Freenet. Anonymity Napster, Gnutella, Kazaa do not provide anonymity Users know who they are downloading from Others know who sent a query Freenet.

FreenetFreenet

AnonymityAnonymity

Napster, Gnutella, Kazaa do not provide anonymityUsers know who they are downloading

fromOthers know who sent a query

FreenetDesigned to provide anonymity among

other features

FreenetFreenet

Data flows in reverse path of query Impossible to know if a user is initiating or forwarding a query Impossible to know if a user is consuming or forwarding data

“Smart” queries Requests

get routed to correct peer by incremental discovery

* Figure from “Protecting Freedom of Information Online with Freenet”, Ian Clarke and Scott Miller. IEEE Internet Computing, Jan/Feb 2002

FreenetFreenet

Peer-to-peer indexing and searching service

Peer-to-peer file downloading Files served use the same route

as searches (not point-to-point) Provides for anonymity

FreenetFreenet

Completely anonymous, for producers or consumers of information

Resistance to attempts by third parties to deny access to information

Goals: Anonymity for producers and consumers Deniability for information storers Resistance to denial attacks Efficient storing and routing Does NOT provide

Permanent file storage Load balancing

FreenetFreenet

Somewhat similar to Gnutella but… As file passes through ‘vine-like’

framework, the file makes a copy of itself at each point along its route

Implemented encryption to hid the originating point of the file

Vision of open source project is to allow all information, copyrighted or not, to be distributed anonymously and untraceable in a p2p network

http://www.freenet.org

Freenet historyFreenet history

Final Year project Ian Clarke , Edinburgh University, Scotland, June, 1999

Sourceforge Project, most active V.0.1 (released March 2000) Latest version(Sept, 2001): 0.4

What is Freenet and Why?What is Freenet and Why?

Distributed, Peer to Peer, file sharing system

Completely anonymous, for producers or consumers of information

Resistance to attempts by third parties to deny access to information

Us er

User

User User

UserUser

User User

•Each user acts independently

•There is no central directory server

•Peers directly change file information among each other in a query

Architecture of Gnutella and FreenetArchitecture of Gnutella and Freenet

File Discovery Mechanisms in File Discovery Mechanisms in Freenet: Chain ModeFreenet: Chain Mode A request for a file can be forwarded

through many different nodes. If a node does not have the document that

the requestor is looking for, it forwards the request to one of its neighbor that is more likely to have the document The messages form a chain as each node

forwards the request to the next node Message times out after passing through a

certain number of nodes, so that huge chains don’t form.

The chain ends when the message times out or when a node replies with the data.

File Discovery Mechanisms in File Discovery Mechanisms in Freenet: Chain ModeFreenet: Chain Mode

Us er

User

User User

UserUser

User User

A

B

C

D

E

F

G

H *

Computer A send its query to its neighbor B, which forwards it to one of its neighbor D, which in turn forwards it to one of its neighbor G, finally, the query reach H who has the requested data

The reply is passed back through each node that forwarded the request, back to the original node that started the chain

Advantages and Disadvantages Advantages and Disadvantages of Chain Mode in Searchingof Chain Mode in Searching

Advantages: Fast discovery with less network

traffic in average case Search stops once the requested file

is found More scalable

Disadvantages: Slow discovery in worst case

Worst Case Scenario in Chain Worst Case Scenario in Chain Mode DiscoveryMode Discovery

Us er

User

User User

UserUser

User UserC

D

E

F

User

User

A

B

H*

J

IComputer H has the requested file, but the query never reaches it because of poor routingdecision at computer G

Instead, the query ends up with no file found

G

FreenetFreenet

It aims: To allow people to distribute material

anonymously. To allow people to retrieve material

anonymously. To make the removal of material almost

insuperably difficult. To operate without central control.

operation of freenetoperation of freenet

Searches are only passed to one other servent, which pass it on. After no positive response from that chain, another servent is tried.

But the entire document sought is passed along, unless it is too large

Servents keep caches of popular documents until no one asks for it for a long time.

popular documents frequent and close to users.

searching on freenetsearching on freenet

You basically can not search on freenet.

Each document has an identifier The identifier and the document can

not be changed. This will make it difficult to use it

on its own as a device for people to exchange copyrighted material.

Some security and authentication Some security and authentication issuesissues

How to ensure anonymity: Nodes can lie randomly about the

requests and claim to be the origin or the destination of a request

Hop-To-Live values are fuzzy Then it’s impossible to trace back a

document to its original node Similarly, it’s impossible to discover

which node inserted a given document.

ScalabilityScalability

X-axis: # of nodes Y-axis: # of

pathlength The relation

between network size and average pathlenth.

Initially, 20 nodes. Add nodes regularly.

Fault ToleranceFault Tolerance

X-axis: # of nodes failing

Y-axis: # of pathlength The median pathlength

remains below 20 even when up to 30% nodes fails.

Small world ModelSmall world Model

X-axis: # of nodes failing

Y-axis: # of pathlength Most of nodes have

only few connections while a small number of news have large set of connections.

It follows power law

Is it Perfect?Is it Perfect?

How long will it take to search or insert? Trade off between anonymity and searching

efforts: Chord vs Freenet Have no idea about if search fails due to

no such document or just didn’t find it. File lifetime

Freenet doesn’t guarantee a document you submit today will exist tomorrow