<s>
HTTP	B-Application
cookies	I-Application
(	O
also	O
called	O
web	B-Application
cookies	I-Application
,	O
Internet	B-Application
cookies	I-Application
,	O
browser	B-Application
cookies	I-Application
,	O
or	O
simply	O
cookies	B-Application
)	O
are	O
small	O
blocks	O
of	O
data	B-General_Concept
created	O
by	O
a	O
web	B-Application
server	I-Application
while	O
a	O
user	O
is	O
browsing	O
a	O
website	O
and	O
placed	O
on	O
the	O
user	O
's	O
computer	O
or	O
other	O
device	O
by	O
the	O
user	O
's	O
web	B-Application
browser	I-Application
.	O
</s>
<s>
Cookies	B-Application
are	O
placed	O
on	O
the	O
device	O
used	O
to	O
access	O
a	O
website	O
,	O
and	O
more	O
than	O
one	O
cookie	B-Application
may	O
be	O
placed	O
on	O
a	O
user	O
's	O
device	O
during	O
a	O
session	O
.	O
</s>
<s>
Cookies	B-Application
serve	O
useful	O
and	O
sometimes	O
essential	O
functions	O
on	O
the	O
web	O
.	O
</s>
<s>
They	O
enable	O
web	B-Application
servers	I-Application
to	O
store	O
stateful	B-Application
information	O
(	O
such	O
as	O
items	O
added	O
in	O
the	O
shopping	O
cart	O
in	O
an	O
online	O
store	O
)	O
on	O
the	O
user	O
's	O
device	O
or	O
to	O
track	O
the	O
user	O
's	O
browsing	O
activity	O
(	O
including	O
clicking	O
particular	O
buttons	O
,	O
logging	O
in	O
,	O
or	O
recording	O
which	O
pages	B-Protocol
were	I-Protocol
visited	I-Protocol
in	I-Protocol
the	I-Protocol
past	I-Protocol
)	O
.	O
</s>
<s>
Authentication	B-Application
cookies	I-Application
are	O
commonly	O
used	O
by	O
web	B-Application
servers	I-Application
to	O
authenticate	O
that	O
a	O
user	O
is	O
logged	O
in	O
,	O
and	O
with	O
which	O
account	O
they	O
are	O
logged	O
in	O
.	O
</s>
<s>
Without	O
the	O
cookie	B-Application
,	O
users	O
would	O
need	O
to	O
authenticate	O
themselves	O
by	O
logging	O
in	O
on	O
each	O
page	O
containing	O
sensitive	O
information	O
that	O
they	O
wish	O
to	O
access	O
.	O
</s>
<s>
The	O
security	O
of	O
an	O
authentication	B-Application
cookie	I-Application
generally	O
depends	O
on	O
the	O
security	O
of	O
the	O
issuing	O
website	O
and	O
the	O
user	O
's	O
web	B-Application
browser	I-Application
,	O
and	O
on	O
whether	O
the	O
cookie	B-Application
data	B-General_Concept
is	O
encrypted	O
.	O
</s>
<s>
Security	O
vulnerabilities	O
may	O
allow	O
a	O
cookie	B-Application
's	O
data	B-General_Concept
to	O
be	O
read	O
by	O
an	O
attacker	O
,	O
used	O
to	O
gain	O
access	O
to	O
user	O
data	B-General_Concept
,	O
or	O
used	O
to	O
gain	O
access	O
(	O
with	O
the	O
user	O
's	O
credentials	O
)	O
to	O
the	O
website	O
to	O
which	O
the	O
cookie	B-Application
belongs	O
(	O
see	O
cross-site	O
scripting	O
and	O
cross-site	B-Protocol
request	I-Protocol
forgery	I-Protocol
for	O
examples	O
)	O
.	O
</s>
<s>
Tracking	B-Application
cookies	B-Application
,	O
and	O
especially	O
third-party	O
tracking	B-Application
cookies	B-Application
,	O
are	O
commonly	O
used	O
as	O
ways	O
to	O
compile	O
long-term	O
records	O
of	O
individuals	O
 '	O
browsing	B-Protocol
histories	I-Protocol
a	O
potential	O
privacy	O
concern	O
that	O
prompted	O
European	O
and	O
U.S.	O
lawmakers	O
to	O
take	O
action	O
in	O
2011	O
.	O
</s>
<s>
European	O
law	O
requires	O
that	O
all	O
websites	O
targeting	O
European	O
Union	O
member	O
states	B-Application
gain	O
"	O
informed	O
consent	O
"	O
from	O
users	O
before	O
storing	O
non-essential	O
cookies	B-Application
on	O
their	O
device	O
.	O
</s>
<s>
The	O
term	O
cookie	B-Application
was	O
coined	O
by	O
web-browser	B-Application
programmer	O
Lou	O
Montulli	O
.	O
</s>
<s>
It	O
was	O
derived	O
from	O
the	O
term	O
magic	O
cookie	B-Application
,	O
which	O
is	O
a	O
packet	O
of	O
data	B-General_Concept
a	O
program	O
receives	O
and	O
sends	O
back	O
unchanged	O
,	O
used	O
by	O
Unix	B-Application
programmers	O
.	O
</s>
<s>
The	O
term	O
magic	O
cookie	B-Application
itself	O
derives	O
from	O
the	O
fortune	O
cookie	B-Application
,	O
a	O
wafer	O
with	O
a	O
paper	O
message	O
inside	O
.	O
</s>
<s>
Magic	O
cookies	B-Application
were	O
already	O
used	O
in	O
computing	O
when	O
computer	O
programmer	O
Lou	O
Montulli	O
had	O
the	O
idea	O
of	O
using	O
them	O
in	O
web	O
communications	O
in	O
June	O
1994	O
.	O
</s>
<s>
MCI	O
did	O
not	O
want	O
its	O
servers	O
to	O
have	O
to	O
retain	O
partial	O
transaction	O
states	B-Application
,	O
which	O
led	O
them	O
to	O
ask	O
Netscape	O
to	O
find	O
a	O
way	O
to	O
store	O
that	O
state	O
in	O
each	O
user	O
's	O
computer	O
instead	O
.	O
</s>
<s>
Cookies	B-Application
provided	O
a	O
solution	O
to	O
the	O
problem	O
of	O
reliably	O
implementing	O
a	O
virtual	B-Application
shopping	I-Application
cart	I-Application
.	O
</s>
<s>
Together	O
with	O
John	O
Giannandrea	O
,	O
Montulli	O
wrote	O
the	O
initial	O
Netscape	O
cookie	B-Application
specification	O
the	O
same	O
year	O
.	O
</s>
<s>
Version	O
0.9beta	O
of	O
Mosaic	B-Protocol
Netscape	I-Protocol
,	O
released	O
on	O
October	O
13	O
,	O
1994	O
,	O
supported	O
cookies	B-Application
.	O
</s>
<s>
The	O
first	O
use	O
of	O
cookies	B-Application
(	O
out	O
of	O
the	O
labs	O
)	O
was	O
checking	O
whether	O
visitors	O
to	O
the	O
Netscape	O
website	O
had	O
already	O
visited	O
the	O
site	O
.	O
</s>
<s>
Montulli	O
applied	O
for	O
a	O
patent	O
for	O
the	O
cookie	B-Application
technology	O
in	O
1995	O
,	O
which	O
was	O
granted	O
in	O
1998	O
.	O
</s>
<s>
Support	O
for	O
cookies	B-Application
was	O
integrated	O
with	O
Internet	B-Application
Explorer	I-Application
in	O
version	O
2	O
,	O
released	O
in	O
October	O
1995	O
.	O
</s>
<s>
The	O
introduction	O
of	O
cookies	B-Application
was	O
not	O
widely	O
known	O
to	O
the	O
public	O
at	O
the	O
time	O
.	O
</s>
<s>
In	O
particular	O
,	O
cookies	B-Application
were	O
accepted	O
by	O
default	O
,	O
and	O
users	O
were	O
not	O
notified	O
of	O
their	O
presence	O
.	O
</s>
<s>
The	O
public	O
learned	O
about	O
cookies	B-Application
after	O
the	O
Financial	O
Times	O
published	O
an	O
article	O
about	O
them	O
on	O
February	O
12	O
,	O
1996	O
.	O
</s>
<s>
In	O
the	O
same	O
year	O
,	O
cookies	B-Application
received	O
a	O
lot	O
of	O
media	O
attention	O
,	O
especially	O
because	O
of	O
potential	O
privacy	O
implications	O
.	O
</s>
<s>
Cookies	B-Application
were	O
discussed	O
in	O
two	O
U.S.	O
Federal	O
Trade	O
Commission	O
hearings	O
in	O
1996	O
and	O
1997	O
.	O
</s>
<s>
The	O
development	O
of	O
the	O
formal	O
cookie	B-Application
specifications	O
was	O
already	O
ongoing	O
.	O
</s>
<s>
Two	O
alternative	O
proposals	O
for	O
introducing	O
state	O
in	O
HTTP	B-Protocol
transactions	O
had	O
been	O
proposed	O
by	O
Brian	O
Behlendorf	O
and	O
David	O
Kristol	O
respectively	O
.	O
</s>
<s>
In	O
February	O
1996	O
,	O
the	O
working	O
group	O
identified	O
third-party	O
cookies	B-Application
as	O
a	O
considerable	O
privacy	O
threat	O
.	O
</s>
<s>
It	O
specifies	O
that	O
third-party	O
cookies	B-Application
were	O
either	O
not	O
allowed	O
at	O
all	O
,	O
or	O
at	O
least	O
not	O
enabled	O
by	O
default	O
.	O
</s>
<s>
At	O
this	O
time	O
,	O
advertising	O
companies	O
were	O
already	O
using	O
third-party	O
cookies	B-Application
.	O
</s>
<s>
The	O
recommendation	O
about	O
third-party	O
cookies	B-Application
of	O
RFC	O
2109	O
was	O
not	O
followed	O
by	O
Netscape	O
and	O
Internet	B-Application
Explorer	I-Application
.	O
</s>
<s>
RFC	O
2965	O
added	O
a	O
Set-Cookie2	O
header	B-Protocol
field	I-Protocol
,	O
which	O
informally	O
came	O
to	O
be	O
called	O
"	O
RFC	O
2965-style	O
cookies	B-Application
"	O
as	O
opposed	O
to	O
the	O
original	O
Set-Cookie	O
header	B-Protocol
field	I-Protocol
which	O
was	O
called	O
"	O
Netscape-style	O
cookies	B-Application
"	O
.	O
</s>
<s>
Set-Cookie2	O
was	O
seldom	O
used	O
,	O
however	O
,	O
and	O
was	O
deprecated	B-General_Concept
in	O
RFC	O
6265	O
in	O
April	O
2011	O
which	O
was	O
written	O
as	O
a	O
definitive	O
specification	O
for	O
cookies	B-Application
as	O
used	O
in	O
the	O
real	O
world	O
.	O
</s>
<s>
No	O
modern	O
browser	B-Application
recognizes	O
the	O
Set-Cookie2	O
header	B-Protocol
field	I-Protocol
.	O
</s>
<s>
A	O
session	O
cookie	B-Application
(	O
also	O
known	O
as	O
an	O
in-memory	O
cookie	B-Application
,	O
transient	O
cookie	B-Application
or	O
non-persistent	O
cookie	B-Application
)	O
exists	O
only	O
in	O
temporary	O
memory	O
while	O
the	O
user	O
navigates	O
a	O
website	O
.	O
</s>
<s>
Session	O
cookies	B-Application
expire	O
or	O
are	O
deleted	O
when	O
the	O
user	O
closes	O
the	O
web	B-Application
browser	I-Application
.	O
</s>
<s>
Session	O
cookies	B-Application
are	O
identified	O
by	O
the	O
browser	B-Application
by	O
the	O
absence	O
of	O
an	O
expiration	O
date	O
assigned	O
to	O
them	O
.	O
</s>
<s>
A	O
persistent	O
cookie	B-Application
expires	O
at	O
a	O
specific	O
date	O
or	O
after	O
a	O
specific	O
length	O
of	O
time	O
.	O
</s>
<s>
For	O
the	O
persistent	O
cookie	B-Application
's	O
lifespan	O
set	O
by	O
its	O
creator	O
,	O
its	O
information	O
will	O
be	O
transmitted	O
to	O
the	O
server	O
every	O
time	O
the	O
user	O
visits	O
the	O
website	O
that	O
it	O
belongs	O
to	O
,	O
or	O
every	O
time	O
the	O
user	O
views	O
a	O
resource	O
belonging	O
to	O
that	O
website	O
from	O
another	O
website	O
(	O
such	O
as	O
an	O
advertisement	O
)	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
