<s>
The	B-Application
Great	I-Application
Firewall	I-Application
(	O
GFW	O
;	O
)	O
is	O
the	O
combination	O
of	O
legislative	O
actions	O
and	O
technologies	O
enforced	O
by	O
the	O
People	O
's	O
Republic	O
of	O
China	O
to	O
regulate	O
the	O
Internet	O
domestically	O
.	O
</s>
<s>
The	B-Application
Great	I-Application
Firewall	I-Application
operates	O
by	O
checking	O
transmission	B-Protocol
control	I-Protocol
protocol	I-Protocol
(	O
TCP	O
)	O
packets	O
for	O
keywords	O
or	O
sensitive	O
words	O
.	O
</s>
<s>
If	O
the	B-Application
keywords	I-Application
or	O
sensitive	O
words	O
appear	O
in	O
the	O
TCP	O
packets	O
,	O
access	O
will	O
be	O
closed	O
.	O
</s>
<s>
If	O
one	O
link	O
is	O
closed	O
,	O
more	O
links	O
from	O
the	O
same	O
machine	O
will	O
be	O
blocked	O
by	O
the	B-Application
Great	I-Application
Firewall	I-Application
.	O
</s>
<s>
Google	B-Application
Search	I-Application
,	O
Facebook	B-Application
,	O
Twitter	B-Application
,	O
Wikipedia	O
,	O
and	O
others	O
)	O
and	O
mobile	O
apps	O
,	O
and	O
requiring	O
foreign	O
companies	O
to	O
adapt	O
to	O
domestic	O
regulations	O
.	O
</s>
<s>
Besides	O
censorship	O
,	O
the	B-Application
Great	I-Application
Firewall	I-Application
has	O
also	O
influenced	O
the	O
development	O
of	O
China	O
's	O
internal	O
internet	O
economy	O
by	O
giving	O
preference	O
to	O
domestic	O
companies	O
and	O
reducing	O
the	O
effectiveness	O
of	O
products	O
from	O
foreign	O
internet	O
companies	O
.	O
</s>
<s>
The	O
techniques	O
deployed	O
by	O
the	O
Chinese	O
government	O
to	O
maintain	O
control	O
of	O
the	B-Application
Great	I-Application
Firewall	I-Application
can	O
include	O
modifying	O
search	O
results	O
for	O
terms	O
,	O
such	O
as	O
they	O
did	O
following	O
Ai	O
Weiwei	O
’s	O
arrest	O
,	O
and	O
petitioning	O
global	O
conglomerates	O
to	O
remove	O
content	O
,	O
as	O
happened	O
when	O
they	O
petitioned	O
Apple	O
to	O
remove	O
the	O
Quartz	O
business	O
news	O
publication	O
’s	O
app	O
from	O
its	O
Chinese	O
App	O
Store	O
after	O
reporting	O
on	O
the	O
2019	O
–	O
2020	O
Hong	O
Kong	O
protests	O
.	O
</s>
<s>
The	B-Application
Great	I-Application
Firewall	I-Application
was	O
formerly	O
operated	O
by	O
the	O
SIIO	O
,	O
as	O
part	O
of	O
the	O
Golden	O
Shield	O
Project	O
.	O
</s>
<s>
Since	O
2013	O
,	O
the	O
firewall	B-Application
is	O
technically	O
operated	O
by	O
the	O
Cyberspace	O
Administration	O
of	O
China	O
(	O
CAC	O
)	O
,	O
which	O
is	O
the	O
entity	O
in	O
charge	O
of	O
translating	O
the	O
Chinese	O
Communist	O
Party	O
's	O
doctrine	O
and	O
policy	O
into	O
technical	O
specifications	O
.	O
</s>
<s>
As	O
mentioned	O
in	O
the	O
"	O
one	O
country	O
,	O
two	O
systems	O
"	O
principle	O
,	O
China	O
's	O
special	O
administrative	O
regions	O
(	O
SARs	O
)	O
such	O
as	O
Hong	O
Kong	O
and	O
Macau	O
are	O
not	O
affected	O
by	O
the	O
