1 Authenticated Adversarial Routing Yair Amir, Paul Bunn, Rafail Ostrovsky 6 th IACR Theory of Cryptography Conference March 15, 2009

2 Authenticated Adversarial Routing Problem Statement Solution Ideas Conclusion

3 Authenticated Adversarial Routing Problem Statement Adversarial Networks Statement of Result Previous Work Solution Ideas Conclusion

4 The Network S R {m 1, m 2, m 3, …} Most basic task: two “uncorrupted” nodes need to communicate

5 The Adversary For clarity, break-up adversary into 2 (collaborating) adversaries: Node-controlling Malicious Adversary Edge-scheduling Adversary

6 Edge-Scheduling Adversary S R End-to-End, Synchronous Only 1 packet can cross an edge per round Controls Edges (Up/Down) {m 1, m 2, m 3, …}

7 Edge-Scheduling Adversary End-to-End, Synchronous Only 1 packet can cross an edge per round Controls Edges (Up/Down) Conforming (Always a Path!) S R {m 1, m 2, m 3, …}

8 Node-Controlling Adversary Controls Nodes “Malicious” ⇒ Nodes act arbitrarily “Dynamic” ⇒ Adaptive corruption Conforming (Always a Path!) Polynomially Bounded S R {m 1, m 2, m 3, …}

9 Node-Controlling Adversary S R Controls Nodes “Malicious” ⇒ Nodes act arbitrarily “Dynamic” ⇒ Adaptive corruption Conforming (Always a Path!) # Malicious nodes allowed >> n/2 {m 1, m 2, m 3, …}

10 The Problem: Goals of Routing S R Correctness: “Packets are output by R without duplication or omission” Throughput: Number of messages received as a function of time Memory per Node {m 1, m 2, m 3, …}

11 Our Main Result Theorem (informal): If OWF’s exist THEN routing that is resilient against any poly-time conforming (node- controlling + edge-scheduling) adversary can be achieved with: Throughput: Linear O(t ) rounds  t packets delivered Memory per Node: O(n 4 log n) Proof is constructive, local control

12 History of Routing in Malicious Networks Fault Detection, Fault Localization [Awerbuch Holmer Nita-Rotaru Rubens 02] [Barak Goldberg Xiao 08] A priori select a single-path Fault Detection/Localization performed on this path After identifying fault, new path selected Open in [BGX 08]: how do we handle adaptive routing?

13 Authenticated Adversarial Routing Problem Statement Solution Ideas Naïve Solutions Dynamic Topology Networks - [AG 88] [AMS 89] [AGR 92] [AAGMRS 97] [KOR 98] Highlights of our Solution Conclusion

14 Naïve Solutions Flooding: Sender floods one message + index + signature Nodes broadcast message with highest index Receiver floods confirmation of receipt + signature Nodes broadcast confirmation with highest index S R {m 1, m 2, m 3, …}

15 Naïve Solutions Flooding: Slow: Delivery is sublinear Expensive (Pay for Bandwidth Used) S R {m 1, m 2, m 3, …}

16 Slide Protocol “Slide” Protocol: [Afek Gafni 88], [Awerbuch Mansour Shavit 89], [Afek Gafni Rosen 92], [Afek Awerbuch Gafni Mansour Rosen Shavit 97] How it works: Edges viewed as directional Internal nodes maintain buffers on every edge (size n) Protocol proceeds in 3 steps: { … … … … … … n

17 … … … … … … ……………… RS …… “Slide” Protocol: [Afek Gafni 88], [Awerbuch Mansour Shavit 89], [Afek Gafni Rosen 92], [Afek Awerbuch Gafni Mansour Rosen Shavit 97] How it works: Edges viewed as directional Internal nodes maintain buffers on every edge (size n) Protocol proceeds in 3 steps: Slide Protocol n {

18 “Slide” Protocol: [Afek Gafni 88], [Awerbuch Mansour Shavit 89], [Afek Gafni Rosen 92], [Afek Awerbuch Gafni Mansour Rosen Shavit 97] How it works: Edges viewed as directional Internal nodes maintain buffers on every edge (size n) Protocol proceeds in 3 steps: …………………… RS H = n H = n-1 H = 2 H = 1 H = n-1 H = 2H = 1H = 0 1) Communicate Heights 2) Transfer Packets3) Re-Shuffle Locally Slide Protocol

