<s>
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
is	O
a	O
cryptographic	B-Protocol
protocol	I-Protocol
designed	O
to	O
provide	O
communications	O
security	O
over	O
a	O
computer	O
network	O
.	O
</s>
<s>
The	O
protocol	B-Protocol
is	O
widely	O
used	O
in	O
applications	O
such	O
as	O
email	O
,	O
instant	B-Application
messaging	I-Application
,	O
and	O
voice	B-Application
over	I-Application
IP	I-Application
,	O
but	O
its	O
use	O
in	O
securing	O
HTTPS	B-Protocol
remains	O
the	O
most	O
publicly	O
visible	O
.	O
</s>
<s>
The	O
TLS	B-Protocol
protocol	I-Protocol
aims	O
primarily	O
to	O
provide	O
security	O
,	O
including	O
privacy	O
(	O
confidentiality	O
)	O
,	O
integrity	O
,	O
and	O
authenticity	O
through	O
the	O
use	O
of	O
cryptography	O
,	O
such	O
as	O
the	O
use	O
of	O
certificates	O
,	O
between	O
two	O
or	O
more	O
communicating	O
computer	O
applications	O
.	O
</s>
<s>
It	O
runs	O
in	O
the	O
presentation	B-Application
layer	I-Application
and	O
is	O
itself	O
composed	O
of	O
two	O
layers	O
:	O
the	O
TLS	O
record	O
and	O
the	O
TLS	O
handshake	B-Protocol
protocols	I-Protocol
.	O
</s>
<s>
The	O
closely	O
related	O
Datagram	B-Protocol
Transport	I-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
DTLS	B-Protocol
)	O
is	O
a	O
communications	O
protocol	B-Protocol
that	O
provides	O
security	O
to	O
datagram-based	O
applications	O
.	O
</s>
<s>
TLS	O
builds	O
on	O
the	O
now-deprecated	O
SSL	O
(	O
Secure	B-Protocol
Sockets	I-Protocol
Layer	I-Protocol
)	O
specifications	O
(	O
1994	O
,	O
1995	O
,	O
1996	O
)	O
developed	O
by	O
Netscape	B-Protocol
Communications	I-Protocol
for	O
adding	O
the	O
HTTPS	B-Protocol
protocol	B-Protocol
to	O
their	O
Navigator	B-Protocol
web	B-Application
browser	I-Application
.	O
</s>
<s>
Client-server	B-Operating_System
applications	O
use	O
the	O
TLS	B-Protocol
protocol	I-Protocol
to	O
communicate	O
across	O
a	O
network	O
in	O
a	O
way	O
designed	O
to	O
prevent	O
eavesdropping	O
and	O
tampering	O
.	O
</s>
<s>
Since	O
applications	O
can	O
communicate	O
either	O
with	O
or	O
without	O
TLS	O
(	O
or	O
SSL	O
)	O
,	O
it	O
is	O
necessary	O
for	O
the	O
client	B-Protocol
to	O
request	O
that	O
the	O
server	B-Application
set	O
up	O
a	O
TLS	O
connection	O
.	O
</s>
<s>
One	O
of	O
the	O
main	O
ways	O
of	O
achieving	O
this	O
is	O
to	O
use	O
a	O
different	O
port	B-Protocol
number	I-Protocol
for	O
TLS	O
connections	O
.	O
</s>
<s>
Port	O
80	O
is	O
typically	O
used	O
for	O
unencrypted	O
HTTP	B-Protocol
traffic	O
while	O
port	O
443	O
is	O
the	O
common	O
port	O
used	O
for	O
encrypted	O
HTTPS	B-Protocol
traffic	O
.	O
</s>
<s>
Another	O
mechanism	O
is	O
to	O
make	O
a	O
protocol-specific	O
STARTTLS	B-Protocol
request	O
to	O
the	O
server	B-Application
to	O
switch	O
the	O
connection	O
to	O
TLS	O
–	O
for	O
example	O
,	O
when	O
using	O
the	O
mail	O
and	O
news	B-Application
protocols	O
.	O
</s>
<s>
Once	O
the	O
client	B-Protocol
and	O
server	B-Application
have	O
agreed	O
to	O
use	O
TLS	O
,	O
they	O
negotiate	O
a	O
stateful	B-Application
connection	O
by	O
using	O
a	O
handshaking	O
procedure	O
(	O
see	O
)	O
.	O
</s>
<s>
The	O
protocols	O
use	O
a	O
handshake	B-Protocol
with	O
an	O
asymmetric	B-Application
cipher	I-Application
to	O
establish	O
not	O
only	O
cipher	B-Application
settings	O
but	O
also	O
a	O
session-specific	O
shared	B-Algorithm
key	I-Algorithm
with	O
which	O
further	O
communication	O
is	O
encrypted	O
using	O
a	O
symmetric	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
During	O
this	O
handshake	B-Protocol
,	O
the	O
client	B-Protocol
and	O
server	B-Application
agree	O
on	O
various	O
parameters	O
used	O
to	O
establish	O
the	O
connection	O
's	O
security	O
:	O
</s>
<s>
The	O
handshake	B-Protocol
begins	O
when	O
a	O
client	B-Protocol
connects	O
to	O
a	O
TLS-enabled	O
server	B-Application
requesting	O
a	O
secure	B-Protocol
connection	I-Protocol
and	O
the	O
client	B-Protocol
presents	O
a	O
list	O
of	O
supported	O
cipher	B-Protocol
suites	I-Protocol
(	O
ciphers	B-Application
and	O
hash	B-Algorithm
functions	I-Algorithm
)	O
.	O
</s>
<s>
From	O
this	O
list	O
,	O
the	O
server	B-Application
picks	O
a	O
cipher	B-Application
and	O
hash	B-Algorithm
function	I-Algorithm
that	O
it	O
also	O
supports	O
and	O
notifies	O
the	O
client	B-Protocol
of	O
the	O
decision	O
.	O
</s>
<s>
The	O
server	B-Application
usually	O
then	O
provides	O
identification	O
in	O
the	O
form	O
of	O
a	O
digital	O
certificate	O
.	O
</s>
<s>
The	O
certificate	O
contains	O
the	O
server	B-Protocol
name	I-Protocol
,	O
the	O
trusted	O
certificate	B-Architecture
authority	I-Architecture
(	O
CA	O
)	O
that	O
vouches	O
for	O
the	O
authenticity	O
of	O
the	O
certificate	O
,	O
and	O
the	O
server	B-Application
's	O
public	B-Application
encryption	I-Application
key	I-Application
.	O
</s>
<s>
The	O
client	B-Protocol
confirms	O
the	O
validity	O
of	O
the	O
certificate	O
before	O
proceeding	O
.	O
</s>
<s>
To	O
generate	O
the	O
session	O
keys	O
used	O
for	O
the	O
secure	B-Protocol
connection	I-Protocol
,	O
the	O
client	B-Protocol
either	O
:	O
</s>
<s>
uses	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
key	I-Protocol
exchange	I-Protocol
(	O
or	O
its	O
variant	O
elliptic-curve	B-Protocol
DH	I-Protocol
)	O
to	O
securely	O
generate	O
a	O
random	O
and	O
unique	O
session	O
key	O
for	O
encryption	O
and	O
decryption	O
that	O
has	O
the	O
additional	O
property	O
of	O
forward	O
secrecy	O
:	O
if	O
the	O
server	B-Application
's	O
private	B-Application
key	I-Application
is	O
disclosed	O
in	O
future	O
,	O
it	O
cannot	O
be	O
used	O
to	O
decrypt	O
the	O
current	O
session	O
,	O
even	O
if	O
the	O
session	O
is	O
intercepted	O
and	O
recorded	O
by	O
a	O
third	O
party	O
.	O
</s>
<s>
This	O
concludes	O
the	O
handshake	B-Protocol
and	O
begins	O
the	O
secured	O
connection	O
,	O
which	O
is	O
encrypted	O
and	O
decrypted	O
with	O
the	O
session	O
key	O
until	O
the	O
connection	O
closes	O
.	O
</s>
<s>
If	O
any	O
one	O
of	O
the	O
above	O
steps	O
fails	O
,	O
then	O
the	O
TLS	O
handshake	B-Protocol
fails	O
and	O
the	O
connection	O
is	O
not	O
created	O
.	O
</s>
<s>
TLS	O
and	O
SSL	O
do	O
not	O
fit	O
neatly	O
into	O
any	O
single	O
layer	O
of	O
the	O
OSI	O
model	O
or	O
the	O
TCP/IP	B-Protocol
model	I-Protocol
.	O
</s>
<s>
TLS	O
runs	O
"	O
on	O
top	O
of	O
some	O
reliable	O
transport	B-Architecture
protocol	I-Architecture
(	O
e.g.	O
,	O
TCP	B-Protocol
)	O
,	O
"	O
which	O
would	O
imply	O
that	O
it	O
is	O
above	O
the	O
transport	B-Architecture
layer	I-Architecture
.	O
</s>
<s>
It	O
serves	O
encryption	O
to	O
higher	O
layers	O
,	O
which	O
is	O
normally	O
the	O
function	O
of	O
the	O
presentation	B-Application
layer	I-Application
.	O
</s>
<s>
However	O
,	O
applications	O
generally	O
use	O
TLS	O
as	O
if	O
it	O
were	O
a	O
transport	B-Architecture
layer	I-Architecture
,	O
even	O
though	O
applications	O
using	O
TLS	O
must	O
actively	O
control	O
initiating	O
TLS	O
handshakes	B-Protocol
and	O
handling	O
of	O
exchanged	O
authentication	O
certificates	O
.	O
</s>
<s>
When	O
secured	O
by	O
TLS	O
,	O
connections	O
between	O
a	O
client	B-Protocol
(	O
e.g.	O
,	O
a	O
web	B-Application
browser	I-Application
)	O
and	O
a	O
server	B-Application
(	O
e.g.	O
,	O
wikipedia.org	O
)	O
will	O
have	O
all	O
of	O
the	O
following	O
properties	O
:	O
</s>
<s>
The	O
connection	O
is	O
private	O
(	O
or	O
has	O
confidentiality	O
)	O
because	O
a	O
symmetric-key	B-Algorithm
algorithm	I-Algorithm
is	O
used	O
to	O
encrypt	O
the	O
data	O
transmitted	O
.	O
</s>
<s>
The	O
keys	O
for	O
this	O
symmetric	B-Algorithm
encryption	I-Algorithm
are	O
generated	O
uniquely	O
for	O
each	O
connection	O
and	O
are	O
based	O
on	O
a	O
shared	O
secret	O
that	O
was	O
negotiated	O
at	O
the	O
start	O
of	O
the	O
session	O
.	O
</s>
<s>
The	O
server	B-Application
and	O
client	B-Protocol
negotiate	O
the	O
details	O
of	O
which	O
encryption	O
algorithm	O
and	O
cryptographic	O
keys	O
to	O
use	O
before	O
the	O
first	O
byte	O
of	O
data	O
is	O
transmitted	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
The	O
identity	O
of	O
the	O
communicating	O
parties	O
can	O
be	O
authenticated	O
using	O
public-key	B-Application
cryptography	I-Application
.	O
</s>
<s>
This	O
authentication	O
is	O
required	O
for	O
the	O
server	B-Application
and	O
optional	O
for	O
the	O
client	B-Protocol
.	O
</s>
<s>
The	O
connection	O
is	O
reliable	O
(	O
or	O
has	O
integrity	O
)	O
because	O
each	O
message	O
transmitted	O
includes	O
a	O
message	B-Algorithm
integrity	I-Algorithm
check	I-Algorithm
using	O
a	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
to	O
prevent	O
undetected	O
loss	O
or	O
alteration	O
of	O
the	O
data	O
during	O
transmission	O
.	O
</s>
<s>
Attempts	O
have	O
been	O
made	O
to	O
subvert	O
aspects	O
of	O
the	O
communications	O
security	O
that	O
TLS	O
seeks	O
to	O
provide	O
,	O
and	O
the	O
protocol	B-Protocol
has	O
been	O
revised	O
several	O
times	O
to	O
address	O
these	O
security	O
threats	O
.	O
</s>
<s>
Developers	O
of	O
web	B-Application
browsers	I-Application
have	O
repeatedly	O
revised	O
their	O
products	O
to	O
defend	O
against	O
potential	O
security	O
weaknesses	O
after	O
these	O
were	O
discovered	O
(	O
see	O
TLS/SSL	B-Protocol
support	O
history	O
of	O
web	B-Application
browsers	I-Application
)	O
.	O
</s>
<s>
Datagram	B-Protocol
Transport	I-Protocol
Layer	I-Protocol
Security	I-Protocol
,	O
abbreviated	O
DTLS	B-Protocol
,	O
is	O
a	O
related	O
communications	O
protocol	B-Protocol
providing	O
security	O
to	O
datagram-based	O
applications	O
by	O
allowing	O
them	O
to	O
communicate	O
in	O
a	O
way	O
designed	O
to	O
prevent	O
eavesdropping	O
,	O
tampering	O
,	O
or	O
message	O
forgery	O
.	O
</s>
<s>
The	O
DTLS	B-Protocol
protocol	B-Protocol
is	O
based	O
on	O
the	O
stream-oriented	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
protocol	B-Protocol
and	O
is	O
intended	O
to	O
provide	O
similar	O
security	O
guarantees	O
.	O
</s>
<s>
However	O
,	O
unlike	O
TLS	O
,	O
it	O
can	O
be	O
used	O
with	O
most	O
datagram	B-Protocol
oriented	O
protocols	O
including	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
,	O
Datagram	B-Protocol
Congestion	I-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
DCCP	B-Protocol
)	O
,	O
Control	O
And	O
Provisioning	O
of	O
Wireless	O
Access	O
Points	O
(	O
CAPWAP	O
)	O
,	O
Stream	B-Protocol
Control	I-Protocol
Transmission	I-Protocol
Protocol	I-Protocol
(	O
SCTP	B-Protocol
)	O
encapsulation	O
,	O
and	O
Secure	B-Protocol
Real-time	I-Protocol
Transport	I-Protocol
Protocol	I-Protocol
(	O
SRTP	O
)	O
.	O
</s>
<s>
As	O
the	O
DTLS	B-Protocol
protocol	B-Protocol
datagram	B-Protocol
preserves	O
the	O
semantics	O
of	O
the	O
underlying	O
transport	O
—	O
the	O
application	O
it	O
does	O
not	O
suffer	O
from	O
the	O
delays	O
associated	O
with	O
stream	B-Architecture
protocols	O
,	O
however	O
the	O
application	O
has	O
to	O
deal	O
with	O
packet	B-Protocol
reordering	I-Protocol
,	O
loss	O
of	O
datagram	B-Protocol
and	O
data	O
larger	O
than	O
the	O
size	O
of	O
a	O
datagram	B-Protocol
network	B-Protocol
packet	I-Protocol
.	O
</s>
<s>
Because	O
DTLS	B-Protocol
uses	O
