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Securing Ad Hoc Network Routing Protocols

Securing Ad Hoc Network Routing Protocols. Yih-Chun Hu. April 24, 2008. Attacks Against Routing. Attacker causes packets normally routed through itself to instead use a worse route Example: Fail to advertise a route Attacker receives a packet for forwarding but instead discards it

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Securing Ad Hoc Network Routing Protocols

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  1. Securing Ad Hoc Network Routing Protocols Yih-Chun Hu April 24, 2008

  2. Attacks Against Routing • Attacker causes packets normally routed through itself to instead use a worse route • Example: Fail to advertise a route • Attacker receives a packet for forwarding but instead discards it • Example: Save own bandwidth or CPU time • Attacker causes packets normally routed elsewhere to instead go through itself • Example: Claim good routes to far-away nodes

  3. Normal Distance Vector Routing • In normal Distance Vector routing, each node maintains a routing table: Example table at A: A B C D

  4. Normal Distance Vector Routing • Computed using Distributed Bellman-Ford: • Each node periodically broadcasts routing table • For each routing table entry received, compare best known route with newinformation To D: 3 hops via B E 2 X X A B C D E D is 1 hop away

  5. Distance Fraud Attack • A very strong attack against distance vector • Attacker claims very short routes to entire network • Disconnects large portions of the network C J G A K S E D B H F

  6. SEAD Threat Model • Attacker cannot replay messages in entirety: • Equivalent to “wormhole” attack • Attackers compromise some network nodes: • Best security if only one node is compromised • Or, if compromised nodes don’t collaborate • Goal: Prevent attackers from affecting routes to non-compromised nodes

  7. My Solution: SEAD To solve distance fraud, authenticate distances For each destination D: • To claim distance m, need authenticator aD,m • Attacker can’t reduce distance m • Next hop can derive its authenticator aD,m+1 • Authenticators should be efficient to verify aD,2 aD,1 aD,0 A B C D

  8. C1 = H(C0) Building Blocks: Hash Chains • Uses a one-way hash function H:{0,1}*→{0,1}ρ • Pick a random C0 • Compute each chain value Ci = Hi(C0) C0

  9. C2 = H(C1) Building Blocks: Hash Chains • Uses a one-way hash function H:{0,1}*→{0,1}ρ • Pick a random C0 • Compute each chain value Ci = Hi(C0) C0 C1

  10. C1 C3 = H(C2) =H(C0) Building Blocks: Hash Chains • Uses a one-way hash function H:{0,1}*→{0,1}ρ • Pick a random C0 • Compute each chain value Ci = Hi(C0) C0 C2 =H(C1) • Given any authentic chain value Ci: • Can compute later values Cj for j > i • Can efficiently verify all values Cj • Hard to generate earlier values Cj for j < i

  11. Hash Chains for Distance Authentication

  12. C0 C1 C2 C3 Distance Authentication Details • Distance vector protocols define a maximum distance k • Each node D: • Generates a hash chain k+1 values long • Distributes ck to allow verification • Then authenticator aD,i = ci • Conceptually change hash chains frequently Distance 0 Distance 1 Distance 2

  13. SEAD Stops (Most) Distance Fraud • Everyone knows C3 • Source D announces C0 for distance 0 • Neighbor C announces C1 fordistance 1 • Attacker B can’t announce lower distance! D C B Distance 0 Distance 1 Distance 2 C0 C1 C2 C3

  14. SequenceNumbers First proposed in DSDV for loop-freedom: • Each node maintains a sequence number • Each node increments its sequence number each time it sends an update about itself • An advertised route is “better” if either: • Has a higher (more recent) sequence number • Sequence numbers equal, and distance is shorter • SEAD also gets loop-freedom, plus a guarantee of fresh distance information

  15. Distance 0 Distance 1 Distance 2 Sequence 3 Sequence 1 Sequence 0 Securing Sequence Numbers • Each node generates a hash chain and distributes the last element (C12) for verification • Each sequence number has 3 hash chain values: • Within a sequence number: • C{0,3,6,9} represent distance 0 • C{1,4,7,10} represent distance 1 • C{2,5,8,11} represent distance 2 • In our example, maximum distance is 3 Sequence 2 C0 C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12

  16. Distance 0 Distance 1 Distance 2 Sequence 3 Sequence 1 Sequence 0 SEAD Stops (Most) Distance Fraud • Source D announces C3 for distance 0 sequence 2 • Neighbor C announces C4 fordistance 1 sequence 2 • Attacker B can’t announce lower distance! • Due to inherent flooding, useless to announce lower distance with lower sequence number D C B Sequence 2 C0 C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12

