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Laboratory for Computer Communications and Application (LCA)

Mobility Helps Security in Ad Hoc Networks. Sr dj an Č apkun joint work with Jean-Pierre Hubaux and Levente Buttyàn + { srdan.capkun , jean-pierre.hubaux}@epfl.ch, buttyan@hit.bme.hu. Laboratory for Computer Communications and Application (LCA)

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Laboratory for Computer Communications and Application (LCA)

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  1. Mobility Helps Security in Ad Hoc Networks Srdjan Čapkun joint work with Jean-Pierre Hubaux and Levente Buttyàn+ {srdan.capkun, jean-pierre.hubaux}@epfl.ch, buttyan@hit.bme.hu Laboratory for Computer Communications and Application (LCA) Swiss Federal Institute of Technology (EPFL) + Now with Laboratory of Cryptography and Systems Security (CrySyS) Department of Telecommunications Budapest University of Technology and Economics

  2. Does mobility increase or reduce security ? • Mobility is usually perceived as a major security challenge • Wireless communications • Unpredictable location of the user/node • Sporadic availability of the user/node • Higher vulnerability of the device • Reduced computing capability of the devices • However, very often, people gather and move to increase security • Face to face meetings • Transport of assets and documents • Authentication by physical presence • - In spite of the popularity of PDAs and mobile phones, this mobility has not been exploited to provide digital security • - So far, client-server security has been considered as a priority (e-business) • - Peer-to-peer security is still in its infancy

  3. Mobile ad hoc networks with a central authority • off-line or on-line authority • nodes or authorities generate keys • authorities certify keys and node ids • authorities control network security settings and membership • Fully self-organized mobile ad hoc networks • no central authority (not even in the initialization phase !) • each user/node generates its own keys and negotiates keys with other users • membership and security controlled by users themselves Two scenarios CA trust trust trust trust trust trust trust trust trust Authority-based Fully self organized

  4. Secure routing requirements and assumptions • A network controlled by the central authority • All security associations established between all nodes prior to protocol execution • The most stringent assumption: Routes are established between nodes with which a source and the destination have security associations m i j • Secure routing proposals • - Securing Ad Hoc Routing Protocols, Zappata, Asokan, WiSe, 2002 • Ariande, Hu, Perrig, Johnson, MobiCom 2002 • Secure Routing for Ad Hoc Networks, Papadimitratos, Haas CNDS, 2002 • A Secure Routing Protocol for Ad Hoc Networks, Sanzgiri et al. ICNP, 2002 • SEAD, Hu, Perrig, Johnson, WMCSA 2002

  5. Solutions proposed so far (not exhaustive) • Providing. Robust and Ubiquitous Security Support for MANETs(threshold cryptography, cooperation)UCLA:Kong et al., ICNP 2001 • Key Agreement in Ad Hoc Networks(shared password)Asokan and Ginzboorg, Computer Communications 2000 • Securing Ad Hoc Networks (1999)   (threshold cryptography, servers)Cornell: Zhou and Haas, IEEE Network 1999 • Ariadne(Key distribution with on-line servers) Hu et al., Mobicom 2002 • Self-organized Public-Key Management for Mobile Ad Hoc Networks(certificate chains) EPFL: Capkun et al., TMC 2003 • SUCV (Montenegro and Castelluccia) NDSS 2002 • CAM (O'Shea and Roe) ACM Computer Communications Review 2001 Key management in Ad Hoc networks

  6. Routing can not work until security associations are set up. • Security associations can not be set up via • multi-hop routes because routing does not work • Existing solutions: • Preloading all pairs of keys into nodes (it makes it difficult to introduce new keys and to perform rekeying) • On-line authentication servers (problematic availability and in some cases routing-security inter-dependence, rekeying) • CAM, SUCV Routing – security interdependence i j

  7. Mobility helps security of routing - Each node holds a certificate that bind its id with its public key, signed by the CA { A,PuKA} sPuKCA A B { B, PuKB} sPuKCA • Wireless channel • Typically long distance • No integrity • No confidentiality Certificate that binds B’s Public key with his id, issued and signed by the central authority