UDP	O
or	O
SCTP	B-Protocol
rather	O
than	O
TCP	B-Protocol
,	O
it	O
avoids	O
the	O
"	O
TCP	B-Protocol
meltdown	O
problem	O
"	O
,	O
when	O
being	O
used	O
to	O
create	O
a	O
VPN	B-Application
tunnel	O
.	O
</s>
<s>
The	O
original	O
2006	O
release	O
of	O
DTLS	B-Protocol
version	O
1.0	O
was	O
not	O
a	O
standalone	O
document	O
.	O
</s>
<s>
Similarly	O
the	O
followup	O
2012	O
release	O
of	O
DTLS	B-Protocol
is	O
a	O
delta	O
to	O
TLS	O
1.2	O
.	O
</s>
<s>
It	O
was	O
given	O
the	O
version	O
number	O
of	O
DTLS	B-Protocol
1.2	O
to	O
match	O
its	O
TLS	O
version	O
.	O
</s>
<s>
Lastly	O
,	O
the	O
2022	O
DTLS	B-Protocol
1.3	O
is	O
a	O
delta	O
to	O
TLS	O
1.3	O
.	O
</s>
<s>
Like	O
the	O
two	O
previous	O
versions	O
,	O
DTLS	B-Protocol
1.3	O
is	O
intended	O
to	O
provide	O
"	O
equivalent	O
security	O
guarantees	O
[	O
to	O
TLS	O
1.3	O
]	O
with	O
the	O
exception	O
of	O
order	O
protection/non	O
-replayability	O
"	O
.	O
</s>
<s>
Many	O
VPN	B-Application
clients	I-Application
including	O
Cisco	O
AnyConnect	O
&	O
InterCloud	O
Fabric	O
,	O
OpenConnect	B-Application
,	O
ZScaler	O
tunnel	O
,	O
F5	O
Networks	O
Edge	O
VPN	B-Application
Client	I-Application
,	O
and	O
Citrix	B-Application
Systems	I-Application
NetScaler	O
use	O
DTLS	B-Protocol
to	O
secure	O
UDP	O
traffic	O
.	O
</s>
<s>
In	O
addition	O
all	O
modern	O
web	B-Application
browsers	I-Application
support	O
DTLS-SRTP	O
for	O
WebRTC	B-Protocol
.	O
</s>
<s>
The	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
Protocol	I-Protocol
(	O
TLS	O
)	O
,	O
together	O
with	O
several	O
other	O
basic	O
network	O
security	O
platforms	O
,	O
was	O
developed	O
through	O
a	O
joint	O
initiative	O
begun	O
in	O
August	O
1986	O
,	O
among	O
the	O
National	O
Security	O
Agency	O
,	O
the	O
National	O
Bureau	O
of	O
Standards	O
,	O
the	O
Defense	O
Communications	O
Agency	O
,	O
and	O
twelve	O
communications	O
and	O
computer	O
corporations	O
who	O
initiated	O
a	O
special	O
project	O
called	O
the	O
Secure	O
Data	O
Network	O
System	O
(	O
SDNS	O
)	O
.	O
</s>
<s>
Originally	O
known	O
as	O
the	O
SP4	O
protocol	B-Protocol
,	O
it	O
was	O
renamed	O
TLS	O
and	O
subsequently	O
published	O
in	O
1995	O
as	O
international	O
standard	O
ITU-T	O
X.274	O
|	O
ISO/IEC	O
10736:1995	O
.	O
</s>
<s>
Early	O
research	O
efforts	O
towards	O
transport	B-Protocol
layer	I-Protocol
security	I-Protocol
included	O
the	O
Secure	B-Protocol
Network	I-Protocol
Programming	I-Protocol
(	O
SNP	O
)	O
application	B-Application
programming	I-Application
interface	I-Application
(	O
API	B-Application
)	O
,	O
which	O
in	O
1993	O
explored	O
the	O
approach	O
of	O
having	O
a	O
secure	O
transport	B-Architecture
layer	I-Architecture
API	B-Application
closely	O
resembling	O
Berkeley	B-Protocol
sockets	I-Protocol
,	O
to	O
facilitate	O
retrofitting	O
pre-existing	O
network	O
applications	O
with	O
security	O
measures	O
.	O
</s>
<s>
Netscape	B-Protocol
developed	O
the	O
original	O
SSL	O
protocols	O
,	O
and	O
Taher	O
Elgamal	O
,	O
chief	O
scientist	O
at	O
Netscape	B-Protocol
Communications	I-Protocol
from	O
1995	O
to	O
1998	O
,	O
has	O
been	O
described	O
as	O
the	O
"	O
father	O
of	O
SSL	O
"	O
.	O
</s>
<s>
SSL	O
version	O
1.0	O
was	O
never	O
publicly	O
released	O
because	O
of	O
serious	O
security	O
flaws	O
in	O
the	O
protocol	B-Protocol
.	O
</s>
<s>
It	O
had	O
a	O
weak	O
MAC	B-Algorithm
construction	O
that	O
used	O
the	O
MD5	B-Algorithm
hash	I-Algorithm
function	O
with	O
a	O
secret	O
prefix	O
,	O
making	O
it	O
vulnerable	O
to	O
length	O
extension	O
attacks	O
.	O
</s>
<s>
And	O
it	O
provided	O
no	O
protection	O
for	O
either	O
the	O
opening	O
handshake	B-Protocol
or	O
an	O
explicit	O
message	O
close	O
,	O
both	O
of	O
which	O
meant	O
man-in-the-middle	O
attacks	O
could	O
go	O
undetected	O
.	O
</s>
<s>
Moreover	O
,	O
SSL	O
2.0	O
assumed	O
a	O
single	O
service	O
and	O
a	O
fixed	O
domain	O
certificate	O
,	O
conflicting	O
with	O
the	O
widely	O
used	O
feature	O
of	O
virtual	O
hosting	O
in	O
Web	B-Application
servers	I-Application
,	O
so	O
most	O
websites	O
were	O
effectively	O
impaired	O
from	O
using	O
SSL	O
.	O
</s>
<s>
These	O
flaws	O
necessitated	O
the	O
complete	O
redesign	O
of	O
the	O
protocol	B-Protocol
to	O
SSL	O
version	O
3.0	O
.	O
</s>
<s>
Released	O
in	O
1996	O
,	O
it	O
was	O
produced	O
by	O
Paul	O
Kocher	O
working	O
with	O
Netscape	B-Protocol
engineers	O
Phil	O
Karlton	O
and	O
Alan	O
Freier	O
,	O
with	O
a	O
reference	O
implementation	O
by	O
Christopher	O
Allen	O
and	O
Tim	O
Dierks	O
of	O
Consensus	O
Development	O
.	O
</s>
<s>
Newer	O
versions	O
of	O
SSL/TLS	B-Protocol
are	O
based	O
on	O
SSL	O
3.0	O
.	O
</s>
<s>
In	O
2014	O
,	O
SSL	O
3.0	O
was	O
found	O
to	O
be	O
vulnerable	O
to	O
the	O
POODLE	B-Protocol
attack	I-Protocol
that	O
affects	O
all	O
block	O
ciphers	B-Application
in	O
SSL	O
;	O
RC4	B-Algorithm
,	O
the	O
only	O
non-block	O
cipher	B-Application
supported	O
by	O
SSL	O
3.0	O
,	O
is	O
also	O
feasibly	O
broken	O
as	O
used	O
in	O
SSL	O
3.0	O
.	O
</s>
<s>
As	O
stated	O
in	O
the	O
RFC	O
,	O
"	O
the	O
differences	O
between	O
this	O
protocol	B-Protocol
and	O
SSL	O
3.0	O
are	O
not	O
dramatic	O
,	O
but	O
they	O
are	O
significant	O
enough	O
to	O
preclude	O
interoperability	O
between	O
TLS	O
1.0	O
and	O
SSL	O
3.0	O
"	O
.	O
</s>
<s>
Tim	O
Dierks	O
later	O
wrote	O
that	O
these	O
changes	O
,	O
and	O
the	O
renaming	O
from	O
"	O
SSL	O
"	O
to	O
"	O
TLS	O
"	O
,	O
were	O
a	O
face-saving	O
gesture	O
to	O
Microsoft	O
,	O
"	O
so	O
it	O
would	O
n't	O
look	O
 [ like ] 	O
the	O
IETF	O
was	O
just	O
rubberstamping	O
Netscape	B-Protocol
's	O
protocol	B-Protocol
"	O
.	O
</s>
<s>
In	O
October	O
2018	O
,	O
Apple	O
,	O
Google	B-Application
,	O
Microsoft	O
,	O
and	O
Mozilla	B-Operating_System
jointly	O
announced	O
they	O
would	O
deprecate	O
TLS	O
1.0	O
and	O
1.1	O
in	O
March	O
2020	O
.	O
</s>
<s>
Added	O
protection	O
against	O
cipher-block	O
chaining	O
(	O
CBC	O
)	O
attacks	O
.	O
</s>
<s>
The	O
implicit	O
initialization	B-Algorithm
vector	I-Algorithm
(	O
IV	B-Algorithm
)	O
was	O
replaced	O
with	O
an	O
explicit	O
IV	B-Algorithm
.	O
</s>
<s>
Support	O
for	O
TLS	O
versions	O
1.0	O
and	O
1.1	O
was	O
widely	O
deprecated	O
by	O
web	O
sites	O
around	O
2020	O
,	O
disabling	O
access	O
to	O
Firefox	B-Application
versions	O
before	O
24	O
and	O
Chromium-based	B-Language
browsers	I-Language
before	O
29	O
.	O
</s>
<s>
The	O
MD5	B-Algorithm
and	O
SHA-1	B-Algorithm
combination	O
in	O
the	O
pseudorandom	B-Error_Name
function	O
(	O
PRF	O
)	O
was	O
replaced	O
with	O
SHA-256	B-Algorithm
,	O
with	O
an	O
option	O
to	O
use	O
cipher	B-Protocol
suite	I-Protocol
specified	O
PRFs	O
.	O
</s>
<s>
The	O
MD5	B-Algorithm
and	O
SHA-1	B-Algorithm
combination	O
in	O
the	O
finished	O
message	O
hash	B-Algorithm
was	O
replaced	O
with	O
SHA-256	B-Algorithm
,	O
with	O
an	O
option	O
to	O
use	O
cipher	B-Protocol
suite	I-Protocol
specific	O
hash	B-Error_Name
algorithms	I-Error_Name
.	O
</s>
<s>
However	O
,	O
the	O
size	O
of	O
the	O
hash	B-Algorithm
in	O
the	O
finished	O
message	O
must	O
still	O
be	O
at	O
least	O
96	O
bits	O
.	O
</s>
<s>
The	O
MD5	B-Algorithm
and	O
SHA-1	B-Algorithm
combination	O
in	O
the	O
digitally	O
signed	O
element	O
was	O
replaced	O
with	O
a	O
single	O
hash	B-Algorithm
negotiated	O
during	O
handshake	B-Protocol
,	O
which	O
defaults	O
to	O
SHA-1	B-Algorithm
.	O
</s>
<s>
Enhancement	O
in	O
the	O
client	B-Protocol
's	O
and	O
server	B-Application
's	O
ability	O
to	O
specify	O
which	O
hashes	B-Algorithm
and	O
signature	O
algorithms	O
they	O
accept	O
.	O
</s>
<s>
Expansion	O
of	O
support	O
for	O
authenticated	B-Algorithm
encryption	I-Algorithm
ciphers	B-Application
,	O
used	O
mainly	O
for	O
Galois/Counter	B-Algorithm
Mode	I-Algorithm
(	O
GCM	B-Algorithm
)	O
and	O
CCM	B-Algorithm
mode	I-Algorithm
of	O
Advanced	B-Algorithm
Encryption	I-Algorithm
Standard	I-Algorithm
(	O
AES	B-Algorithm
)	O
encryption	O
.	O
</s>
<s>
TLS	O
Extensions	O
definition	O
and	O
AES	B-Algorithm
cipher	I-Algorithm
suites	O
were	O
added	O
.	O
</s>
<s>
All	O
TLS	O
versions	O
were	O
further	O
refined	O
in	O
in	O
March	O
2011	O
,	O
removing	O
their	O
backward	O
compatibility	O
with	O
SSL	O
such	O
that	O
TLS	O
sessions	O
never	O
negotiate	O
the	O
use	O
of	O
Secure	B-Protocol
Sockets	I-Protocol
Layer	I-Protocol
(	O
SSL	O
)	O
version	O
2.0	O
.	O
</s>
<s>
Network	B-Protocol
Security	I-Protocol
Services	I-Protocol
(	O
NSS	B-Protocol
)	O
,	O
the	O
cryptography	O
library	O
developed	O
by	O
Mozilla	B-Operating_System
and	O
used	O
by	O
its	O
web	B-Application
browser	I-Application
Firefox	B-Application
,	O
enabled	O
TLS	O
1.3	O
by	O
default	O
in	O
February	O
2017	O
.	O
</s>
<s>
TLS	O
1.3	O
support	O
was	O
subsequently	O
added	O
—	O
but	O
due	O
to	O
compatibility	O
issues	O
for	O
a	O
small	O
number	O
of	O
users	O
,	O
not	O
automatically	O
enabled	O
—	O
to	O
Firefox	B-Application
52.0	O
,	O
which	O
was	O
released	O
in	O
March	O
2017	O
.	O
</s>
<s>
TLS	O
1.3	O
was	O
enabled	O
by	O
default	O
in	O
May	O
2018	O
with	O
the	O
release	O
of	O
Firefox	B-Application
60.0	O
.	O
</s>
<s>
Google	B-Application
Chrome	I-Application
set	O
TLS	O
1.3	O
as	O
the	O
default	O
version	O
for	O
a	O
short	O
time	O
in	O
2017	O
.	O
</s>
<s>
The	O
intolerance	O
of	O
the	O
new	O
version	O
of	O
TLS	O
was	O
protocol	B-Protocol
ossification	I-Protocol
;	O
middleboxes	O
had	O
ossified	O
the	O
protocol	B-Protocol
's	O
version	O
parameter	O
.	O
</s>
<s>
This	O
change	O
occurred	O
very	O
late	O
in	O
the	O
design	O
process	O
,	O
only	O
having	O
been	O
discovered	O
during	O
browser	B-Application
deployment	O
.	O
</s>
<s>
'	O
Greasing	O
 '	O
an	O
extension	O
point	O
,	O
where	O
one	O
protocol	B-Protocol
participant	O
claims	O
support	O
for	O
non-existent	O
extensions	O
to	O
ensure	O
that	O
unrecognised-but-actually-existent	O
extensions	O
are	O
tolerated	O
and	O
so	O
to	O
resist	O
ossification	O
,	O
was	O
originally	O
designed	O
for	O
TLS	O
,	O
but	O
it	O
has	O
since	O
been	O
adopted	O
elsewhere	O
.	O
</s>
<s>
During	O
the	O
IETF	O
100	O
Hackathon	O
,	O
which	O
took	O
place	O
in	O
Singapore	O
in	O
2017	O
,	O
the	O
TLS	O
Group	O
worked	O
on	O
adapting	O
open-source	B-Application
applications	I-Application
to	O
use	O
TLS	O
1.3	O
.	O
</s>
<s>
wolfSSL	B-Protocol
enabled	O
the	O
use	O
of	O
TLS	O
1.3	O
as	O
of	O
version	O
3.11.1	O
,	O
released	O
in	O
May	O
2017	O
.	O
</s>
<s>
As	O
the	O
first	O
commercial	O
TLS	O
1.3	O
implementation	O
,	O
wolfSSL	B-Protocol
3.11.1	O
supported	O
Draft	O
18	O
and	O
now	O
supports	O
Draft	O
28	O
,	O
the	O
final	O
version	O
,	O
as	O
well	O
as	O
many	O
older	O
versions	O
.	O
</s>
<s>
In	O
September	O
2018	O
,	O
the	O
popular	O
OpenSSL	B-Language
project	O
released	O
version	O
1.1.1	O
of	O
its	O
library	O
,	O
in	O
which	O
support	O
for	O
TLS	O
1.3	O
was	O
"	O
the	O
headline	O
new	O
feature	O
"	O
.	O
</s>
<s>
Support	O
for	O
TLS	O
1.3	O
was	O
first	O
added	O
to	O
Schannel	B-Protocol
with	O
Windows	B-Application
11	I-Application
and	O
Windows	B-Device
Server	I-Device
2022	I-Device
.	O
</s>
<s>
The	O
Electronic	O
Frontier	O
Foundation	O
praised	O
TLS	O
1.3	O
and	O