persistent	O
cookies	B-Application
are	O
sometimes	O
referred	O
to	O
as	O
tracking	B-Application
cookies	B-Application
because	O
they	O
can	O
be	O
used	O
by	O
advertisers	O
to	O
record	O
information	O
about	O
a	O
user	O
's	O
web	O
browsing	O
habits	O
over	O
an	O
extended	O
period	O
of	O
time	O
.	O
</s>
<s>
Persistent	O
cookies	B-Application
are	O
also	O
used	O
for	O
reasons	O
such	O
as	O
keeping	O
users	O
logged	O
into	O
their	O
accounts	O
on	O
websites	O
,	O
to	O
avoid	O
re-entering	O
login	O
credentials	O
at	O
every	O
visit	O
.	O
</s>
<s>
A	O
secure	B-Application
cookie	I-Application
can	O
only	O
be	O
transmitted	O
over	O
an	O
encrypted	O
connection	O
(	O
i.e.	O
</s>
<s>
HTTPS	B-Protocol
)	O
.	O
</s>
<s>
HTTP	B-Protocol
)	O
.	O
</s>
<s>
This	O
makes	O
the	O
cookie	B-Application
less	O
likely	O
to	O
be	O
exposed	O
to	O
cookie	B-Application
theft	O
via	O
eavesdropping	B-Protocol
.	O
</s>
<s>
A	O
cookie	B-Application
is	O
made	O
secure	O
by	O
adding	O
the	O
Secure	O
flag	O
to	O
the	O
cookie	B-Application
.	O
</s>
<s>
An	O
http-only	O
cookie	B-Application
cannot	O
be	O
accessed	O
by	O
client-side	O
APIs	O
,	O
such	O
as	O
JavaScript	B-Language
.	O
</s>
<s>
This	O
restriction	O
eliminates	O
the	O
threat	O
of	O
cookie	B-Application
theft	O
via	O
cross-site	O
scripting	O
(	O
XSS	O
)	O
.	O
</s>
<s>
However	O
,	O
the	O
cookie	B-Application
remains	O
vulnerable	O
to	O
cross-site	B-Protocol
tracing	I-Protocol
(	O
XST	O
)	O
and	O
cross-site	B-Protocol
request	I-Protocol
forgery	I-Protocol
(	O
CSRF	B-Protocol
)	O
attacks	O
.	O
</s>
<s>
A	O
cookie	B-Application
is	O
given	O
this	O
characteristic	O
by	O
adding	O
the	O
HttpOnly	O
flag	O
to	O
the	O
cookie	B-Application
.	O
</s>
<s>
In	O
2016	O
Google	B-Application
Chrome	I-Application
version	O
51	O
introduced	O
a	O
new	O
kind	O
of	O
cookie	B-Application
with	O
attribute	O
SameSite	O
.	O
</s>
<s>
With	O
attribute	O
SameSite	O
=	O
Strict	O
,	O
the	O
browsers	B-Application
would	O
only	O
send	O
cookies	B-Application
to	O
a	O
target	O
domain	O
that	O
is	O
the	O
same	O
as	O
the	O
origin	O
domain	O
.	O
</s>
<s>
This	O
would	O
effectively	O
mitigate	O
cross-site	B-Protocol
request	I-Protocol
forgery	I-Protocol
(	O
CSRF	B-Protocol
)	O
attacks	O
.	O
</s>
<s>
With	O
SameSite	O
=	O
Lax	O
,	O
browsers	B-Application
would	O
send	O
cookies	B-Application
with	O
requests	O
to	O
a	O
target	O
domain	O
even	O
it	O
is	O
different	O
from	O
the	O
origin	O
domain	O
,	O
but	O
only	O
for	O
safe	O
requests	O
such	O
as	O
GET	O
(	O
POST	O
is	O
unsafe	O
)	O
and	O
not	O
third-party	O
cookies	B-Application
(	O
inside	O
iframe	O
)	O
.	O
</s>
<s>
Attribute	O
SameSite	O
=	O
None	O
would	O
allow	O
third-party	O
(	O
cross-site	O
)	O
cookies	B-Application
,	O
however	O
,	O
most	O
browsers	B-Application
require	O
secure	O
attribute	O
on	O
SameSite	O
=	O
None	O
cookies	B-Application
.	O
</s>
<s>
The	O
Same-site	O
cookie	B-Application
is	O
incorporated	O
into	O
to	O
update	O
RFC	O
6265	O
(	O
if	O
approved	O
)	O
.	O
</s>
<s>
Chrome	B-Application
,	O
Firefox	B-Application
,	O
Microsoft	O
Edge	O
all	O
started	O
to	O
support	O
Same-site	O
cookies	B-Application
.	O
</s>
<s>
The	O
key	O
of	O
rollout	O
is	O
the	O
treatment	O
of	O
existing	O
cookies	B-Application
without	O
the	O
SameSite	O
attribute	O
defined	O
,	O
Chrome	B-Application
has	O
been	O
treating	O
those	O
existing	O
cookies	B-Application
as	O
if	O
SameSite	O
=	O
None	O
,	O
this	O
would	O
keep	O
all	O
website/applications	O
run	O
as	O
before	O
.	O
</s>
<s>
Google	B-Application
intended	O
to	O
change	O
that	O
default	O
to	O
SameSite	O
=	O
Lax	O
in	O
February	O
2020	O
,	O
the	O
change	O
would	O
break	O
those	O
applications/websites	O
that	O
rely	O
on	O
third-party/cross	O
-site	O
cookies	B-Application
,	O
but	O
without	O
SameSite	O
attribute	O
defined	O
.	O
</s>
<s>
Given	O
the	O
extensive	O
changes	O
for	O
web	O
developers	O
and	O
COVID-19	O
circumstances	O
,	O
Google	B-Application
temporarily	O
rolled	O
back	O
the	O
SameSite	O
cookie	B-Application
change	O
.	O
</s>
<s>
A	O
supercookie	O
is	O
a	O
cookie	B-Application
with	O
an	O
origin	O
of	O
a	O
top-level	O
domain	O
(	O
such	O
as	O
.com	O
)	O
or	O
a	O
public	O
suffix	O
(	O
such	O
as	O
.co.uk	O
)	O
.	O
</s>
<s>
Ordinary	O
cookies	B-Application
,	O
by	O
contrast	O
,	O
have	O
an	O
origin	O
of	O
a	O
specific	O
domain	O
name	O
,	O
such	O
as	O
example.com	O
.	O
</s>
<s>
Supercookies	O
can	O
be	O
a	O
potential	O
security	O
concern	O
and	O
are	O
therefore	O
often	O
blocked	O
by	O
web	B-Application
browsers	I-Application
.	O
</s>
<s>
If	O
unblocked	O
by	O
the	O
browser	B-Application
,	O
an	O
attacker	O
in	O
control	O
of	O
a	O
malicious	O
website	O
could	O
set	O
a	O
supercookie	O
and	O
potentially	O
disrupt	O
or	O
impersonate	O
legitimate	O
user	O
requests	O
to	O
another	O
website	O
that	O
shares	O
the	O
same	O
top-level	O
domain	O
or	O
public	O
suffix	O
as	O
the	O
malicious	O
website	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
supercookie	O
with	O
an	O
origin	O
of	O
.com	O
,	O
could	O
maliciously	O
affect	O
a	O
request	O
made	O
to	O
example.com,	O
even	O
if	O
the	O
cookie	B-Application
did	O
not	O
originate	O
from	O
example.com	O
.	O
</s>
<s>
The	O
Public	B-Protocol
Suffix	I-Protocol
List	I-Protocol
helps	O
to	O
mitigate	O
the	O
risk	O
that	O
supercookies	O
pose	O
.	O
</s>
<s>
The	O
Public	B-Protocol
Suffix	I-Protocol
List	I-Protocol
is	O
a	O
cross-vendor	O
initiative	O
that	O
aims	O
to	O
provide	O
an	O
accurate	O
and	O
up-to-date	O
list	O
of	O
domain	O
name	O
suffixes	O
.	O
</s>
<s>
Older	O
versions	O
of	O
browsers	B-Application
may	O
not	O
have	O
an	O
up-to-date	O
list	O
,	O
and	O
will	O
therefore	O
be	O
vulnerable	O
to	O
supercookies	O
from	O
certain	O
domains	O
.	O
</s>
<s>
The	O
term	O
supercookie	O
is	O
sometimes	O
used	O
for	O
tracking	B-Application
technologies	O
that	O
do	O
not	O
rely	O
on	O
HTTP	B-Application
cookies	I-Application
.	O
</s>
<s>
Two	O
such	O
supercookie	O
mechanisms	O
were	O
found	O
on	O
Microsoft	O
websites	O
in	O
August	O
2011	O
:	O
cookie	B-Application
syncing	O
that	O
respawned	O
MUID	O
(	O
machine	O
unique	O
identifier	O
)	O
cookies	B-Application
,	O
and	O
ETag	B-Protocol
cookies	B-Application
.	O
</s>
<s>
In	O
a	O
2021	O
blog	O
post	O
,	O
Mozilla	O
used	O
the	O
term	O
supercookie	O
to	O
refer	O
to	O
the	O
use	O
of	O
browser	B-Protocol
cache	I-Protocol
as	O
a	O
means	O
of	O
tracking	B-Application
users	O
across	O
sites	O
.	O
</s>
<s>
A	O
zombie	O
cookie	B-Application
is	O
data	B-General_Concept
and	O
code	O
that	O
has	O
been	O
placed	O
by	O
a	O
web	B-Application
server	I-Application
on	O
a	O
visitor	O
's	O
computer	O
or	O
other	O
device	O
in	O
a	O
hidden	O
location	O
outside	O
the	O
visitor	O
's	O
web	B-Application
browser	I-Application
's	O
dedicated	O
cookie	B-Application
storage	O
location	O
,	O
and	O
that	O
automatically	O
recreates	O
a	O
HTTP	B-Application
cookie	I-Application
as	O
a	O
regular	O
cookie	B-Application
after	O
the	O
original	O
cookie	B-Application
had	O
been	O
deleted	O
.	O
</s>
<s>
The	O
zombie	O
cookie	B-Application
may	O
be	O
stored	O
in	O
multiple	O
locations	O
,	O
such	O
as	O
Flash	B-Operating_System
Local	I-Operating_System
shared	I-Operating_System
object	I-Operating_System
,	O
HTML5	B-Application
Web	I-Application
storage	I-Application
,	O
and	O
other	O
client-side	O
and	O
even	O
server-side	O
locations	O
,	O
and	O
when	O
absence	O
is	O
detected	O
in	O
one	O
of	O
the	O
locations	O
,	O
the	O
missing	O
instance	O
is	O
recreated	O
by	O
the	O
JavaScript	B-Language
code	O
using	O
the	O
data	B-General_Concept
stored	O
in	O
other	O
locations	O
.	O
</s>
<s>
A	O
cookie	B-Application
wall	O
pops	O
up	O
on	O
a	O
website	O
and	O
informs	O
the	O
user	O
of	O
the	O
website	O
's	O
cookie	B-Application
usage	O
.	O
</s>
<s>
It	O
has	O
no	O
reject	O
option	O
,	O
and	O
the	O
website	O
is	O
not	O
accessible	O
without	O
tracking	B-Application
cookies	B-Application
.	O
</s>
<s>
A	O
cookie	B-Application
consists	O
of	O
the	O
following	O
components	O
:	O
</s>
<s>
Zero	O
or	O
more	O
attributes	O
(	O
name/value	B-Application
pairs	I-Application
)	O
.	O
</s>
<s>
Attributes	O
store	O
information	O
such	O
as	O
the	O
cookie	B-Application
's	O
expiration	O
,	O
domain	O
,	O
and	O
flags	O
(	O
such	O
as	O
Secure	O
and	O
HttpOnly	O
)	O
.	O
</s>
<s>
Cookies	B-Application
were	O
originally	O
introduced	O
to	O
provide	O
a	O
way	O
for	O
users	O
to	O
record	O
items	O
they	O
want	O
to	O
purchase	O
as	O
they	O
navigate	O
throughout	O
a	O
website	O
(	O
a	O
virtual	B-Application
shopping	I-Application
cart	I-Application
or	O
shopping	O
basket	O
)	O
.	O
</s>
<s>
Today	O
,	O
however	O
,	O
the	O
contents	O
of	O
a	O
user	O
's	O
shopping	O
cart	O
are	O
usually	O
stored	O
in	O
a	O
database	O
on	O
the	O
server	O
,	O
rather	O
than	O
in	O
a	O
cookie	B-Application
on	O
the	O
client	O
.	O
</s>
<s>
To	O
keep	O
track	O
of	O
which	O
user	O
is	O
assigned	O
to	O
which	O
shopping	O
cart	O
,	O
the	O
server	O
sends	O
a	O
cookie	B-Application
to	O
the	O
client	O
that	O
contains	O
a	O
unique	O
session	O
identifier	O
(	O
typically	O
,	O
a	O
long	O
string	O
of	O
