Present Paper: Protecting Free Expression Online on Freenet
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Publication Authors: I. Clarke, S. G. Miller, T. W. Hong, O. Sandberg, and B. Wiley Presented in the class: Advanced Topics in Distributed Systems (CE7490) by Mr.Sivadon Chaisiri
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- 1. Protecting Free Expression Online with Freenet I. Clarke, S. G. Miller, T. W. Hong, O. Sandberg, and B. Wiley Presented by Sivadon Chaisiri Related paper: Freenet: A Distributed Anonymous Information Storage and Retrieval System
- 2. O utline
- Overview of Freenet
- Freenet Architecture
- Performance Analysis
- Summary
- Review
- Q&A
- 3.
- " I worry about my child and the Internet all the time, even though she's too young to have logged on yet . Here's what I worry about . I worry that 10 or 15 years from now, she will come to me and say 'Daddy, where were you when they took freedom of the press away from the Internet? ' "
- Mike Godwin, Electronic Frontier Foundation
- 4. O verview of F reenet
- Freenet is an adaptive peer-to-peer system
- P ermits the publication and retrieval of data without fear of censorship
- Freenets Goals
- Censorship-resistance
- Privacy for users (publishers, requestors, and holders) - anonymity
- High availability , reliability and scalability
- 5. F reenet A rchitecture
- Overview
- GUID Keys
- Routing
- Adding nodes
- Inserting files
- Managing data stores
- 6. G UID K eys 1/4
- GUID ( file key / URI of files ) are assigned for files obtained by a hash function (SHA-1 / SHA-256)
- Types of GUID keys
- Content-hash key (CHK)
- Keyword-signed key (KSK)
- Signed-subspace key (SSK)
- Updateable Subspace Key (USK)
- Each node maintains a data store table and a routing table
- 7. G UID K eys 2/4
- C ontent- H ash K ey ( CHK )
- Used for unchangeable files
- To retrieve a file, a requestor needs CHK as the search key
- Not human-friendly (unreadable key)
- 8. G UID K eys 3/4
- S igned- S ubspace K ey ( SSK )
- Used for creating a personal namespace that anyone can read but only its publisher can write to
- Define a short description of a file (Human-friendly key)
- Example, /politics/us/pentagon-papers
- /politics/china/tiananmen-papers
- A requestor needs (public key, desc) as a search key
- 9. R outing 1/3
- Freenet uses a steepest-ascent hill-climbing search
- Generate a query message (incl. the search key and TTL)
- Forwards the message to the node that it thinks is closest to the target file (called the target node )
- When receiving a query, the node checks its data store
- Found the file, return it back along the same path
- File not found, Repeat 2.
- 10. R outing 2/3
- Example, Node A is requesting a file
- A B and E may cache the file (become the new holders)
- 11. I nserting F ile s 1/2
- Follow the same path as same as retrieving a file
- Create an insert message (incl. the file key+TTL)
- Each node forwards the message to the target node
- When receiving a query, the node checks its data store
- TTL > 0, repeat 2
- TTL = 0, the final node returns all clear message
- The publisher submit the file along the chain
- 12. I nserting F ile s 2/2
- Example, Node A is inserting a file
- B C and D become the new holders
- 13. A dding N odes 1/2
- A new node generates a key pair and a random number
- The new node sends an announcement message (incl. TTL, public-key, physical address, hash number) to an existing node
- When receiving the message, the node randomly select a node, then forward the message to it
- Until TTL = 0,
- Every node in the chain assigns the new node a GUID by using some shared random numbers
- 14. H a = SHA(R a ) R a = rnd() R b = rnd() H b = SHA(H a + R b ) R c = rnd() H c = SHA(H b + R c ) C b = SHA(H b ) C c = SHA(H c ) H a H b TTL=3 TTL=2 TTL=1 TTL=0 GUID( A ) = SHA(R a + R b + R c + R d ) A dding N odes 2/2 R d = rnd() H c H c , R d H b , R c , R d H a , R b , R c , R d C a = SHA(H a ) A B C D
- 15. M anaging D ata S tores
- Users cannot be allowed to control the data stores
- When storing a file (as the holder), it may evict some files if no more space
- Data store is managed as an LRU algorithm
- Holders should not reveal their data stores to others even themselves
- Before inserting a file, a publisher should encrypt the file by a symmetric key
- 16. P erformance A nalysis 1/4
- Simulations
- Based on a small-word network model
- Observe Freenets characteristics
- Scalability
- Fault-tolerance
- 17. P erformance A nalysis 2/4
- 18. P erformance A nalysis 3/4
- 19. P erformance A nalysis 4/4
- 20. P erformance A nalysis
- 21. S ummary
- Freenet is an unstructured p2p storage system
- Deal with privacy and censorship-resistance
- Freenet is scale on a large network, and robust against large failures
- 22. R eview
- Closet key Closest Meaning
- Disperse files of the similar topics
- Prevent single point of failures
- Freenet s Weakness
- No file-lifetime guarantees
- Due to its goal, no content censorship of illegal/corrupt/fake files
- DoS Attacks
- 23. R eference
- Ian Clarke, Scott G. Miller, Theodore W. Hong, Oskar Sandberg, and Brandon Wiley, Protecting Free Expression Online with Freenet , IEEE Internet Computing, JAN/FEB 2002
- Ian Clarke, Scott G. Miller, Theodore W. Hong, Oskar Sandberg, and Brandon Wiley, Freenet: A Distributed Anonymous Information Storage and Retrieval System , In Proc. Of the ICSI Workshop on Design Issues in Anonymity and Unobservability, Berkeley, CA, 2000
- http:// freenetproject.org
- http://en.wikipedia.org/wiki/Freenet
- 24. Q & A
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