expressed	O
concern	O
about	O
the	O
variant	O
protocol	B-Protocol
Enterprise	O
Transport	O
Security	O
(	O
ETS	O
)	O
that	O
intentionally	O
disables	O
important	O
security	O
measures	O
in	O
TLS	O
1.3	O
.	O
</s>
<s>
Originally	O
called	O
Enterprise	O
TLS	O
(	O
eTLS	O
)	O
,	O
ETS	O
is	O
a	O
published	O
standard	O
known	O
as	O
the	O
'	O
ETSI	O
TS103523-3	O
'	O
,	O
"	O
Middlebox	O
Security	B-Protocol
Protocol	I-Protocol
,	O
Part3	O
:	O
Enterprise	O
Transport	O
Security	O
"	O
.	O
</s>
<s>
ETS	O
does	O
not	O
support	O
forward	O
secrecy	O
so	O
as	O
to	O
allow	O
third-party	O
organizations	O
connected	O
to	O
the	O
proprietary	O
networks	O
to	O
be	O
able	O
to	O
use	O
their	O
private	B-Application
key	I-Application
to	O
monitor	O
network	O
traffic	O
for	O
the	O
detection	O
of	O
malware	O
and	O
to	O
make	O
it	O
easier	O
to	O
conduct	O
audits	O
.	O
</s>
<s>
A	O
digital	O
certificate	O
certifies	O
the	O
ownership	O
of	O
a	O
public	B-Application
key	I-Application
by	O
the	O
named	O
subject	O
of	O
the	O
certificate	O
,	O
and	O
indicates	O
certain	O
expected	O
usages	O
of	O
that	O
key	O
.	O
</s>
<s>
This	O
allows	O
others	O
(	O
relying	O
parties	O
)	O
to	O
rely	O
upon	O
signatures	O
or	O
on	O
assertions	O
made	O
by	O
the	O
private	B-Application
key	I-Application
that	O
corresponds	O
to	O
the	O
certified	O
public	B-Application
key	I-Application
.	O
</s>
<s>
TLS	O
typically	O
relies	O
on	O
a	O
set	O
of	O
trusted	O
third-party	O
certificate	B-Architecture
authorities	I-Architecture
to	O
establish	O
the	O
authenticity	O
of	O
certificates	O
.	O
</s>
<s>
According	O
to	O
Netcraft	O
,	O
who	O
monitors	O
active	O
TLS	O
certificates	O
,	O
the	O
market-leading	O
certificate	B-Architecture
authority	I-Architecture
(	O
CA	O
)	O
has	O
been	O
Symantec	O
since	O
the	O
beginning	O
of	O
their	O
survey	O
(	O
or	O
VeriSign	B-Application
before	O
the	O
authentication	O
services	O
business	O
unit	O
was	O
purchased	O
by	O
Symantec	O
)	O
.	O
</s>
<s>
In	O
2017	O
,	O
Symantec	O
sold	O
its	O
TLS/SSL	B-Protocol
business	O
to	O
DigiCert	O
.	O
</s>
<s>
In	O
an	O
updated	O
report	O
,	O
it	O
was	O
shown	O
that	O
IdenTrust	O
,	O
DigiCert	O
,	O
and	O
Sectigo	O
are	O
the	O
top	O
3	O
certificate	B-Architecture
authorities	I-Architecture
in	O
terms	O
of	O
market	O
share	O
since	O
May	O
2019	O
.	O
</s>
<s>
As	O
a	O
consequence	O
of	O
choosing	O
X.509	O
certificates	O
,	O
certificate	B-Architecture
authorities	I-Architecture
and	O
a	O
public	B-Architecture
key	I-Architecture
infrastructure	I-Architecture
are	O
necessary	O
to	O
verify	O
the	O
relation	O
between	O
a	O
certificate	O
and	O
its	O
owner	O
,	O
as	O
well	O
as	O
to	O
generate	O
,	O
sign	O
,	O
and	O
administer	O
the	O
validity	O
of	O
certificates	O
.	O
</s>
<s>
While	O
this	O
can	O
be	O
more	O
convenient	O
than	O
verifying	O
the	O
identities	O
via	O
a	O
web	O
of	O
trust	O
,	O
the	O
2013	O
mass	O
surveillance	O
disclosures	O
made	O
it	O
more	O
widely	O
known	O
that	O
certificate	B-Architecture
authorities	I-Architecture
are	O
a	O
weak	O
point	O
from	O
a	O
security	O
standpoint	O
,	O
allowing	O
man-in-the-middle	O
attacks	O
(	O
MITM	O
)	O
if	O
the	O
certificate	B-Architecture
authority	I-Architecture
cooperates	O
(	O
or	O
is	O
compromised	O
)	O
.	O
</s>
<s>
Before	O
a	O
client	B-Protocol
and	O
server	B-Application
can	O
begin	O
to	O
exchange	O
information	O
protected	O
by	O
TLS	O
,	O
they	O
must	O
securely	O
exchange	O
or	O
agree	O
upon	O
an	O
encryption	O
key	O
and	O
a	O
cipher	B-Application
to	O
use	O
when	O
encrypting	O
data	O
(	O
see	O
)	O
.	O
</s>
<s>
Among	O
the	O
methods	O
used	O
for	O
key	O
exchange/agreement	O
are	O
:	O
public	O
and	O
private	B-Application
keys	I-Application
generated	O
with	O
RSA	B-Architecture
(	O
denoted	O
TLS_RSA	O
in	O
the	O
TLS	O
handshake	B-Protocol
protocol	B-Protocol
)	O
,	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
(	O
TLS_DH	O
)	O
,	O
ephemeral	B-Protocol
Diffie	I-Protocol
–	I-Protocol
Hellman	I-Protocol
(	O
TLS_DHE	O
)	O
,	O
elliptic-curve	B-Protocol
Diffie	I-Protocol
–	I-Protocol
Hellman	I-Protocol
(	O
TLS_ECDH	O
)	O
,	O
ephemeral	O
elliptic-curve	B-Protocol
Diffie	I-Protocol
–	I-Protocol
Hellman	I-Protocol
(	O
TLS_ECDHE	O
)	O
,	O
anonymous	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
(	O
TLS_DH_anon	O
)	O
,	O
pre-shared	B-Protocol
key	I-Protocol
(	O
TLS_PSK	O
)	O
and	O
Secure	B-Protocol
Remote	I-Protocol
Password	I-Protocol
(	O
TLS_SRP	O
)	O
.	O
</s>
<s>
The	O
TLS_DH_anon	O
and	O
TLS_ECDH_anon	O
key	O
agreement	O
methods	O
do	O
not	O
authenticate	O
the	O
server	B-Application
or	O
the	O
user	O
and	O
hence	O
are	O
rarely	O
used	O
because	O
those	O
are	O
vulnerable	O
to	O
man-in-the-middle	O
attacks	O
.	O
</s>
<s>
Public	B-Application
key	I-Application
certificates	O
used	O
during	O
exchange/agreement	O
also	O
vary	O
in	O
the	O
size	O
of	O
the	O
public/private	O
encryption	O
keys	O
used	O
during	O
the	O
exchange	O
and	O
hence	O
the	O
robustness	O
of	O
the	O
security	O
provided	O
.	O
</s>
<s>
In	O
July	O
2013	O
,	O
Google	B-Application
announced	O
that	O
it	O
would	O
no	O
longer	O
use	O
1024-bit	O
public	B-Application
keys	I-Application
and	O
would	O
switch	O
instead	O
to	O
2048-bit	O
keys	O
to	O
increase	O
the	O
security	O
of	O
the	O
TLS	B-Protocol
encryption	I-Protocol
it	O
provides	O
to	O
its	O
users	O
because	O
the	O
encryption	O
strength	O
is	O
directly	O
related	O
to	O
the	O
key	O
size	O
.	O
</s>
<s>
+Cipher	O
security	O
against	O
publicly	O
known	O
feasible	O
attacksCipherProtocol	O
versionStatusTypeAlgorithmNominal	O
strength	O
(	O
bits	O
)	O
SSL	O
2.0SSL	O
3.0	O
must	O
be	O
implemented	O
to	O
fix	O
a	O
renegotiation	O
flaw	O
that	O
would	O
otherwise	O
break	O
this	O
protocol.If	O
libraries	O
implement	O
fixes	O
listed	O
in	O
,	O
this	O
violates	O
the	O
SSL	O
3.0	O
specification	O
,	O
which	O
the	O
IETF	O
cannot	O
change	O
unlike	O
TLS	O
.	O
</s>
<s>
Most	O
current	O
libraries	O
implement	O
the	O
fix	O
and	O
disregard	O
the	O
violation	O
that	O
this	O
causes.The	O
BEAST	O
attack	O
breaks	O
all	O
block	O
ciphers	B-Application
(	O
CBC	O
ciphers	B-Application
)	O
used	O
in	O
SSL	O
3.0	O
and	O
TLS	O
1.0	O
unless	O
mitigated	O
by	O
the	O
client	B-Protocol
and/or	O
the	O
server	B-Application
.	O
</s>
<s>
See	O
.The	O
POODLE	B-Protocol
attack	I-Protocol
breaks	O
all	O
block	O
ciphers	B-Application
(	O
CBC	O
ciphers	B-Application
)	O
used	O
in	O
SSL	O
3.0	O
unless	O
mitigated	O
by	O
the	O
client	B-Protocol
and/or	O
the	O
server	B-Application
.	O
</s>
<s>
See	O
.TLS	O
1.0TLS	O
1.1TLS	O
1.2TLS	O
1.3Block	O
cipherwithmode	O
of	O
operationAES	O
GCMAEAD	O
ciphers	B-Application
(	O
such	O
as	O
GCM	B-Algorithm
and	O
CCM	B-Algorithm
)	O
can	O
only	O
be	O
used	O
in	O
TLS	O
1.2	O
or	O
later.256	O
,	O
128Defined	O
for	O
TLS	O
1.2	O
in	O
RFCsAES	O
CCMAES	O
CBCCamellia	O
GCM256	O
,	O
128Camellia	O
CBCARIA	O
GCM256	O
,	O
128ARIA	O
CBCSEED	O
CBC1283DES	O
EDE	O
CBCCBC	O
ciphers	B-Application
can	O
be	O
attacked	O
with	O
the	O
Lucky	B-Protocol
Thirteen	I-Protocol
attack	I-Protocol
if	O
the	O
library	O
is	O
not	O
written	O
carefully	O
to	O
eliminate	O
timing	O
side	O
channels.112GOST	O
28147-89	O
CNT256Defined	O
in	O
IDEA	B-Algorithm
CBC128Removed	O
from	O
TLS	O
1.2DES	O
CBC564040-bit	O
strength	O
cipher	B-Protocol
suites	I-Protocol
were	O
intentionally	O
designed	O
with	O
reduced	O
key	O
lengths	O
to	O
comply	O
with	O
since-rescinded	O
US	O
regulations	O
forbidding	O
the	O
export	O
of	O
cryptographic	O
software	O
containing	O
certain	O
strong	O
encryption	O
algorithms	O
(	O
see	O
Export	O
of	O
cryptography	O
from	O
the	O
United	O
States	O
)	O
.	O
</s>
<s>
A	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
(	O
MAC	B-Algorithm
)	O
is	O
used	O
for	O
data	O
integrity	O
.	O
</s>
<s>
HMAC	B-Algorithm
is	O
used	O
for	O
CBC	O
mode	O
of	O
block	O
ciphers	B-Application
.	O
</s>
<s>
Authenticated	B-Algorithm
encryption	I-Algorithm
(	O
AEAD	B-Algorithm
)	O
such	O
as	O
GCM	B-Algorithm
and	O
CCM	B-Algorithm
mode	I-Algorithm
uses	O
AEAD-integrated	O
MAC	B-Algorithm
and	O
does	O
n't	O
use	O
HMAC	B-Algorithm
.	O
</s>
<s>
HMAC-based	O
PRF	O
,	O
or	O
HKDF	B-Algorithm
is	O
used	O
for	O
TLS	O
handshake	B-Protocol
.	O
</s>
<s>
In	O
applications	O
design	O
,	O
TLS	O
is	O
usually	O
implemented	O
on	O
top	O
of	O
Transport	B-Architecture
Layer	I-Architecture
protocols	O
,	O
encrypting	O
all	O
of	O
the	O
protocol-related	O
data	O
of	O
protocols	O
such	O
as	O
HTTP	B-Protocol
,	O
FTP	B-Protocol
,	O
SMTP	B-Protocol
,	O
NNTP	B-Protocol
and	O
XMPP	B-Protocol
.	O
</s>
<s>
Historically	O
,	O
TLS	O
has	O
been	O
used	O
primarily	O
with	O
reliable	O
transport	B-Architecture
protocols	I-Architecture
such	O
as	O
the	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	B-Protocol
)	O
.	O
</s>
<s>
However	O
,	O
it	O
has	O
also	O
been	O
implemented	O
with	O
datagram-oriented	O
transport	B-Architecture
protocols	I-Architecture
,	O
such	O
as	O
the	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
and	O
the	O
Datagram	B-Protocol
Congestion	I-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
DCCP	B-Protocol
)	O
,	O
usage	O
of	O
which	O
has	O
been	O
standardized	O
independently	O
using	O
the	O
term	O
Datagram	B-Protocol
Transport	I-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
DTLS	B-Protocol
)	O
.	O
</s>
<s>
A	O
primary	O
use	O
of	O
TLS	O
is	O
to	O
secure	O
World	O
Wide	O
Web	O
traffic	O
between	O
a	O
website	O
and	O
a	O
web	B-Application
browser	I-Application
encoded	O
with	O
the	O
HTTP	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
This	O
use	O
of	O
TLS	O
to	O
secure	O
HTTP	B-Protocol
traffic	O
constitutes	O
the	O
HTTPS	B-Protocol
protocol	B-Protocol
.	O
</s>
<s>
+Website	O
protocol	B-Protocol
support	O
(	O
May	O
2022	O
)	O
ProtocolversionWebsitesupportAs	O
of	O
May	O
07	O
,	O
2022	O
.	O
</s>
<s>
,	O
the	O
latest	O
versions	O
of	O
all	O
major	O
web	B-Application
browsers	I-Application
support	O
TLS	O
1.0	O
,	O
1.1	O
,	O
and	O
1.2	O
,	O
and	O
have	O
them	O
enabled	O
by	O
default	O
.	O
</s>
<s>
However	O
,	O
not	O
all	O
supported	O
Microsoft	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
support	O
the	O
latest	O
version	O
of	O
IE	O
.	O
</s>
<s>
Additionally	O
,	O
many	O
Microsoft	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
currently	O
support	O
multiple	O
versions	O
of	O
IE	O
,	O
but	O
this	O
has	O
changed	O
according	O
to	O
Microsoft	O
's	O
,	O
"	O
beginning	O
January	O
12	O
,	O
2016	O
,	O
only	O
the	O
most	O
current	O
version	O
of	O
Internet	O
Explorer	O
available	O
for	O
a	O
supported	O
operating	O
system	O
will	O
receive	O
technical	O
support	O
and	O
security	O
updates.	O
"	O
</s>
<s>
Since	O
June	O
15	O
,	O
2022	O
,	O
Internet	B-Application
Explorer	I-Application
11	I-Application
dropped	O
support	O
for	O
Windows	O
10	O
editions	O
which	O
follow	O
Microsoft	O
's	O
Modern	O
Lifecycle	O
Policy	O
.	O
</s>
<s>
Mitigations	O
against	O
POODLE	B-Protocol
attack	I-Protocol
:	O
some	O
browsers	B-Application
already	O
prevent	O
fallback	O
to	O
SSL	O
3.0	O
