Present Paper: Protecting Free Expression Online on Freenet

  • 834 views
Uploaded on

Publication Authors: I. Clarke, S. G. Miller, T. W. Hong, O. Sandberg, and B. Wiley …

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

More in: Technology , Business
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Be the first to comment
No Downloads

Views

Total Views
834
On Slideshare
0
From Embeds
0
Number of Embeds
1

Actions

Shares
Downloads
11
Comments
0
Likes
1

Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
    No notes for slide

Transcript

  • 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
    • Freenet’s 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
    Ex. Data Store Ex. Routing Table F001 A50031 F004 F003 F002 FILE E9005C 872350 A5D033 KEY 152.195.200.102 101.72.100.214 64.75.32.88 158.108.216.7 IP ADDR 6D8FB7 329004 A5D030 A50001 KEY
  • 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)
    File SHA CHK
  • 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
    Public key SSK Private key Description SHA SHA concat SHA File Signing Signature
  • 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
    Requestor Holder
    • A B and E may cache the file (become the new holders)
    A B C F E D 1 2 3 4 11 10 9 5 8 6 7 12 Data request Data reply Request fail
  • 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
    Publisher TTL=3 TTL=2 TTL=1 TTL=0
    • B C and D become the new holders
    insert all clear copy A B C D
  • 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 Freenet’s 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