random	O
letters	O
and	O
numbers	O
)	O
.	O
</s>
<s>
Because	O
cookies	B-Application
are	O
sent	O
to	O
the	O
server	O
with	O
every	O
request	O
the	O
client	O
makes	O
,	O
that	O
session	O
identifier	O
will	O
be	O
sent	O
back	O
to	O
the	O
server	O
every	O
time	O
the	O
user	O
visits	O
a	O
new	O
page	O
on	O
the	O
website	O
,	O
which	O
lets	O
the	O
server	O
know	O
which	O
shopping	O
cart	O
to	O
display	O
to	O
the	O
user	O
.	O
</s>
<s>
Another	O
popular	O
use	O
of	O
cookies	B-Application
is	O
for	O
logging	O
into	O
websites	O
.	O
</s>
<s>
When	O
the	O
user	O
visits	O
a	O
website	O
's	O
login	O
page	O
,	O
the	O
web	B-Application
server	I-Application
typically	O
sends	O
the	O
client	O
a	O
cookie	B-Application
containing	O
a	O
unique	O
session	O
identifier	O
.	O
</s>
<s>
Because	O
session	O
cookies	B-Application
only	O
contain	O
a	O
unique	O
session	O
identifier	O
,	O
this	O
makes	O
the	O
amount	O
of	O
personal	O
information	O
that	O
a	O
website	O
can	O
save	O
about	O
each	O
user	O
virtually	O
limitless	O
—	O
the	O
website	O
is	O
not	O
limited	O
to	O
restrictions	O
concerning	O
how	O
large	O
a	O
cookie	B-Application
can	O
be	O
.	O
</s>
<s>
Session	O
cookies	B-Application
also	O
help	O
to	O
improve	O
page	O
load	O
times	O
,	O
since	O
the	O
amount	O
of	O
information	O
in	O
a	O
session	O
cookie	B-Application
is	O
small	O
and	O
requires	O
little	O
bandwidth	O
.	O
</s>
<s>
Cookies	B-Application
can	O
be	O
used	O
to	O
remember	O
information	O
about	O
the	O
user	O
in	O
order	O
to	O
show	O
relevant	O
content	O
to	O
that	O
user	O
over	O
time	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
web	B-Application
server	I-Application
might	O
send	O
a	O
cookie	B-Application
containing	O
the	O
username	O
that	O
was	O
last	O
used	O
to	O
log	O
into	O
a	O
website	O
,	O
so	O
that	O
it	O
may	O
be	O
filled	O
in	O
automatically	O
the	O
next	O
time	O
the	O
user	O
logs	O
in	O
.	O
</s>
<s>
Many	O
websites	O
use	O
cookies	B-Application
for	O
personalization	O
based	O
on	O
the	O
user	O
's	O
preferences	O
.	O
</s>
<s>
Users	O
select	O
their	O
preferences	O
by	O
entering	O
them	O
in	O
a	O
web	B-General_Concept
form	I-General_Concept
and	O
submitting	O
the	O
form	O
to	O
the	O
server	O
.	O
</s>
<s>
The	O
server	O
encodes	O
the	O
preferences	O
in	O
a	O
cookie	B-Application
and	O
sends	O
the	O
cookie	B-Application
back	O
to	O
the	O
browser	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
the	B-Application
Google	I-Application
search	B-Application
engine	I-Application
once	O
used	O
cookies	B-Application
to	O
allow	O
users	O
(	O
even	O
non-registered	O
ones	O
)	O
to	O
decide	O
how	O
many	O
search	B-Application
results	I-Application
per	O
page	O
they	O
wanted	O
to	O
see	O
.	O
</s>
<s>
Also	O
,	O
DuckDuckGo	B-Application
uses	O
cookies	B-Application
to	O
allow	O
users	O
to	O
set	O
the	O
viewing	O
preferences	O
like	O
colors	O
of	O
the	O
web	O
page	O
.	O
</s>
<s>
Tracking	B-Application
cookies	B-Application
are	O
used	O
to	O
track	O
users	O
 '	O
web	O
browsing	O
habits	O
.	O
</s>
<s>
This	O
can	O
also	O
be	O
done	O
to	O
some	O
extent	O
by	O
using	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
computer	O
requesting	O
the	O
page	O
or	O
the	O
referer	B-Protocol
field	O
of	O
the	O
HTTP	B-Protocol
request	O
header	O
,	O
but	O
cookies	B-Application
allow	O
for	O
greater	O
precision	O
.	O
</s>
<s>
If	O
the	O
user	O
requests	O
a	O
page	O
of	O
the	O
site	O
,	O
but	O
the	O
request	O
contains	O
no	O
cookie	B-Application
,	O
the	O
server	O
presumes	O
that	O
this	O
is	O
the	O
first	O
page	O
visited	O
by	O
the	O
user	O
.	O
</s>
<s>
So	O
the	O
server	O
creates	O
a	O
unique	O
identifier	O
(	O
typically	O
a	O
string	O
of	O
random	O
letters	O
and	O
numbers	O
)	O
and	O
sends	O
it	O
as	O
a	O
cookie	B-Application
back	O
to	O
the	O
browser	B-Application
together	O
with	O
the	O
requested	O
page	O
.	O
</s>
<s>
From	O
this	O
point	O
on	O
,	O
the	O
cookie	B-Application
will	O
automatically	O
be	O
sent	O
by	O
the	O
browser	B-Application
to	O
the	O
server	O
every	O
time	O
a	O
new	O
page	O
from	O
the	O
site	O
is	O
requested	O
.	O
</s>
<s>
The	O
server	O
not	O
only	O
sends	O
the	O
page	O
as	O
usual	O
but	O
also	O
stores	O
the	O
URL	O
of	O
the	O
requested	O
page	O
,	O
the	O
date/time	O
of	O
the	O
request	O
,	O
and	O
the	O
cookie	B-Application
in	O
a	O
log	O
file	O
.	O
</s>
<s>
Corporations	O
exploit	O
users	O
 '	O
web	O
habits	O
by	O
tracking	B-Application
cookies	B-Application
to	O
collect	O
information	O
about	O
buying	O
habits	O
.	O
</s>
<s>
The	O
Wall	O
Street	O
Journal	O
found	O
that	O
America	O
's	O
top	O
fifty	O
websites	O
installed	O
an	O
average	O
of	O
sixty-four	O
pieces	O
of	O
tracking	B-Application
technology	O
onto	O
computers	O
,	O
resulting	O
in	O
a	O
total	O
of	O
3,180	O
tracking	B-Application
files	O
.	O
</s>
<s>
The	O
data	B-General_Concept
can	O
then	O
be	O
collected	O
and	O
sold	O
to	O
bidding	O
corporations	O
.	O
</s>
<s>
Cookies	B-Application
are	O
arbitrary	O
pieces	O
of	O
data	B-General_Concept
,	O
usually	O
chosen	O
and	O
first	O
sent	O
by	O
the	O
web	B-Application
server	I-Application
,	O
and	O
stored	O
on	O
the	O
client	O
computer	O
by	O
the	O
web	B-Application
browser	I-Application
.	O
</s>
<s>
The	O
browser	B-Application
then	O
sends	O
them	O
back	O
to	O
the	O
server	O
with	O
every	O
request	O
,	O
introducing	O
states	B-Application
(	O
memory	O
of	O
previous	O
events	O
)	O
into	O
otherwise	O
stateless	O
HTTP	B-Protocol
transactions	O
.	O
</s>
<s>
Without	O
cookies	B-Application
,	O
each	O
retrieval	O
of	O
a	O
web	O
page	O
or	O
component	O
of	O
a	O
web	O
page	O
would	O
be	O
an	O
isolated	O
event	O
,	O
largely	O
unrelated	O
to	O
all	O
other	O
page	O
views	O
made	O
by	O
the	O
user	O
on	O
the	O
website	O
.	O
</s>
<s>
Although	O
cookies	B-Application
are	O
usually	O
set	O
by	O
the	O
web	B-Application
server	I-Application
,	O
they	O
can	O
also	O
be	O
set	O
by	O
the	O
client	O
using	O
a	O
scripting	O
language	O
such	O
as	O
JavaScript	B-Language
(	O
unless	O
the	O
cookie	B-Application
's	O
HttpOnly	O
flag	O
is	O
set	O
,	O
in	O
which	O
case	O
the	O
cookie	B-Application
cannot	O
be	O
modified	O
by	O
scripting	O
languages	O
)	O
.	O
</s>
<s>
The	O
cookie	B-Application
specifications	O
require	O
that	O
browsers	B-Application
meet	O
the	O
following	O
requirements	O
in	O
order	O
to	O
support	O
cookies	B-Application
:	O
</s>
<s>
Can	O
support	O
cookies	B-Application
as	O
large	O
as	O
4,096	O
bytes	B-Application
in	O
size	O
.	O
</s>
<s>
Can	O
support	O
at	O
least	O
50	O
cookies	B-Application
per	O
domain	O
(	O
i.e.	O
</s>
<s>
Can	O
support	O
at	O
least	O
3,000	O
cookies	B-Application
in	O
total	O
.	O
</s>
<s>
Cookies	B-Application
are	O
set	O
using	O
the	O
Set-Cookie	O
header	B-Protocol
field	I-Protocol
,	O
sent	O
in	O
an	O
HTTP	B-Protocol
response	O
from	O
the	O
web	B-Application
server	I-Application
.	O
</s>
<s>
This	O
header	B-Protocol
field	I-Protocol
instructs	O
the	O
web	B-Application
browser	I-Application
to	O
store	O
the	O
cookie	B-Application
and	O
send	O
it	O
back	O
in	O
future	O
requests	O
to	O
the	O
server	O
(	O
the	O
browser	B-Application
will	O
ignore	O
this	O
header	B-Protocol
field	I-Protocol
if	O
it	O
does	O
not	O
support	O
cookies	B-Application
or	O
has	O
disabled	O
cookies	B-Application
)	O
.	O
</s>
<s>
As	O
an	O
example	O
,	O
the	O
browser	B-Application
sends	O
its	O
first	O
HTTP	B-Protocol
request	O
for	O
the	O
homepage	O
of	O
the	O
www.example.org	O
website	O
:	O
</s>
<s>
The	O
server	O
responds	O
with	O
two	O
Set-Cookie	O
header	O
fields	O
:	O
</s>
<s>
The	O
server	O
's	O
HTTP	B-Protocol
response	O
contains	O
the	O
contents	O
of	O
the	O
website	O
's	O
homepage	O
.	O
</s>
<s>
But	O
it	O
also	O
instructs	O
the	O
browser	B-Application
to	O
set	O
two	O
cookies	B-Application
.	O
</s>
<s>
The	O
first	O
,	O
theme	O
,	O
is	O
considered	O
to	O
be	O
a	O
session	O
cookie	B-Application
since	O
it	O
does	O
not	O
have	O
an	O
Expires	O
or	O
Max-Age	O
attribute	O
.	O
</s>
<s>
Session	O
cookies	B-Application
are	O
intended	O
to	O
be	O
deleted	O
by	O
the	O
browser	B-Application
when	O
the	O
browser	B-Application
closes	O
.	O
</s>
<s>
The	O
second	O
,	O
sessionToken	O
,	O
is	O
considered	O
to	O
be	O
a	O
persistent	O
cookie	B-Application
since	O
it	O
contains	O
an	O
Expires	O
attribute	O
,	O
which	O
instructs	O
the	O
browser	B-Application
to	O
delete	O
the	O
cookie	B-Application
at	O
a	O
specific	O
date	O
and	O
time	O
.	O
</s>
<s>
Next	O
,	O
the	O
browser	B-Application
sends	O
another	O
request	O
to	O
visit	O
the	O
spec.html	O
page	O
on	O
the	O
website	O
.	O
</s>
<s>
This	O
request	O
contains	O
a	O
Cookie	B-Application
header	B-Protocol
field	I-Protocol
,	O
which	O
contains	O
the	O
two	O
cookies	B-Application
that	O
the	O
server	O
instructed	O
the	O
browser	B-Application
to	O
set	O
:	O
</s>
<s>
This	O
way	O
,	O
the	O
server	O
knows	O
that	O
this	O
HTTP	B-Protocol
request	O
is	O
related	O
to	O
the	O
previous	O
one	O
.	O
</s>
<s>
The	O
server	O
would	O
answer	O
by	O
sending	O
the	O
requested	O
page	O
,	O
possibly	O
including	O
more	O
Set-Cookie	O
header	O
fields	O
in	O
the	O
HTTP	B-Protocol
response	O
in	O
order	O
to	O
