Present Paper: Protecting Free Expression Online on Freenet

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

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 Freenets characteristics

Scalability

Fault-tolerance

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

Present Paper: Protecting Free Expression Online on Freenet

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