
Control
Car
power -
line
CAN-Bus
Anywhere
Any time
Any device TV
Power Station
power line network
Internet
WLAN: AP
Wireless
Network
DECT
Bluetooth

4. IEEE security
There are many different electronic devices for e-payment system. Different banks may be concerted in e-payment and the financial network is neccessary. E-payment flatform is built connecting the financial network and other open network, where the electronic devices can communicate with the flatform. PC is the most common device. Other devices include mobile devices, e.g. laptop, PDA, mobile telephone, ATM(Automatic Teller Machine), POS(Position of Sale), telephone and terminal. The electronic devices can connect the e-payment flatform using different open network.

5. IEEE 802.11 security Many users use no encryption/authentication
Still packet-sniffing and various attacks easy!
Securing
encryption, authentication
first attempt at security:
Wired Equivalent Privacy (WEP): a failure
current attempt: i

6. Wired Equivalent Privacy (WEP):
authentication as in protocol ap4.0
host requests authentication from access point
access point sends 128 bit nonce
host encrypts nonce using shared symmetric key
access point decrypts nonce, authenticates host
no key distribution mechanism
authentication: knowing the shared key is enough

7. WEP data encryption
Host/AP share 40 bit symmetric key (semi-permanent)
Host appends 24-bit initialization vector (IV) to create 64-bit key
64 bit key used to generate stream of keys, kiIV
kiIV used to encrypt ith byte, di, in frame:
ci = di XOR kiIV
IV and encrypted bytes, ci sent in frame

8. Sender-side WEP encryption

9. Breaking 802.11 WEP encryption
Security hole:
24-bit IV, one IV per frame, -> IV’s eventually reused
IV transmitted in plaintext -> IV reuse detected
Attack:
Trudy causes Alice to encrypt known plaintext d1 d2 d3 d4 …
Trudy sees: ci = di XOR kiIV
Trudy knows ci di, so can compute kiIV
Trudy knows encrypting key sequence k1IV k2IV k3IV …
Next time IV is used, Trudy can decrypt!

10. 802.11i: improved security
numerous (stronger) forms of encryption possible
provides key distribution
uses authentication server separate from access point

11. 802.11i: four phases of operation
AP: access point
STA:
client station
AS:
Authentication
server
wired
network
1 Discovery of
security capabilities
STA and AS mutually authenticate
Together generate Master Key (MK).
AP servers as “pass through” 2 3
STA derives
Pairwise Master Key (PMK) 3
AS derives
same PMK,
sends to AP 4
STA, AP use PMK
to derive Temporal Key (TK)
used for message encryption and integrity

12. Bluetooth security
There are many different electronic devices for e-payment system. Different banks may be concerted in e-payment and the financial network is neccessary. E-payment flatform is built connecting the financial network and other open network, where the electronic devices can communicate with the flatform. PC is the most common device. Other devices include mobile devices, e.g. laptop, PDA, mobile telephone, ATM(Automatic Teller Machine), POS(Position of Sale), telephone and terminal. The electronic devices can connect the e-payment flatform using different open network.

13. Bluetooth Security - Components
Security is based on the SAFER+ security protocol (J. Massey)
All link-level security is based on 128-bit link keys
A secret PIN number (variable from 4 to 16 octets) which is common to the two devices wishing to communicate forms one of the key inputs into forming the initial link key.
Authentication in Bluetooth uses a device-to-device challenge and response scheme to determine if the two devices share a common link key
Encryption generates a cipher stream based on an encryption key which is generated from a common link key – encryption is symmetrical
Link keys can be semi-permanent or temporary

14. Bluetooth Security – Link keys
In order to accommodate for different types of applications, four types of link keys have been defined:
the unit key KA: Semi permanent key generated in every unit only once during factory setup
the combination key KAB: This is dependent on two units and is unique for a particular pair of devices – more secure than a unit key
the master key Kmaster: Temporary key used for point to multipoint broadcast communications and will replace the current link key until peer-to-peer communications resume
the initialization key Kinit: The is a temporary key which is used when no combination or unit keys have been exchanged yet. It is generated using a PIN code as one of its inputs
In addition to these keys there is an encryption key, denoted Kc. This key is derived from the current link key.