  17. SEAD Neighbor Authentication Use any efficient, secure neighbor authentication, or can also use all-pairs O(n2) keys for authentication: • Each node maintains a neighbor table • Node A adds node B when A hears a distance 0 advertisement for B with fresh sequence number • Triggers A’s advertisement, for which B hears a distance 0 advertisement for A • A and B now include symmetric authenticators(e.g., HMAC) for each other in each update • Stop after missing 3 consecutive sequence numbers

  18. SEAD Loop-Freedom SEAD is loop-free unless attacker is in the loop Correctness argument: • Suppose there is a loop • The (sequence number, distance) always gets strictly better at the next hop unless: • The next hop is an attacker, or • The attacker forged the next-hop in the routing update • But each next-hop is authenticated • Therefore, the loop either terminates or there is an attacker in the loop

  19. Simulation Methodology • ns-2 simulator with Monarch wireless extensions • Random waypoint mobility model • 20 sources, 4 packets per second per source • 10 different simulation runs at each pause time • Under attack by a single attacker: • DSDV: attacker claims distance 0 everywhere • SEAD: attacker performs same distance fraud 700m×700m 50 nodes

  20. Packet Delivery Ratio: SEAD vs DSDV

  21. Other Approaches to Secure Routing • Hop-by-hop authentication (verifies identity of neighbor, but neighbor give any distance)[Kumar], [Baker and Atkinson], [Malkin] • Limit routes based on full knowledge of original wired network topology [Smith et al.] • SAODV secures hop count with a hash chain, but uses a new chain for each sequence number, and uses expensive digital signatures

  22. Remaining Problems in SEAD • “Same Distance” Fraud: • Attacker replays distance and authenticator • Solution: Bind forwarding node to authenticator • Denial-of-Service attack: • Claim a very high sequence number • Solution: One chain per sequence number • Larger metric spaces: • Verifying even one sequence number may be expensive (e.g., latency or policy metrics) • Solution: Cheaper hash chain traversal

  23. Bind Authenticator to Forwarding Node For each destination D and distance m: • Split the single authenticator aD,m into many node-specific authenticators • For each possible forwarding node F, there exists an associated authenticatoraD,m,F Properties of node-specific authenticators: • Attacker can’t replay another node’s authenticator • Next hop can derive its authenticator for distance m+1

  24. Building Blocks: Hash Trees • Merkle Tree allows authentication of a collection of values given a single authentic value: Distribute root to all verifiers P = H(L || R) b’i = H(bi) bi

  25. b0 b0 ’ ci ci+1 Hash Chain: b01 b1 ’ b1 Hash Tree Chain: ci+1 ’ b2 b2 b23 ci ’ b3 b3 Hash Tree Chains • I developed the hash tree chain: b’j = H(bi) bj = H(ci|| j)

  26. ’ ’ b0 Distance 0 Distance 1 b0 ’ b0 b0 b0 b0 b1 ’ ’ ’ Distance 0 Distance 1 Distance 2 b1 b01 b01 b1 b1 b1 b1 ’ ’ c0 c1 c2 b23 b23 b2 b2 b2 b2 ’ ’ b23 b23 b3 b3 b3 b3 Using Hash Tree Chains • One step in the chain corresponds to a distance • Each bi corresponds to a forwarding node • Attacker must produce its bi to replay distance C0 C1 C2 C3 bj = H(c1|| j) bj = H(c0|| j)

  27. Remaining Problems in SEAD • “Same Distance” Fraud: • Attacker replays distance and authenticator • Solution: Bind forwarding node to authenticator • Denial-of-Service attack: • Claim a very high sequence number • Solution: One chain per sequence number • Larger metric spaces: • Verifying even one sequence number may be expensive (e.g., latency or policy metrics) • Solution: Cheaper hash chain traversal

  28. Skipchains • We want to efficiently skip over many elements of a hash chain • Suppose you had an efficient, chained one-time signature scheme • Each step in the chain allows you to sign one value • Intuition: • Each step represents a length n segment of hash chain • Sign the anchor of the segment using that step

  29. Skipchains • Each vi corresponds to a length n segment of the hash chain: hi,n-1, hi,n-2, …, hi,0 where hi,j = Hn-j(vi) • Represent hash chain step k by hëk/nû,k mod n • Sign hëk/nû, 0 with vëk/nû to allow verification

  30. Received value Known authentic value Skipchain Properties • Behaves like a long one-way chain • Divides hash chain into blocks of n elements • Use signature chain to skip n steps at low cost

  31. From Generate Skipchain Properties • Behaves like a long one-way chain • Divides hash chain into blocks of n elements • Use signature chain to skip n steps at low cost

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