Denial-of-Service Resilience in Peer-to-Peer Systems

D. Dumitriu, E. Knightly, A. Kuzmanovic, I. Stoica and W. Zwaenepoel

Presenter: Yan Gao

Outline

Background P2P File Sharing

DoS Scenario File-targeted DoS attacks Network-targeted DoS attacks

Model Simulation Study

Gnutella Overview Peer-to-peer indexing and searching

service Built on top of an unstructured overlay

network Two level hierarchy Peer-to-peer point-to-point file

downloading using HTTP P2P file sharing application on top of an

overlay network Nodes maintain open TCP connections Messages are broadcasted (flooded) or back-

propagated

Gnutella － unstructured p2p system

A given file can be stored at any node

Original version used scoped flooding to locate a file flexible and robust, not scalable

Two-level hierarchy (KaZaA) Leaf nodes & supernodes

Hierarchy p2p systems are scalable than the original one

Freenet － unstructured p2p network

Aim － to provide anonymity and censorship resistance

Each file is assigned a unique ID by hashing the file content

Each node maintains a routing table Insert

The file is routed according to its ID and stored at all nodes along the path

Retrieve The file is copied along the path from the source to

the requester It is hard to locate all copies of a specific file Trying to locate a file will result in the file

being copied at even more nodes

Structured p2p networks Partition a global ID space across all nodes

Each node － for a chunk of the ID space Each file is associated with a unique ID

A file can be stored at an arbitrary node Efficient in locating such a node

Given an ID, find the node responsible for that ID

Find the node responsible for a given ID by contacting only O(logN) nodes

Example: CAN, Chord, Pastry, Tapestry, Kademlia

Structella—hybrid proposal

Use flooding to locate files, but in a more efficient way

Use the underlying structure of Pastry to send no more than one flood message per virtual link Reduce the flooding cost by a factor of k

Note: This paper assume that the replies are sent back to the requester using the Pastry routing protocol.

Outline

Background P2P File Sharing

DoS Scenario File-targeted DoS attacks Network-targeted DoS attacks

Model Simulation Study

File-targeted DoS attacks － pollution attacks

Malicious node advertises a corrupted file, and eventually distributes this copy

The p2p network topology does not play a role in the effectiveness

The user-behavior factors determine the spread of polluted files Willingness to share files Speediness in removing corrupted files Persistence in downloading files under

attack Attack against a single file

Attacker wants to prevent spread of file

Attack Model

Attacker responds to queries for a particular file

Replies with a very high bandwidth and low waiting time, to be attractive

Serves fake content for the file Requires relatively large resources

Attacker serves 10% of file

Analytical Model: Spreading Content

Spreading polluted and good copies

Non-cooperative users

Effect of User Persistence

Here it is!

Counterstrategy: Parallel Download

File-targeted DoS attacks

System is really quite vulnerable Attacker, however, requires large

resources to mount the attack FYI, there is evidence that these

pollution attacks are being carried out

Network-targeted DoS attacks

Directed against unstructured p2p networks like Gnutella or Kazaa

Attack against whole p2p network Attacker wants to significantly reduce

system goodput

System model

Two phase user-system interaction Query

User sends query for particular file Responses are received and stored

Download One or more responses are selected

based on policy Downloads are initiated

Attacker Strategy

False content attack Respond to all queries pointing to self Modify all replies and redirect to self Serve bad files

Slow node attack Modify all replies and redirect to

slowest nodes, advertising high speed for them.

Client Strategy

Download peer selection policy: Best

by expected download time Random Redundant best File chunking Reputation systems Detection

Network-targeted DoS attacks Again, systems are very vulnerable Again, attackers require quite large

resources to mount attack Random selection counterstrategy

effective However, it prevents selection of high

bandwidth peers Non-attack performance is significantly

reduced

Outline

Background P2P File Sharing

DoS Scenario File-targeted DoS attacks Network-targeted DoS attacks

Model Simulation Study

Supernodes and hierarchy

Long paths for anonymity

Power-law topologies

Outline Background

P2P File Sharing Gnutella

DoS Scenario System model Attacker strategy Client strategy

Model Simulation Study

Simulation Preliminaries Discrete event simulation Two peer classes

Leaf nodes (80%) – 56Kb to 1Mb Supernodes (20%) – 1Mb to 10Mb

Asymmetric bandwidth Upstream ¼ of downstream

Zipf file distribution TCP max-min fairness

Baseline Experiments

Baseline attack

System Factors

Overlay structure and hierarchy

System Factors

Path length

Victim counter strategies Random redundant downloads

1 or more in parallel Lowers base performance VERY MUCH Much less vulnerable to attack

Best redundant download Best N by estimated time in parallel Lowers base performance Moves system breaking point far out

Conclusions File-targeted attacks are inefficient in

cooperative p2p environment It is insufficient to only transmit false info to

launch an attack in p2p networks Structured p2p systems are more resilient

than hierarchical p2p systems System goodput degrades tremendously with

the number of malicious nodes in both cases Reputation systems are largely ineffective Randomization techniques are indeed able to

transform the system’s resilience from a devastating hyperexponential scaling to a more resilient linear scaling

Thank you!