instruct	O
the	O
browser	B-Application
to	O
add	O
new	O
cookies	B-Application
,	O
modify	O
existing	O
cookies	B-Application
,	O
or	O
remove	O
existing	O
cookies	B-Application
.	O
</s>
<s>
To	O
remove	O
a	O
cookie	B-Application
,	O
the	O
server	O
must	O
include	O
a	O
Set-Cookie	O
header	B-Protocol
field	I-Protocol
with	O
an	O
expiration	O
date	O
in	O
the	O
past	O
.	O
</s>
<s>
The	O
value	O
of	O
a	O
cookie	B-Application
may	O
consist	O
of	O
any	O
printable	O
ASCII	B-Protocol
character	I-Protocol
(	O
!	O
</s>
<s>
The	O
name	O
of	O
a	O
cookie	B-Application
excludes	O
the	O
same	O
characters	O
,	O
as	O
well	O
as	O
=	O
,	O
since	O
that	O
is	O
the	O
delimiter	O
between	O
the	O
name	O
and	O
value	O
.	O
</s>
<s>
The	O
cookie	B-Application
standard	O
RFC	O
2965	O
is	O
more	O
restrictive	O
but	O
not	O
implemented	O
by	O
browsers	B-Application
.	O
</s>
<s>
The	O
term	O
cookie	B-Application
crumb	O
is	O
sometimes	O
used	O
to	O
refer	O
to	O
a	O
cookie	B-Application
's	O
name	B-Application
–	I-Application
value	I-Application
pair	I-Application
.	O
</s>
<s>
Cookies	B-Application
can	O
also	O
be	O
set	O
by	O
scripting	O
languages	O
such	O
as	O
JavaScript	B-Language
that	O
run	O
within	O
the	O
browser	B-Application
.	O
</s>
<s>
In	O
JavaScript	B-Language
,	O
the	O
object	O
document.cookie	O
is	O
used	O
for	O
this	O
purpose	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
instruction	O
document.cookie	O
=	O
"	O
temperature	O
=	O
20	O
"	O
creates	O
a	O
cookie	B-Application
of	O
name	O
temperature	O
and	O
value	O
20	O
.	O
</s>
<s>
In	O
addition	O
to	O
a	O
name	O
and	O
value	O
,	O
cookies	B-Application
can	O
also	O
have	O
one	O
or	O
more	O
attributes	O
.	O
</s>
<s>
Browsers	B-Application
do	O
not	O
include	O
cookie	B-Application
attributes	O
in	O
requests	O
to	O
the	O
server	O
—	O
they	O
only	O
send	O
the	O
cookie	B-Application
's	O
name	O
and	O
value	O
.	O
</s>
<s>
Cookie	B-Application
attributes	O
are	O
used	O
by	O
browsers	B-Application
to	O
determine	O
when	O
to	O
delete	O
a	O
cookie	B-Application
,	O
block	O
a	O
cookie	B-Application
or	O
whether	O
to	O
send	O
a	O
cookie	B-Application
to	O
the	O
server	O
.	O
</s>
<s>
The	O
Domain	O
and	O
Path	O
attributes	O
define	O
the	O
scope	O
of	O
the	O
cookie	B-Application
.	O
</s>
<s>
They	O
essentially	O
tell	O
the	O
browser	B-Application
what	O
website	O
the	O
cookie	B-Application
belongs	O
to	O
.	O
</s>
<s>
For	O
security	O
reasons	O
,	O
cookies	B-Application
can	O
only	O
be	O
set	O
on	O
the	O
current	O
resource	O
's	O
top	O
domain	O
and	O
its	O
subdomains	O
,	O
and	O
not	O
for	O
another	O
domain	O
and	O
its	O
subdomains	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
website	O
example.org	O
cannot	O
set	O
a	O
cookie	B-Application
that	O
has	O
a	O
domain	O
of	O
foo.com	O
because	O
this	O
would	O
allow	O
the	O
website	O
example.org	O
to	O
control	O
the	O
cookies	B-Application
of	O
the	O
domain	O
foo.com	O
.	O
</s>
<s>
If	O
a	O
cookie	B-Application
's	O
Domain	O
and	O
Path	O
attributes	O
are	O
not	O
specified	O
by	O
the	O
server	O
,	O
they	O
default	O
to	O
the	O
domain	O
and	O
path	O
of	O
the	O
resource	O
that	O
was	O
requested	O
.	O
</s>
<s>
However	O
,	O
in	O
most	O
browsers	B-Application
there	O
is	O
a	O
difference	O
between	O
a	O
cookie	B-Application
set	O
from	O
foo.com	O
without	O
a	O
domain	O
,	O
and	O
a	O
cookie	B-Application
set	O
with	O
the	O
foo.com	O
domain	O
.	O
</s>
<s>
In	O
the	O
former	O
case	O
,	O
the	O
cookie	B-Application
will	O
only	O
be	O
sent	O
for	O
requests	O
to	O
foo.com,	O
also	O
known	O
as	O
a	O
host-only	O
cookie	B-Application
.	O
</s>
<s>
A	O
notable	O
exception	O
to	O
this	O
general	O
rule	O
is	O
Edge	O
prior	O
to	O
Windows	O
10	O
RS3	O
and	O
Internet	B-Application
Explorer	I-Application
prior	O
to	O
IE	O
11	O
and	O
Windows	O
10	O
RS4	O
(	O
April	O
2018	O
)	O
,	O
which	O
always	O
sends	O
cookies	B-Application
to	O
subdomains	O
regardless	O
of	O
whether	O
the	O
cookie	B-Application
was	O
set	O
with	O
or	O
without	O
a	O
domain	O
.	O
</s>
<s>
Below	O
is	O
an	O
example	O
of	O
some	O
Set-Cookie	O
header	O
fields	O
in	O
the	O
HTTP	B-Protocol
response	O
of	O
a	O
website	O
after	O
a	O
user	O
logged	O
in	O
.	O
</s>
<s>
The	O
HTTP	B-Protocol
request	O
was	O
sent	O
to	O
a	O
webpage	O
within	O
the	O
docs.foo.com	O
subdomain	O
:	O
</s>
<s>
The	O
first	O
cookie	B-Application
,	O
LSID	O
,	O
has	O
no	O
Domain	O
attribute	O
,	O
and	O
has	O
a	O
Path	O
attribute	O
set	O
to	O
/accounts	O
.	O
</s>
<s>
This	O
tells	O
the	O
browser	B-Application
to	O
use	O
the	O
cookie	B-Application
only	O
when	O
requesting	O
pages	O
contained	O
in	O
docs.foo.com/accounts	O
(	O
the	O
domain	O
is	O
derived	O
from	O
the	O
request	O
domain	O
)	O
.	O
</s>
<s>
The	O
other	O
two	O
cookies	B-Application
,	O
HSID	O
and	O
SSID	O
,	O
would	O
be	O
used	O
when	O
the	O
browser	B-Application
requests	O
any	O
subdomain	O
in	O
.foo.com	O
on	O
any	O
path	O
(	O
for	O
example	O
www.foo.com/bar	O
)	O
.	O
</s>
<s>
The	O
Expires	O
attribute	O
defines	O
a	O
specific	O
date	O
and	O
time	O
for	O
when	O
the	O
browser	B-Application
should	O
delete	O
the	O
cookie	B-Application
.	O
</s>
<s>
Alternatively	O
,	O
the	O
Max-Age	O
attribute	O
can	O
be	O
used	O
to	O
set	O
the	O
cookie	B-Application
's	O
expiration	O
as	O
an	O
interval	O
of	O
seconds	O
in	O
the	O
future	O
,	O
relative	O
to	O
the	O
time	O
the	O
browser	B-Application
received	O
the	O
cookie	B-Application
.	O
</s>
<s>
Below	O
is	O
an	O
example	O
of	O
three	O
Set-Cookie	O
header	O
fields	O
that	O
were	O
received	O
from	O
a	O
website	O
after	O
a	O
user	O
logged	O
in	O
:	O
</s>
<s>
The	O
first	O
cookie	B-Application
,	O
lu	O
,	O
is	O
set	O
to	O
expire	O
sometime	O
on	O
15	O
January	O
2013	O
.	O
</s>
<s>
It	O
will	O
be	O
used	O
by	O
the	O
client	O
browser	B-Application
until	O
that	O
time	O
.	O
</s>
<s>
The	O
second	O
cookie	B-Application
,	O
made_write_conn	O
,	O
does	O
not	O
have	O
an	O
expiration	O
date	O
,	O
making	O
it	O
a	O
session	O
cookie	B-Application
.	O
</s>
<s>
It	O
will	O
be	O
deleted	O
after	O
the	O
user	O
closes	O
their	O
browser	B-Application
.	O
</s>
<s>
The	O
third	O
cookie	B-Application
,	O
reg_fb_gate	O
,	O
has	O
its	O
value	O
changed	O
to	O
deleted	O
,	O
with	O
an	O
expiration	O
time	O
in	O
the	O
past	O
.	O
</s>
<s>
The	O
browser	B-Application
will	O
delete	O
this	O
cookie	B-Application
right	O
away	O
because	O
its	O
expiration	O
time	O
is	O
in	O
the	O
past	O
.	O
</s>
<s>
Note	O
that	O
cookie	B-Application
will	O
only	O
be	O
deleted	O
if	O
the	O
domain	O
and	O
path	O
attributes	O
in	O
the	O
Set-Cookie	O
field	O
match	O
the	O
values	O
used	O
when	O
the	O
cookie	B-Application
was	O
created	O
.	O
</s>
<s>
Internet	B-Application
Explorer	I-Application
did	O
not	O
support	O
Max-Age	O
.	O
</s>
<s>
The	O
Secure	O
attribute	O
is	O
meant	O
to	O
keep	O
cookie	B-Application
communication	O
limited	O
to	O
encrypted	O
transmission	O
,	O
directing	O
browsers	B-Application
to	O
use	O
cookies	B-Application
only	O
via	O
secure/encrypted	B-Protocol
connections	O
.	O
</s>
<s>
However	O
,	O
if	O
a	O
web	B-Application
server	I-Application
sets	O
a	O
cookie	B-Application
with	O
a	O
secure	O
attribute	O
from	O
a	O
non-secure	O
connection	O
,	O
the	O
cookie	B-Application
can	O
still	O
be	O
intercepted	O
when	O
it	O
is	O
sent	O
to	O
the	O
user	O
by	O
man-in-the-middle	O
attacks	O
.	O
</s>
<s>
Therefore	O
,	O
for	O
maximum	O
security	O
,	O
cookies	B-Application
with	O
the	O
Secure	O
attribute	O
should	O
only	O
be	O
set	O
over	O
a	O
secure	O
connection	O
.	O
</s>
<s>
The	O
HttpOnly	O
attribute	O
directs	O
browsers	B-Application
not	O
to	O
expose	O
cookies	B-Application
through	O
channels	O
other	O
than	O
HTTP	B-Protocol
(	O
and	O
HTTPS	B-Protocol
)	O
requests	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
cookie	B-Application
cannot	O
be	O
accessed	O
via	O
client-side	O
scripting	O
languages	O
(	O
notably	O
JavaScript	B-Language
)	O
,	O
and	O
therefore	O
cannot	O
be	O
stolen	O
easily	O
via	O
cross-site	O
scripting	O
(	O
a	O
pervasive	O
attack	O
technique	O
)	O
.	O
</s>
<s>
Most	O
modern	O
browsers	B-Application
support	O
cookies	B-Application
and	O
allow	O
the	O
user	O
to	O
disable	O
them	O
.	O
</s>
<s>
To	O
enable	O
or	O
disable	O
cookies	B-Application
completely	O
,	O
so	O
that	O
they	O
are	O
always	O
accepted	O
or	O
always	O
blocked	O
.	O
</s>
<s>
To	O
view	O
and	O
selectively	O
delete	O
cookies	B-Application
using	O
a	O
cookie	B-Application
manager	O
.	O
</s>
<s>
To	O
fully	O
wipe	O
all	O
private	O
data	B-General_Concept
,	O
including	O
cookies	B-Application
.	O
</s>
<s>
Add-on	O
tools	O
for	O
managing	O
cookie	B-Application
permissions	O
also	O
exist	O
.	O
</s>
<s>
Cookies	B-Application
have	O
some	O
important	O
implications	O
for	O
the	O
privacy	O
and	O
anonymity	O
of	O
web	O
users	O
.	O
</s>
<s>
While	O
cookies	B-Application
are	O
sent	O
only	O
to	O
the	O
server	O
setting	O
them	O
or	O
a	O
server	O
in	O
the	O
same	O
Internet	O
domain	O
,	O
a	O
web	O
page	O
may	O
contain	O
images	O
or	O
other	O
components	O
stored	O
on	O
servers	O
in	O
other	O
domains	O
.	O
</s>
<s>
Cookies	B-Application
that	O
are	O
set	O