;	O
however	O
,	O
this	O
mitigation	O
needs	O
to	O
be	O
supported	O
by	O
not	O
only	O
clients	O
but	O
also	O
servers	O
.	O
</s>
<s>
Disabling	O
SSL	O
3.0	O
itself	O
,	O
implementation	O
of	O
"	O
anti-POODLE	O
record	O
splitting	O
"	O
,	O
or	O
denying	O
CBC	O
ciphers	B-Application
in	O
SSL	O
3.0	O
is	O
required	O
.	O
</s>
<s>
Google	B-Application
Chrome	I-Application
:	O
complete	O
(	O
TLS_FALLBACK_SCSV	O
is	O
implemented	O
since	O
version	O
33	O
,	O
fallback	O
to	O
SSL	O
3.0	O
is	O
disabled	O
since	O
version	O
39	O
,	O
SSL	O
3.0	O
itself	O
is	O
disabled	O
by	O
default	O
since	O
version	O
40	O
.	O
</s>
<s>
Mozilla	B-Application
Firefox	I-Application
:	O
complete	O
(	O
support	O
of	O
SSL	O
3.0	O
itself	O
is	O
dropped	O
since	O
version	O
39	O
.	O
</s>
<s>
Version	O
10	O
and	O
older	O
are	O
still	O
vulnerable	O
against	O
POODLE	B-Protocol
.	O
)	O
</s>
<s>
Opera	B-Application
:	O
complete	O
(	O
TLS_FALLBACK_SCSV	O
is	O
implemented	O
since	O
version	O
20	O
,	O
"	O
anti-POODLE	O
record	O
splitting	O
"	O
,	O
which	O
is	O
effective	O
only	O
with	O
client-side	B-Operating_System
implementation	O
,	O
is	O
implemented	O
since	O
version	O
25	O
,	O
SSL	O
3.0	O
itself	O
is	O
disabled	O
by	O
default	O
since	O
version	O
27	O
.	O
</s>
<s>
Safari	B-Application
:	O
complete	O
(	O
only	O
on	O
OS	B-Operating_System
X	I-Operating_System
10.8	O
and	O
later	O
and	O
iOS	B-Application
8	O
,	O
CBC	O
ciphers	B-Application
during	O
fallback	O
to	O
SSL	O
3.0	O
is	O
denied	O
,	O
but	O
this	O
means	O
it	O
will	O
use	O
RC4	B-Algorithm
,	O
which	O
is	O
not	O
recommended	O
as	O
well	O
.	O
</s>
<s>
Support	O
of	O
SSL	O
3.0	O
itself	O
is	O
dropped	O
on	O
OS	B-Operating_System
X	I-Operating_System
10.11	O
and	O
later	O
and	O
iOS	B-Application
9	O
.	O
)	O
</s>
<s>
Mitigation	O
against	O
RC4	B-Algorithm
attacks	O
:	O
</s>
<s>
Google	B-Application
Chrome	I-Application
disabled	O
RC4	B-Algorithm
except	O
as	O
a	O
fallback	O
since	O
version	O
43	O
.	O
</s>
<s>
RC4	B-Algorithm
is	O
disabled	O
since	O
Chrome	B-Application
48	O
.	O
</s>
<s>
Firefox	B-Application
disabled	O
RC4	B-Algorithm
except	O
as	O
a	O
fallback	O
since	O
version	O
36	O
.	O
</s>
<s>
Firefox	B-Application
44	O
disabled	O
RC4	B-Algorithm
by	O
default	O
.	O
</s>
<s>
Opera	B-Application
disabled	O
RC4	B-Algorithm
except	O
as	O
a	O
fallback	O
since	O
version	O
30	O
.	O
</s>
<s>
RC4	B-Algorithm
is	O
disabled	O
since	O
Opera	B-Application
35	O
.	O
</s>
<s>
Internet	O
Explorer	O
for	O
Windows	O
7/Server	O
2008	O
R2	O
and	O
for	O
Windows	O
8/Server	O
2012	O
have	O
set	O
the	O
priority	O
of	O
RC4	B-Algorithm
to	O
lowest	O
and	O
can	O
also	O
disable	O
RC4	B-Algorithm
except	O
as	O
a	O
fallback	O
through	O
registry	O
settings	O
.	O
</s>
<s>
Internet	B-Application
Explorer	I-Application
11	I-Application
Mobile	O
11	O
for	O
Windows	B-Protocol
Phone	I-Protocol
8.1	I-Protocol
disable	O
RC4	B-Algorithm
except	O
as	O
a	O
fallback	O
if	O
no	O
other	O
enabled	O
algorithm	O
works	O
.	O
</s>
<s>
Edge	O
and	O
IE	B-Application
11	I-Application
disable	O
RC4	B-Algorithm
completely	O
in	O
August	O
2016	O
.	O
</s>
<s>
The	O
Android	B-Application
Browser	B-Application
included	O
with	O
Android	B-Application
4.0	I-Application
and	O
older	O
is	O
still	O
vulnerable	O
to	O
the	O
FREAK	O
attack	O
.	O
</s>
<s>
Internet	B-Application
Explorer	I-Application
11	I-Application
Mobile	O
is	O
still	O
vulnerable	O
to	O
the	O
FREAK	O
attack	O
.	O
</s>
<s>
Google	B-Application
Chrome	I-Application
,	O
Internet	O
Explorer	O
(	O
desktop	O
)	O
,	O
Safari	B-Application
(	O
desktop	O
&	O
mobile	O
)	O
,	O
and	O
Opera	B-Application
(	O
mobile	O
)	O
have	O
FREAK	O
mitigations	O
in	O
place	O
.	O
</s>
<s>
Mozilla	B-Application
Firefox	I-Application
on	O
all	O
platforms	O
and	O
Google	B-Application
Chrome	I-Application
on	O
Windows	O
were	O
not	O
affected	O
by	O
FREAK	O
.	O
</s>
<s>
Most	O
SSL	O
and	O
TLS	O
programming	O
libraries	O
are	O
free	B-Application
and	I-Application
open	I-Application
source	I-Application
software	I-Application
.	O
</s>
<s>
BoringSSL	B-Protocol
,	O
a	O
fork	O
of	O
OpenSSL	B-Language
for	O
Chrome/Chromium	O
and	O
Android	B-Application
as	O
well	O
as	O
other	O
Google	B-Application
applications	O
.	O
</s>
<s>
Botan	B-Protocol
,	O
a	O
BSD-licensed	O
cryptographic	O
library	O
written	O
in	O
C++	O
.	O
</s>
<s>
Delphi	B-Language
programmers	O
may	O
use	O
a	O
library	O
called	O
Indy	B-Language
which	O
utilizes	O
OpenSSL	B-Language
or	O
alternatively	O
ICS	O
which	O
supports	O
TLS	O
1.3	O
now	O
.	O
</s>
<s>
LibreSSL	B-Language
:	O
a	O
fork	O
of	O
OpenSSL	B-Language
by	O
OpenBSD	O
project	O
.	O
</s>
<s>
Schannel	B-Protocol
:	O
an	O
implementation	O
of	O
SSL	O
and	O
TLS	O
Microsoft	B-Application
Windows	I-Application
as	O
part	O
of	O
its	O
package	O
.	O
</s>
<s>
Secure	O
Transport	O
:	O
an	O
implementation	O
of	O
SSL	O
and	O
TLS	O
used	O
in	O
OS	B-Operating_System
X	I-Operating_System
and	O
iOS	B-Application
as	O
part	O
of	O
their	O
packages	O
.	O
</s>
<s>
wolfSSL	B-Protocol
(	O
previously	O
CyaSSL	B-Protocol
)	O
:	O
Embedded	O
SSL/TLS	B-Protocol
Library	O
with	O
a	O
strong	O
focus	O
on	O
speed	O
and	O
size	O
.	O
</s>
<s>
"	O
The	O
root	O
cause	O
of	O
most	O
of	O
these	O
vulnerabilities	O
is	O
the	O
terrible	O
design	O
of	O
the	O
APIs	B-Application
to	O
the	O
underlying	O
SSL	O
libraries	O
.	O
</s>
<s>
Instead	O
of	O
expressing	O
high-level	O
security	O
properties	O
of	O
network	O
tunnels	O
such	O
as	O
confidentiality	O
and	O
authentication	O
,	O
these	O
APIs	B-Application
expose	O
low-level	O
details	O
of	O
the	O
SSL	O
protocol	B-Protocol
to	O
application	O
developers	O
.	O
</s>
<s>
As	O
a	O
consequence	O
,	O
developers	O
often	O
use	O
SSL	O
APIs	B-Application
incorrectly	O
,	O
misinterpreting	O
and	O
misunderstanding	O
their	O
manifold	O
parameters	O
,	O
options	O
,	O
side	O
effects	O
,	O
and	O
return	O
values.	O
"	O
</s>
<s>
The	O
Simple	B-Protocol
Mail	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
SMTP	B-Protocol
)	O
can	O
also	O
be	O
protected	O
by	O
TLS	O
.	O
</s>
<s>
These	O
applications	O
use	O
public	B-Application
key	I-Application
certificates	O
to	O
verify	O
the	O
identity	O
of	O
endpoints	O
.	O
</s>
<s>
TLS	O
can	O
also	O
be	O
used	O
for	O
tunnelling	O
an	O
entire	O
network	O
stack	O
to	O
create	O
a	O
VPN	B-Application
,	O
which	O
is	O
the	O
case	O
with	O
OpenVPN	B-Language
and	O
OpenConnect	B-Application
.	O
</s>
<s>
There	O
has	O
also	O
been	O
substantial	O
development	O
since	O
the	O
late	O
1990s	O
in	O
creating	O
client	B-Protocol
technology	O
outside	O
of	O
Web-browsers	B-Application
,	O
in	O
order	O
to	O
enable	O
support	O
for	O
client/server	B-Operating_System
applications	O
.	O
</s>
<s>
Compared	O
to	O
traditional	O
IPsec	B-Protocol
VPN	B-Application
technologies	O
,	O
TLS	O
has	O
some	O
inherent	O
advantages	O
in	O
firewall	O
and	O
NAT	B-Protocol
traversal	O
that	O
make	O
it	O
easier	O
to	O
administer	O
for	O
large	O
remote-access	O
populations	O
.	O
</s>
<s>
TLS	O
is	O
also	O
a	O
standard	O
method	O
for	O
protecting	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
(	O
SIP	O
)	O
application	O
signaling	O
.	O
</s>
<s>
TLS	O
can	O
be	O
used	O
for	O
providing	O
authentication	O
and	O
encryption	O
of	O
the	O
SIP	O
signalling	O
associated	O
with	O
VoIP	B-Application
and	O
other	O
SIP-based	O
applications	O
.	O
</s>
<s>
Significant	O
attacks	O
against	O
TLS/SSL	B-Protocol
are	O
listed	O
below	O
.	O
</s>
<s>
In	O
February	O
2015	O
,	O
IETF	O
issued	O
an	O
informational	O
RFC	O
summarizing	O
the	O
various	O
known	O
attacks	O
against	O
TLS/SSL	B-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
it	O
allows	O
an	O
attacker	O
who	O
can	O
hijack	O
an	O
https	B-Protocol
connection	O
to	O
splice	O
their	O
own	O
requests	O
into	O
the	O
beginning	O
of	O
the	O
conversation	O
the	O
client	B-Protocol
has	O
with	O
the	O
web	B-Application
server	I-Application
.	O
</s>
<s>
The	O
attacker	O
ca	O
n't	O
actually	O
decrypt	O
the	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
communication	O
,	O
so	O
it	O
is	O
different	O
from	O
a	O
typical	O
man-in-the-middle	O
attack	O
.	O
</s>
<s>
A	O
short-term	O
fix	O
is	O
for	O
web	B-Application
servers	I-Application
to	O
stop	O
allowing	O
renegotiation	O
,	O
which	O
typically	O
will	O
not	O
require	O
other	O
changes	O
unless	O
client	B-Protocol
certificate	O
authentication	O
is	O
used	O
.	O
</s>
<s>
It	O
will	O
require	O
the	O
client	B-Protocol
and	O
server	B-Application
to	O
include	O
and	O
verify	O
information	O
about	O
previous	O
handshakes	B-Protocol
in	O
any	O
renegotiation	O
handshakes	B-Protocol
.	O
</s>
<s>
A	O
protocol	B-Protocol
downgrade	I-Protocol
attack	I-Protocol
(	O
also	O
called	O
a	O
version	B-Protocol
rollback	I-Protocol
attack	I-Protocol
)	O
tricks	O
a	O
web	B-Application
server	I-Application
into	O
negotiating	O
connections	O
with	O
previous	O
versions	O
of	O
TLS	O
(	O
such	O
as	O
SSLv2	O
)	O
that	O
have	O
long	O
since	O
been	O
abandoned	O
as	O
insecure	O
.	O
</s>
<s>
Previous	O
modifications	O
to	O
the	O
original	O
protocols	O
,	O
like	O
False	O
Start	O
(	O
adopted	O
and	O
enabled	O
by	O
Google	B-Application
Chrome	I-Application
)	O
or	O
Snap	O
Start	O
,	O
reportedly	O
introduced	O
limited	O
TLS	B-Protocol
protocol	I-Protocol
downgrade	B-Protocol
attacks	I-Protocol
or	O
allowed	O
modifications	O
to	O
the	O
cipher	B-Protocol
suite	I-Protocol
list	O
sent	O
by	O
the	O
client	B-Protocol
to	O
the	O
server	B-Application
.	O
</s>
<s>
In	O
doing	O
so	O
,	O
an	O
attacker	O
might	O
succeed	O
in	O
influencing	O
the	O
cipher	B-Protocol
suite	I-Protocol
selection	O
in	O
an	O
attempt	O
to	O
downgrade	O
the	O
cipher	B-Protocol
suite	I-Protocol
negotiated	O
to	O
use	O
either	O
a	O
weaker	O
symmetric	B-Algorithm
encryption	I-Algorithm
algorithm	O
or	O
a	O
weaker	O
key	O
exchange	O
.	O
</s>
<s>
Encryption	O
downgrade	B-Protocol
attacks	I-Protocol
can	O
force	O
servers	O
and	O
clients	O
to	O
negotiate	O
a	O
connection	O
using	O
cryptographically	O
weak	O
keys	O
.	O
</s>
<s>
In	O
2014	O
,	O
a	O
man-in-the-middle	O
attack	O
called	O
FREAK	O
was	O
discovered	O
affecting	O
the	O
OpenSSL	B-Language
stack	O
,	O
the	O
default	O
Android	B-Application
web	B-Application
browser	I-Application
,	O
and	O
some	O
Safari	B-Application
browsers	I-Application
.	O
</s>
<s>
Logjam	O
is	O
a	O
security	O
exploit	O
discovered	O
in	O
May	O
2015	O
that	O
exploits	O
the	O
option	O
of	O
using	O
legacy	O
"	O
export-grade	O
"	O
512-bit	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
groups	O
dating	O
back	O
to	O
the	O
1990s	O
.	O
</s>
<s>
It	O
forces	O
susceptible	O
servers	O
to	O
downgrade	O
to	O
cryptographically	O
weak	O
512-bit	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
groups	O
.	O
</s>
<s>
An	O
attacker	O
can	O
then	O
deduce	O
the	O
keys	O
the	O
client	B-Protocol
and	O
server	B-Application
determine	O
using	O
the	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
key	I-Protocol
exchange	I-Protocol
.	O
</s>
<s>
The	O
DROWN	O
attack	O
is	O
an	O
exploit	O
