1 The Pollution Attack in P2P Live Video Streaming: Measurement Results and Defenses Prithula Dhungel Xiaojun Hei Keith W. Ross Nitesh Saxena Polytechnic University

2 The Pollution Attack Attacker joins an ongoing video channel Attacker advertises it has a large number of chunks W hen neighbors request chunks, attacker sends bogus chunks Receiver plays back bogus chunks Each receiver may further forward the polluted chunks

3 Peer Polluter request

4 Contributions Identified the pollution attack in P2P live video streaming applications Verify via experimental results (in PPLive) that pollution attack can be devastating Survey possible defenses against the attack

5 Pollution Experiment Figure: PPLive pollution experiment setup

6 Measurement Results (1) Figure: Number of peers viewing channel over experiment periods

7 Brooklyn Peer Figure: Clean and polluted chunks to/from Brooklyn peer

8 Hong Kong Peer Figure: Clean and polluted chunks to/from Hong Kong peer

9 Pollution Defense Mechanisms Blacklisting Traffic Encryption Chunk Signing –Sign-All Approach –Signature-Amortization Approaches Star Chaining Merkle Tree –Sign-and-Correct Approach

10 Chunk Signing Use PKI Every video source has public-private key pair Source uses private key to sign the chunks Receiver uses public key of source to verify integrity of chunk

11 Sign-All (1) Source –Source signs each chunk –Sends signature (authentication information) with corresponding chunk Receiver –Verifies each chunk individually using authentication information and public key of source

12 Sign-All (2) Chunk processing independence Bandwidth overhead -For a stream of m chunks, m signatures For 372 kbps channel with chunk size of 4000 bytes, around 3% Computation overhead - 1 (expensive) signature operation per chunk

13 Block Signing Chunks organized into blocks –Each block contains n chunks After generating n chunks, hash concatenation of all hashes, and sign result Reduces computation But cant verify individual chunks

14 Star Chaining Chunks organized into blocks –Each block contains n chunks After generating n chunks, calculate authentication information for each chunk –Signed hash of concatenation of all chunk hashes –Along with, all hashes of other n-1 chunks Receiver, chunk by chunk: –Applies public key to get hash of hashes –Verifies by concatenating hash of current chunk with those of the n-1 chunks, and taking hash

15 Star Chaining Computation overhead –> 1 signature per block Loss –> If some chunks are lost in block, can still decode rest Bandwidth overhead -> for block of n chunks, n-1 hashes + n signatures For channel of bitrate 372 kbps and chunk size of 4000 bytes, n = 32, about 16%

16 Merkle Tree Computation overhead –> 1 signature per block Loss –> If some chunks are lost in block, can still decode rest Bandwidth overhead -> nlog 2 n hashes + n signatures (about 5%)

17 Conclusion The pollution attack can be devastating Defenses: –Signature Amortization (Merkle Tree) – less computational overhead and delay at receiver but more bandwidth overhead –Sign-and-Correct – less bandwidth requirement but higher processing delay and computational requirement Based on requirements of the application, either of the two could be used

18 References [1] C. K.Wong and S. S. Lam. Digital signatures for flows and multicasts. IEEE/ACM Trans. Netw., [2] A. Lysyanskaya, R. Tamassia, and N. Triandopoulos. Multicast authentication in fully adversarial networks. In IEEE Symposium on Security and Privacy, 2004.

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