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OblivP2P: An Oblivious Peer-to- Peer Content Sharing System Yaoqi Jia, Tarik Moataz, Shruti Tople and Prateek Saxena National University of Singapore 1 Traffic Analysis in P2P Systems P2P content sharing systems 150 million users/month

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SLIDE 1

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

Yaoqi Jia, Tarik Moataz, Shruti Tople and Prateek Saxena

National University of Singapore

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SLIDE 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

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SLIDE 3

What can an Adversary do?

  • Leakage Channels

– Plaintext data

  • Secure channel

– Length

  • Padding

– Time

  • Fixed Interval

– Access Patterns

Assume existing defenses

Linkability

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SLIDE 4

Problem

Current Solutions

– Anonymous Systems e.g., Mix Networks, Tor

Is anonymizing enough?

Adversary

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Hide Online Identity Unlinkability

üLong term üGlobal

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SLIDE 5

Contributions

  • Guarantee unlinkability
  • Obliviousness in P2P systems

OblivP2P Protocol

  • Link:

https://github.com/jiayaoqijia/OblivP2P- Code

Implementation

  • No Centralized Bottleneck
  • Linear Scalability with peers

Evaluation

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SLIDE 6

Problem

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SLIDE 7

Insufficiency of Existing Solutions

Mixnet Round 1 Mixnet Round 2

Intersection, Hitting Set [AK’03] or Statistical Disclosure Attacks [KP’04]

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SLIDE 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?

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SLIDE 9

Problem Definition

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Trusted Tracker

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SLIDE 10

ORAM Background

  • 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

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4 3 6 7

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SLIDE 11

Mapping ORAM to P2P

Trusted Client Untrusted Server

Position Map, Stash

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2

4 3 6 7

pat h

Trusted Tracker

Position Map, Stash

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Peers

Peer-to-Peer Network

OblivP2P-0 Protocol

Initiator Fetch path Decrypt Request Fetch a path Re-encrypt 2 2 Decrypt Send 2

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SLIDE 12

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

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SLIDE 13

OblivP2P-1 Protocol

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SLIDE 14

Naïve approach: Removing Bottleneck

Trusted Tracker

Position Map, Stash Initiator Request Send < path, position, key > 2 Decrypt

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Peers

Peer-to-Peer Network

Fetch a path

Performance Security

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SLIDE 15

Challenges

  • 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

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2

Less frequently accessed Recently accessed

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SLIDE 16

New Primitive: Oblivious Selection

Selects a block without :

Block Position Cryptographic Key

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No Centralized Bottleneck

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SLIDE 17

Construction

  • Step 1: PIR over ORAM

– Obliviously select a block from a path

Trusted Tracker

Initiator Request

Compute an Encrypted Share using PIR

Send PIR metadata

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2

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2

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2 2

Block Position

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No Centralized Bottleneck Cryptographic Key

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SLIDE 18

Construction

Trusted Tracker

Initiator

Compute a Decrypted Share using SH-PRG

Send key share Dec Block

  • Step 2: Seed-Homomorphic PRG

– Decrypt shares without giving away the key

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Block Position No Centralized Bottleneck Cryptographic Key Cryptographic Key

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SLIDE 19

Security

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SLIDE 20

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

  • blivious P2P protocol

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SLIDE 21

Evaluation

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SLIDE 22

Experimental Setup

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

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SLIDE 23

No Centralized Bottleneck

~ 1 MB /req ~ 128 MB /req

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SLIDE 24

Linear Scalability with Peers

3.59MB/ sec

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  • Larger networks can scale up performance

– 3.59 MB/s is due to our limited test infrastructure

  • Bottleneck remaining is purely computational
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SLIDE 25

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

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SLIDE 26

Thanks!

Email : shruti90@comp.nus.edu.sg

Link: https://github.com/jiayaoqijia/OblivP2P-Code

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