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OblivP2P: An Oblivious Peer-to-Peer Content Sharing System

OblivP2P: An Oblivious Peer-to-Peer Content Sharing System. Yaoqi Jia , Tarik Moataz , Shruti Tople and Prateek Saxena National University of Singapore. Traffic Analysis in P2P Systems. P2P c ontent sharing systems 150 million users/month 3.35% of all world bandwidth

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OblivP2P: An Oblivious Peer-to-Peer Content Sharing System

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  1. OblivP2P: An Oblivious Peer-to-Peer Content Sharing System YaoqiJia, TarikMoataz, Shruti Tople and PrateekSaxena National University of Singapore

  2. Traffic Analysis in P2P Systems • P2P content sharing systems • 150 million users/month • 3.35%of all world bandwidth • Long term global traffic analysis • E.g., ISP’s,Global BitTorrent Monitor, Bitstalker

  3. What can an Adversary do? • Leakage Channels • Plaintext data • Secure channel • Length • Padding • Time • Fixed Interval • Access Patterns Assume existing defenses Linkability

  4. Problem Current Solutions • Anonymous Systems e.g., Mix Networks, Tor Hide Online Identity Unlinkability • Long term • Global Adversary Is anonymizing enough?

  5. Contributions

  6. Problem

  7. Insufficiency of Existing Solutions Mixnet Round 1 Mixnet Round 2 Intersection, Hitting Set [AK’03] or Statistical Disclosure Attacks [KP’04]

  8. Main Insight: Oblivious Access Pattern • Oblivious RAM • Hide access patterns between CPU and memory • Data is shuffled in the memory periodically • Applied to: • Cloud Storage [SS’13A], [SS’13B],[LO’13] • Filesystem[WST’12] • Can we directly apply ORAM to P2P systems?

  9. ORAM Background 1 2 • Tree-Based ORAM (Path ORAM) • Read • Fetches a path from the tree containing the block • Stores the path in the local storage (stash) • Write • Selects a random path in the tree • Shuffles the blocks in the stash and the path 3 4 5 6 7

  10. Mapping ORAM to P2P Send Re-encrypt 1 1 2 2 2 2 2 Trusted Tracker Trusted Client 3 3 4 4 5 5 6 6 7 7 Position Map, Stash Position Map, Stash Request Fetcha path Decrypt Decrypt Fetch path Initiator Untrusted Server path Peers Peer-to-Peer Network OblivP2P-0 Protocol

  11. OblivP2P-0: Tracker as bottleneck • Tracker fetches O(log N) blocks per access 118 MB /req for 2 million users ≈ Max Bandwidth Need a Distributed Oblivious P2P Protocol

  12. OblivP2P-1 Protocol

  13. Naïve approach: Removing Bottleneck Send < path, position, key > 1 2 2 Trusted Tracker 3 Performance 4 5 Position Map, Stash 6 7 Security Request Decrypt Initiator Fetcha path Peers Peer-to-Peer Network

  14. Challenges 1 2 • ORAM writes • Recently accessed block at the root • Less frequently accessed block at the leaves • “Block History” • Shared resources • Security flaw in P2P systems • Multiple users access the same resource 5 Recently accessed Less frequently accessed

  15. New Primitive:Oblivious Selection Selects a block without: Block Position Cryptographic Key No Centralized Bottleneck

  16. Construction 1 1 1 2 2 2 2 • Step 1: PIR over ORAM • Obliviously select a block from a path 5 5 5 Trusted Tracker Send PIR metadata Request Compute an Encrypted Share using PIR Initiator Block Position Cryptographic Key No Centralized Bottleneck

  17. Construction • Step 2: Seed-HomomorphicPRG • Decrypt shares without giving away the key Trusted Tracker Send key share Compute a Decrypted Share using SH-PRG Initiator Dec Block Block Position Cryptographic Key No Centralized Bottleneck Cryptographic Key

  18. Security

  19. OblivP2P is an Oblivious P2P Protocol Any two equal length access sequences by two peers are indistinguishable for any p.p.t. “honest-but-curious” adversary • Number of dishonest peers is in O(Nε), where ε<1 • Theorem: If ∀N > 1, and ∀ε < 1, ∃m > 1 such that 2logN·m·(1−ε) ∈ negl(λ) then OBLIVP2P-1 is an oblivious P2P protocol

  20. Evaluation

  21. Experimental Setup • 15 DeterLab servers – (214)16000 peers • Each server shares a bandwidth of 128 MBps • Block size of 512 KB similar to BitTorrent

  22. No Centralized Bottleneck ~ 128 MB /req ~ 1 MB /req

  23. Linear Scalability with Peers 3.59MB/ sec • Larger networks can scale up performance • 3.59 MB/s is due to our limited test infrastructure • Bottleneck remaining is purely computational

  24. Take Away! • Propose hiding data access patterns in P2P systems • OblivP2P - First work to repurpose ORAM in Peer-to-Peer systems • OblivP2P is linearly scalable and highly parallelizable with the peers in the network

  25. Thanks! • Email : shruti90@comp.nus.edu.sg • Link: https://github.com/jiayaoqi/OblivP2P-Code

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