that	O
attacks	O
servers	O
supporting	O
contemporary	O
SSL/TLS	B-Protocol
protocol	B-Protocol
suites	O
by	O
exploiting	O
their	O
support	O
for	O
the	O
obsolete	O
,	O
insecure	O
,	O
SSLv2	O
protocol	B-Protocol
to	O
leverage	O
an	O
attack	O
on	O
connections	O
using	O
up-to-date	O
protocols	O
that	O
would	O
otherwise	O
be	O
secure	O
.	O
</s>
<s>
DROWN	O
exploits	O
a	O
vulnerability	O
in	O
the	O
protocols	O
used	O
and	O
the	O
configuration	O
of	O
the	O
server	B-Application
,	O
rather	O
than	O
any	O
specific	O
implementation	O
error	O
.	O
</s>
<s>
On	O
September	O
23	O
,	O
2011	O
,	O
researchers	O
Thai	O
Duong	O
and	O
Juliano	O
Rizzo	O
demonstrated	O
a	O
proof	O
of	O
concept	O
called	O
BEAST	O
(	O
Browser	B-Application
Exploit	O
Against	O
SSL/TLS	B-Protocol
)	O
using	O
a	O
Java	B-Application
applet	I-Application
to	O
violate	O
same	B-Protocol
origin	I-Protocol
policy	I-Protocol
constraints	O
,	O
for	O
a	O
long-known	O
cipher	B-Application
block	O
chaining	O
(	O
CBC	O
)	O
vulnerability	O
in	O
TLS	O
1.0	O
:	O
an	O
attacker	O
observing	O
2	O
consecutive	O
ciphertext	O
blocks	O
C0	O
,	O
C1	O
can	O
test	O
if	O
the	O
plaintext	O
block	O
P1	O
is	O
equal	O
to	O
x	O
by	O
choosing	O
the	O
next	O
plaintext	O
block	O
P2	O
=	O
x	O
C0	O
C1	O
;	O
as	O
per	O
CBC	O
operation	O
,	O
C2	O
=	O
E(C1 P2 )	O
=	O
E(C1 x C0 C1 )	O
=	O
E(C0 x )	O
,	O
which	O
will	O
be	O
equal	O
to	O
C1	O
if	O
x	O
=	O
P1	O
.	O
</s>
<s>
RC4	B-Algorithm
as	O
a	O
stream	B-Algorithm
cipher	I-Algorithm
is	O
immune	O
to	O
BEAST	O
attack	O
.	O
</s>
<s>
Therefore	O
,	O
RC4	B-Algorithm
was	O
widely	O
used	O
as	O
a	O
way	O
to	O
mitigate	O
BEAST	O
attack	O
on	O
the	O
server	B-Application
side	O
.	O
</s>
<s>
However	O
,	O
in	O
2013	O
,	O
researchers	O
found	O
more	O
weaknesses	O
in	O
RC4	B-Algorithm
.	O
</s>
<s>
Thereafter	O
enabling	O
RC4	B-Algorithm
on	O
server	B-Application
side	O
was	O
no	O
longer	O
recommended	O
.	O
</s>
<s>
Chrome	B-Application
and	O
Firefox	B-Application
themselves	O
are	O
not	O
vulnerable	O
to	O
BEAST	O
attack	O
,	O
however	O
,	O
Mozilla	B-Operating_System
updated	O
their	O
NSS	B-Protocol
libraries	O
to	O
mitigate	O
BEAST-like	O
attacks	O
.	O
</s>
<s>
NSS	B-Protocol
is	O
used	O
by	O
Mozilla	B-Application
Firefox	I-Application
and	O
Google	B-Application
Chrome	I-Application
to	O
implement	O
SSL	O
.	O
</s>
<s>
Some	O
web	B-Application
servers	I-Application
that	O
have	O
a	O
broken	O
implementation	O
of	O
the	O
SSL	O
specification	O
may	O
stop	O
working	O
as	O
a	O
result	O
.	O
</s>
<s>
Microsoft	O
released	O
Security	O
Bulletin	O
MS12-006	O
on	O
January	O
10	O
,	O
2012	O
,	O
which	O
fixed	O
the	O
BEAST	O
vulnerability	O
by	O
changing	O
the	O
way	O
that	O
the	O
Windows	O
Secure	O
Channel	O
(	O
Schannel	B-Protocol
)	O
component	O
transmits	O
encrypted	O
network	B-Protocol
packets	I-Protocol
from	O
the	O
server	B-Application
end	O
.	O
</s>
<s>
Users	O
of	O
Internet	O
Explorer	O
(	O
prior	O
to	O
version	O
11	O
)	O
that	O
run	O
on	O
older	O
versions	O
of	O
Windows	O
(	O
Windows	B-Device
7	I-Device
,	O
Windows	B-Application
8	I-Application
and	O
Windows	B-Device
Server	I-Device
2008	I-Device
R2	I-Device
)	O
can	O
restrict	O
use	O
of	O
TLS	O
to	O
1.1	O
or	O
higher	O
.	O
</s>
<s>
Apple	O
fixed	O
BEAST	O
vulnerability	O
by	O
implementing	O
1/n	O
-1	O
split	O
and	O
turning	O
it	O
on	O
by	O
default	O
in	O
OS	B-Operating_System
X	I-Operating_System
Mavericks	I-Operating_System
,	O
released	O
on	O
October	O
22	O
,	O
2013	O
.	O
</s>
<s>
The	O
authors	O
of	O
the	O
BEAST	O
attack	O
are	O
also	O
the	O
creators	O
of	O
the	O
later	O
CRIME	O
attack	O
,	O
which	O
can	O
allow	O
an	O
attacker	O
to	O
recover	O
the	O
content	O
of	O
web	B-Application
cookies	I-Application
when	O
data	B-General_Concept
compression	I-General_Concept
is	O
used	O
along	O
with	O
TLS	O
.	O
</s>
<s>
When	O
used	O
to	O
recover	O
the	O
content	O
of	O
secret	O
authentication	B-Application
cookies	I-Application
,	O
it	O
allows	O
an	O
attacker	O
to	O
perform	O
session	B-Protocol
hijacking	I-Protocol
on	O
an	O
authenticated	O
web	O
session	O
.	O
</s>
<s>
While	O
the	O
CRIME	O
attack	O
was	O
presented	O
as	O
a	O
general	O
attack	O
that	O
could	O
work	O
effectively	O
against	O
a	O
large	O
number	O
of	O
protocols	O
,	O
including	O
but	O
not	O
limited	O
to	O
TLS	O
,	O
and	O
application-layer	O
protocols	O
such	O
as	O
SPDY	B-Protocol
or	O
HTTP	B-Protocol
,	O
only	O
exploits	O
against	O
TLS	O
and	O
SPDY	B-Protocol
were	O
demonstrated	O
and	O
largely	O
mitigated	O
in	O
browsers	B-Application
and	O
servers	O
.	O
</s>
<s>
The	O
CRIME	O
exploit	O
against	O
HTTP	B-Protocol
compression	I-Protocol
has	O
not	O
been	O
mitigated	O
at	O
all	O
,	O
even	O
though	O
the	O
authors	O
of	O
CRIME	O
have	O
warned	O
that	O
this	O
vulnerability	O
might	O
be	O
even	O
more	O
widespread	O
than	O
SPDY	B-Protocol
and	O
TLS	O
compression	B-General_Concept
combined	O
.	O
</s>
<s>
In	O
2013	O
a	O
new	O
instance	O
of	O
the	O
CRIME	O
attack	O
against	O
HTTP	B-Protocol
compression	I-Protocol
,	O
dubbed	O
BREACH	B-Protocol
,	O
was	O
announced	O
.	O
</s>
<s>
Based	O
on	O
the	O
CRIME	O
attack	O
a	O
BREACH	B-Protocol
attack	O
can	O
extract	O
login	O
tokens	O
,	O
email	O
addresses	O
or	O
other	O
sensitive	O
information	O
from	O
TLS	O
encrypted	O
web	O
traffic	O
in	O
as	O
little	O
as	O
30	O
seconds	O
(	O
depending	O
on	O
the	O
number	O
of	O
bytes	O
to	O
be	O
extracted	O
)	O
,	O
provided	O
the	O
attacker	O
tricks	O
the	O
victim	O
into	O
visiting	O
a	O
malicious	O
web	O
link	O
or	O
is	O
able	O
to	O
inject	O
content	O
into	O
valid	O
pages	O
the	O
user	O
is	O
visiting	O
(	O
ex	O
:	O
a	O
wireless	O
network	O
under	O
the	O
control	O
of	O
the	O
attacker	O
)	O
.	O
</s>
<s>
All	O
versions	O
of	O
TLS	O
and	O
SSL	O
are	O
at	O
risk	O
from	O
BREACH	B-Protocol
regardless	O
of	O
the	O
encryption	O
algorithm	O
or	O
cipher	B-Application
used	O
.	O
</s>
<s>
Unlike	O
previous	O
instances	O
of	O
CRIME	O
,	O
which	O
can	O
be	O
successfully	O
defended	O
against	O
by	O
turning	O
off	O
TLS	O
compression	B-General_Concept
or	O
SPDY	B-Protocol
header	O
compression	B-General_Concept
,	O
BREACH	B-Protocol
exploits	O
HTTP	B-Protocol
compression	I-Protocol
which	O
cannot	O
realistically	O
be	O
turned	O
off	O
,	O
as	O
virtually	O
all	O
web	B-Application
servers	I-Application
rely	O
upon	O
it	O
to	O
improve	O
data	O
transmission	O
speeds	O
for	O
users	O
.	O
</s>
<s>
Earlier	O
TLS	O
versions	O
were	O
vulnerable	O
against	O
the	O
padding	B-Application
oracle	I-Application
attack	I-Application
discovered	O
in	O
2002	O
.	O
</s>
<s>
A	O
novel	O
variant	O
,	O
called	O
the	O
Lucky	B-Protocol
Thirteen	I-Protocol
attack	I-Protocol
,	O
was	O
published	O
in	O
2013	O
.	O
</s>
<s>
Some	O
experts	O
also	O
recommended	O
avoiding	O
triple	B-Algorithm
DES	I-Algorithm
CBC	O
.	O
</s>
<s>
Since	O
the	O
last	O
supported	O
ciphers	B-Application
developed	O
to	O
support	O
any	O
program	O
using	O
Windows	B-Application
XP	I-Application
's	O
SSL/TLS	B-Protocol
library	O
like	O
Internet	O
Explorer	O
on	O
Windows	B-Application
XP	I-Application
are	O
RC4	B-Algorithm
and	O
Triple-DES	B-Algorithm
,	O
and	O
since	O
RC4	B-Algorithm
is	O
now	O
deprecated	O
(	O
see	O
discussion	O
of	O
RC4	B-Algorithm
attacks	O
)	O
,	O
this	O
makes	O
it	O
difficult	O
to	O
support	O
any	O
version	O
of	O
SSL	O
for	O
any	O
program	O
using	O
this	O
library	O
on	O
XP	B-Application
.	O
</s>
<s>
A	O
fix	O
was	O
released	O
as	O
the	O
Encrypt-then-MAC	O
extension	O
to	O
the	O
TLS	O
specification	O
,	O
released	O
as	O
.	O
</s>
<s>
The	O
Lucky	B-Protocol
Thirteen	I-Protocol
attack	I-Protocol
can	O
be	O
mitigated	O
in	O
TLS	O
1.2	O
by	O
using	O
only	O
AES_GCM	O
ciphers	B-Application
;	O
AES_CBC	O
remains	O
vulnerable	O
.	O
</s>
<s>
On	O
October	O
14	O
,	O
2014	O
,	O
Google	B-Application
researchers	O
published	O
a	O
vulnerability	O
in	O
the	O
design	O
of	O
SSL	O
3.0	O
,	O
which	O
makes	O
CBC	O
mode	B-Algorithm
of	I-Algorithm
operation	I-Algorithm
with	O
SSL	O
3.0	O
vulnerable	O
to	O
a	O
padding	B-Application
attack	I-Application
(	O
)	O
.	O
</s>
<s>
They	O
named	O
this	O
attack	O
POODLE	B-Protocol
(	O
Padding	B-Protocol
Oracle	I-Protocol
On	I-Protocol
Downgraded	I-Protocol
Legacy	I-Protocol
Encryption	I-Protocol
)	O
.	O
</s>
<s>
Although	O
this	O
vulnerability	O
only	O
exists	O
in	O
SSL	O
3.0	O
and	O
most	O
clients	O
and	O
servers	O
support	O
TLS	O
1.0	O
and	O
above	O
,	O
all	O
major	O
browsers	B-Application
voluntarily	O
downgrade	O
to	O
SSL	O
3.0	O
if	O
the	O
handshakes	B-Protocol
with	O
newer	O
versions	O
of	O
TLS	O
fail	O
unless	O
they	O
provide	O
the	O
option	O
for	O
a	O
user	O
or	O
administrator	O
to	O
disable	O
SSL	O
3.0	O
and	O
the	O
user	O
or	O
administrator	O
does	O
so	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
man-in-the-middle	O
can	O
first	O
conduct	O
a	O
version	B-Protocol
rollback	I-Protocol
attack	I-Protocol
and	O
then	O
exploit	O
this	O
vulnerability	O
.	O
</s>
<s>
On	O
December	O
8	O
,	O
2014	O
,	O
a	O
variant	O
of	O
POODLE	B-Protocol
was	O
announced	O
that	O
impacts	O
TLS	O
implementations	O
that	O
do	O
not	O
properly	O
enforce	O
padding	O
byte	O
requirements	O
.	O
</s>
<s>
Despite	O
the	O
existence	O
of	O
attacks	O
on	O
RC4	B-Algorithm
that	O
broke	O
its	O
security	O
,	O
cipher	B-Protocol
suites	I-Protocol
in	O
SSL	O
and	O
TLS	O
that	O
were	O
based	O
on	O
RC4	B-Algorithm
were	O
still	O
considered	O
secure	O
prior	O
to	O
2013	O
based	O
on	O
the	O
way	O
in	O
which	O
they	O
were	O
used	O
in	O
SSL	O
and	O
TLS	O
.	O
</s>
<s>
In	O
2011	O
,	O
the	O
RC4	B-Algorithm
suite	O
was	O
actually	O
recommended	O
as	O
a	O
work	O
around	O
for	O
the	O
BEAST	O
attack	O
.	O
</s>
<s>
New	O
forms	O
of	O
attack	O
disclosed	O
in	O
March	O
2013	O
conclusively	O
demonstrated	O
the	O
feasibility	O
of	O
breaking	O
RC4	B-Algorithm
in	O
TLS	O
,	O
suggesting	O
it	O
was	O
not	O
a	O
good	O
workaround	O
for	O
BEAST	O
.	O
</s>
<s>
An	O
attack	O
scenario	O
was	O
proposed	O
by	O
AlFardan	O
,	O
Bernstein	O
,	O
Paterson	O
,	O
Poettering	O
and	O
Schuldt	O
that	O
used	O
newly	O
discovered	O
statistical	O
biases	O
in	O
the	O
RC4	B-Algorithm
key	O
table	O
to	O
recover	O
parts	O
of	O
the	O
plaintext	O
with	O
a	O
large	O
number	O
of	O
TLS	B-Protocol
encryptions	I-Protocol
.	O
</s>
<s>
An	O
attack	O
on	O
RC4	B-Algorithm
in	O
TLS	O
and	O
SSL	O
that	O
requires	O
13	O
×	O
220	O
encryptions	O
to	O
break	O
RC4	B-Algorithm
was	O
unveiled	O
on	O
8	O
July	O
2013	O
and	O
later	O
described	O
as	O
"	O
feasible	O
"	O
in	O
the	O
accompanying	O
presentation	O
at	O
a	O
USENIX	B-Operating_System
Security	I-Operating_System
Symposium	I-Operating_System
in	O
August	O
2013	O
.	O
</s>
<s>
In	O
July	O
2015	O
,	O
subsequent	O
improvements	O
in	O
the	O
attack	O
make	O
it	O
increasingly	O
practical	O
to	O
defeat	O
the	O
security	O
of	O
RC4-encrypted	O
TLS	O
.	O
</s>
<s>
As	O
many	O
modern	O
browsers	B-Application
have	O
been	O
designed	O
to	O
defeat	O
BEAST	O
attacks	O
(	O
except	O
Safari	B-Application
for	O
Mac	O
OS	O
X	O
10.7	O
or	O
earlier	O
,	O
for	O
