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Having Fun with P2P. Keith W. Ross Polytechnic University http://cis.poly.edu/~ross. Many Apps Migrating Client-Server to P2P. File sharing File and patch distribution Live video streaming Video on demand VoIP Hybrid CDN/P2P. Today’s Talk. P2P security Is BitTorrent Unstoppable?

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having fun with p2p

Having Fun with P2P

Keith W. Ross

Polytechnic University


many apps migrating client server to p2p
Many Apps Migrating Client-Server to P2P
  • File sharing
  • File and patch distribution
  • Live video streaming
  • Video on demand
  • VoIP
  • Hybrid CDN/P2P
today s talk
Today’s Talk
  • P2P security
    • Is BitTorrent Unstoppable?
  • Survey of P2P video streaming research
    • Creating an open P2P video streaming ecosystem

Research supported by: NSF, Microsoft, Movie Labs, Huawei, Verizon, Panasonic, Len Shustek

why study p2p security
Why study P2P Security?
  • P2P is potentially more vulnerable than client server.
  • Need to understand the security issues for architecting future P2P apps
  • Attacks from entertainment industry reveal weak spots in P2P
Security work joint with:

Jian Liang

Naoum Naoumov

Rakesh Kumar

Prithula Dhungel

Xiaojun Hei

Di Wu

earlier work on kazaa and edonkey
Earlier work onKazaa and eDonkey
  • FastTrack/Kazaa
    • Unstructured P2P network
  • Overnet/Kad
    • Structured (DHT) P2P network
    • Part of eDonkey/eMule
file pollution infocom 05
File Pollution: Infocom 05

original content

polluted content



file pollution
File Pollution





file sharing








file pollution1
File Pollution

Unsuspecting users

spread pollution !

file pollution2
File Pollution

Unsuspecting users

spread pollution !


index poisoning infocom 06
Index Poisoning: Infocom 06

index titlelocationbigparty

file sharing


index poisoning
Index Poisoning

index titlelocationbigparty

index titlelocationbigparty

is bittorrent unstoppable
Is BitTorrent Unstoppable?

(IPTPS 2008; extended version available)

  • How can record/movie companies limit piracy in BitTorrent?
    • Suing companies?
    • Suing users?
    • Internet attacks?
  • How vulnerable is BitTorrent to attacks?

torrent: group of

peers exchanging

chunks of a file

tracker: tracks peers

in torrent; providestracker list



torrent index server:search for torrents;provides .torrent file


bittorrent ecosystem
BitTorrent Ecosystem
  • Open protocol
    • 50+ client implementations
    • Dozens of tracker implementations
    • Dozens of torrent location sites
  • 5 million simultaneous users & growing
  • Evolving:
    • Peer discovery: DHTs, gossiping
    • Proprietary protocols, private torrents
bittorrent basics
Seeds and leechers

File divided into 256KB pieces. Each piece is 16 blocks.

Download blocks and assemble pieces

Hash piece to check integrity

Peers advertise pieces they have to neighbors

Peer sends blocks to four neighbors currently sending it data at the highest rate

And also to one random neighbor

BitTorrent Basics
classes of bittorrent attacks
Classes of BitTorrent Attacks

Attacks against an existing torrent

  • against leechers
  • against initial seed
  • against peer discovery
  • against peer discover

Decoy attacks: attacker creates own torrent

  • Seeding a polluted file
  • Seeding a file and delivering only 99%
fake block attack
Fake Block Attack
  • Attacker establishes TCP connections with legitimate peers
  • Peer downloads one fake block from attacker
    • and 15 good blocks from legit peers
    • Hash failure – download is prolonged

Acknowledgment: Thanks to Vishal Misra for bringing this attack to our attention.

simple analysis of fake block attack
Simple analysis of fake block attack

What is the probability of a hash failure?

