Network Access Control for Mobile Ad Hoc Network

1. Network Access Control for Mobile Ad Hoc Network Pan Wang North Carolina State University

2. Outline • Background • Problem statement • Related work • Proposed scheme • Key Synchronization • Packet Retransmission • Analysis, simulation and field test • Summary

3. Background • Mobile Ad Hoc Network (MANET) • A MANET consists of mobile platforms (e.g., a router with multiple hosts and wireless communications devices), which are free to move about arbitrarily. --IETF RFC2501 • Characteristics of MANET • No pre-determined infrastructure • Ease of deployment • Dynamic topologies (e.g., mobility, network partition ) • Constrained resources (e.g., bandwidth, energy )

4. Background (Cont) • Network access control • Not media access control • Who has the right to access the network • Physical* • Technical * • Administrative * • Firewalls • Conventional network • Using network topology and service information *H. F. Tipton, Handbook of information security management

5. Problem Statement • An attacker may inject “bogus” packets to consume the network resources, or insert itself into critical routes • No mature access control scheme for MANET • more complicated due to open media and dynamic topology

6. Related Work • DHCP Access Control Gateway • Kerberos • Distributed firewall • Pebblenets • Distributed access control scheme for consumer operated MANET • LHAP

7. C A B D S S S M, KF(i) M, KF(I+1) Cert &Commit Related Work --Cont • LHAP: a lightweight hop-by-hop authentication protocol for ad-hoc networks • Based on one-way key chain and TESLA • Hop-by-hop authentication • Each transmitted packet associated with a traffic key, • Receiver (or intermediate node) verifies to decide whether forward (accept) the packet

8. K1-4 K1-2 K3-4 k2 k1 k3 k4 M1 M2 M3 M4 Proposed Scheme – cryptographic tools • Group key agreement • Group key distribution • Controller chooses key • Stateful vs. Stateless • Stateless key distribution • Each user is assigned an unique set of personal keys • New key is encrypted with the personal keys only known to the legitimate users • Nice stateless property

9. Proposed Scheme – underlying models • Network model • All nodes come from one domain • A node’s access to the network is controlled by a domain manager (i.e., key manager) • Each node has a unique ID and a set of personal secret keys • Attack model • Attackers inject packets to deplete the resources of node relaying the packets

10. pan wang: Proposed Scheme - outline • Basic idea • Cryptography-oriented (using group key) • Authenticate all the packets with a network-wide access control (group session) key. • Any “bogus” packet that has incorrect authentication information will be filtered out immediately. • As a result, illegitimate nodes will be excluded from communication (routes).

11. Research challenges • Two critical challenges • Synchronization of network access control key • Interaction between data transmission and key distribution If these two challenges can be solved, the proposed group key based network access control scheme will be done.

12. Key Synchronization • Problem statement • A key update message may fail to propagate across MANET. Thus, two legitimate user may simultaneously hold different session key (lack of key synchronization)

13. Key Synchronization (Cont-1) • An example of lack of key synchronization

14. Key Synchronization (Cont-2) • Solution • Exploit the stateless feature of the proposed stateless group key distribution scheme • Each user buffers the key update message most recently received • Transmit the buffered message to the other users that are using old session keys

15. Key Synchronization (Cont-3) • Scheme details • Proactive part • Broadcast the buffered key update message every t time unites • Reactive part • Send a key synchronization request, if a received packet has higher session ID • Send the buffered key update message, if a received packet has a lower session ID

16. Broadcast S S S S S E E E E E F F F F F B B B B B S C C C C C M M M M M L L L L L E J J J J J F A A A A A G G G G G B C M L H H H H H D D D D D J K K K K K A G N I I I I I N N N N H D K I N Represents a node that has the most recent key Key Synchronization (Cont-4) • Illustration of the proposed key synchronization scheme

17. Key Synchronization (Cont-5) • Security analysis (possible attacks) • Resource consumption via forged key update message • Solution: lightweight authentication methods (One-way key chain & Merkle hash tree) • Resource consumption via forged data packet • Constrained to one-hop • Logically partition MANET via refusing forwarding key update message • Multiple paths, watchdog

18. Key Synchronization (Cont-6) • One-way key chain

19. Key Synchronization (Cont-7) • Merkle hash tree

20. Key Synchronization (Cont-8) • Performance analysis • Rely on the adopted stateless group key distribution scheme • Storage • One message • Computation • Communication • Depends on t and number of users using an old key

21. Packet Retransmission • Problem statement • The interaction between data transmission and key distribution. That is, in the case of a lack of key synchronization, a user may receives some (unverified) packets authenticated with a different session key.

22. Packet Retransmission (Cont-1) • Possible options • Simply drop • Buffer and then verify • Synchronize the keys before sending every data packet • All of them have serious drawbacks

23. Packet Retransmission (Cont-2) • Proposed solution • Drop, synchronize keys, and then retransmit. • ACK mechanism • Unicast & broadcast

24. Algorithm of the proposed scheme

25. Packet Retransmission (Cont-3) • Security analysis (possible attacks) • Resource consumption attack • Forged ACK message • Packet modification

26. Packet Retransmission (Cont-4) • Performance analysis • Computation • Authentication & verification • Pentium 4 2.1 GHz processor * MD5 216.674 MB/s SHA-1 67.977 MB/s • Communication • Retransmission rate

27. Simulation Evaluation • The simulation modal • 40/80 nodes randomly placed in a fixed area (a square of size 1km x 1km) • Random walk with a maximum speed 20m/s • Communication range 200m • 2000 simulations, using different random number seeds

28. Simulation Evaluation (Cont-2) Average percentage of nodes which got the latest session key

29. Simulation Evaluation (Cont-3) Average percentage of nodes which got the latest session key

30. Simulation Evaluation (Cont-4)

31. Implementation • Based on Netfilter • Two daemons • Adopt the stateless scheme proposed by Liu & Ning

32. Field Test • Test bed • One Dell P4 laptop with Linux 9.0 (kernel 2.4.20) • Two Compaq iPAQ 3970 PDAs with Familiar v0.7.2 (kernel 2.4.19-rmk-pxal-hh30) • Lucent Orinoco wireless cards • Tests • Key distribution • User revocation • Packet authentication and verification • Key synchronization

33. Summary • Network access control is an important issue for MANET • Cryptography-oriented solution exploiting the stateless feature of stateless group key distribution scheme • Simulation as well as functioning prototype indicates it practical and effective

34. Question