iOS	B-Application
6	O
or	O
earlier	O
,	O
and	O
for	O
Windows	O
;	O
see	O
)	O
,	O
RC4	B-Algorithm
is	O
no	O
longer	O
a	O
good	O
choice	O
for	O
TLS	O
1.0	O
.	O
</s>
<s>
The	O
CBC	O
ciphers	B-Application
which	O
were	O
affected	O
by	O
the	O
BEAST	O
attack	O
in	O
the	O
past	O
have	O
become	O
a	O
more	O
popular	O
choice	O
for	O
protection	O
.	O
</s>
<s>
Mozilla	B-Operating_System
and	O
Microsoft	O
recommend	O
disabling	O
RC4	B-Algorithm
where	O
possible	O
.	O
</s>
<s>
prohibits	O
the	O
use	O
of	O
RC4	B-Algorithm
cipher	I-Algorithm
suites	O
in	O
all	O
versions	O
of	O
TLS	O
.	O
</s>
<s>
On	O
September	O
1	O
,	O
2015	O
,	O
Microsoft	O
,	O
Google	B-Application
and	O
Mozilla	B-Operating_System
announced	O
that	O
RC4	B-Algorithm
cipher	I-Algorithm
suites	O
would	O
be	O
disabled	O
by	O
default	O
in	O
their	O
browsers	B-Application
(	O
Microsoft	B-Application
Edge	I-Application
,	O
Internet	B-Application
Explorer	I-Application
11	I-Application
on	O
Windows	O
7/8.1/10	O
,	O
Firefox	B-Application
,	O
and	O
Chrome	B-Application
)	O
in	O
early	O
2016	O
.	O
</s>
<s>
When	O
the	O
request	O
to	O
sign	O
out	O
is	O
sent	O
,	O
the	O
attacker	O
injects	O
an	O
unencrypted	O
TCP	B-Protocol
FIN	O
message	O
(	O
no	O
more	O
data	O
from	O
sender	O
)	O
to	O
close	O
the	O
connection	O
.	O
</s>
<s>
The	O
server	B-Application
therefore	O
does	O
n't	O
receive	O
the	O
logout	O
request	O
and	O
is	O
unaware	O
of	O
the	O
abnormal	O
termination	O
.	O
</s>
<s>
Published	O
in	O
July	O
2013	O
,	O
the	O
attack	O
causes	O
web	O
services	O
such	O
as	O
Gmail	B-Application
and	O
Hotmail	B-Operating_System
to	O
display	O
a	O
page	O
that	O
informs	O
the	O
user	O
that	O
they	O
have	O
successfully	O
signed-out	O
,	O
while	O
ensuring	O
that	O
the	O
user	O
's	O
browser	B-Application
maintains	O
authorization	O
with	O
the	O
service	O
,	O
allowing	O
an	O
attacker	O
with	O
subsequent	O
access	O
to	O
the	O
browser	B-Application
to	O
access	O
and	O
take	O
over	O
control	O
of	O
the	O
user	O
's	O
logged-in	O
account	O
.	O
</s>
<s>
The	O
attack	O
does	O
not	O
rely	O
on	O
installing	O
malware	O
on	O
the	O
victim	O
's	O
computer	O
;	O
attackers	O
need	O
only	O
place	O
themselves	O
between	O
the	O
victim	O
and	O
the	O
web	B-Application
server	I-Application
(	O
e.g.	O
,	O
by	O
setting	O
up	O
a	O
rogue	O
wireless	O
hotspot	O
)	O
.	O
</s>
<s>
Another	O
possibility	O
is	O
when	O
using	O
FTP	B-Protocol
the	O
data	O
connection	O
can	O
have	O
a	O
false	O
FIN	O
in	O
the	O
data	O
stream	B-Architecture
,	O
and	O
if	O
the	O
protocol	B-Protocol
rules	O
for	O
exchanging	O
close_notify	O
alerts	O
is	O
not	O
adhered	O
to	O
a	O
file	O
can	O
be	O
truncated	O
.	O
</s>
<s>
In	O
February	O
2013	O
two	O
researchers	O
from	O
Royal	O
Holloway	O
,	O
University	O
of	O
London	O
discovered	O
a	O
timing	O
attack	O
which	O
allowed	O
them	O
to	O
recover	O
(	O
parts	O
of	O
the	O
)	O
plaintext	O
from	O
a	O
DTLS	B-Protocol
connection	O
using	O
the	O
OpenSSL	B-Language
or	O
GnuTLS	B-Application
implementation	O
of	O
DTLS	B-Protocol
when	O
Cipher	B-Application
Block	O
Chaining	O
mode	O
encryption	O
was	O
used	O
.	O
</s>
<s>
This	O
attack	O
,	O
discovered	O
in	O
mid-2016	O
,	O
exploits	O
weaknesses	O
in	O
the	O
Web	B-Protocol
Proxy	I-Protocol
Autodiscovery	I-Protocol
Protocol	I-Protocol
(	O
WPAD	B-Protocol
)	O
to	O
expose	O
the	O
URL	O
that	O
a	O
web	O
user	O
is	O
attempting	O
to	O
reach	O
via	O
a	O
TLS-enabled	O
web	O
link	O
.	O
</s>
<s>
Document	O
sharing	O
services	O
,	O
such	O
as	O
those	O
offered	O
by	O
Google	B-Application
and	O
Dropbox	O
,	O
also	O
work	O
by	O
sending	O
a	O
user	O
a	O
security	O
token	O
that	O
's	O
included	O
in	O
the	O
URL	O
.	O
</s>
<s>
The	O
exploit	O
works	O
against	O
almost	O
all	O
browsers	B-Application
and	O
operating	O
systems	O
.	O
</s>
<s>
The	O
Sweet32	O
attack	O
breaks	O
all	O
64-bit	O
block	O
ciphers	B-Application
used	O
in	O
CBC	O
mode	O
as	O
used	O
in	O
TLS	O
by	O
exploiting	O
a	O
birthday	O
attack	O
and	O
either	O
a	O
man-in-the-middle	O
attack	O
or	O
injection	O
of	O
a	O
malicious	O
JavaScript	B-Language
into	O
a	O
web	O
page	O
.	O
</s>
<s>
The	O
purpose	O
of	O
the	O
man-in-the-middle	O
attack	O
or	O
the	O
JavaScript	B-Language
injection	O
is	O
to	O
allow	O
the	O
attacker	O
to	O
capture	O
enough	O
traffic	O
to	O
mount	O
a	O
birthday	O
attack	O
.	O
</s>
<s>
The	O
Heartbleed	B-Error_Name
bug	I-Error_Name
is	O
a	O
serious	O
vulnerability	O
specific	O
to	O
the	O
implementation	O
of	O
SSL/TLS	B-Protocol
in	O
the	O
popular	O
OpenSSL	B-Language
cryptographic	O
software	O
library	O
,	O
affecting	O
versions	O
1.0.1	O
to	O
1.0.1f	O
.	O
</s>
<s>
This	O
weakness	O
,	O
reported	O
in	O
April	O
2014	O
,	O
allows	O
attackers	O
to	O
steal	O
private	B-Application
keys	I-Application
from	O
servers	O
that	O
should	O
normally	O
be	O
protected	O
.	O
</s>
<s>
The	O
Heartbleed	B-Error_Name
bug	I-Error_Name
allows	O
anyone	O
on	O
the	O
Internet	O
to	O
read	O
the	O
memory	O
of	O
the	O
systems	O
protected	O
by	O
the	O
vulnerable	O
versions	O
of	O
the	O
OpenSSL	B-Language
software	O
.	O
</s>
<s>
This	O
compromises	O
the	O
secret	O
private	B-Application
keys	I-Application
associated	O
with	O
the	O
public	O
certificates	O
used	O
to	O
identify	O
the	O
service	O
providers	O
and	O
to	O
encrypt	O
the	O
traffic	O
,	O
the	O
names	O
and	O
passwords	O
of	O
the	O
users	O
and	O
the	O
actual	O
content	O
.	O
</s>
<s>
The	O
vulnerability	O
is	O
caused	O
by	O
a	O
buffer	B-General_Concept
over-read	I-General_Concept
bug	O
in	O
the	O
OpenSSL	B-Language
software	O
,	O
rather	O
than	O
a	O
defect	O
in	O
the	O
SSL	O
or	O
TLS	B-Protocol
protocol	I-Protocol
specification	O
.	O
</s>
<s>
In	O
September	O
2014	O
,	O
a	O
variant	O
of	O
Daniel	O
Bleichenbacher	O
's	O
PKCS	O
#1	O
v1.5	O
RSA	B-Architecture
Signature	O
Forgery	O
vulnerability	O
was	O
announced	O
by	O
Intel	O
Security	O
Advanced	O
Threat	O
Research	O
.	O
</s>
<s>
This	O
attack	O
,	O
dubbed	O
BERserk	O
,	O
is	O
a	O
result	O
of	O
incomplete	O
ASN.1	O
length	O
decoding	O
of	O
public	B-Application
key	I-Application
signatures	O
in	O
some	O
SSL	O
implementations	O
,	O
and	O
allows	O
a	O
man-in-the-middle	O
attack	O
by	O
forging	O
a	O
public	B-Application
key	I-Application
signature	O
.	O
</s>
<s>
The	O
Komodia	O
library	O
was	O
designed	O
to	O
intercept	O
client-side	B-Operating_System
TLS/SSL	B-Protocol
traffic	O
for	O
parental	O
control	O
and	O
surveillance	O
,	O
but	O
it	O
was	O
also	O
used	O
in	O
numerous	O
adware	O
programs	O
,	O
including	O
Superfish	O
,	O
that	O
were	O
often	O
surreptitiously	O
installed	O
unbeknownst	O
to	O
the	O
computer	O
user	O
.	O
</s>
<s>
In	O
turn	O
,	O
these	O
potentially	B-Application
unwanted	I-Application
programs	I-Application
installed	O
the	O
corrupt	O
root	O
certificate	O
,	O
allowing	O
attackers	O
to	O
completely	O
control	O
web	O
traffic	O
and	O
confirm	O
false	O
websites	O
as	O
authentic	O
.	O
</s>
<s>
In	O
May	O
2016	O
,	O
it	O
was	O
reported	O
that	O
dozens	O
of	O
Danish	O
HTTPS-protected	O
websites	O
belonging	O
to	O
Visa	O
Inc	O
.	O
were	O
vulnerable	O
to	O
attacks	O
allowing	O
hackers	O
to	O
inject	O
malicious	O
code	O
and	O
forged	O
content	O
into	O
the	O
browsers	B-Application
of	O
visitors	O
.	O
</s>
<s>
The	O
attacks	O
worked	O
because	O
the	O
TLS	O
implementation	O
used	O
on	O
the	O
affected	O
servers	O
incorrectly	O
reused	O
random	O
numbers	O
(	O
nonces	O
)	O
that	O
are	O
intended	O
to	O
be	O
used	O
only	O
once	O
,	O
ensuring	O
that	O
each	O
TLS	O
handshake	B-Protocol
is	O
unique	O
.	O
</s>
<s>
In	O
February	O
2017	O
,	O
an	O
implementation	O
error	O
caused	O
by	O
a	O
single	O
mistyped	O
character	O
in	O
code	O
used	O
to	O
parse	O
HTML	O
created	O
a	O
buffer	O
overflow	O
error	O
on	O
Cloudflare	B-Application
servers	O
.	O
</s>
<s>
Similar	O
in	O
its	O
effects	O
to	O
the	O
Heartbleed	B-Error_Name
bug	I-Error_Name
discovered	O
in	O
2014	O
,	O
this	O
overflow	O
error	O
,	O
widely	O
known	O
as	O
Cloudbleed	B-Error_Name
,	O
allowed	O
unauthorized	O
third	O
parties	O
to	O
read	O
data	O
in	O
the	O
memory	O
of	O
programs	O
running	O
on	O
the	O
servers	O
—	O
data	O
that	O
should	O
otherwise	O
have	O
been	O
protected	O
by	O
TLS	O
.	O
</s>
<s>
Forward	O
secrecy	O
is	O
a	O
property	O
of	O
cryptographic	O
systems	O
which	O
ensures	O
that	O
a	O
session	O
key	O
derived	O
from	O
a	O
set	O
of	O
public	O
and	O
private	B-Application
keys	I-Application
will	O
not	O
be	O
compromised	O
if	O
one	O
of	O
the	O
private	B-Application
keys	I-Application
is	O
compromised	O
in	O
the	O
future	O
.	O
</s>
<s>
Without	O
forward	O
secrecy	O
,	O
if	O
the	O
server	B-Application
's	O
private	B-Application
key	I-Application
is	O
compromised	O
,	O
not	O
only	O
will	O
all	O
future	O
TLS-encrypted	O
sessions	O
using	O
that	O
server	B-Application
certificate	O
be	O
compromised	O
,	O
but	O
also	O
any	O
past	O
sessions	O
that	O
used	O
it	O
as	O
well	O
(	O
provided	O
that	O
these	O
past	O
sessions	O
were	O
intercepted	O
and	O
stored	O
at	O
the	O
time	O
of	O
transmission	O
)	O
.	O
</s>
<s>
An	O
implementation	O
of	O
TLS	O
can	O
provide	O
forward	O
secrecy	O
by	O
requiring	O
the	O
use	O
of	O
ephemeral	B-Protocol
Diffie	I-Protocol
–	I-Protocol
Hellman	I-Protocol
key	O
exchange	O
to	O
establish	O
session	O
keys	O
,	O
and	O
some	O
notable	O
TLS	O
implementations	O
do	O
so	O
exclusively	O
:	O
e.g.	O
,	O
Gmail	B-Application
and	O
other	O
Google	B-Application
HTTPS	B-Protocol
services	O
that	O
use	O
OpenSSL	B-Language
.	O
</s>
<s>
However	O
,	O
many	O
clients	O
and	O
servers	O
supporting	O
TLS	O
(	O
including	O
browsers	B-Application
and	O
web	B-Application
servers	I-Application
)	O
are	O
not	O
configured	O
to	O
implement	O
such	O
restrictions	O
.	O
</s>
<s>
In	O
practice	O
,	O
unless	O
a	O
web	O
service	O
uses	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
key	I-Protocol
exchange	I-Protocol
to	O
implement	O
forward	O
secrecy	O
,	O
all	O
of	O
the	O
encrypted	O
web	O
traffic	O
to	O
and	O
from	O
that	O
service	O
can	O
be	O
decrypted	O
by	O
a	O
third	O
party	O
if	O
it	O
obtains	O
the	O
server	B-Application
's	O
master	O
(	O
private	O
)	O
key	O
;	O
e.g.	O
,	O
by	O
means	O
of	O
a	O
court	O
order	O
.	O
</s>
<s>
Even	O
where	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
key	I-Protocol
exchange	I-Protocol
is	O
implemented	O
,	O
server-side	O
session	O
management	O
mechanisms	O
can	O
impact	O
forward	O
secrecy	O
.	O
</s>
<s>
The	O
use	O
of	O
TLS	O
session	O
tickets	O
(	O
a	O
TLS	O
extension	O
)	O
causes	O
the	O
session	O
to	O
be	O
protected	O
by	O
AES128-CBC-SHA256	O
regardless	O
of	O
any	O
other	O
negotiated	O
TLS	O
parameters	O
,	O
including	O
forward	O
secrecy	O
ciphersuites	B-Protocol
,	O
and	O
the	O
long-lived	O
TLS	O
session	O
ticket	O
keys	O
defeat	O
the	O
attempt	O
to	O
implement	O
forward	O
secrecy	O
.	O
</s>
<s>
Stanford	O
University	O
research	O
in	O
2014	O
also	O
found	O
that	O
of	O
473,802	O
TLS	O
servers	O
surveyed	O
,	O
82.9	O
%	O
of	O
the	O
servers	O
deploying	O
ephemeral	B-Protocol
Diffie	I-Protocol
–	I-Protocol
Hellman	I-Protocol
(	O