during	O
retrieval	O
of	O
these	O
components	O
are	O
called	O
third-party	O
cookies	B-Application
.	O
</s>
<s>
A	O
third-party	O
cookie	B-Application
,	O
belongs	O
to	O
a	O
domain	O
different	O
from	O
the	O
one	O
shown	O
in	O
the	O
address	O
bar	O
.	O
</s>
<s>
This	O
sort	O
of	O
cookie	B-Application
typically	O
appears	O
when	O
web	O
pages	O
feature	O
content	O
from	O
external	O
websites	O
,	O
such	O
as	O
banner	O
advertisements	O
.	O
</s>
<s>
This	O
opens	O
up	O
the	O
potential	O
for	O
tracking	B-Application
the	O
user	O
's	O
browsing	B-Protocol
history	I-Protocol
and	O
is	O
used	O
by	O
advertisers	O
to	O
serve	O
relevant	O
advertisements	O
to	O
each	O
user	O
.	O
</s>
<s>
This	O
website	O
contains	O
an	O
advertisement	O
from	O
ad.foxytracking.com,	O
which	O
,	O
when	O
downloaded	O
,	O
sets	O
a	O
cookie	B-Application
belonging	O
to	O
the	O
advertisement	O
's	O
domain	O
(	O
ad.foxytracking.com	O
)	O
.	O
</s>
<s>
Then	O
,	O
the	O
user	O
visits	O
another	O
website	O
,	O
www.foo.com	O
,	O
which	O
also	O
contains	O
an	O
advertisement	O
from	O
ad.foxytracking.com	O
and	O
sets	O
a	O
cookie	B-Application
belonging	O
to	O
that	O
domain	O
(	O
ad.foxytracking.com	O
)	O
.	O
</s>
<s>
Eventually	O
,	O
both	O
of	O
these	O
cookies	B-Application
will	O
be	O
sent	O
to	O
the	O
advertiser	O
when	O
loading	O
their	O
advertisements	O
or	O
visiting	O
their	O
website	O
.	O
</s>
<s>
The	O
advertiser	O
can	O
then	O
use	O
these	O
cookies	B-Application
to	O
build	O
up	O
a	O
browsing	B-Protocol
history	I-Protocol
of	O
the	O
user	O
across	O
all	O
the	O
websites	O
that	O
have	O
ads	O
from	O
this	O
advertiser	O
,	O
through	O
the	O
use	O
of	O
the	O
HTTP	B-Protocol
referer	I-Protocol
header	B-Protocol
field	I-Protocol
.	O
</s>
<s>
,	O
some	O
websites	O
were	O
setting	O
cookies	B-Application
readable	O
for	O
over	O
100	O
third-party	O
domains	O
.	O
</s>
<s>
On	O
average	O
,	O
a	O
single	O
website	O
was	O
setting	O
10	O
cookies	B-Application
,	O
with	O
a	O
maximum	O
number	O
of	O
cookies	B-Application
(	O
first	O
-	O
and	O
third-party	O
)	O
reaching	O
over	O
800	O
.	O
</s>
<s>
The	O
older	O
standards	O
for	O
cookies	B-Application
,	O
RFC	O
2109	O
and	O
RFC	O
2965	O
,	O
recommend	O
that	O
browsers	B-Application
should	O
protect	O
user	O
privacy	O
and	O
not	O
allow	O
sharing	O
of	O
cookies	B-Application
between	O
servers	O
by	O
default	O
.	O
</s>
<s>
However	O
,	O
the	O
newer	O
standard	O
,	O
RFC	O
6265	O
,	O
explicitly	O
allows	O
user	O
agents	O
to	O
implement	O
whichever	O
third-party	O
cookie	B-Application
policy	O
they	O
wish	O
.	O
</s>
<s>
Most	O
modern	O
web	B-Application
browsers	I-Application
contain	O
privacy	O
settings	O
that	O
can	O
block	O
third-party	O
cookies	B-Application
,	O
and	O
some	O
now	O
block	O
all	O
third-party	O
cookies	B-Application
by	O
default	O
-	O
as	O
of	O
July	O
2020	O
,	O
such	O
browsers	B-Application
include	O
Apple	B-Application
Safari	I-Application
,	O
Firefox	B-Application
,	O
and	O
Brave	B-Application
.	O
</s>
<s>
Safari	B-Application
allows	O
embedded	O
sites	O
to	O
use	O
Storage	O
Access	O
API	O
to	O
request	O
permission	O
to	O
set	O
first-party	B-Application
cookies	I-Application
.	O
</s>
<s>
In	O
May	O
2020	O
,	O
Google	B-Application
Chrome	I-Application
introduced	O
new	O
features	O
to	O
block	O
third-party	O
cookies	B-Application
by	O
default	O
in	O
its	O
Incognito	O
mode	O
for	O
private	O
browsing	O
,	O
making	O
blocking	O
optional	O
during	O
normal	O
browsing	O
.	O
</s>
<s>
The	O
same	O
update	O
also	O
added	O
an	O
option	O
to	O
block	O
first-party	B-Application
cookies	I-Application
.	O
</s>
<s>
Chrome	B-Application
plans	O
to	O
start	O
blocking	O
third-party	O
cookies	B-Application
by	O
default	O
in	O
late	O
2024	O
.	O
</s>
<s>
The	O
possibility	O
of	O
building	O
a	O
profile	O
of	O
users	O
is	O
a	O
privacy	O
threat	O
,	O
especially	O
when	O
tracking	B-Application
is	O
done	O
across	O
multiple	O
domains	O
using	O
third-party	O
cookies	B-Application
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
some	O
countries	O
have	O
legislation	O
about	O
cookies	B-Application
.	O
</s>
<s>
Website	O
operators	O
who	O
do	O
not	O
disclose	O
third-party	O
cookie	B-Application
use	O
to	O
consumers	O
run	O
the	O
risk	O
of	O
harming	O
consumer	O
trust	O
if	O
cookie	B-Application
use	O
is	O
discovered	O
.	O
</s>
<s>
Having	O
clear	O
disclosure	O
(	O
such	O
as	O
in	O
a	O
privacy	O
policy	O
)	O
tends	O
to	O
eliminate	O
any	O
negative	O
effects	O
of	O
such	O
cookie	B-Application
discovery	O
.	O
</s>
<s>
The	O
United	O
States	B-Application
government	O
has	O
set	O
strict	O
rules	O
on	O
setting	O
cookies	B-Application
in	O
2000	O
after	O
it	O
was	O
disclosed	O
that	O
the	O
White	O
House	O
drug	O
policy	O
office	O
used	O
cookies	B-Application
to	O
track	O
computer	O
users	O
viewing	O
its	O
online	O
anti-drug	O
advertising	O
.	O
</s>
<s>
In	O
2002	O
,	O
privacy	O
activist	O
Daniel	O
Brandt	O
found	O
that	O
the	O
CIA	O
had	O
been	O
leaving	O
persistent	O
cookies	B-Application
on	O
computers	O
that	O
had	O
visited	O
its	O
website	O
.	O
</s>
<s>
When	O
notified	O
it	O
was	O
violating	O
policy	O
,	O
CIA	O
stated	O
that	O
these	O
cookies	B-Application
were	O
not	O
intentionally	O
set	O
and	O
stopped	O
setting	O
them	O
.	O
</s>
<s>
On	O
December	O
25	O
,	O
2005	O
,	O
Brandt	O
discovered	O
that	O
the	O
National	O
Security	O
Agency	O
(	O
NSA	O
)	O
had	O
been	O
leaving	O
two	O
persistent	O
cookies	B-Application
on	O
visitors	O
 '	O
computers	O
due	O
to	O
a	O
software	O
upgrade	O
.	O
</s>
<s>
After	O
being	O
informed	O
,	O
the	O
NSA	O
immediately	O
disabled	O
the	O
cookies	B-Application
.	O
</s>
<s>
In	O
2002	O
,	O
the	O
European	O
Union	O
launched	O
the	O
Directive	O
on	O
Privacy	O
and	O
Electronic	O
Communications	O
(	O
e-Privacy	O
Directive	O
)	O
,	O
a	O
policy	O
requiring	O
end	O
users	O
 '	O
consent	O
for	O
the	O
placement	O
of	O
cookies	B-Application
,	O
and	O
similar	O
technologies	O
for	O
storing	O
and	O
accessing	O
information	O
on	O
users	O
 '	O
equipment	O
.	O
</s>
<s>
In	O
particular	O
,	O
Article	O
5	O
Paragraph	O
3	O
mandates	O
that	O
storing	O
technically	O
unnecessary	O
data	B-General_Concept
on	O
a	O
user	O
's	O
computer	O
can	O
only	O
be	O
done	O
if	O
the	O
user	O
is	O
provided	O
information	O
about	O
how	O
this	O
data	B-General_Concept
is	O
used	O
,	O
and	O
the	O
user	O
is	O
given	O
the	O
possibility	O
of	O
denying	O
this	O
storage	O
operation	O
.	O
</s>
<s>
The	O
Directive	O
does	O
not	O
require	O
users	O
to	O
authorise	O
or	O
be	O
provided	O
notice	O
of	O
cookie	B-Application
usage	O
that	O
are	O
functionally	O
required	O
for	O
delivering	O
a	O
service	O
they	O
have	O
requested	O
,	O
for	O
example	O
to	O
retain	O
settings	O
,	O
store	O
log-in	O
sessions	O
,	O
or	O
remember	O
what	O
is	O
in	O
a	O
user	O
's	O
shopping	O
basket	O
.	O
</s>
<s>
Instead	O
of	O
having	O
an	O
option	O
for	O
users	O
to	O
opt	O
out	O
of	O
cookie	B-Application
storage	O
,	O
the	O
revised	O
Directive	O
requires	O
consent	O
to	O
be	O
obtained	O
for	O
cookie	B-Application
storage	O
.	O
</s>
<s>
The	O
definition	O
of	O
consent	O
is	O
cross-referenced	O
to	O
the	O
definition	O
in	O
European	O
data	B-General_Concept
protection	O
law	O
,	O
firstly	O
the	O
Data	B-General_Concept
Protection	O
Directive	O
1995	O
and	O
subsequently	O
the	O
General	O
Data	B-General_Concept
Protection	O
Regulation	O
(	O
GDPR	O
)	O
.	O
</s>
<s>
As	O
the	O
definition	O
of	O
consent	O
was	O
strengthened	O
in	O
the	O
text	O
of	O
the	O
GDPR	O
,	O
this	O
had	O
the	O
effect	O
of	O
increasing	O
the	O
quality	O
of	O
consent	O
required	O
by	O
those	O
storing	O
and	O
accessing	O
information	O
such	O
as	O
cookies	B-Application
on	O
users	O
devices	O
.	O
</s>
<s>
In	O
a	O
case	O
decided	O
under	O
the	O
Data	B-General_Concept
Protection	O
Directive	O
however	O
,	O
the	O
Court	O
of	O
Justice	O
of	O
the	O
European	O
Union	O
later	O
confirmed	O
however	O
that	O
the	O
previous	O
law	O
implied	O
the	O
same	O
strong	O
quality	O
of	O
consent	O
as	O
the	O
current	O
instrument	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
requirement	O
of	O
consent	O
which	O
stems	O
from	O
storing	O
or	O
accessing	O
information	O
on	O
a	O
user	O
's	O
terminal	O
device	O
,	O
the	O
information	O
in	O
many	O
cookies	B-Application
will	O
be	O
considered	O
personal	O
data	B-General_Concept
under	O
the	O
GDPR	O
alone	O
,	O
and	O
will	O
require	O
a	O
legal	O
basis	O
to	O
process	O
.	O
</s>
<s>
This	O
has	O
been	O
the	O
case	O
since	O
the	O
1995	O
Data	B-General_Concept
Protection	O
Directive	O
,	O
which	O
used	O
an	O
identical	O
definition	O
of	O
personal	O
data	B-General_Concept
,	O
although	O
the	O
GDPR	O
in	O
interpretative	O
Recital	O
30	O
clarifies	O
that	O
cookie	B-Application
identifiers	O
are	O
included	O
.	O
</s>
<s>
While	O
not	O
all	O
data	B-General_Concept
processing	O
under	O
the	O
GDPR	O
requires	O
consent	O
,	O
the	O
characteristics	O
of	O
behavioural	O
advertising	O
mean	O
that	O
it	O
is	O
difficult	O
or	O
impossible	O
to	O
justify	O
under	O
any	O
other	O
ground	O
.	O
</s>
<s>
Consent	O
under	O
the	O
combination	O
of	O
the	O
GDPR	O
and	O
e-Privacy	O