19 RS “Slide” Protocol: [Afek Gafni 88], [Awerbuch Mansour Shavit 89], [Afek Gafni Rosen 92], [Afek Awerbuch Gafni Mansour Rosen Shavit 97] How it works: Edges viewed as directional Internal nodes maintain buffers on every edge (size n) Protocol proceeds in 3 steps: 1) Communicate Heights 2) Transfer Packets3) Re-Shuffle Locally Slide Protocol Packets “flow” downhill from S to R

20 Correctness: Throughput: Memory: Linear (Optimal with respect to Conforming Adversary!) O(n 2 log n) “Slide” Protocol: [Afek Gafni 88], [Awerbuch Mansour Shavit 89], [Afek Gafni Rosen 92], [Afek Awerbuch Gafni Mansour Rosen Shavit 97] How it works: Edges viewed as directional Internal nodes maintain buffers on every edge (size n) Protocol proceeds in 3 steps: 1) Communicate Heights 2) Transfer Packets3) Re-Shuffle Locally Slide Protocol

21 Towards Our Solution S R Assume signatures for all packets Adv cannot insert “new” packets – are we done? NO! We must counter all malicious behavior: Examples: Message Deletion; Message Duplication; “Play- Dead”; … {m 1, m 2, m 3, …}

22 Sketch of Proof Start with “Slide” protocol Every message of O(n 3 ) bits is expanded into a codeword of O(n 3 ) packets Sender signs all packets he inserts “Routing with Responsibility”: Every time a packet is transferred across an edge, adjacent nodes sign various forms of communication

23 After the O(n 3 ) rounds allotted to the transfer of any message, we prove one of the following happens: 1. R can decode the codeword Successful message transmission Great, proceed to the next message! 2. R did not receive 8 n 3 packets Packet Deletion Keep track (signed) volume across each edge of total volume 3. R has received a duplicated packet Packet Duplication + Packet Deletion Keep track (signed) # of appearances of each packet across each edge 4. S was not able to insert 12n 3 packets Packet Duplication Keep track (signed) of potential changes across each edge Sketch of Proof

24 Blacklist Non-responding nodes put on blacklist by sender Control information is flooded Control info is much smaller then messages, so does not impact throughput Blacklisted nodes don’t transfer messages (until they are removed) Nodes crucial to link S and R won’t remain on blacklist for long

25 Authenticated Adversarial Routing Problem Statement Solution Approach and Description Conclusion

26 Conclusion 1 st routing protocol secure against (node-controlling+edge-scheduling) conforming adversary Same Throughput as non-secure protocols: Throughput: Linear (Optimal!) More Memory as non-secure protocols, but still polynomial: Memory: O(n 4 log n) vs. O(n 2 log n)

27 After the O(n 3 ) rounds allotted to the transfer of any message, we prove one of the following happens: 1. R can decode the codeword “Successful” message transmission 2. R did not receive 8 n 3 packets Packet Deletion 3. R has received a duplicated packet Packet Duplication + Packet Deletion 4. S was not able to insert 12n 3 packets Packet Duplication Sketch of Proof AB 57

28 Sketch of Proof AB P 102 (5, P 102 ) After the O(n 3 ) rounds allotted to the transfer of any message, we prove one of the following happens: 1. R can decode the codeword “Successful” message transmission 2. R did not receive 8 n 3 packets Packet Deletion 3. R has received a duplicated packet Packet Duplication + Packet Deletion 4. S was not able to insert 12n 3 packets Packet Duplication

29 Sketch of Proof AB (-5,3) (-3, 2) C D After the O(n 3 ) rounds allotted to the transfer of any message, we prove one of the following happens: 1. R can decode the codeword “Successful” message transmission 2. R did not receive 8 n 3 packets Packet Deletion 3. R has received a duplicated packet Packet Duplication + Packet Deletion 4. S was not able to insert 12n 3 packets Packet Duplication