firewall	B-Application
,	O
as	O
SARs	O
have	O
their	O
own	O
governmental	O
and	O
legal	O
systems	O
and	O
therefore	O
enjoy	O
a	O
higher	O
degree	O
of	O
autonomy	O
.	O
</s>
<s>
The	O
term	O
Great	B-Application
Firewall	I-Application
of	I-Application
China	I-Application
is	O
a	O
combination	O
of	O
the	O
word	O
firewall	B-Application
with	O
the	O
Great	O
Wall	O
of	O
China	O
.	O
</s>
<s>
The	O
phrase	O
"	O
Great	B-Application
Firewall	I-Application
of	I-Application
China	I-Application
"	O
was	O
first	O
used	O
in	O
print	O
by	O
Australian	O
sinologist	O
Geremie	O
Barmé	O
in	O
1997	O
.	O
</s>
<s>
At	O
the	O
exhibition	O
,	O
many	O
western	O
high-tech	O
products	O
,	O
including	O
Internet	B-Application
security	I-Application
,	O
video	O
monitoring	O
and	O
human	O
face	O
recognition	O
were	O
purchased	O
.	O
</s>
<s>
Fang	O
Binxing	O
is	O
known	O
for	O
his	O
substantial	O
contribution	O
to	O
China	O
's	O
Internet	O
censorship	O
infrastructure	O
,	O
and	O
has	O
been	O
dubbed	O
"	O
Father	O
of	O
China	O
's	O
Great	B-Application
Fire	I-Application
Wall	I-Application
"	O
.	O
</s>
<s>
The	O
latter	O
definition	O
of	O
online	O
activities	O
punishable	O
under	O
CL97	O
,	O
or	O
"	O
crimes	O
carried	O
out	O
over	O
computer	O
networks	O
"	O
,	O
is	O
used	O
as	O
justification	O
for	O
the	B-Application
Great	I-Application
Firewall	I-Application
,	O
and	O
can	O
be	O
cited	O
when	O
the	O
government	O
blocks	O
any	O
ISP	O
,	O
gateway	O
connections	O
,	O
or	O
any	O
access	O
to	O
anything	O
on	O
the	O
internet	O
.	O
</s>
<s>
Baidu	B-Application
over	O
Google	B-Application
.	I-Application
</s>
<s>
As	O
part	O
of	O
the	B-Application
Great	I-Application
Firewall	I-Application
,	O
beginning	O
in	O
2003	O
,	O
China	O
started	O
the	O
Golden	O
Shield	O
Project	O
,	O
a	O
massive	O
surveillance	O
and	O
censoring	O
system	O
,	O
the	O
hardware	O
for	O
which	O
was	O
provided	O
by	O
mostly	O
U.S.	O
companies	O
,	O
including	O
Cisco	O
Systems	O
.	O
</s>
<s>
However	O
,	O
by	O
late	O
2007	O
,	O
the	O
Golden	O
Shield	O
Project	O
proved	O
to	O
operate	O
sporadically	O
at	O
best	O
,	O
as	O
users	O
had	O
long	O
adapted	O
to	O
internet	O
blocking	O
by	O
using	O
proxy	B-Application
servers	I-Application
,	O
among	O
other	O
strategies	O
,	O
to	O
make	O
communications	O
and	O
circumnavigate	O
to	O
blocked	O
content	O
.	O
</s>
<s>
One	O
function	O
of	O
the	O
Chinese	O
firewall	B-Application
is	O
to	O
selectively	O
prevent	O
content	O
from	O
being	O
accessed	O
.	O
</s>
<s>
MethodDescriptionIP	O
range	O
ban	O
using	O
black	O
holesThe	O
Chinese	O
firewall	B-Application
maintains	O
a	O
list	O
of	O
IP	B-Protocol
ranges	I-Protocol
that	O
are	O
automatically	O
dropped	O
(	O
network	B-Protocol
black-holing	I-Protocol
)	O
.	O
</s>
<s>
Because	O
of	O
the	O
complexity	O
involved	O
in	O
maintaining	O
a	O
large	O