Directive	O
has	O
to	O
meet	O
a	O
number	O
of	O
conditions	O
in	O
relation	O
to	O
cookies	B-Application
.	O
</s>
<s>
It	O
must	O
be	O
freely	O
given	O
and	O
unambiguous	O
:	O
preticked	O
boxes	O
were	O
banned	O
under	O
both	O
the	O
Data	B-General_Concept
Protection	O
Directive	O
1995	O
and	O
the	O
GDPR	O
(	O
Recital	O
32	O
)	O
.	O
</s>
<s>
It	O
must	O
be	O
specific	O
and	O
informed	O
,	O
meaning	O
that	O
consent	O
relates	O
to	O
particular	O
purposes	O
for	O
the	O
use	O
of	O
this	O
data	B-General_Concept
,	O
and	O
all	O
organisations	O
seeking	O
to	O
use	O
this	O
consent	O
must	O
be	O
specifically	O
named	O
.	O
</s>
<s>
The	O
Court	O
of	O
Justice	O
of	O
the	O
European	O
Union	O
has	O
also	O
ruled	O
that	O
consent	O
must	O
be	O
'	O
efficient	O
and	O
timely	O
 '	O
,	O
meaning	O
that	O
it	O
must	O
be	O
gained	O
before	O
cookies	B-Application
are	O
laid	O
and	O
data	B-General_Concept
processing	O
begins	O
instead	O
of	O
afterwards	O
.	O
</s>
<s>
However	O
,	O
scholars	O
note	O
that	O
the	O
onerous	O
nature	O
of	O
cookie	B-Application
pop-ups	O
stems	O
from	O
an	O
attempt	O
to	O
continue	O
to	O
operate	O
a	O
business	O
model	O
through	O
convoluted	O
requests	O
that	O
may	O
be	O
incompatible	O
with	O
the	O
GDPR	O
.	O
</s>
<s>
A	O
study	O
scraping	O
10,000	O
UK	O
websites	O
found	O
that	O
only	O
11.8	O
%	O
of	O
sites	O
adhered	O
to	O
minimal	O
legal	O
requirements	O
,	O
with	O
only	O
33.4	O
%	O
of	O
websites	O
studied	O
providing	O
a	O
mechanism	O
to	O
reject	O
cookies	B-Application
that	O
was	O
as	O
easy	O
to	O
use	O
as	O
accepting	O
them	O
.	O
</s>
<s>
A	O
study	O
of	O
17,000	O
websites	O
found	O
that	O
84%	O
of	O
sites	O
breached	O
this	O
criterion	O
,	O
finding	O
additionally	O
that	O
many	O
laid	O
third	O
party	O
cookies	B-Application
with	O
no	O
notice	O
at	O
all	O
.	O
</s>
<s>
The	O
UK	O
regulator	O
,	O
the	O
Information	O
Commissioner	O
's	O
Office	O
,	O
stated	O
in	O
2019	O
that	O
the	O
industry	O
's	O
'	O
Transparency	O
and	O
Consent	O
Framework	O
 '	O
from	O
the	O
advertising	O
technology	O
group	O
the	O
Interactive	O
Advertising	O
Bureau	O
was	O
'	O
insufficient	O
to	O
ensure	O
transparency	O
and	O
fair	O
processing	O
of	O
the	O
personal	O
data	B-General_Concept
in	O
question	O
and	O
therefore	O
also	O
insufficient	O
to	O
provide	O
for	O
free	O
and	O
informed	O
consent	O
,	O
with	O
attendant	O
implications	O
for	O
PECR	O
 [ e-Privacy ] 	O
compliance.	O
'	O
</s>
<s>
A	O
W3C	O
specification	O
called	O
P3P	O
was	O
proposed	O
for	O
servers	O
to	O
communicate	O
their	O
privacy	O
policy	O
to	O
browsers	B-Application
,	O
allowing	O
automatic	O
,	O
user-configurable	O
handling	O
.	O
</s>
<s>
Third-party	O
cookies	B-Application
can	O
be	O
blocked	O
by	O
most	O
browsers	B-Application
to	O
increase	O
privacy	O
and	O
reduce	O
tracking	B-Application
by	O
advertising	O
and	O
tracking	B-Application
companies	O
without	O
negatively	O
affecting	O
the	O
user	O
's	O
web	O
experience	O
on	O
all	O
sites	O
.	O
</s>
<s>
Some	O
sites	O
operate	O
'	O
cookie	B-Application
walls	O
 '	O
,	O
which	O
make	O
access	O
to	O
a	O
site	O
conditional	O
on	O
allowing	O
cookies	B-Application
either	O
technically	O
in	O
a	O
browser	B-Application
,	O
through	O
pressing	O
'	O
accept	O
 '	O
,	O
or	O
both	O
.	O
</s>
<s>
In	O
2020	O
,	O
the	O
European	O
Data	B-General_Concept
Protection	O
Board	O
,	O
composed	O
of	O
all	O
EU	O
data	B-General_Concept
protection	O
regulators	O
,	O
stated	O
that	O
cookie	B-Application
walls	O
were	O
illegal.In	O
order	O
for	O
consent	O
to	O
be	O
freely	O
given	O
,	O
access	O
to	O
services	O
and	O
functionalities	O
must	O
not	O
be	O
made	O
conditional	O
on	O
the	O
consent	O
of	O
a	O
user	O
to	O
the	O
storing	O
of	O
information	O
,	O
or	O
gaining	O
of	O
access	O
to	O
information	O
already	O
stored	O
,	O
in	O
the	O
terminal	O
equipment	O
of	O
a	O
user	O
(	O
so	O
called	O
cookie	B-Application
walls	O
)	O
.Many	O
advertising	O
operators	O
have	O
an	O
opt-out	O
option	O
to	O
behavioural	O
advertising	O
,	O
with	O
a	O
generic	O
cookie	B-Application
in	O
the	O
browser	B-Application
stopping	O
behavioural	O
advertising	O
.	O
</s>
<s>
However	O
,	O
this	O
is	O
often	O
ineffective	O
against	O
many	O
forms	O
of	O
tracking	B-Application
,	O
such	O
as	O
first-party	O
tracking	B-Application
that	O
is	O
growing	O
in	O
popularity	O
to	O
avoid	O
the	O
impact	O
of	O
browsers	B-Application
blocking	O
third	O
party	O
cookies	B-Application
.	O
</s>
<s>
Furthermore	O
,	O
if	O
such	O
a	O
setting	O
is	O
more	O
difficult	O
to	O
place	O
than	O
the	O
acceptance	O
of	O
tracking	B-Application
,	O
it	O
remains	O
in	O
breach	O
of	O
the	O
conditions	O
of	O
the	O
e-Privacy	O
Directive	O
.	O
</s>
<s>
Most	O
websites	O
use	O
cookies	B-Application
as	O
the	O
only	O
identifiers	O
for	O
user	O
sessions	O
,	O
because	O
other	O
methods	O
of	O
identifying	O
web	O
users	O
have	O
limitations	O
and	O
vulnerabilities	O
.	O
</s>
<s>
If	O
a	O
website	O
uses	O
cookies	B-Application
as	O
session	O
identifiers	O
,	O
attackers	O
can	O
impersonate	O
users	O
 '	O
requests	O
by	O
stealing	O
a	O
full	O
set	O
of	O
victims	O
 '	O
cookies	B-Application
.	O
</s>
<s>
From	O
the	O
web	B-Application
server	I-Application
's	O
point	O
of	O
view	O
,	O
a	O
request	O
from	O
an	O
attacker	O
then	O
has	O
the	O
same	O
authentication	O
as	O
the	O
victim	O
's	O
requests	O
;	O
thus	O
the	O
request	O
is	O
performed	O
on	O
behalf	O
of	O
the	O
victim	O
's	O
session	O
.	O
</s>
<s>
Listed	O
here	O
are	O
various	O
scenarios	O
of	O
cookie	B-Application
theft	O
and	O
user	O
session	O
hijacking	O
(	O
even	O
without	O
stealing	O
user	O
cookies	B-Application
)	O
that	O
work	O
with	O
websites	O
relying	O
solely	O
on	O
HTTP	B-Application
cookies	I-Application
for	O
user	O
identification	O
.	O
</s>
<s>
This	O
traffic	O
includes	O
cookies	B-Application
sent	O
on	O
ordinary	O
unencrypted	O
HTTP	B-Protocol
sessions	O
.	O
</s>
<s>
Where	O
network	O
traffic	O
is	O
not	O
encrypted	O
,	O
attackers	O
can	O
therefore	O
read	O
the	O
communications	O
of	O
other	O
users	O
on	O
the	O
network	O
,	O
including	O
HTTP	B-Application
cookies	I-Application
as	O
well	O
as	O
the	O
entire	O
contents	O
of	O
the	O
conversations	O
,	O
for	O
the	O
purpose	O
of	O
a	O
man-in-the-middle	O
attack	O
.	O
</s>
<s>
An	O
attacker	O
could	O
use	O
intercepted	O
cookies	B-Application
to	O
impersonate	O
a	O
user	O
and	O
perform	O
a	O
malicious	O
task	O
,	O
such	O
as	O
transferring	O
money	O
out	O
of	O
the	O
victim	O
's	O
bank	O
account	O
.	O
</s>
<s>
This	O
issue	O
can	O
be	O
resolved	O
by	O
securing	O
the	O
communication	O
between	O
the	O
user	O
's	O
computer	O
and	O
the	O
server	O
by	O
employing	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
HTTPS	B-Protocol
protocol	O
)	O
to	O
encrypt	O
the	O
connection	O
.	O
</s>
<s>
A	O
server	O
can	O
specify	O
the	O
Secure	O
flag	O
while	O
setting	O
a	O
cookie	B-Application
,	O
which	O
will	O
cause	O
the	O
browser	B-Application
to	O
send	O
the	O
cookie	B-Application
only	O
over	O
an	O
encrypted	O
channel	O
,	O
such	O
as	O
a	O
TLS	O
connection	O
.	O
</s>
<s>
If	O
an	O
attacker	O
is	O
able	O
to	O
cause	O
a	O
DNS	B-Protocol
server	I-Protocol
to	O
cache	O
a	O
fabricated	O
DNS	O
entry	O
(	O
called	O
DNS	O
cache	O
poisoning	O
)	O
,	O
then	O
this	O
could	O
allow	O
the	O
attacker	O
to	O
gain	O
access	O
to	O
a	O
user	O
's	O
cookies	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
an	O
attacker	O
could	O
use	O
DNS	O
cache	O
poisoning	O
to	O
create	O
a	O
fabricated	O
DNS	O
entry	O
of	O
f12345.www.example.com	O
that	O
points	O
to	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
attacker	O
's	O
server	O
.	O
</s>
<s>
Since	O
f12345.www.example.com	O
is	O
a	O
sub-domain	O
of	O
www.example.com	O
,	O
victims	O
 '	O
browsers	B-Application
would	O
submit	O
all	O
example.com-related	O
cookies	B-Application
to	O
the	O
attacker	O
's	O
server	O
.	O
</s>
<s>
If	O
an	O
attacker	O
is	O
able	O
to	O
accomplish	O
this	O
,	O
it	O
is	O
usually	O
the	O
fault	O
of	O
the	O
Internet	O
Service	O
Providers	O
for	O
not	O
properly	O
securing	O
their	O
DNS	B-Protocol
servers	I-Protocol
.	O
</s>
<s>
However	O
,	O
the	O
severity	O
of	O
this	O
attack	O
can	O
be	O
lessened	O
if	O
the	O
target	O
website	O
uses	O
secure	B-Application
cookies	I-Application
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
attacker	O
would	O
have	O
the	O
extra	O
challenge	O
of	O
obtaining	O
the	O
target	O
website	O
's	O
TLS	O
certificate	O
from	O
a	O
certificate	B-Architecture
authority	I-Architecture
,	O
since	O
secure	B-Application
cookies	I-Application
can	O
only	O
be	O
transmitted	O
over	O
an	O
encrypted	O
connection	O
.	O
</s>
<s>
Without	O
a	O
matching	O
TLS	O
certificate	O
,	O
victims	O
 '	O
browsers	B-Application
would	O
display	O
a	O
warning	O
message	O
about	O
the	O
attacker	O
's	O
invalid	O
certificate	O
,	O
which	O
would	O
help	O
deter	O
users	O
from	O
visiting	O
the	O
attacker	O
's	O
fraudulent	O
website	O
and	O
sending	O
the	O
attacker	O
their	O
cookies	B-Application
.	O
</s>
<s>
Cookies	B-Application
can	O
also	O
be	O
stolen	O
using	O
a	O
technique	O
called	O
cross-site	O
scripting	O
.	O
</s>