  • n = # neighbors advertising piece
  • m = attack nodes (m < n)
  • k = # neighbors from which it is downloading the 16 blocks
connection attack
Connection attack
  • Attacker establishes many TCP connections to each target peer.
    • Doesn’t upload any blocks
    • Chatty peer: keeps connection active with repeated BT handshake messages
passive measurements
Passive Measurements
  • Collect traces while downloading
    • Azureus and uTorrent
    • DSL and Ethernet
    • 54 downloads of “Foo Fighters” (108 MB)
  • Developed parser to analyze BT trace
  • To estimate download time without attack:
    • Obtain blacklist from torrentfreak.com
    • Use Peer Guardian to prevent connections to blacklisted peers
azureus results
Azureus results
  • Download is NOT being prolonged by more than 50% for DSL
zoom in one azureus trace
Zoom in one Azureus trace

Chatty-peers make upa major fraction of the useful peers.

passive measurement conclusions
Passive Measurement Conclusions
  • Anti-P2P companies applying different strategies for different BT clients
  • Largely ineffective for Ethernet clients
  • For DSL, download time increases by 30-60%
active measurements
Active Measurements
  • Crawl peers in torrent and identify
    • Fake-block attack peers
    • Chatty peers
  • Looked at 8 box-office movie torrents
    • Some under attack; some not
  • Crawler speaks Azureus protocol to Azureus peers
    • and conventional protocol to all other peers
active measurement conclusions
Active Measurement Conclusions
  • Several, but not all, top-box movies are under attack
  • Published blacklists do not cover all the attackers in a torrent
  • Most attackers enter through gossiping
seed attack
Seed Attack
  • “Nip in the bud”
  • Make many connections to seed, download at high rate
  • Rationale: Conventional algo gives all its bandwidth to 5 highest downloaders
planet lab experiments
Planet Lab experiments
  • Put 30 leechers on PL nodes; upload capacity capped at 512 kbps
  • Seed upload capacity 160 kbps
    • Azureus and uTorrent
  • 0-60 attack peers
  • Start seed, start 5 leechers, start attack peers, start 25 leechers
seed attack results
Seed attack results


attacker bandwidth

bittorrent conclusions
BitTorrent Conclusions
  • Attacks against leechers can prolong downloads
    • But is 50% enough?
    • Blacklists are helpful; adaptive blacklist is needed
  • Seed is surprisingly resilient to attacks
  • Attacks must be tailored to client types
  • BitTorrent ecosystem is difficult to stop!
today s talk1
Today’s Talk
  • P2P security
    • Is BitTorrent Unstoppable?
  • Survey of P2P video streaming research
    • Creating an open P2P video streaming ecosystem

Research supported by: NSF, Microsoft, Movie Labs, Huawei, Verizon, Panasonic, Len Shustek

live streaming faculty collaborators
Live Streaming: Faculty Collaborators

ProfessorYong Liu


Shiv Panwar


Yao Wang

and Professor Nitsesh Saxena (CS)

basic idea p2p live streaming
obtain list

of peers


Basic idea P2P live streaming





of video

@ polytechnic
@ Polytechnic
  • Infrastructure for measuring P2P live video systems
    • Xiaojun Hei, Jian Liang, Yong Liu
  • Stochastic modeling of P2P live streaming
    • Rakesh Kumar, Yong Liu
  • Incentives and scalable video for live P2P streaming
    • Zhengye Liu, Yanming Shen, Shiv Panwar, Yao Wang
  • Security of P2P live streaming systems
    • Prithula Dhungel, Xiaojun Hei, Nitesh Saxena
  • P2P VoD, Hybrid P2P-CDN
    • Angela Wang, MSR colleagues
  • Developing our own live P2P video system
    • Master’s students
open p2p live streaming
Open P2P Live Streaming
  • Create an ecosystem for live streaming
  • Need incentives
    • The more you upload the better the quality
  • Layered video
    • Chunk-based
    • Substream-based
  • Accommodate user generated content