1. Mobile and Wireless Networking
Lecture 21 Dr. Xinbing Wang

2. Overview of the Course
Part 1: Wireless communication systems (Chapter 1)
Flexibility to support roaming
Limitations: Geographical coverage, transmission rate, and transmission errors
Part 2: Wireless communication technology
Radio propagation (Chapter 5)
Spread spectrum (Chapter 7)
Part 3: Current wireless systems
Cellular network architecture (Chapter 10)
Mobile IP (Chapter 12)
Wireless LAN (Chapter 11/13/14)
Part 4: Other wireless networks
Ad hoc networks (Reading materials)
Sensor networks (Reading materials)
Wireless PAN (Chapter 15)
Satellite systems (Chapter 9)
Part 5: Wireless Security
In our daily lives, wireless communication technology is used everywhere, from VCR remote control, to satellite weather forecast. The common characteristics of wireless communication systems is that there is no physical (visible) lines between two communication parties.
Therefore, a wireless system is able to support user roaming. For example, we do not have to use a remote control in a particular position to.., we can use our cellular phones almost everywhere.
However, there are many impairments to a wireless channel, causing a lot of limitations to wireless communications system such as geographical.. (signal fading, additional noise, cochannel interference. Wireless systems also suffers from limit usable spectral width, so that the transmission rate is relatively low.
Specifically, wireless cellular systems based on radio propagation has been evolving from narrow band (1G, late 170s) to wide-band(3G).
With their geographical coverage limitation, wireless systems need a backbone network to extend their geographical coverage to enable global communications.
The interoworking of a wireless network as the front-end and the Internet as the backbone has received much attention in recent years.
So we will first take a look at the network architecture of current wireless systems,…, Then we will talk about the evolution from 2G to 3G systems.
Dr. Xinbing Wang

3. Security in Wireless Networks
Wireless security issues
General topics on security
Layered security solutions
Security solutions in wireless networks
Security in UMTS
Security in Mobile IP networks
WLANs: WEP
Secure AODV for mobile ad hoc networks
Dr. Xinbing Wang

4. Security Principles Authentication Access control and authorization
Nonrepudiation
A user/process be identifiable and accountable for its actions in a manner that prohibits the user or process from denying its involvement at a late date.
Privacy and confidentiality
To protect information from unauthorized disclosure.
A very tricky and contentious issue ( be anonymous and confidential).
Cryptography, steganography, digital watermarking.
Integrity
To verify the accuracy of what is sent or delivered and that the process/component has not been altered in some way (often, take for granted).
Auditing: to review the activities to ensure that whatever was performed was appropriate for the given entity.
Dr. Xinbing Wang

5. WLAN: Wired Equivalent Privacy (WEP) Protocol
As its name, the goal of WEP is to provide a level of privacy that is equivalent to a wired LAN.
The WEP algorithm is used
To protect wireless networks from eavesdropping.
To prevent unauthorized access to wireless networks.
WEP replies on a default set of keys that are shared between wireless devices and APs.
A client with the correct key can communicate with any AP on the wireless network; without the key, a link-level connection request is rejected.
If it is configured to do so, the wireless devices and APs will also encrypt data before transmitting it, and an integrity check ensures that packets are not modified in transit.
Dr. Xinbing Wang

6. Authentication Frame
Based on an RSA RC4 (stream cipher) algorithm, this simple WEP algorithm has following properties
Reasonably strong: a brute force attack on this algorithm is difficult because every frame is sent with an initialization vector (IV), which restarts the PseudoRandom Number Generator (PRNG) for each frame.
Self-synchronizing: like in any LANs, the wireless stations work in a connectionless environment where packets may get lost. The WEP algorithm resynchronizes at each message.
Dr. Xinbing Wang

7. Authentication Frame (2)
24-bit
40-bit
IV Key
Encrypted data
32-bit
Payload ICV
RC4
Payload ICV
WEP Frame
Header IV key number
Payload ICV
ICV: Integrity Check Value
Dr. Xinbing Wang

8. Access Control List
Access control list can provide a minimal level of security.
It is based on the Ethernet MAC addresses of the clients.
This list consists of the MAC addresses of all of its clients and only the clients whose MAC addresses are listed can access.
Dr. Xinbing Wang

9. Using the WEP
There are two methods specified in IEEE for using the WEP.
A station or an AP can decrypt packets enciphered with any of four keys (provided through a window).
To use key-mapping table where each unique MAC address can have separate keys.
The use of a separate key for each client mitigates the cryptographic attacks found by others.
The disadvantage is that all of these keys should be configured manually on each device or AP.
Dr. Xinbing Wang

10. Weakness in WEP WEP is weak against the following attacks (RC4 and IV)
Active attacks that inject new traffic from unauthorized mobile stations
The attack knows the exact plain text for one encrypted message.
Active attacks to decrypt traffic based on fooling the APs.
The attacker fools the AP: it makes a guess about the header of the packet; not the packet’s content. All he/she needs to do is to guess the destination address.
Dr. Xinbing Wang