<s>
This	O
occurs	O
when	O
an	O
attacker	O
takes	O
advantage	O
of	O
a	O
website	O
that	O
allows	O
its	O
users	O
to	O
post	O
unfiltered	O
HTML	B-Language
and	O
JavaScript	B-Language
content	O
.	O
</s>
<s>
By	O
posting	O
malicious	O
HTML	B-Language
and	O
JavaScript	B-Language
code	O
,	O
the	O
attacker	O
can	O
cause	O
the	O
victim	O
's	O
web	B-Application
browser	I-Application
to	O
send	O
the	O
victim	O
's	O
cookies	B-Application
to	O
a	O
website	O
the	O
attacker	O
controls	O
.	O
</s>
<s>
When	O
another	O
user	O
clicks	O
on	O
this	O
link	O
,	O
the	O
browser	B-Application
executes	O
the	O
piece	O
of	O
code	O
within	O
the	O
onclick	O
attribute	O
,	O
thus	O
replacing	O
the	O
string	O
document.cookie	O
with	O
the	O
list	O
of	O
cookies	B-Application
that	O
are	O
accessible	O
from	O
the	O
current	O
page	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
this	O
list	O
of	O
cookies	B-Application
is	O
sent	O
to	O
the	O
attacker.com	O
server	O
.	O
</s>
<s>
If	O
the	O
attacker	O
's	O
malicious	O
posting	O
is	O
on	O
an	O
HTTPS	B-Protocol
website	I-Protocol
https://www.example.com	O
,	O
secure	B-Application
cookies	I-Application
will	O
also	O
be	O
sent	O
to	O
attacker.com	O
in	O
plain	O
text	O
.	O
</s>
<s>
Such	O
attacks	O
can	O
be	O
mitigated	O
by	O
using	O
HttpOnly	O
cookies	B-Application
.	O
</s>
<s>
These	O
cookies	B-Application
will	O
not	O
be	O
accessible	O
by	O
client-side	O
scripting	O
languages	O
like	O
JavaScript	B-Language
,	O
and	O
therefore	O
,	O
the	O
attacker	O
will	O
not	O
be	O
able	O
to	O
gather	O
these	O
cookies	B-Application
.	O
</s>
<s>
In	O
older	O
versions	O
of	O
many	O
browsers	B-Application
,	O
there	O
were	O
security	O
holes	O
in	O
the	O
implementation	O
of	O
the	O
XMLHttpRequest	B-Protocol
API	O
.	O
</s>
<s>
This	O
API	O
allows	O
pages	O
to	O
specify	O
a	O
proxy	B-Application
server	I-Application
that	O
would	O
get	O
the	O
reply	O
,	O
and	O
this	O
proxy	B-Application
server	I-Application
is	O
not	O
subject	O
to	O
the	O
same-origin	B-Protocol
policy	I-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
a	O
victim	O
is	O
reading	O
an	O
attacker	O
's	O
posting	O
on	O
www.example.com	O
,	O
and	O
the	O
attacker	O
's	O
script	O
is	O
executed	O
in	O
the	O
victim	O
's	O
browser	B-Application
.	O
</s>
<s>
The	O
script	O
generates	O
a	O
request	O
to	O
www.example.com	O
with	O
the	O
proxy	B-Application
server	I-Application
attacker.com	O
.	O
</s>
<s>
Since	O
the	O
request	O
is	O
for	O
www.example.com	O
,	O
all	O
example.com	O
cookies	B-Application
will	O
be	O
sent	O
along	O
with	O
the	O
request	O
,	O
but	O
routed	O
through	O
the	O
attacker	O
's	O
proxy	B-Application
server	I-Application
.	O
</s>
<s>
Hence	O
,	O
the	O
attacker	O
would	O
be	O
able	O
to	O
harvest	O
the	O
victim	O
's	O
cookies	B-Application
.	O
</s>
<s>
This	O
attack	O
would	O
not	O
work	O
with	O
secure	B-Application
cookies	I-Application
,	O
since	O
they	O
can	O
only	O
be	O
transmitted	O
over	O
HTTPS	B-Protocol
connections	I-Protocol
,	O
and	O
the	O
HTTPS	B-Protocol
protocol	O
dictates	O
end-to-end	O
encryption	O
(	O
i.e.	O
</s>
<s>
the	O
information	O
is	O
encrypted	O
on	O
the	O
user	O
's	O
browser	B-Application
and	O
decrypted	O
on	O
the	O
destination	O
server	O
)	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
proxy	B-Application
server	I-Application
would	O
only	O
see	O
the	O
raw	O
,	O
encrypted	O
bytes	B-Application
of	O
the	O
HTTP	B-Protocol
request	O
.	O
</s>
<s>
Suppose	O
that	O
Mallory	O
has	O
crafted	O
an	O
HTML	B-Language
image	O
element	O
that	O
references	O
an	O
action	O
on	O
Bob	O
's	O
bank	O
's	O
website	O
(	O
rather	O
than	O
an	O
image	O
file	O
)	O
,	O
e.g.	O
,	O
</s>
<s>
If	O
Bob	O
's	O
bank	O
keeps	O
his	O
authentication	O
information	O
in	O
a	O
cookie	B-Application
,	O
and	O
if	O
the	O
cookie	B-Application
has	O
n't	O
expired	O
,	O
then	O
the	O
attempt	O
by	O
Bob	O
's	O
browser	B-Application
to	O
load	O
the	O
image	O
will	O
submit	O
the	O
withdrawal	O
form	O
with	O
his	O
cookie	B-Application
,	O
thus	O
authorizing	O
a	O
transaction	O
without	O
Bob	O
's	O
approval	O
.	O
</s>
<s>
Cookiejacking	O
is	O
an	O
attack	O
against	O
Internet	B-Application
Explorer	I-Application
which	O
allows	O
the	O
attacker	O
to	O
steal	O
session	O
cookies	B-Application
of	O
a	O
user	O
by	O
tricking	O
a	O
user	O
into	O
dragging	O
an	O
object	O
across	O
the	O
screen	O
.	O
</s>
<s>
Microsoft	O
deemed	O
the	O
flaw	O
low-risk	O
because	O
of	O
"	O
the	O
level	O
of	O
required	O
user	O
interaction	O
"	O
,	O
and	O
the	O
necessity	O
of	O
having	O
a	O
user	O
already	O
logged	O
into	O
the	O
website	O
whose	O
cookie	B-Application
is	O
stolen	O
.	O
</s>
<s>
Despite	O
this	O
,	O
a	O
researcher	O
tried	O
the	O
attack	O
on	O
150	O
of	O
their	O
Facebook	O
friends	O
and	O
obtained	O
cookies	B-Application
of	O
80	O
of	O
them	O
via	O
social	O
engineering	O
.	O
</s>
<s>
Besides	O
privacy	O
concerns	O
,	O
cookies	B-Application
also	O
have	O
some	O
technical	O
drawbacks	O
.	O
</s>
<s>
In	O
particular	O
,	O
they	O
do	O
not	O
always	O
accurately	O
identify	O
users	O
,	O
they	O
can	O
be	O
used	O
for	O
security	O
attacks	O
,	O
and	O
they	O
are	O
often	O
at	O
odds	O
with	O
the	O
Representational	B-Protocol
State	I-Protocol
Transfer	I-Protocol
(	O
REST	B-Protocol
)	O
software	O
architectural	O
style	O
.	O
</s>
<s>
If	O
more	O
than	O
one	O
browser	B-Application
is	O
used	O
on	O
a	O
computer	O
,	O
each	O
usually	O
has	O
a	O
separate	O
storage	O
area	O
for	O
cookies	B-Application
.	O
</s>
<s>
Hence	O
,	O
cookies	B-Application
do	O
not	O
identify	O
a	O
person	O
,	O
but	O
a	O
combination	O
of	O
a	O
user	O
account	O
,	O
a	O
computer	O
,	O
and	O
a	O
web	B-Application
browser	I-Application
.	O
</s>
<s>
Thus	O
,	O
anyone	O
who	O
uses	O
multiple	O
accounts	O
,	O
computers	O
,	O
or	O
browsers	B-Application
has	O
multiple	O
sets	O
of	O
cookies	B-Application
.	O
</s>
<s>
Likewise	O
,	O
cookies	B-Application
do	O
not	O
differentiate	O
between	O
multiple	O
users	O
who	O
share	O
the	O
same	O
user	O
account	O
,	O
computer	O
,	O
and	O
browser	B-Application
.	O
</s>
<s>
Some	O
of	O
the	O
operations	O
that	O
can	O
be	O
done	O
using	O
cookies	B-Application
can	O
also	O
be	O
done	O
using	O
other	O
mechanisms	O
.	O
</s>
<s>
A	O
JSON	B-General_Concept
Web	I-General_Concept
Token	I-General_Concept
(	O
JWT	O
)	O
is	O
a	O
self-contained	O
packet	O
of	O
information	O
that	O
can	O
be	O
used	O
to	O
store	O
user	O
identity	O
and	O
authenticity	O
information	O
.	O
</s>
<s>
This	O
allows	O
them	O
to	O
be	O
used	O
in	O
place	O
of	O
session	O
cookies	B-Application
.	O
</s>
<s>
Unlike	O
cookies	B-Application
,	O
which	O
are	O
automatically	O
attached	O
to	O
each	O
HTTP	B-Protocol
request	O
by	O
the	O
browser	B-Application
,	O
JWTs	O
must	O
be	O
explicitly	O
attached	O
to	O
each	O
HTTP	B-Protocol
request	O
by	O
the	O
web	O
application	O
.	O
</s>
<s>
The	O
HTTP	B-Protocol
protocol	I-Protocol
includes	O
the	O
basic	B-Protocol
access	I-Protocol
authentication	I-Protocol
and	O
the	O
digest	B-Protocol
access	I-Protocol
authentication	I-Protocol
protocols	O
,	O
which	O
allow	O
access	O
to	O
a	O
web	O
page	O
only	O
when	O
the	O
user	O
has	O
provided	O
the	O
correct	O
username	O
and	O
password	O
.	O
</s>
<s>
If	O
the	O
server	O
requires	O
such	O
credentials	O
for	O
granting	O
access	O
to	O
a	O
web	O
page	O
,	O
the	O
browser	B-Application
requests	O
them	O
from	O
the	O
user	O
and	O
,	O
once	O
obtained	O
,	O
the	O
browser	B-Application
stores	O
and	O
sends	O
them	O
in	O
every	O
subsequent	O
page	O
request	O
.	O
</s>
<s>
The	O
query	B-Protocol
string	I-Protocol
part	O
of	O
the	O
URL	O
is	O
the	O
part	O
that	O
is	O
typically	O
used	O
for	O
this	O
purpose	O
,	O
but	O
other	O
parts	O
can	O
be	O
used	O
as	O
well	O
.	O
</s>
<s>
The	B-Application
Java	I-Application
Servlet	I-Application
and	O
PHP	B-Application
session	O
mechanisms	O
both	O
use	O
this	O
method	O
if	O
cookies	B-Application
are	O
not	O
enabled	O
.	O
</s>
<s>
This	O
method	O
consists	O
of	O
the	O
web	B-Application
server	I-Application
appending	O
query	B-Protocol
strings	I-Protocol
containing	O
a	O
unique	O
session	O
identifier	O
to	O
all	O
the	O
links	O
inside	O
of	O
a	O
web	O
page	O
.	O
</s>
<s>
When	O
the	O
user	O
follows	O
a	O
link	O
,	O
the	O
browser	B-Application
sends	O
the	O
query	B-Protocol
string	I-Protocol
to	O
the	O
server	O
,	O
allowing	O
the	O
server	O
to	O
identify	O
the	O
user	O
and	O
maintain	O
state	O
.	O
</s>
<s>
These	O
kinds	O
of	O
query	B-Protocol
strings	I-Protocol
are	O
very	O
similar	O
to	O
cookies	B-Application
in	O
that	O
both	O
contain	O
arbitrary	O
pieces	O
of	O
information	O
chosen	O
by	O
the	O
server	O
and	O
both	O
are	O
sent	O
back	O
to	O
the	O
server	O
on	O
every	O
request	O
.	O
</s>
<s>
Since	O
a	O
query	B-Protocol
string	I-Protocol
is	O
part	O
of	O
a	O
URL	O
,	O
if	O
that	O
URL	O
is	O
later	O
reused	O
,	O
the	O
same	O
attached	O
piece	O
of	O
information	O
will	O
be	O
sent	O
to	O
the	O
server	O
,	O
which	O
could	O
lead	O
to	O
confusion	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
the	O
preferences	O
of	O
a	O
user	O
are	O
encoded	O
in	O
the	O
query	B-Protocol
string	I-Protocol