,	O
up-to-date	O
banned	O
network	O
list	O
with	O
dynamic	O
IPs	O
(	O
and	O
as	O
this	O
method	O
has	O
proven	O
incompatible	O
with	O
services	O
using	O
content	B-Operating_System
delivery	I-Operating_System
networks	I-Operating_System
)	O
it	O
is	O
usually	O
used	O
as	O
a	O
last	O
resort	O
,	O
with	O
other	O
blocking	O
methods	O
preferred	O
(	O
such	O
as	O
filtering	O
based	O
on	O
QoS	O
)	O
.	O
</s>
<s>
DNS	O
spoofing	O
,	O
filtering	O
and	O
redirectionOne	O
part	O
of	O
the	O
Chinese	O
firewall	B-Application
is	O
made	O
of	O
liar	O
DNS	O
servers	O
and	O
DNS	B-Protocol
hijackers	I-Protocol
returning	O
incorrect	O
IP	B-Protocol
addresses	I-Protocol
.	O
</s>
<s>
Contrary	O
to	O
popular	O
belief	O
,	O
foreign	O
DNS	O
resolvers	O
such	O
as	O
Google	B-Protocol
Public	I-Protocol
DNS	I-Protocol
IP	B-Protocol
address	I-Protocol
8.8.8.8	B-Protocol
are	O
reported	O
to	O
work	O
correctly	O
inside	O
the	O
country	O
;	O
however	O
,	O
these	O
DNS	O
servers	O
are	O
also	O
subject	O
to	O
hijacking	O
as	O
their	O
connections	O
are	O
not	O
encrypted	O
:	O
DNS	O
queries	O
do	O
reach	O
the	O
DNS	O
server	O
,	O
but	O
if	O
the	O
request	O
matches	O
a	O
banned	O
keyword	O
,	O
the	O
firewall	B-Application
will	O
inject	O
a	O
fake	O
DNS	O
reply	O
before	O
the	O
legitimate	O
DNS	O
reply	O
arrives	O
.	O
</s>
<s>
The	O
vast	O
majority	O
of	O
these	O
fake	O
responses	O
contain	O
public	O
IP	B-Protocol
addresses	I-Protocol
of	O
U.S.	O
companies	O
,	O
including	O
Facebook	B-Application
,	O
Twitter	B-Application
,	O
and	O
Dropbox	O
.	O
</s>
<s>
Typical	O
circumvention	O
methods	O
include	O
modifying	O
the	O
Hosts	B-Protocol
file	I-Protocol
,	O
typing	O
the	O
IP	B-Protocol
address	I-Protocol
instead	O
of	O
the	O
domain	O
name	O
in	O
a	O
Web	B-Application
browser	I-Application
or	O
using	O
DNS	O
over	O
TLS/HTTPS.URL	O
filtering	O
using	O
transparent	O
proxiesThe	O
Chinese	O
firewall	B-Application
is	O
made	O
of	O
transparent	O
proxies	O
filtering	O
web	O
traffic	O
.	O
</s>
<s>
These	O
proxies	O
scan	O
the	O
requested	O
URI	B-Protocol
,	O
the	O
"	O
Host	O
"	O
Header	O
and	O
the	O
content	O
of	O
the	O
web	O
page	O
(	O
for	O
HTTP	O
requests	O
)	O
or	O
the	O
Server	B-Protocol
Name	I-Protocol
Indication	I-Protocol
(	O
for	O
HTTPS	B-Protocol
requests	O
)	O
for	O
target	O
keywords	O
.	O
</s>
<s>
Encrypting	O
the	O
Server	B-Protocol
Name	I-Protocol
Indication	I-Protocol
can	O
be	O
used	O
to	O
bypass	O
this	O
method	O
of	O
filtering	O
.	O
</s>
<s>
It	O
is	O
currently	O
in	O
development	O
by	O
the	O
IETF	O
,	O
and	O
is	O
offered	O
as	O
a	O
setting	O
in	O
Firefox.Quality	O
of	O
service	O
filteringSince	O
2012	O
,	O
the	O
GFW	O
is	O
able	O
to	O
"	O
learn	O
,	O
filter	O
,	O
and	O
block	O
"	O
users	O
based	O
on	O
traffic	O
behavior	O
,	O
using	O
deep	B-Application
packet	I-Application
