Authentication & Intrusion Prevention for Multi-Link Wireless Networks

1. Authentication & Intrusion Prevention for Multi-Link Wireless Networks Raphael Frank 20 October 2007

2. Overview 1 2 3 4 5 6  Introduction  Authentication in WMN using exisitng protocols  Emerging Security Issues  Authentication protocol based on WMN properties  Security Analysis  Conclusion

3. Introduction • What is Wireless Mesh Network (WMN)? • Mesh Nodes: Devices with at least two radio interfaces • Mesh nodes form together a wireless network (Ad-Hoc) • Second interface (AP) is used by mobile clients to connect to the network • Hot Spots (HS): Mesh Nodes equipped with a wired internet connection • Transient Access Points (TAP): Mesh Nodes without wired internet connection  Provide Internet Access to Mobile Clients by using the WMN as a backhaul

4. Authentication in WMN using existing protocols (1) • Authentication protocols for the State of the Art of Wireless Networks • IEEE 802.11: • First WiFi standard released in 1997 • Provides Data encryption and authentication • IEEE 802.11i: • Most recent security standard released in 2004 • Provides a robust data encryption and includes an external authentication framework

5. Authentication in WMN using existing protocols (2) • IEEE 802.11 • Encryption Protocol Wired Equivalent Privacy (WEP), based on shared-key (Key length 64 or 128 bit) • Authentication based on the knowledge of the shared-key • Security Goals: • Prevent Eavesdropping  PRIVACY • Prevent Message Modification  INTEGRITY • Network Access Control  AUTHENTICATION • Weaknesses – None of the security goals are met: • Key stream reuse  PRICACY • CRC attacks  INTEGRITY • Authentication Spoofing  AUTHENTICATION

6. Authentication in WMN using existing protocols (3) • IEEE 802.11i • Encryption Protocol WiFi Protected Access 1 & 2 (WPA1 & WPA2) • Provides robust security properties • Authentication performed using the Extensible Authentication Protocol (EAP) • Needs a centralize authentication server • Different authentication possibilities (EAP methods)

7. Authentication in WMN using existing protocols (4) • Extensible Authentication Protocol (EAP) • Used in wireless and fixed networks • Port Based Network Access • Authentication framework • Currently about 40 different EAP methods • Commonly used methods : EAP-TLS, EAP-TTLS

8. Emerging Security issues(1) Problems with the standard protocols • Originally developed for the State of the Art of Wireless Networks • Security only for the first wireless link  no End-To-End features • Privacy: No data encryption after the first hop • Authentication: No Layer 2 authentication after the first hop • Single point of failure: Centralized Authentication Server • Mesh nodes cannot be considered as trustworthy • No topology authentication

9. Emerging Security issues(2) • What are the problems related to the architecture of a WMN? • Mesh nodes cannot be considered as trustworthy • They are often deployed in a hostile environment • An attacker can spoof and/or take over a mesh node • No topology authentication • An attacker can easily inject a malicious node into the WMN • Gain access to the network • Perform Denial of Service (DoS) • Perform Man in the Middle Attacks (MitM)

10. Definition of a new authentication protocol (1) • Why a new protocol? • No standardized security protocols for WMN • The existing protocols do not meet the requirements • What should the protocol provide? • “Real-time/Continuous” Authentication  Acceptable performance • Authentication of every participating node of WMN  Topology authentication • Authentication of the network traffic • Trustworthy mesh nodes  Mesh Node Access Control • Attack Detection/Reaction mechanism

11. Definition of a new authentication protocol (2) • How does it work? • Based on digital signatures to verify integrity and authenticity • Hybrid authentication protocol using symmetric and asymmetric cryptography • Offers the best properties in terms of security and performance • The administrator plays the role of the CA • Provides the needed keys to the Nodes

12. Definition of a new authentication protocol (3) • What are the required keys? • Every node is in possession • Personal Public Key • Personal Private Key • Personal Secret Key  symmetric • Public Key of the Administrator • Nodelist  Containing the allowed communication neighbors • After initialization  different public/secret keys of neighbor nodes • The procedure can be subdivided in two operations: • I)  Initialization of a new node • II)  Information transmission }  asymmetric

13. Definition of a new authentication protocol (4) • Initialization of a new node (asymmetric) • Node A wants register to the WMN broadcast A : Nodelist Cert(A) Signature WMN Initialization message • The receiving node B • Checks if it is included in the node list (NL) • Checks the signature  Using the Public Key of the Admin • B encrypts its secret key and sends it to A • After a successful decryption, A encrypts its secret key and sends it to B

14. Definition of a new authentication protocol (5) Node B Node A • Initialization of a new node (asymmetric) • Node A wants register to the WMN (1) Broadcast: NL, Cert(A), SIG{[NL,Cert(A)], PrivK(Admin)} (2) ENC{[Cert(B),K(B),T1], PubK(A)} (3) ENC{[K(A),T2], PubK(A)}

15. Definition of a new authentication protocol (6) • Information transmission (symmetric) • Every node needs to have the secret key of its neighbor nodes  Initialization • Symmetric Signature  Message Authentication Code (MAC) = Fingerprint encrypted using a secret key  Faster • Node A wants to send a message to node C via node B Send via node B A : Data Timestamp Signature C Message to be transferred

16. Definition of a new authentication protocol (7) Node A Node B Node C • Information transmission (symmetric) • Signature verification and newly generated at every hop of the transmission path • A different Timestamp guarantees a different signature (1) MSG, T1, SIG{(MSG,T1), K(A)} (2) MSG, T2, SIG{(MSG,T2), K(B)} (4) MSG, T4, SIG{(MSG,T4), K(B)} (3) MSG, T3, SIG{(MSG,T3), K(C)}

17. Definition of a new authentication protocol (8) How to create trustworthy nodes? • We need to guarantee that a attacker cannot retrieve the sensitive data (Keys, Nodelist, …) form a mesh node Mesh Node Access Control • Before an attacker gains access to a node, the keys are erased a replaced by dummy values • Consequence Neighbor nodes will fail to verify the messages form the attacked node and drop them • Passive attack detection • The node is automatically excluded form the WMN

18. Definition of a new authentication protocol (9)

19. Security Analysis (1) Security & Performance Requirements • Acceptable performance : YES Using symmetric signatures • Topology authentication : YES Every node participating in a communication is authenticated • Authentication of the traffic : YES The source of every message is known • Trustworthy mesh nodes : YES Mesh Node Access Control • Attack Detection and Reaction : YES Corrupt Nodes are detected and excluded form the WMN

20. Security Analysis (2) Other Security features • No replay attacks using timestamps • No single point of failure No centralized entity • Node Spoofing/Injection not possible  Topology authentication The attacker does not know the needed keys Man in the Middle Attack can be used to perform DoS • If an attacker modifies a transient message, it will be discarded

21. Conclusion What’s next? • Extend the authentication protocol • Implementation of a prototype • Client/User authentication • Add an administration procedure • Remotely reintroduce attacked node into the WMN • Attack reporting • Privacy and Performance on WMN need to be considered as well • Release of a security standard for WMN • IEEE 802.11s?

22. The end … Thank you for your attention Questions? Raphael.Frank@uni.lu Wiki.uni.lu/Secan-Lab