DHE	B-Protocol
)	O
key	O
exchange	O
to	O
support	O
forward	O
secrecy	O
were	O
using	O
weak	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
parameters	O
.	O
</s>
<s>
Since	O
late	O
2011	O
,	O
Google	B-Application
has	O
provided	O
forward	O
secrecy	O
with	O
TLS	O
by	O
default	O
to	O
users	O
of	O
its	O
Gmail	B-Application
service	O
,	O
along	O
with	O
Google	B-Application
Docs	I-Application
and	O
encrypted	O
search	O
,	O
among	O
other	O
services	O
.	O
</s>
<s>
Since	O
November	O
2013	O
,	O
Twitter	B-Application
has	O
provided	O
forward	O
secrecy	O
with	O
TLS	O
to	O
users	O
of	O
its	O
service	O
.	O
</s>
<s>
,	O
about	O
80%	O
of	O
TLS-enabled	O
websites	O
are	O
configured	O
to	O
use	O
cipher	B-Protocol
suites	I-Protocol
that	O
provide	O
forward	O
secrecy	O
to	O
most	O
web	B-Application
browsers	I-Application
.	O
</s>
<s>
TLS	O
interception	O
(	O
or	O
HTTPS	B-Protocol
interception	O
if	O
applied	O
particularly	O
to	O
that	O
protocol	B-Protocol
)	O
is	O
the	O
practice	O
of	O
intercepting	O
an	O
encrypted	O
data	O
stream	B-Architecture
in	O
order	O
to	O
decrypt	O
it	O
,	O
read	O
and	O
possibly	O
manipulate	O
it	O
,	O
and	O
then	O
re-encrypt	O
it	O
and	O
send	O
the	O
data	O
on	O
its	O
way	O
again	O
.	O
</s>
<s>
This	O
is	O
done	O
by	O
way	O
of	O
a	O
"	O
transparent	O
proxy	O
"	O
:	O
the	O
interception	O
software	O
terminates	O
the	O
incoming	O
TLS	O
connection	O
,	O
inspects	O
the	O
HTTP	B-Protocol
plaintext	O
,	O
and	O
then	O
creates	O
a	O
new	O
TLS	O
connection	O
to	O
the	O
destination	O
.	O
</s>
<s>
TLS/HTTPS	O
interception	O
is	O
used	O
as	O
an	O
information	O
security	O
measure	O
by	O
network	O
operators	O
in	O
order	O
to	O
be	O
able	O
to	O
scan	O
for	O
and	O
protect	O
against	O
the	O
intrusion	O
of	O
malicious	O
content	O
into	O
the	O
network	O
,	O
such	O
as	O
computer	O
viruses	O
and	O
other	O
malware	O
.	O
</s>
<s>
Such	O
content	O
could	O
otherwise	O
not	O
be	O
detected	O
as	O
long	O
as	O
it	O
is	O
protected	O
by	O
encryption	O
,	O
which	O
is	O
increasingly	O
the	O
case	O
as	O
a	O
result	O
of	O
the	O
routine	O
use	O
of	O
HTTPS	B-Protocol
and	O
other	O
secure	O
protocols	O
.	O
</s>
<s>
A	O
significant	O
drawback	O
of	O
TLS/HTTPS	O
interception	O
is	O
that	O
it	O
introduces	O
new	O
security	O
risks	O
of	O
its	O
own	O
.	O
</s>
<s>
A	O
2017	O
study	O
found	O
that	O
"	O
HTTPS	B-Protocol
interception	O
has	O
become	O
startlingly	O
widespread	O
,	O
and	O
that	O
interception	O
products	O
as	O
a	O
class	O
have	O
a	O
dramatically	O
negative	O
impact	O
on	O
connection	O
security	O
"	O
.	O
</s>
<s>
The	O
TLS	B-Protocol
protocol	I-Protocol
exchanges	O
records	O
,	O
which	O
encapsulate	O
the	O
data	O
to	O
be	O
exchanged	O
in	O
a	O
specific	O
format	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
Each	O
record	O
can	O
be	O
compressed	O
,	O
padded	O
,	O
appended	O
with	O
a	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
(	O
MAC	B-Algorithm
)	O
,	O
or	O
encrypted	O
,	O
all	O
depending	O
on	O
the	O
state	O
of	O
the	O
connection	O
.	O
</s>
<s>
The	O
specifications	O
(	O
cipher	B-Protocol
suite	I-Protocol
,	O
keys	O
etc	O
.	O
)	O
</s>
<s>
required	O
to	O
exchange	O
application	O
data	O
by	O
TLS	O
,	O
are	O
agreed	O
upon	O
in	O
the	O
"	O
TLS	O
handshake	B-Protocol
"	O
between	O
the	O
client	B-Protocol
requesting	O
the	O
data	O
and	O
the	O
server	B-Application
responding	O
to	O
requests	O
.	O
</s>
<s>
The	O
protocol	B-Protocol
therefore	O
defines	O
both	O
the	O
structure	O
of	O
payloads	O
transferred	O
in	O
TLS	O
and	O
the	O
procedure	O
to	O
establish	O
and	O
monitor	O
the	O
transfer	O
.	O
</s>
<s>
When	O
the	O
connection	O
starts	O
,	O
the	O
record	O
encapsulates	O
a	O
"	O
control	O
"	O
protocol	B-Protocol
–	O
the	O
handshake	B-Protocol
messaging	O
protocol	B-Protocol
(	O
content	O
type	O
22	O
)	O
.	O
</s>
<s>
This	O
protocol	B-Protocol
is	O
used	O
to	O
exchange	O
all	O
the	O
information	O
required	O
by	O
both	O
sides	O
for	O
the	O
exchange	O
of	O
the	O
actual	O
application	O
data	O
by	O
TLS	O
.	O
</s>
<s>
These	O
may	O
vary	O
according	O
to	O
the	O
demands	O
of	O
the	O
client	B-Protocol
and	O
server	B-Application
–	O
i.e.	O
,	O
there	O
are	O
several	O
possible	O
procedures	O
to	O
set	O
up	O
the	O
connection	O
.	O
</s>
<s>
A	O
typical	O
connection	O
example	O
follows	O
,	O
illustrating	O
a	O
handshake	B-Protocol
where	O
the	O
server	B-Application
(	O
but	O
not	O
the	O
client	B-Protocol
)	O
is	O
authenticated	O
by	O
its	O
certificate	O
:	O
</s>
<s>
A	O
client	B-Protocol
sends	O
a	O
ClientHello	O
message	O
specifying	O
the	O
highest	O
TLS	B-Protocol
protocol	I-Protocol
version	O
it	O
supports	O
,	O
a	O
random	O
number	O
,	O
a	O
list	O
of	O
suggested	O
cipher	B-Protocol
suites	I-Protocol
and	O
suggested	O
compression	B-General_Concept
methods	O
.	O
</s>
<s>
If	O
the	O
client	B-Protocol
is	O
attempting	O
to	O
perform	O
a	O
resumed	O
handshake	B-Protocol
,	O
it	O
may	O
send	O
a	O
session	O
ID	O
.	O
</s>
<s>
If	O
the	O
client	B-Protocol
can	O
use	O
Application-Layer	B-Protocol
Protocol	I-Protocol
Negotiation	I-Protocol
,	O
it	O
may	O
include	O
a	O
list	O
of	O
supported	O
application	O
protocols	O
,	O
such	O
as	O
HTTP/2	B-Protocol
.	O
</s>
<s>
The	O
server	B-Application
responds	O
with	O
a	O
ServerHello	O
message	O
,	O
containing	O
the	O
chosen	O
protocol	B-Protocol
version	O
,	O
a	O
random	O
number	O
,	O
cipher	B-Protocol
suite	I-Protocol
and	O
compression	B-General_Concept
method	O
from	O
the	O
choices	O
offered	O
by	O
the	O
client	B-Protocol
.	O
</s>
<s>
To	O
confirm	O
or	O
allow	O
resumed	O
handshakes	B-Protocol
the	O
server	B-Application
may	O
send	O
a	O
session	O
ID	O
.	O
</s>
<s>
The	O
chosen	O
protocol	B-Protocol
version	O
should	O
be	O
the	O
highest	O
that	O
both	O
the	O
client	B-Protocol
and	O
server	B-Application
support	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
the	O
client	B-Protocol
supports	O
TLS	O
version	O
1.1	O
and	O
the	O
server	B-Application
supports	O
version	O
1.2	O
,	O
version	O
1.1	O
should	O
be	O
selected	O
;	O
version	O
1.2	O
should	O
not	O
be	O
selected	O
.	O
</s>
<s>
The	O
server	B-Application
sends	O
its	O
Certificate	O
message	O
(	O
depending	O
on	O
the	O
selected	O
cipher	B-Protocol
suite	I-Protocol
,	O
this	O
may	O
be	O
omitted	O
by	O
the	O
server	B-Application
)	O
.	O
</s>
<s>
The	O
server	B-Application
sends	O
its	O
ServerKeyExchange	O
message	O
(	O
depending	O
on	O
the	O
selected	O
cipher	B-Protocol
suite	I-Protocol
,	O
this	O
may	O
be	O
omitted	O
by	O
the	O
server	B-Application
)	O
.	O
</s>
<s>
This	O
message	O
is	O
sent	O
for	O
all	O
DHE	B-Protocol
,	O
ECDHE	B-Protocol
and	O
DH_anon	O
cipher	B-Protocol
suites	I-Protocol
.	O
</s>
<s>
The	O
server	B-Application
sends	O
a	O
ServerHelloDone	O
message	O
,	O
indicating	O
it	O
is	O
done	O
with	O
handshake	B-Protocol
negotiation	O
.	O
</s>
<s>
The	O
client	B-Protocol
responds	O
with	O
a	O
ClientKeyExchange	O
message	O
,	O
which	O
may	O
contain	O
a	O
PreMasterSecret	O
,	O
public	B-Application
key	I-Application
,	O
or	O
nothing	O
.	O
</s>
<s>
(	O
Again	O
,	O
this	O
depends	O
on	O
the	O
selected	O
cipher	B-Application
.	O
)	O
</s>
<s>
This	O
PreMasterSecret	O
is	O
encrypted	O
using	O
the	O
public	B-Application
key	I-Application
of	O
the	O
server	B-Application
certificate	O
.	O
</s>
<s>
The	O
client	B-Protocol
and	O
server	B-Application
then	O
use	O
the	O
random	O
numbers	O
and	O
PreMasterSecret	O
to	O
compute	O
a	O
common	O
secret	O
,	O
called	O
the	O
"	O
master	O
secret	O
"	O
.	O
</s>
<s>
All	O
other	O
key	O
data	O
(	O
session	O
keys	O
such	O
as	O
IV	B-Algorithm
,	O
symmetric	B-Algorithm
encryption	I-Algorithm
key	O
,	O
MAC	B-Algorithm
key	O
)	O
for	O
this	O
connection	O
is	O
derived	O
from	O
this	O
master	O
secret	O
(	O
and	O
the	O
client	B-Protocol
-	O
and	O
server-generated	O
random	O
values	O
)	O
,	O
which	O
is	O
passed	O
through	O
a	O
carefully	O
designed	O
pseudorandom	B-Error_Name
function	O
.	O
</s>
<s>
The	O
client	B-Protocol
now	O
sends	O
a	O
ChangeCipherSpec	O
record	O
,	O
essentially	O
telling	O
the	O
server	B-Application
,	O
"	O
Everything	O
I	O
tell	O
you	O
from	O
now	O
on	O
will	O
be	O
authenticated	O
(	O
and	O
encrypted	O
if	O
encryption	O
parameters	O
were	O
present	O
in	O
the	O
server	B-Application
certificate	O
)	O
.	O
</s>
<s>
"	O
The	O
ChangeCipherSpec	O
is	O
itself	O
a	O
record-level	O
protocol	B-Protocol
with	O
content	O
type	O
of	O
20	O
.	O
</s>
<s>
The	O
client	B-Protocol
sends	O
an	O
authenticated	O
and	O
encrypted	O
Finished	O
message	O
,	O
containing	O
a	O
hash	B-Algorithm
and	O
MAC	B-Algorithm
over	O
the	O
previous	O
handshake	B-Protocol
messages	O
.	O
</s>
<s>
The	O
server	B-Application
will	O
attempt	O
to	O
decrypt	O
the	O
client	B-Protocol
's	O
Finished	O
message	O
and	O
verify	O
the	O
hash	B-Algorithm
and	O
MAC	B-Algorithm
.	O
</s>
<s>
If	O
the	O
decryption	O
or	O
verification	O
fails	O
,	O
the	O
handshake	B-Protocol
is	O
considered	O
to	O
have	O
failed	O
and	O
the	O
connection	O
should	O
be	O
torn	O
down	O
.	O
</s>
<s>
Finally	O
,	O
the	O
server	B-Application
sends	O
a	O
ChangeCipherSpec	O
,	O
telling	O
the	O
client	B-Protocol
,	O
"	O
Everything	O
I	O
tell	O
you	O
from	O
now	O
on	O
will	O
be	O
authenticated	O
(	O
and	O
encrypted	O
,	O
if	O
encryption	O
was	O
negotiated	O
)	O
.	O
"	O
</s>
<s>
The	O
server	B-Application
sends	O
its	O
authenticated	O
and	O
encrypted	O
Finished	O
message	O
.	O
</s>
<s>
The	O
client	B-Protocol
performs	O
the	O
same	O
decryption	O
and	O
verification	O
procedure	O
as	O
the	O
server	B-Application
did	O
in	O
the	O
previous	O
step	O
.	O
</s>
<s>
Application	O
phase	O
:	O
at	O
this	O
point	O
,	O
the	O
"	O
handshake	B-Protocol
"	O
is	O
complete	O
and	O
the	O
application	O
protocol	B-Protocol
is	O
enabled	O
,	O
with	O
content	O
type	O
of	O
23	O
.	O
</s>
<s>
Application	O
messages	O
exchanged	O
between	O
client	B-Protocol
and	O
server	B-Application
will	O
also	O
be	O
authenticated	O
and	O
optionally	O
encrypted	O
exactly	O
like	O
in	O
their	O
Finished	O
message	O
.	O
</s>
<s>
Otherwise	O
,	O
the	O
content	O
type	O
will	O
return	O
25	O
and	O
the	O
client	B-Protocol
will	O
not	O
authenticate	O
.	O
</s>
<s>
The	O
following	O
full	O
example	O
shows	O
a	O
client	B-Protocol
being	O
authenticated	O
(	O
in	O
addition	O
to	O
the	O
server	B-Application
as	O
in	O
the	O
example	O
above	O
;	O
see	O
mutual	O
authentication	O
)	O
via	O
TLS	O
using	O
certificates	O
exchanged	O
between	O
both	O
peers	O
.	O
</s>
<s>
A	O
client	B-Protocol
sends	O
a	O
ClientHello	O
message	O
specifying	O
the	O
highest	O
TLS	B-Protocol
protocol	I-Protocol
version	O
it	O
supports	O
,	O
a	O
random	O
number	O
,	O
a	O
list	O
of	O
suggested	O
cipher	B-Protocol
suites	I-Protocol
and	O
compression	B-General_Concept
methods	O
.	O
</s>
<s>
The	O
server	B-Application
responds	O
with	O
a	O
ServerHello	O
message	O
,	O
containing	O
the	O
chosen	O
protocol	B-Protocol
version	O
,	O
a	O
random	O
number	O
,	O
cipher	B-Protocol
suite	I-Protocol
and	O
compression	B-General_Concept
method	O
from	O
the	O
choices	O