15. Bluetooth Security – Generating keys
Generation of Keys uses two “Basic Modes”
Algorithm E22 is used to generate Initialization keys Kinit and Master keys Kmaster where PIN’ is a combination of the bluetooth address and the PIN and L’ is derived from the number of octets in the PIN
Algorithm E21 is used to generate Unit keys and Combination keys where RAND is a 128-bit random number and BD_ADDR is the units bluetooth address

16. Bluetooth Security – key exchange
Exchange of unit keys
A sends the unit key KA to unit B securely by XORing with Kinit
Unit B will store KA as the link key KBA.
Usually the application will let the unit with restricted memory abilities send its unit key to be used as the link key since this unit only has to remember its own unit key
Kinit is discarded once keys have been exchanged

17. Bluetooth Security – key exchange
Creation and exchange of combination keys KAB , KBA
Random numbers (LK_RANDA and LK_RANDB) are generated in Unit A and Unit B
These are exchanged securely by XORing them with the current link key K
Two new random numbers (LK_KA and LK_KB) are generated for LK_RANDA and LK_RANDB using the E21 algorithm
These two random numbers are XORed together to form a new combination key KAB on unit A and KBA on unit B

18. Bluetooth Security – key exchange
Creation and exchange of a master key Kmaster
The master device generates two random numbers (RAND1 and RAND2) and uses the E22 algorithm to generate a random key Kmaster
A third random number (RAND) is generated by the master and sent to the slave
The slave and the master compute an overlay (OVL) using the E22 algorithm with the current key and the new random as inputs
The master key (Kmaster) is sent from the master to the slave by XORing it with the overlay
The slave which has the identical overlay, recalculates Kmaster

19. Bluetooth Security – Authentication
Authentication process using secret key Challenge-Response
Authentication uses a challenge response scheme to check the claimant’s knowledge of a secret key (current link key)
The verifier challenges the claimant to authenticate a random number (AU_RANDA) with an authentication code, E1, and return a result, SRES, which is compared against it’s own generated code SRES’
Authentication is often mutual – Unit A verifying Unit B is followed by Unit B verifying Unit A

20. Bluetooth Security – Encryption Key
Generating the Encryption Key
The encryption key Kc is generated by E3 from a COF (Ciphering Offset Number), the current link key and a 128-bit random number
The COF is either derived from the BD_ADDR of the master if the current link key is a master key otherwise it is generated from the ACO created during authentication
Even though the generated key length is 128 bits this may be shortened due to export encryption laws

21. Bluetooth Payload Encryption
Encryption process by a Running Key Generator RKG (Additive Stream Cipher)

22. Encryption Running-Key Generator E0
Linear Sequence
Generators
De-linearizing
combiners

23. E0: Key Generation Engine Parameters
Primitive LFSR Polynomials

24. Authentication Function E1

25. Authentication Function Ar Block, SAFER + (J. Massey)
Based on PHT:
Pseudo-Hadamard Transform
PHT(x,y) = (2x+y, x+y) mod 2n
Low-Complexity Arithmetic!

26. Wireless Security Still not adequate for today’s Network application Challenges!
There are many different electronic devices for e-payment system. Different banks may be concerted in e-payment and the financial network is neccessary. E-payment flatform is built connecting the financial network and other open network, where the electronic devices can communicate with the flatform. PC is the most common device. Other devices include mobile devices, e.g. laptop, PDA, mobile telephone, ATM(Automatic Teller Machine), POS(Position of Sale), telephone and terminal. The electronic devices can connect the e-payment flatform using different open network.