  8. Establishment of security associations The establishment of security associations within the power range breaks the routing-security interdependence cycle

  9. Discussion: advantages of the mobility approach (1) • Mobile ad hoc networks with authority based security systems • breaks the routing-security dependence circle • automatic establishment of security associations • no user involvement • associations can be established in power range • only off-line authorities are needed • straightforward rekeying

  10. Fully self-organized scenario Visual recognition, conscious establishment of a two-way security association   (Alice, PuKAlice, XYZ) Bob Alice Infrared link (Bob, PuKBob , UVW) • Secure side channel • Typically short distance (a few meters) • Line of sight required • - Ensures integrity • - Confidentiality not required

  11. Two binding techniques Binding of the face or person name with his/her public key  : by the Secure Side Channel, the Friend mechanism and the appropriate protocols Binding of the public key with the NodeId : by CAM or SUCV Assumption: static allocation of the NodeId: NodeId = h(PuK) XYZ • G. O’Shea and and M. Roe: Child-proof authentication for IPv6 (CAM) ACM Computer Communications Review, April 2001 • G. Montenegro and C. Castelluccia: Statistically unique and cryptographically verifiable (SUCV) identifiers and addresses. NDSS 2002

  12. Colin Friends mechanism Alice Bob (Colin’s friend) IR • Colin and Bob are friends: • They have established a Security Association at initialisation • They faithfully share with each other the Security Associations • they have set up with other users

  13. i i i i i i f f f f j j j j j j Mechanisms to establish Security Associations a) Encounter and activation of the SSC b) Mutual friend c) Friend + encounter Exchange of triplets over the secure side channel Two-way SA resulting from a physical encounter Friendship : nodes know each others’ triplets i knows the triplet of j ;the triplet has been obtained from a friend of i j i Note: there is no transitivity of trust (beyond your friends)

  14. Fully self-organized mobile ad hoc networks • There are no central authorities • Each user/node generates its own public/private key pairs • (No) trust transitivity • Intuitive for users • Can be easily implemented (vCard) • Useful for setting up security associations for secure routing in smaller networks or peer-to-peer applications • Requires some time until network is fully secure • User/application oriented Discussion: advantages of the mobility approach (2)

  15. Depends on several factors: • Area size • Number of communication partners: s • Number of nodes: n • Number of friends • Mobility model and its parameters (speed, pause times, …) Pace of establishment of the security associations Established security associations : Desired security associations : Convergence :

  16. Random walk • discrete time • simple, symmetric random walk • area: Bounded and toroid grids (33x33, 100x100, 333x333) • number of nodes: 100 • Random waypoint • most commonly used in mobile ad hoc networks • continuous time • area size: 1000m x1000m • max speed: 5m/s, 20m/s • pause time: 5s, 100s, 200s • security power range: 5m (SSC), 50m 100m (radio) • Common simulation settings • simulations are run 20 times • confidence interval: 95% Mobility models p=1/5 p=1/5 p=1/5 p=1/5 p=1/5

  17. f/8 (Restricted) random waypoint f/8 f/8 f/8 f/8 f/8 f/8 f/8 1-f Any point on the plane If f=0  Regular random waypoint mobility model • Restricts the movement of nodes to a set of points with a predefined probability • area size: 1000m x1000 m • max speed: 5m/s, 20m/s • pause time: 5s, 100s, 200s • restriction probability: 0.1, 0.5, 1 • number of restriction points: 20

  18. Size matters tM=O(NlogN)

  19. Friends help (f+1)

  20. Security range matters

  21. Meeting points help

  22. Pause time

  23. Conclusion and future work • Conclusion • Mobility can help security in mobile ad hoc networks, from the networking layer up to the applications • Mobility “breaks” the security-routing interdependence cycle • The pace of establishment of the security associations is strongly influenced by the area size, the number of friends, and the speed of the nodes • The proposed solution also supports re-keying • The proposed solution can easily be implemented with both symmetric and asymmetric crypto • Current/future work • Closed-form expression for the pace of establishment of security associations with random walk mobility • Application of our scheme to secure routing protocols • Key revocation • Improved scalability • Better mobility models http://www.terminodes.org http://lcawww.epfl.ch/hubaux

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