Monitoring Internet Censorship

55 Pages·2013·4.6 MB·English

by  Giuseppe Aceto

Monitoring Internet
Censorship
part 2
Linux Day 2013
Napoli, October 26 2013
Giuseppe Aceto, [email protected]
Premise – quick check
 We are going to see some “mechanics” of the Internet
to explain how censorship works
 The description will avoid technicisms when possible
 No deep knowledge of computer networks will be implied
but possibly a little introduction to “the Internet” basics
SO
– How many of you knows what the DNS is?
– … and IP?
– … and HTTP?
– … IDS?
2 Monitoring Internet Censorship- Linux Day Napoli Oct.2013
Premise – quick check
 We are going to see some “mechanics” of the Internet
to explain how censorship works
 The description will avoid technicisms when possible
 No deep knowledge of computer networks will be implied
but possibly a little introduction to “the Internet” basics
SO
– How many of you knows what the DNS is?
– … and IP?
– … and HTTP?
– … IDS?
3 Monitoring Internet Censorship- Linux Day Napoli Oct.2013
Basics about Internet: packets
 Information is divided in packets
 Packets are forwarded along a path SENDER-to-RECEIVER by
several (usually<30) intermediate devices “routers”
 Packets are “labeled” with SENDER and RECEIVER
addresses (sort of phone numbers, called “IP addresses”)
– plus other details useful for the service
Mumbo Mumbo Mumbo
jumbo jumbo jumbo
4 Monitoring Internet Censorship- Linux Day Napoli Oct.2013
Basics about Internet: protocols
 The rules to write, split, label, forward, reassemble, read the
messages are called protocols
– Each one has its own business, some work together:
often are wrapped in layers
IP
TCP
HTTP
Content

 HyperText Trasfer Protocol is concerned with providing web
pages, identified by an Uniform Resource Locator (URL):
http://www.foo.org/abc/bar.html
protocol hostname path
5 Monitoring Internet Censorship- Linux Day Napoli Oct.2013
Basics about Internet: a lot happens
TCP
DNS
(connection setup)
(2) “foo.org”
(3) “1.2.3.4”
(1) Enter URL
http://foo.org/bar.html
(4) HTTP GET bar.html
(5) Locate the
(6) HTTP Response resource
(7) Parse HTML
& display
(8) HTTP GET image1
(N) HTTP GET imageX
Potentially many
requests & responses
Browser Web Server
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Access to content: an obstacle course
http://thenextweb.com/asia/2010/01/05/route-gfw-flow-chart/
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IP blocking
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9
Conventional Internet Censorship (1/2)
Censor
Firewall
Censored net
Uncensored net
Alice Block Traffic Bob
9 Monitoring Internet Censorship- Linux Day Napoli Oct.2013
10
Conventional Internet Censorship (2/2)
Censor
Firewall
Censored net
Uncensored net
Alice Block Traffic Bob
For the censor: easy, cheap,
but OVERBLOCKING issues
10 Monitoring Internet Censorship- Linux Day Napoli Oct.2013