inspection	I-Application
.	O
</s>
<s>
This	O
method	O
was	O
originally	O
developed	O
for	O
blocking	O
VPNs	B-Application
and	O
has	O
been	O
extended	O
to	O
become	O
part	O
of	O
the	O
standard	O
filtering	O
system	O
of	O
the	O
GFW	O
.	O
</s>
<s>
The	O
method	O
works	O
by	O
mirroring	O
all	O
traffic	O
(	O
using	O
a	O
network	B-Device
tap	I-Device
)	O
to	O
a	O
dedicated	O
analytics	O
unit	O
,	O
that	O
will	O
then	O
deliver	O
a	O
score	O
for	O
each	O
destination	O
IP	O
based	O
on	O
how	O
suspicious	O
the	O
connection	O
is	O
deemed	O
to	O
be	O
.	O
</s>
<s>
This	O
score	O
is	O
then	O
used	O
to	O
determine	O
a	O
packet	B-Protocol
loss	I-Protocol
rate	I-Protocol
to	O
be	O
implemented	O
by	O
routers	O
of	O
the	O
Chinese	O
firewall	B-Application
,	O
resulting	O
in	O
a	O
slowed	O
connection	O
on	O
the	O
client	O
side	O
.	O
</s>
<s>
It	O
is	O
able	O
to	O
detect	O
traffic	O
protocols	O
(	O
such	O
as	O
SSH	O
tunneling	O
,	O
VPN	B-Application
or	O
Tor	B-Application
protocols	O
)	O
,	O
and	O
can	O
measure	O
the	O
entropy	O
of	O
packets	O
to	O
detect	O
encrypted-over-encrypted	O
traffic	O
(	O
such	O
as	O
HTTPS	B-Protocol
over	O
an	O
SSL	B-Protocol
tunnel	O
)	O
.	O
</s>
<s>
Packet	B-Protocol
forging	I-Protocol
and	O
TCP	O
reset	O
attacksThe	O
Chinese	O
firewall	B-Application
may	O
arbitrarily	O
terminate	O
TCP	O
transmissions	O
,	O
using	O
packet	B-Protocol
forging	I-Protocol
.	O
</s>
<s>
The	O
blocking	O
is	O
performed	O
using	O
a	O
TCP	B-Protocol
reset	I-Protocol
attack	I-Protocol
.	O
</s>
<s>
An	O
efficient	O
circumvention	O
method	O
is	O
to	O
ignore	O
the	O
reset	O
packet	O
sent	O
by	O
the	O
firewall	B-Application
.	O
</s>
<s>
Multiple	O
TLS	B-Protocol
incidents	O
have	O
occurred	O
within	O
the	O
last	O
decade	O
,	O
before	O
the	O
creation	O
of	O
the	O
law	O
.	O
</s>
<s>
On	O
26	O
January	O
2013	O
,	O
the	O
GitHub	B-Application
SSL	B-Protocol
certificate	O
was	O
replaced	O
with	O
a	O
self-signed	O
certificate	O
in	O
China	O
by	O
the	O
GFW	O
.	O
</s>
<s>
On	O
20	O
October	O
2014	O
,	O
the	O
iCloud	O
SSL	B-Protocol
certificate	O
was	O
replaced	O
with	O
a	O
self-signed	O
certificate	O
in	O
China	O
.	O
</s>
<s>
On	O
20	O
March	O
2015	O
,	O
Google	B-Application
detected	O
valid	O
certificates	O
for	O
Google	B-Application
signed	O
by	O
CNNIC	O
in	O
Egypt	O
.	O
</s>
<s>
In	O
response	O
to	O
this	O
event	O
,	O
and	O
after	O
a	O
deeper	O
investigation	O
,	O
the	O
CNNIC	O
certificate	O
was	O
removed	O
by	O
some	O
browsers	B-Application
.	O
</s>
<s>
Due	O
to	O
the	O
removal	O
being	O
based	O
on	O
proof	O
and	O
not	O
suspicion	O
,	O
no	O
other	O
Chinese	O
certificate	O
authority	O
has	O
been	O
removed	O
from	O
web	B-Application
browsers	I-Application
,	O
and	O
some	O
have	O
been	O
added	O
since	O
then	O
.	O
</s>
<s>
This	O
type	O
of	O
attack	O
can	O
be	O
circumvented	O
