Censorship Detection Techniques

Censorship detectionArturo `hellais` Filasto’

Sunday, September 4, 2011

Whoami

• @hellais on twitter

• [email protected]





mailto:[email protected]








What is Censorship?

• Internet filtering is a form of non democratic oppression on people.

• It allows those in power to subvert the reality.


Filternet

• It’s a distorsion of what is in reality the internet.

• Follows the subjectiveness of the authorities

• This does not help humanity


La soluzione a quelli che sono percepiti soggettivamente come contenuti inappropriati è

oggettivamente più contenuti


Tor

• Tor software downloads are currently blocked from China, Iran, Lebanon, Qatar, etc.

• Tor delivers via email, write to [email protected] and we will send you a client to bootstrap a Tor client




Hidden Services

• They allow a server to give access to content anonymously

• This bypasses censorship in place


Tor Hidden Services

• am4wuhz3zifexz5u.onion

• Anonymity for the Server

• DoS protection

• End-To-End encryption


How HS work

Hidden ServerIP

IP

IP

Client


How HS work

Hidden ServerIP

IP

IP

Client

RP


Why use HS

• Avoid retaliation for what you publish

• Securely host and serve content

• Stealth Hidden Service


How filtering is performed

• Depends on the location and entities performing it

• A mix of commercial products and open source software

• Lebanon ISP’s use Free Software

• Syria uses commercial Blue Coat devices

• US/NSA use commercial Narus devices


Filtering taxonomy

• Logging (passive)

• Network and protocol Hijacking

• Injection (modify content, 302, rst etc.)

• Dropping (packets not transmitted)


Filter detection techniques

• Important to classify by risk profile

• People running filter detection tools must know how invasive the technique is


OONI

• Open Observatory of Network Interference

• I am working on this with Jacob Appelbaum as part of The Tor Project

• An extensible and flexible tool to perform censorship detection


Existing testing tools

• Netalyzr, rTurtle, Herdict.

• Unfortunately either the raw data results or even the tools themselves are closed :(

• They only release reports, without the original raw data


Goals for OONI

• Make a something Open Source and publish the raw data collected

• Have hackers write code and sociologist write reports ;)


Filtering detection techniques

• High risk and Active

• request for certain “bad” resources (test censorship lists)

• keyword injection

• anything that may trigger DPI devices

• Low risk and Active

• TTL walking

• Network latency

• Passive

• In the future proxooni to proxy traffic with a SOCKS proxy and detect anomalies as the user does his normal internet activities


Fingerprinting of the application

• Most existing tools that we audited leak who they are

• In OONI reports will only be submitted over Tor


The scientific method

• Control

• What you know is a good result

• It can also be a request done over Tor

• Experiment

• Check if it matches up with the result

• If it does not there is an anomaly that must be explored


Brief excursus on censorship in the

World


Syria: BlueCoat

• They are using commerical bluecoat devices

• Anonymous Telecomix contributors produced a good analysis


Syria: BlueCoat

• SERVER is located outside Syria

• CLIENT1 is located inside Syria

• CLIENT connects to SERVER port 5060, no connection

• CLIENT connects to SERVER port 443, connection works

• CLIENT connects to SERVER port 80, the headers in the response are rewritten


Syria: BlueCoatGET /HTTP/1.1Host: SERVER

User-Agent: Standard-browser-User-AgentAccept: text/html,etc.

Accept-Encoding: gzip,deflate,sdchAccept-Language: en-US,en;q=0.8

Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3X-Forwarded-For: CLIENTCache-Control: max-stale=0

Connection: Keep-AliveX-BlueCoat-Via: 2C044BEC00210EB6


Syria: BlueCoat

• More details and funness to come in the following days ;)


Funny ⅖ Off Topic discovery

• Who has ever used a captive portal?

• Skype makes you pay access with it’s credit

• It has problems doing login

• It uses a captive portal


Iran


Iran

• Nokia has reportedly sold equipment to the Iranian government. It helps wiretap, track, and crush dissenting members of Iranian society. Nokia claims that this is ethical because they were forced to put legal intercepts into their products by the West.


Italy

• Currently two methods are being used:

• DNS based

• ISP level blacklisting


libero.it


Free communications

• Are something that is important to the progress of humanity.


Questions?


Censorship Detection Techniques

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