1. Access Control to BitTorrent
Swarms using Closed Swarms
Dr. Njål Borch
Northern research institute,
Tromsø, Norway

2. Why access control?
• No access control
– Limited commercial possibilities
• DRM
– Control content, not distribution
– Limits usability from end user perspective
• Closed swarms
– Distributed access control mechanism
– Differentiated services
– Control network resources

3. DRM
• Manage restrictions on content
• Favoured by Broadcast TV
– Non-authorized users costs zero
– Loss of profit if people break it
• But online (unicast)?
– Non-authorized user costs money
– Accumulates high bandwidth cost if broken or circumvented

4. Control access to resources
• Central system
– Authentication service
– Username/password
– Fairly simple solution
– Accumulates bandwidth costs
• P2P system
– Cost saving
– Appealing scalability properties
– Centralized access control on central bits
– Leaking nodes
• But: Both (all really) systems can experience leaking content

5. Closed Swarms – the Idea
Create a flexible authentication mechanism for
P2P which is both scalable and allows for
experimental and innovative business models.

6. The nodes
AN L

7. The Math

8. The Math

9. The Math

10. So basically...
• Non-authorized nodes can be of use
– They can even be explicitly allowed
• Can subsidize bandwidth to selected nodes

11. The basics
Proof
of
Access
Node Key
Swarm
Swarm Key
Node

12. The Protocol
Node A
- Generate and send Nonce
- Send signed PoA
- Verify PoA, allow upload
Node B
- Generate and send Nonce
- Verify PoA, allow upload
- Send signed PoA

13. Points
• Seeds do not need to sign and send PoAs
• No central access required to validate PoAs
• No need to know a node's keys in advance
• Only performed on connect (handshake)
• BitTorrent implementation backwards compatible
– But non-CS clients are non-authorized
• Allows easy addition of seeds
– Provide data or a PoA for the seedbox

14. Possible applications
• Sell guarantees
– Free user gets community service. Might VoD, might not.
– Paying customer is guaranteed high speed seeds, will VoD.
• Sell guarantees 2
– Home user can watch a live event, if there is capacity
– A venue can buy access to an event, and is guaranteed seeds.
• Closed group sharing
– Only authorized nodes are allowed access
• Combine with Scalable video coding (SVC)
– SD for free users, pay for HD