by	O
websites	O
implementing	O
Certificate	B-Protocol
Transparency	I-Protocol
and	O
OCSP	B-Protocol
stapling	I-Protocol
or	O
by	O
using	O
browser	B-Application
extensions	O
.	O
</s>
<s>
In	O
addition	O
to	O
previously	O
discussed	O
techniques	O
,	O
the	O
CAC	O
is	O
also	O
using	O
active	O
probing	O
in	O
order	O
to	O
identify	O
and	O
block	O
network	O
services	O
that	O
would	O
help	O
escaping	O
the	O
firewall	B-Application
.	O
</s>
<s>
Multiple	O
services	O
such	O
as	O
Tor	B-Application
or	O
VPN	B-Application
providers	O
reported	O
receiving	O
unsolicited	O
TCP/IP	O
connections	O
shortly	O
after	O
legitimate	O
use	O
,	O
for	O
the	O
purported	O
purpose	O
of	O
network	B-General_Concept
enumeration	I-General_Concept
of	O
services	O
,	O
in	O
particular	O
TLS/SSL	B-Protocol
and	O
Tor	B-Application
services	O
,	O
with	O
the	O
aim	O
of	O
facilitating	O
IP	O
blocking	O
.	O
</s>
<s>
For	O
example	O
,	O
shortly	O
after	O
a	O
VPN	B-Application
request	O
is	O
issued	O
by	O
a	O
legitimate	O
Chinese	O
VPN	B-Application
client	I-Application
and	O
passes	O
outbound	O
though	O
the	B-Application
Great	I-Application
Firewall	I-Application
to	O
a	O
hidden	O
VPN	B-Application
IP	O
,	O
the	B-Application
Great	I-Application
Firewall	I-Application
may	O
detect	O
the	O
activity	O
and	O
issue	O
its	O
own	O
active	O
probe	O
to	O
verify	O
the	O
nature	O
of	O
the	O
previously	O
unknown	O
VPN	B-Application
IP	O
and	O
,	O
if	O
the	O
probe	O
confirms	O
the	O
IP	O
is	O
part	O
of	O
a	O
blacklisted	O
VPN	B-Application
,	O
blacklist	O
the	O
IP	O
.	O
</s>
<s>
The	B-Application
Great	I-Application
Firewall	I-Application
scrapes	O
the	O
IPs	O
of	O
Tor	B-Application
and	O
VPN	B-Application
servers	I-Application
from	O
the	O
official	O
distribution	O
channels	O
,	O
and	O
enumerates	O
them	O
.	O
</s>
<s>
The	O
strategy	O
to	O
resist	O
this	O
attack	O
is	O
to	O
limit	O
the	O
quantity	O
of	O
proxy	B-Application
IPs	I-Application
revealed	O
to	O
each	O
user	O
and	O
making	O
it	O
very	O
difficult	O
for	O
users	O
to	O
create	O
more	O
than	O
one	O
identity	O
.	O
</s>
<s>
The	B-Application
Great	I-Application
Firewall	I-Application
's	O
goal	O
is	O
perceived	O
by	O
the	O
Communist	O
Party	O
as	O
helping	O
to	O
protect	O
the	O
Chinese	O
population	O
by	O
preventing	O
users	O
from	O
accessing	O
these	O
foreign	O
websites	O
which	O
,	O
in	O
their	O
opinion	O
,	O
host	O
content	O
which	O
would	O
be	O
'	O
spiritual	O
pollution	O
 '	O
,	O
( 清除精神污染运动	O
)	O
,	O
as	O
well	O
as	O
information	O
about	O
these	O
sensitive	O
topics	O
.	O
</s>
<s>
Specific	O
English	O
websites	O
blocked	O
or	O
filtered	O
include	O
many	O
popular	O
search	O
engines	O
,	O
social	O
media	O
platforms	O
,	O
information-hosting	O
sites	O
,	O
and	O
video-hosting	O
websites	O
such	O
as	O
Google	B-Application
Search	I-Application
,	O