11. Weakness in WEP (2)
Passive attacks to decrypt traffic based on statistical analysis.
An eavesdropper can intercept all wireless traffic until an IV collision occurs.
By using XOR of two plain text messages, the attacker can obtain the same IV value.
Dictionary-building attacks which allow real-time automated decryption of traffic after some analysis.
Once the plain text for the packet is known, the attacker can compare the RC4 key stream generated by the IV. The latter can be used to decrypt all other packets that utilize the same IV.
Dr. Xinbing Wang

12. Security in Ad hoc Networks
Liabilities in Ad Hoc Networks
Limited physical security
Lack of infrastructure and authorization facilities
Security protocols for wired networks cannot work for ad hoc networks
Volatile network topology makes it hard to detect malicious nodes
Intrinsic mutual trust vulnerable to attacks
Dr. Xinbing Wang

13. Exploits Allowed by Existing Protocols
Attacks using modification
Attacks using impersonation
Attacks using fabrication
Other forms of attacks
Dr. Xinbing Wang

14. Attacks using Modification
Cause redirection of network traffic and Denial of Service (DoS) attacks by
Altering the protocol fields in routing messages
Injecting routing messages into the network with falsified values in these fields.
Dr. Xinbing Wang

15. Attacks: Modification (1)B X M
Source
Destination
RREQB
Sn = 99
Sn = 99
Sn = 10
RREQA
RREQB
Redirection with modified route sequence numbers
Dr. Xinbing Wang

16. Attacks: Modification (2)
RREQB
Hop count = 0
Hop count = 8
Hop count = 0 A B X
Source
Source
Destination
RREQA
Redirection with modified hop counts
Dr. Xinbing Wang

17. Attacks: Modification (2)
RERR A M D C X
Source
Destination
<M,C,D,X>
<M,C,X>
RERR
Denial of service with modified source routes
Dr. Xinbing Wang

18. Attacks: Impersonation
Current ad hoc routing protocols do not authenticate source IP addresses
By masquerading as another node (spoofing), a malicious node can launch many attacks in a network
Spoofing is readily combined with modification attacks to create loops in routes
Dr. Xinbing Wang

19. Attacks: Fabrication -- Example
I am C!!
RERR: D is broken M B D
RERR: D is broken
Routing entries for X
Source A C X
Destination
Routing entries for X
Falsifying route error messages in AODV and DSR
Dr. Xinbing Wang

20. Attacks: Fabrication in DSR
Route Cache Poisoning in DSR
Exploit promiscuous listening to poison route caches
By broadcasting spoofed packets with source routes to X via itself
Neighbouring nodes that overhear the packet transmission may add the route to their route cache
Dr. Xinbing Wang

21. SAODV An extension of the AODV routing protocol
Providing security features like integrity, authentication and non­repudiation
Each node has a signature key pair from a suitable asymmetric cryptosystem
Each node is capable of securely verifying the association between the address of a given ad hoc node and the public key of that node
Dr. Xinbing Wang

22. SAODV: Digital Signature
Used to protect the integrity of the non­mutable data in RREQ and RREP messages
Sign everything but the Hop Count of the AODV message and the Hash from the SAODV extension
When a node receives a routing message, it will verify the signature before any other action
Dr. Xinbing Wang

23. SAODV: Hash Chains
Used to authenticate the hop count of RREQ and RREP messages
Ensures that the hop count has not been decremented by an attacker
Is formed by applying a one-way hash function repeatedly to a seed
Dr. Xinbing Wang

24. SAODV: Route Errors
Route errors have a big amount of mutable information
Every node uses digital signatures to sign the whole message
Any neighbor that receives it verifies the signature
Dr. Xinbing Wang

25. Security Analysis: SAODV (1)
The digital signature serves as proof of validity of the information contained in the routing message
Thus, formation of loops by malicious nodes through spoofing is prevented
Able to detect that the malicious nodes are sending out false messages.
Dr. Xinbing Wang

26. Security Analysis: SAODV (2)
A node attempting to transmit false RERR messages will not succeed
Digital signature will reveal that it is not on the route and hence is not supposed to send a RERR.
Sequence number in the RREQs and RREPs also protected by the digital signature.
Any modifications to the sequence number will invalidate the message
Dr. Xinbing Wang

27. Security Analysis: SAODV (3)
The hop authenticator implemented using hash chains reduces the ability of a malicious node for mounting an attack by modifying the hop count
A malicious node could still perform a limited attack by not incrementing the hop count before forwarding the message.
Can solve by implementing a forward-secure signature scheme.
Results in a loss in efficiency
Dr. Xinbing Wang

28. Summary
SAODV is able to handle all attacks using modification, fabrication or impersonation
However, it is unable to cope with wormhole attacks.
Dr. Xinbing Wang