of	O
a	O
URL	O
and	O
the	O
user	O
sends	O
this	O
URL	O
to	O
another	O
user	O
by	O
e-mail	O
,	O
those	O
preferences	O
will	O
be	O
used	O
for	O
that	O
other	O
user	O
as	O
well	O
.	O
</s>
<s>
Moreover	O
,	O
if	O
the	O
same	O
user	O
accesses	O
the	O
same	O
page	O
multiple	O
times	O
from	O
different	O
sources	O
,	O
there	O
is	O
no	O
guarantee	O
that	O
the	O
same	O
query	B-Protocol
string	I-Protocol
will	O
be	O
used	O
each	O
time	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
a	O
user	O
visits	O
a	O
page	O
by	O
coming	O
from	O
a	O
page	O
internal	O
to	O
the	O
site	O
the	O
first	O
time	O
,	O
and	O
then	O
visits	O
the	O
same	O
page	O
by	O
coming	O
from	O
an	O
external	O
search	B-Application
engine	I-Application
the	O
second	O
time	O
,	O
the	O
query	B-Protocol
strings	I-Protocol
would	O
likely	O
be	O
different	O
.	O
</s>
<s>
If	O
cookies	B-Application
were	O
used	O
in	O
this	O
situation	O
,	O
the	O
cookies	B-Application
would	O
be	O
the	O
same	O
.	O
</s>
<s>
Other	O
drawbacks	O
of	O
query	B-Protocol
strings	I-Protocol
are	O
related	O
to	O
security	O
.	O
</s>
<s>
Storing	O
data	B-General_Concept
that	O
identifies	O
a	O
session	O
in	O
a	O
query	B-Protocol
string	I-Protocol
enables	O
session	B-Protocol
fixation	I-Protocol
attacks	O
,	O
referer	B-Protocol
logging	O
attacks	O
and	O
other	O
security	O
exploits	O
.	O
</s>
<s>
Transferring	O
session	O
identifiers	O
as	O
HTTP	B-Application
cookies	I-Application
is	O
more	O
secure	O
.	O
</s>
<s>
Another	O
form	O
of	O
session	O
tracking	B-Application
is	O
to	O
use	O
web	B-General_Concept
forms	I-General_Concept
with	O
hidden	O
fields	O
.	O
</s>
<s>
This	O
technique	O
is	O
very	O
similar	O
to	O
using	O
URL	B-Protocol
query	I-Protocol
strings	O
to	O
hold	O
the	O
information	O
and	O
has	O
many	O
of	O
the	O
same	O
advantages	O
and	O
drawbacks	O
.	O
</s>
<s>
In	O
fact	O
,	O
if	O
the	O
form	O
is	O
handled	O
with	O
the	O
HTTP	B-Protocol
GET	O
method	O
,	O
then	O
this	O
technique	O
is	O
similar	O
to	O
using	O
URL	B-Protocol
query	I-Protocol
strings	O
,	O
since	O
the	O
GET	O
method	O
adds	O
the	O
form	O
fields	O
to	O
the	O
URL	O
as	O
a	O
query	B-Protocol
string	I-Protocol
.	O
</s>
<s>
But	O
most	O
forms	O
are	O
handled	O
with	O
HTTP	B-Protocol
POST	O
,	O
which	O
causes	O
the	O
form	O
information	O
,	O
including	O
the	O
hidden	O
fields	O
,	O
to	O
be	O
sent	O
in	O
the	O
HTTP	B-Protocol
request	O
body	O
,	O
which	O
is	O
neither	O
part	O
of	O
the	O
URL	O
,	O
nor	O
of	O
a	O
cookie	B-Application
.	O
</s>
<s>
First	O
,	O
having	O
the	O
tracking	B-Application
information	O
placed	O
in	O
the	O
HTTP	B-Protocol
request	O
body	O
rather	O
than	O
in	O
the	O
URL	O
means	O
it	O
will	O
not	O
be	O
noticed	O
by	O
the	O
average	O
user	O
.	O
</s>
<s>
All	O
current	O
web	B-Application
browsers	I-Application
can	O
store	O
a	O
fairly	O
large	O
amount	O
of	O
data	B-General_Concept
(	O
2	O
–	O
32MB	O
)	O
via	O
JavaScript	B-Language
using	O
the	B-General_Concept
DOM	I-General_Concept
property	O
window.name	O
.	O
</s>
<s>
This	O
data	B-General_Concept
can	O
be	O
used	O
instead	O
of	O
session	O
cookies	B-Application
.	O
</s>
<s>
The	O
technique	O
can	O
be	O
coupled	O
with	O
JSON/JavaScript	O
objects	O
to	O
store	O
complex	O
sets	O
of	O
session	O
variables	O
on	O
the	O
client	O
side	O
.	O
</s>
<s>
In	O
some	O
respects	O
,	O
this	O
can	O
be	O
more	O
secure	O
than	O
cookies	B-Application
due	O
to	O
the	O
fact	O
that	O
its	O
contents	O
are	O
not	O
automatically	O
sent	O
to	O
the	O
server	O
on	O
every	O
request	O
like	O
cookies	B-Application
are	O
,	O
so	O
it	O
is	O
not	O
vulnerable	O
to	O
network	O
cookie	B-Application
sniffing	O
attacks	O
.	O
</s>
<s>
Some	O
users	O
may	O
be	O
tracked	O
based	O
on	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
computer	O
requesting	O
the	O
page	O
.	O
</s>
<s>
The	O
server	O
knows	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
computer	O
running	O
the	O
browser	B-Application
(	O
or	O
the	O
proxy	B-Application
,	O
if	O
any	O
is	O
used	O
)	O
and	O
could	O
theoretically	O
link	O
a	O
user	O
's	O
session	O
to	O
this	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
However	O
,	O
IP	B-Protocol
addresses	I-Protocol
are	O
generally	O
not	O
a	O
reliable	O
way	O
to	O
track	O
a	O
session	O
or	O
identify	O
a	O
user	O
.	O
</s>
<s>
This	O
means	O
that	O
several	O
PCs	O
will	O
share	O
a	O
public	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
Furthermore	O
,	O
some	O
systems	O
,	O
such	O
as	O
Tor	B-Application
,	O
are	O
designed	O
to	O
retain	O
Internet	O
anonymity	O
,	O
rendering	O
tracking	B-Application
by	O
IP	B-Protocol
address	I-Protocol
impractical	O
,	O
impossible	O
,	O
or	O
a	O
security	O
risk	O
.	O
</s>
<s>
Because	O
ETags	O
are	O
cached	O
by	O
the	O
browser	B-Application
,	O
and	O
returned	O
with	O
subsequent	O
requests	O
for	O
the	O
same	O
resource	O
,	O
a	O
tracking	B-Application
server	O
can	O
simply	O
repeat	O
any	O
ETag	B-Protocol
received	O
from	O
the	O
browser	B-Application
to	O
ensure	O
an	O
assigned	O
ETag	B-Protocol
persists	O
indefinitely	O
(	O
in	O
a	O
similar	O
way	O
to	O
persistent	O
cookies	B-Application
)	O
.	O
</s>
<s>
Additional	O
caching	O
header	O
fields	O
can	O
also	O
enhance	O
the	O
preservation	O
of	O
ETag	B-Protocol
data	B-General_Concept
.	O
</s>
<s>
ETags	O
can	O
be	O
flushed	O
in	O
some	O
browsers	B-Application
by	O
clearing	O
the	O
browser	B-Protocol
cache	I-Protocol
.	O
</s>
<s>
The	O
browser	B-Protocol
cache	I-Protocol
can	O
also	O
be	O
used	O
to	O
store	O
information	O
that	O
can	O
be	O
used	O
to	O
track	O
individual	O
users	O
.	O
</s>
<s>
This	O
technique	O
takes	O
advantage	O
of	O
the	O
fact	O
that	O
the	O
web	B-Application
browser	I-Application
will	O
use	O
resources	O
stored	O
within	O
the	O
cache	O
instead	O
of	O
downloading	O
them	O
from	O
the	O
website	O
when	O
it	O
determines	O
that	O
the	O
cache	O
already	O
has	O
the	O
most	O
up-to-date	O
version	O
of	O
the	O
resource	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
website	O
could	O
serve	O
a	O
JavaScript	B-Language
file	O
with	O
code	O
that	O
sets	O
a	O
unique	O
identifier	O
for	O
the	O
user	O
(	O
for	O
example	O
,	O
var	O
userId	O
=	O
3243242	O
;	O
)	O
.	O
</s>
<s>
A	O
browser	B-Protocol
fingerprint	I-Protocol
is	O
information	O
collected	O
about	O
a	O
browser	B-Application
's	O
configuration	O
,	O
such	O
as	O
version	O
number	O
,	O
screen	O
resolution	O
,	O
and	O
operating	O
system	O
,	O
for	O
the	O
purpose	O
of	O
identification	O
.	O
</s>
<s>
Fingerprints	O
can	O
be	O
used	O
to	O
fully	O
or	O
partially	O
identify	O
individual	O
users	O
or	O
devices	O
even	O
when	O
cookies	B-Application
are	O
turned	O
off	O
.	O
</s>
<s>
Basic	O
web	B-Application
browser	I-Application
configuration	O
information	O
has	O
long	O
been	O
collected	O
by	O
web	O
analytics	O
services	O
in	O
an	O
effort	O
to	O
accurately	O
measure	O
real	O
human	O
web	O
traffic	O
and	O
discount	O
various	O
forms	O
of	O
click	O
fraud	O
.	O
</s>
<s>
Assimilation	O
of	O
such	O
information	O
into	O
a	O
single	O
string	O
constitutes	O
a	O
device	B-Protocol
fingerprint	I-Protocol
.	O
</s>
<s>
In	O
2010	O
,	O
EFF	O
measured	O
at	O
least	O
18.1	O
bits	O
of	O
entropy	O
possible	O
from	O
browser	B-Protocol
fingerprinting	I-Protocol
.	O
</s>
<s>
Canvas	B-Protocol
fingerprinting	I-Protocol
,	O
a	O
more	O
recent	O
technique	O
,	O
claims	O
to	O
add	O
another	O
5.7	O
bits	O
.	O
</s>
<s>
Some	O
web	B-Application
browsers	I-Application
support	O
persistence	O
mechanisms	O
which	O
allow	O
the	O
page	O
to	O
store	O
the	O
information	O
locally	O
for	O
later	O
use	O
.	O
</s>
<s>
The	O
HTML5	B-Application
standard	O
(	O
which	O
most	O
modern	O
web	B-Application
browsers	I-Application
support	O
to	O
some	O
extent	O
)	O
includes	O
a	O
JavaScript	B-Language
API	O
called	O
Web	B-Application
storage	I-Application
that	O
allows	O
two	O
types	O
of	O
storage	O
:	O
local	O
storage	O
and	O
session	B-Application
storage	I-Application
.	O
</s>
<s>
Local	O
storage	O
behaves	O
similarly	O
to	O
persistent	O
cookies	B-Application
while	O
session	B-Application
storage	I-Application
behaves	O
similarly	O
to	O
session	O
cookies	B-Application
,	O
except	O
that	O
session	B-Application
storage	I-Application
is	O
tied	O
to	O
an	O
individual	O
tab/window	O
'	O
s	O
lifetime	O
(	O
AKA	O
a	O
page	O
session	O
)	O
,	O
not	O
to	O
a	O
whole	O
browser	B-Application
session	O
like	O
session	O
cookies	B-Application
.	O
</s>
<s>
Internet	B-Application
Explorer	I-Application
supports	O
persistent	O
information	O
in	O
the	O
browser	B-Application
's	O
history	O
,	O
in	O
the	O
browser	B-Application
's	O
favorites	O
,	O
in	O
an	O
XML	O
store	O
(	O
"	O
user	O
data	B-General_Concept
"	O
)	O
,	O
or	O
directly	O
within	O
a	O
web	O
page	O
saved	O
to	O
disk	O
.	O
</s>
<s>
Some	O
web	B-Application
browser	I-Application
plugins	O
include	O
persistence	O
mechanisms	O
as	O
well	O
.	O
</s>
<s>
For	O
example	O
,	O
Adobe	B-Operating_System
Flash	I-Operating_System
has	O
Local	B-Operating_System
shared	I-Operating_System
object	I-Operating_System
and	O
Microsoft	B-Application
Silverlight	I-Application
has	O
Isolated	O
storage	O
.	O
</s>