Facebook	B-Application
,	O
Wikipedia	O
,	O
YouTube	B-General_Concept
,	O
Twitter	B-Application
,	O
and	O
many	O
more	O
.	O
</s>
<s>
The	O
Cybersecurity	O
Law	O
behind	O
the	O
firewall	B-Application
being	O
targeted	O
at	O
helping	O
increase	O
internet	O
user	O
privacy	O
,	O
increased	O
protections	O
on	O
personal	O
data	O
,	O
and	O
making	O
companies	O
more	O
responsible	O
for	O
monitoring	O
bad	O
actors	O
,	O
in	O
hopes	O
to	O
make	O
a	O
safer	O
place	O
on	O
the	O
internet	O
for	O
Chinese	O
citizens	O
.	O
</s>
<s>
Censorship	O
of	O
sensitive	O
topics	O
in	O
China	O
has	O
also	O
been	O
easier	O
for	O
the	O
government	O
because	O
of	O
the	O
firewall	B-Application
and	O
its	O
filtering	O
.	O
</s>
<s>
Aside	O
from	O
the	O
social	O
control	O
aspect	O
,	O
the	B-Application
Great	I-Application
Firewall	I-Application
also	O
acts	O
as	O
a	O
form	O
of	O
trade	O
protectionism	O
that	O
has	O
allowed	O
China	O
to	O
grow	O
its	O
own	O
internet	O
giants	O
,	O
such	O
as	O
Tencent	O
,	O
Alibaba	O
,	O
and	O
Baidu	B-Application
.	O
</s>
<s>
China	O
has	O
its	O
own	O
version	O
of	O
many	O
foreign	O
web	O
properties	O
,	O
for	O
example	O
:	O
Bilibili	O
and	O
Tencent	O
Video	O
(	O
YouTube	B-General_Concept
)	O
,	O
Sina	B-Protocol
Weibo	I-Protocol
(	O
Twitter	B-Application
)	O
,	O
Qzone	O
(	O
Facebook	B-Application
)	O
,	O
WeChat	B-Application
(	O
WhatsApp	O
)	O
,	O
Ctrip	O
(	O
Orbitz	O
and	O
others	O
)	O
,	O
and	O
Zhihu	O
(	O
Quora	O
)	O
.	O
</s>
<s>
While	O
the	B-Application
Great	I-Application
Firewall	I-Application
has	O
had	O
an	O
impact	O
on	O
Chinese	O
citizens	O
 '	O
ability	O
to	O
use	O
the	O
internet	O
to	O
find	O
information	O
about	O
sensitive	O
topics	O
about	O
the	O
Communist	O
Party	O
,	O
it	O
has	O
not	O
completely	O
stopped	O
them	O
from	O
doing	O
so	O
.	O
</s>
<s>
The	O
firewall	B-Application
itself	O
has	O
caused	O
much	O
frustration	O
amongst	O
both	O
individuals	O
and	O
internationally	O
operating	O
companies	O
in	O
China	O
,	O
many	O
of	O
whom	O
have	O
turned	O
to	O
VPNs	B-Application
,	O
speaking	O
in	O
codes	O
,	O
and	O
other	O
methods	O
to	O
retain	O
their	O
access	O
to	O
the	O
international	O
internet	O
.	O
</s>
<s>
The	O
use	O
of	O
VPNs	B-Application
in	O
China	O
can	O
provide	O
individuals	O
access	O
to	O
the	O
international	O
internet	O
,	O
but	O
in	O
China	O
,	O
it	O
can	O
be	O
a	O
potential	O
legal	O
risk	O
.	O
</s>
<s>
In	O
2017	O
,	O
the	O
Chinese	O
government	O
declared	O
all	O
unauthorized	O
VPN	B-Application
services	O
to	O
be	O
illegal	O
.	O
</s>
<s>
An	O
example	O
of	O
the	O
use	O
of	O
this	O
punishment	O
is	O
Vera	O
Zhou	O
,	O
a	O
student	O
at	O
the	O
University	O
of	O
Washington	O
,	O
who	O
,	O
when	O
visiting	O
her	O
Hui	O
parents	O
in	O
Xinjiang	O
,	O
China	O
,	O
used	O
a	O
VPN	B-Application
to	O
access	O
her	O
school	O
homework	O
.	O
</s>
<s>
Because	O
the	B-Application
Great	I-Application
Firewall	I-Application
blocks	O
destination	O
IP	B-Protocol
addresses	I-Protocol
and	O
domain	O
names	O
and	O
inspects	O
the	O
data	O
being	O
sent	O
or	O
received	O
,	O
a	O
basic	O
censorship	B-Application
circumvention	I-Application
strategy	O
is	O
to	O
use	O
proxy	O
nodes	O
and	O
encrypt	O
the	O
data	O
.	O
</s>
<s>
Bypassing	O
the	O
firewall	B-Application
is	O
known	O
as	O
( 翻墙	O
,	O
"	O
climb	O
over	O
the	O
wall	O
"	O
)	O
,	O
and	O
most	O
circumvention	O
tools	O
combine	O
these	O
two	O
mechanisms	O
:	O
</s>
<s>
Proxy	B-Application
servers	I-Application
outside	O
China	O
can	O
be	O
used	O
,	O
although	O
using	O
just	O
a	O
simple	O
open	B-Protocol
proxy	I-Protocol
(	O
HTTP	O
or	O
SOCKS	O
)	O
without	O
also	O
using	O
an	O
encrypted	O
tunnel	O
(	O
such	O
as	O
HTTPS	B-Protocol
)	O
does	O
little	O
to	O
circumvent	O
the	O
sophisticated	O
censors	O
.	O
</s>
<s>
Freegate	B-Application
,	O
Ultrasurf	B-Application
,	O
Psiphon	B-Application
,	O
and	O
Lantern	B-Language
are	O
free	O
programs	O
designed	O
and	O
experienced	O
with	O
circumventing	O
the	O
China	O
firewall	B-Application
using	O
multiple	O
open	B-Protocol
proxies	I-Protocol
.	O
</s>
<s>
VPNs	B-Application
(	O
virtual	B-Application
private	I-Application
networks	I-Application
)	O
are	O
one	O
of	O
the	O
most	O
popular	O
tools	O
used	O
by	O
Westerners	O
for	O
bypassing	O
censorship	O
technologies	O
.	O
</s>
<s>
They	O
use	O
the	O
same	O
basic	O
approaches	O
,	O
proxies	O
,	O
and	O
encrypted	O
channels	O
used	O
by	O
other	O
circumvention	O
tools	O
,	O
but	O
depend	O
on	O
a	O
private	O
host	O
,	O
a	O
virtual	O
host	O
,	O
or	O
an	O
account	O
outside	O
of	O
China	O
,	O
rather	O
than	O
open	O
,	O
free	B-Application
proxies	I-Application
.	O
</s>
<s>
Tor	B-Application
partially	O
can	O
be	O
used	O
in	O
China	O
.	O
</s>
<s>
Since	O
2010	O
,	O
almost	O
all	O
bridges	O
at	O
TorProject.org	B-Application
are	O
blocked	O
through	O
proxy	O
distribution	O
.	O
</s>
<s>
Tor	B-Application
still	O
functions	O
in	O
China	O
using	O
Snowflake	O
,	O
independently	O
published	O
Obfs4	O
bridges	O
and	O
meek	O
.	O
</s>
<s>
I2P	B-Protocol
or	O
garlic	B-Protocol
routing	I-Protocol
is	O
useful	O
when	O
properties	O
similar	O
to	O
Tor	B-Application
's	O
anonymity	O
are	O
needed	O
.	O
</s>
<s>
Due	O
to	O
I2P	B-Protocol
being	O
much	O
less	O
popular	O
than	O
Tor	B-Application
,	O
it	O
has	O
faced	O
little	O
to	O
no	O
blocking	O
attempts	O
.	O
</s>
<s>
Using	O
encrypted	B-Protocol
DNS	I-Protocol
may	O
bypass	O
blocking	O
of	O
a	O
few	O
sites	O
including	O
TorProject	O
and	O
all	O
of	O
GitHub	B-Application
,	O
which	O
may	O
be	O
used	O
to	O
obtain	O
further	O
circumvention	O
.	O
</s>
<s>
In	O
2019	O
Firefox	O
released	O
an	O
update	O
to	O
make	O
it	O
easy	O
to	O
enable	O
DNS	B-Protocol
over	I-Protocol
HTTPS	I-Protocol
.	O
</s>
<s>
There	O
is	O
a	O
popular	O
rumour	O
that	O
using	O
IPv6	B-Protocol
bypasses	O
DPI	B-Application
filtering	O
in	O
China	O
.	O
</s>
<s>
The	O
OpenVPN	B-Language
protocol	O
is	O
detected	O
and	O
blocked	O
.	O
</s>
<s>
Connections	O
not	O
using	O
symmetric	O
keys	O
or	O
using	O
"	O
tls-auth	O
"	O
are	O
blocked	O
at	O
handshake	O
,	O
and	O
connections	O
using	O
the	O
new	O
"	O
tls-crypt	O
"	O
option	O
are	O
detected	O
and	O
throttled	O
(	O
under	O
56kbit/s	O
)	O
by	O
the	O
QoS	O
filtering	O
system	O
.	O
</s>
<s>
GRE	B-Protocol
tunnels	I-Protocol
and	O
protocols	O
that	O
use	O
GRE	B-Protocol
(	O
e.g.	O
,	O
PPTP	B-Protocol
)	O
are	O
blocked	O
.	O
</s>
<s>
TLS	B-Protocol
,	O
the	B-Application
Great	I-Application
Firewall	I-Application
can	O
identify	O
the	O
difference	O
between	O
HTTPS	B-Protocol
TLS	B-Protocol
and	O
other	O
implementations	O
by	O
inspecting	O
the	O
handshake	O
parameters	O
.	O
</s>
<s>
In	O
2010	O
,	O
a	O
root	B-Application
name	I-Application
server	I-Application
run	O
by	O
Netrod	O
in	O
China	O
started	O
returning	O
poisoned	O
DNS	O
results	O
to	O
global	O
users	O
,	O
preventing	O
users	O
in	O
Chile	O
and	O
the	O
U.S.	O
from	O
accessing	O
sites	O
such	O
as	O
Facebook	B-Application
.	I-Application
</s>
<s>
Since	O
at	O
least	O
2015	O
,	O
the	O
Russian	O
Roskomnadzor	O
agency	O
collaborates	O
with	O
Chinese	B-Application
Great	I-Application
Firewall	I-Application
security	O
officials	O
in	O
implementing	O
its	O
data	O
retention	O
and	O
filtering	O
infrastructure	O
.	O
</s>
<s>
Especially	O
since	O
2022	O
Russian	O
invasion	O
of	O
Ukraine	O
,	O
in	O
order	O
to	O
combat	O
disinformation	O
and	O
enforce	O
the	O
war	O
censorship	O
law	O
,	O
Russian	O
authorities	O
were	O
making	O
an	O
internet	O
surveillance	O
system	O
akin	O
to	O
Chinese	B-Application
Great	I-Application
Firewall	I-Application
.	O
</s>
<s>
The	O
United	O
States	O
Trade	O
Representative	O
's	O
(	O
USTR	O
)	O
"	O
National	O
Trade	O
Estimate	O
Report	O
"	O
in	O
2016	O
referred	O
the	O
China	O
's	O
digital	O
Great	B-Application
Firewall	I-Application
:	O
"	O
China	O
's	O
filtering	O
of	O
cross-border	O
Internet	O
traffic	O
has	O
posed	O
a	O
significant	O
burden	O
to	O
foreign	O
suppliers.	O
"	O
</s>
<s>
Claude	O
Barfield	O
,	O
the	O
American	O
Enterprise	O
Institute	O
's	O
expert	O
of	O
International	O
trade	O
,	O
suggested	O
that	O
the	O
U.S.	O
government	O
should	O
bring	O
a	O
case	O
against	O
the	O
Firewall	B-Application
,	O
a	O
huge	O
trade	O
barrier	O
,	O
in	O
the	O
World	O
Trade	O
Organization	O
in	O
January	O
2017	O
.	O
</s>
<s>
Eight	O
of	O
the	O
24	O
more	O
trafficked	O
websites	O
in	O
China	O
have	O
been	O
blocked	O
by	O
the	B-Application
Great	I-Application
Firewall	I-Application
.	O
</s>