offered	O
by	O
the	O
client	B-Protocol
.	O
</s>
<s>
The	O
server	B-Application
may	O
also	O
send	O
a	O
session	O
id	O
as	O
part	O
of	O
the	O
message	O
to	O
perform	O
a	O
resumed	O
handshake	B-Protocol
.	O
</s>
<s>
The	O
server	B-Application
sends	O
its	O
Certificate	O
message	O
(	O
depending	O
on	O
the	O
selected	O
cipher	B-Protocol
suite	I-Protocol
,	O
this	O
may	O
be	O
omitted	O
by	O
the	O
server	B-Application
)	O
.	O
</s>
<s>
The	O
server	B-Application
sends	O
its	O
ServerKeyExchange	O
message	O
(	O
depending	O
on	O
the	O
selected	O
cipher	B-Protocol
suite	I-Protocol
,	O
this	O
may	O
be	O
omitted	O
by	O
the	O
server	B-Application
)	O
.	O
</s>
<s>
This	O
message	O
is	O
sent	O
for	O
all	O
DHE	B-Protocol
,	O
ECDHE	B-Protocol
and	O
DH_anon	O
ciphersuites	B-Protocol
.	O
</s>
<s>
The	O
server	B-Application
sends	O
a	O
CertificateRequest	O
message	O
,	O
to	O
request	O
a	O
certificate	O
from	O
the	O
client	B-Protocol
.	O
</s>
<s>
The	O
server	B-Application
sends	O
a	O
ServerHelloDone	O
message	O
,	O
indicating	O
it	O
is	O
done	O
with	O
handshake	B-Protocol
negotiation	O
.	O
</s>
<s>
The	O
client	B-Protocol
responds	O
with	O
a	O
Certificate	O
message	O
,	O
which	O
contains	O
the	O
client	B-Protocol
's	O
certificate	O
,	O
but	O
not	O
its	O
private	B-Application
key	I-Application
.	O
</s>
<s>
The	O
client	B-Protocol
sends	O
a	O
ClientKeyExchange	O
message	O
,	O
which	O
may	O
contain	O
a	O
PreMasterSecret	O
,	O
public	B-Application
key	I-Application
,	O
or	O
nothing	O
.	O
</s>
<s>
(	O
Again	O
,	O
this	O
depends	O
on	O
the	O
selected	O
cipher	B-Application
.	O
)	O
</s>
<s>
This	O
PreMasterSecret	O
is	O
encrypted	O
using	O
the	O
public	B-Application
key	I-Application
of	O
the	O
server	B-Application
certificate	O
.	O
</s>
<s>
The	O
client	B-Protocol
sends	O
a	O
CertificateVerify	O
message	O
,	O
which	O
is	O
a	O
signature	O
over	O
the	O
previous	O
handshake	B-Protocol
messages	O
using	O
the	O
client	B-Protocol
's	O
certificate	O
's	O
private	B-Application
key	I-Application
.	O
</s>
<s>
This	O
signature	O
can	O
be	O
verified	O
by	O
using	O
the	O
client	B-Protocol
's	O
certificate	O
's	O
public	B-Application
key	I-Application
.	O
</s>
<s>
This	O
lets	O
the	O
server	B-Application
know	O
that	O
the	O
client	B-Protocol
has	O
access	O
to	O
the	O
private	B-Application
key	I-Application
of	O
the	O
certificate	O
and	O
thus	O
owns	O
the	O
certificate	O
.	O
</s>
<s>
The	O
client	B-Protocol
and	O
server	B-Application
then	O
use	O
the	O
random	O
numbers	O
and	O
PreMasterSecret	O
to	O
compute	O
a	O
common	O
secret	O
,	O
called	O
the	O
"	O
master	O
secret	O
"	O
.	O
</s>
<s>
All	O
other	O
key	O
data	O
(	O
"	O
session	O
keys	O
"	O
)	O
for	O
this	O
connection	O
is	O
derived	O
from	O
this	O
master	O
secret	O
(	O
and	O
the	O
client	B-Protocol
-	O
and	O
server-generated	O
random	O
values	O
)	O
,	O
which	O
is	O
passed	O
through	O
a	O
carefully	O
designed	O
pseudorandom	B-Error_Name
function	O
.	O
</s>
<s>
The	O
client	B-Protocol
now	O
sends	O
a	O
ChangeCipherSpec	O
record	O
,	O
essentially	O
telling	O
the	O
server	B-Application
,	O
"	O
Everything	O
I	O
tell	O
you	O
from	O
now	O
on	O
will	O
be	O
authenticated	O
(	O
and	O
encrypted	O
if	O
encryption	O
was	O
negotiated	O
)	O
.	O
</s>
<s>
"	O
The	O
ChangeCipherSpec	O
is	O
itself	O
a	O
record-level	O
protocol	B-Protocol
and	O
has	O
type	O
20	O
and	O
not	O
22	O
.	O
</s>
<s>
Finally	O
,	O
the	O
client	B-Protocol
sends	O
an	O
encrypted	O
Finished	O
message	O
,	O
containing	O
a	O
hash	B-Algorithm
and	O
MAC	B-Algorithm
over	O
the	O
previous	O
handshake	B-Protocol
messages	O
.	O
</s>
<s>
The	O
server	B-Application
will	O
attempt	O
to	O
decrypt	O
the	O
client	B-Protocol
's	O
Finished	O
message	O
and	O
verify	O
the	O
hash	B-Algorithm
and	O
MAC	B-Algorithm
.	O
</s>
<s>
If	O
the	O
decryption	O
or	O
verification	O
fails	O
,	O
the	O
handshake	B-Protocol
is	O
considered	O
to	O
have	O
failed	O
and	O
the	O
connection	O
should	O
be	O
torn	O
down	O
.	O
</s>
<s>
Finally	O
,	O
the	O
server	B-Application
sends	O
a	O
ChangeCipherSpec	O
,	O
telling	O
the	O
client	B-Protocol
,	O
"	O
Everything	O
I	O
tell	O
you	O
from	O
now	O
on	O
will	O
be	O
authenticated	O
(	O
and	O
encrypted	O
if	O
encryption	O
was	O
negotiated	O
)	O
.	O
"	O
</s>
<s>
The	O
server	B-Application
sends	O
its	O
own	O
encrypted	O
Finished	O
message	O
.	O
</s>
<s>
The	O
client	B-Protocol
performs	O
the	O
same	O
decryption	O
and	O
verification	O
procedure	O
as	O
the	O
server	B-Application
did	O
in	O
the	O
previous	O
step	O
.	O
</s>
<s>
Application	O
phase	O
:	O
at	O
this	O
point	O
,	O
the	O
"	O
handshake	B-Protocol
"	O
is	O
complete	O
and	O
the	O
application	O
protocol	B-Protocol
is	O
enabled	O
,	O
with	O
content	O
type	O
of	O
23	O
.	O
</s>
<s>
Application	O
messages	O
exchanged	O
between	O
client	B-Protocol
and	O
server	B-Application
will	O
also	O
be	O
encrypted	O
exactly	O
like	O
in	O
their	O
Finished	O
message	O
.	O
</s>
<s>
Public	B-Application
key	I-Application
operations	O
(	O
e.g.	O
,	O
RSA	B-Architecture
)	O
are	O
relatively	O
expensive	O
in	O
terms	O
of	O
computational	O
power	O
.	O
</s>
<s>
TLS	O
provides	O
a	O
secure	O
shortcut	O
in	O
the	O
handshake	B-Protocol
mechanism	O
to	O
avoid	O
these	O
operations	O
:	O
resumed	O
sessions	O
.	O
</s>
<s>
Apart	O
from	O
the	O
performance	O
benefit	O
,	O
resumed	O
sessions	O
can	O
also	O
be	O
used	O
for	O
single	O
sign-on	O
,	O
as	O
it	O
guarantees	O
that	O
both	O
the	O
original	O
session	O
and	O
any	O
resumed	O
session	O
originate	O
from	O
the	O
same	O
client	B-Protocol
.	O
</s>
<s>
This	O
is	O
of	O
particular	O
importance	O
for	O
the	O
FTP	B-Protocol
over	I-Protocol
TLS/SSL	I-Protocol
protocol	B-Protocol
,	O
which	O
would	O
otherwise	O
suffer	O
from	O
a	O
man-in-the-middle	O
attack	O
in	O
which	O
an	O
attacker	O
could	O
intercept	O
the	O
contents	O
of	O
the	O
secondary	O
data	O
connections	O
.	O
</s>
<s>
The	O
TLS	O
1.3	O
handshake	B-Protocol
was	O
condensed	O
to	O
only	O
one	O
round	O
trip	O
compared	O
to	O
the	O
two	O
round	O
trips	O
required	O
in	O
previous	O
versions	O
of	O
TLS/SSL	B-Protocol
.	O
</s>
<s>
First	O
the	O
client	B-Protocol
sends	O
a	O
clientHello	O
message	O
to	O
the	O
server	B-Application
that	O
contains	O
a	O
list	O
of	O
supported	O
ciphers	B-Application
in	O
order	O
of	O
the	O
client	B-Protocol
's	O
preference	O
and	O
makes	O
a	O
guess	O
on	O
what	O
key	O
algorithm	O
will	O
be	O
used	O
so	O
that	O
it	O
can	O
send	O
a	O
secret	O
key	O
to	O
share	O
if	O
needed	O
.	O
</s>
<s>
By	O
making	O
a	O
guess	O
at	O
what	O
key	O
algorithm	O
will	O
be	O
used	O
,	O
the	O
server	B-Application
eliminates	O
a	O
round	O
trip	O
.	O
</s>
<s>
After	O
receiving	O
the	O
clientHello	O
,	O
the	O
server	B-Application
sends	O
a	O
serverHello	O
with	O
its	O
key	O
,	O
a	O
certificate	O
,	O
the	O
chosen	O
cipher	B-Protocol
suite	I-Protocol
and	O
the	O
finished	O
message	O
.	O
</s>
<s>
After	O
the	O
client	B-Protocol
receives	O
the	O
server	B-Application
's	O
finished	O
message	O
,	O
it	O
now	O
is	O
coordinated	O
with	O
the	O
server	B-Application
on	O
which	O
cipher	B-Protocol
suite	I-Protocol
to	O
use	O
.	O
</s>
<s>
In	O
an	O
ordinary	O
full	O
handshake	B-Protocol
,	O
the	O
server	B-Application
sends	O
a	O
session	O
id	O
as	O
part	O
of	O
the	O
ServerHello	O
message	O
.	O
</s>
<s>
The	O
client	B-Protocol
associates	O
this	O
session	O
id	O
with	O
the	O
server	B-Application
's	O
IP	O
address	O
and	O
TCP	B-Protocol
port	I-Protocol
,	O
so	O
that	O
when	O
the	O
client	B-Protocol
connects	O
again	O
to	O
that	O
server	B-Application
,	O
it	O
can	O
use	O
the	O
session	O
id	O
to	O
shortcut	O
the	O
handshake	B-Protocol
.	O
</s>
<s>
In	O
the	O
server	B-Application
,	O
the	O
session	O
id	O
maps	O
to	O
the	O
cryptographic	O
parameters	O
previously	O
negotiated	O
,	O
specifically	O
the	O
"	O
master	O
secret	O
"	O
.	O
</s>
<s>
Both	O
sides	O
must	O
have	O
the	O
same	O
"	O
master	O
secret	O
"	O
or	O
the	O
resumed	O
handshake	B-Protocol
will	O
fail	O
(	O
this	O
prevents	O
an	O
eavesdropper	O
from	O
using	O
a	O
session	O
id	O
)	O
.	O
</s>
<s>
In	O
the	O
RFCs	O
,	O
this	O
type	O
of	O
handshake	B-Protocol
is	O
called	O
an	O
abbreviated	O
handshake	B-Protocol
.	O
</s>
<s>
It	O
is	O
also	O
described	O
in	O
the	O
literature	O
as	O
a	O
restart	O
handshake	B-Protocol
.	O
</s>
<s>
A	O
client	B-Protocol
sends	O
a	O
ClientHello	O
message	O
specifying	O
the	O
highest	O
TLS	B-Protocol
protocol	I-Protocol
version	O
it	O
supports	O
,	O
a	O
random	O
number	O
,	O
a	O
list	O
of	O
suggested	O
cipher	B-Protocol
suites	I-Protocol
and	O
compression	B-General_Concept
methods	O
.	O
</s>
<s>
The	O
server	B-Application
responds	O
with	O
a	O
ServerHello	O
message	O
,	O
containing	O
the	O
chosen	O
protocol	B-Protocol
version	O
,	O
a	O
random	O
number	O
,	O
cipher	B-Protocol
suite	I-Protocol
and	O
compression	B-General_Concept
method	O
from	O
the	O
choices	O
offered	O
by	O
the	O
client	B-Protocol
.	O
</s>
<s>
If	O
the	O
server	B-Application
recognizes	O
the	O
session	O
id	O
sent	O
by	O
the	O
client	B-Protocol
,	O
it	O
responds	O
with	O
the	O
same	O
session	O
id	O
.	O
</s>
<s>
The	O
client	B-Protocol
uses	O
this	O
to	O
recognize	O
that	O
a	O
resumed	O
handshake	B-Protocol
is	O
being	O
performed	O
.	O
</s>
<s>
If	O
the	O
server	B-Application
does	O
not	O
recognize	O
the	O
session	O
id	O
sent	O
by	O
the	O
client	B-Protocol
,	O
it	O
sends	O
a	O
different	O
value	O
for	O
its	O
session	O
id	O
.	O
</s>
<s>
This	O
tells	O
the	O
client	B-Protocol
that	O
a	O
resumed	O
handshake	B-Protocol
will	O
not	O
be	O
performed	O
.	O
</s>
<s>
At	O
this	O
point	O
,	O
both	O
the	O
client	B-Protocol
and	O
server	B-Application
have	O
the	O
"	O
master	O
secret	O
"	O
and	O
random	O
data	O
to	O
generate	O
the	O
key	O
data	O
to	O
be	O
used	O
for	O
this	O
connection	O
.	O
</s>
<s>
The	O
server	B-Application
now	O
sends	O
a	O
ChangeCipherSpec	O
record	O
,	O
essentially	O
telling	O
the	O
client	B-Protocol
,	O
"	O
Everything	O
I	O
tell	O
you	O
from	O
now	O
on	O
will	O
be	O
encrypted.	O
"	O
</s>
<s>
The	O
ChangeCipherSpec	O
is	O
itself	O
a	O
record-level	O
protocol	B-Protocol
and	O
has	O
type	O
20	O
and	O
not	O
22	O
.	O
</s>
<s>
Finally	O
,	O
the	O
server	B-Application
sends	O
an	O
encrypted	O
Finished	O
message	O
,	O
containing	O
a	O
hash	B-Algorithm
and	O
MAC	B-Algorithm
over	O
the	O
previous	O
handshake	B-Protocol
messages	O
.	O
</s>
<s>
The	O
client	B-Protocol
will	O
attempt	O
to	O
decrypt	O
the	O
server	B-Application
's	O
Finished	O
message	O
and	O
verify	O
the	O
hash	B-Algorithm
and	O
MAC	B-Algorithm
.	O
</s>
<s>
If	O
the	O
decryption	O
or	O
verification	O
fails	O
,	O
the	O
handshake	B-Protocol
is	O
considered	O
to	O
have	O
failed	O
and	O
the	O
connection	O
should	O
be	O
torn	O
down	O
.	O
</s>
<s>
Finally	O
,	O
the	O
client	B-Protocol
sends	O
a	O
ChangeCipherSpec	O
,	O
telling	O
the	O
server	B-Application
,	O
"	O
Everything	O
I	O
tell	O
you	O
from	O
now	O
on	O
will	O
be	O
encrypted.	O
"	O
</s>
<s>
The	O
client	B-Protocol
sends	O
its	O
own	O
encrypted	O
Finished	O
message	O
.	O
</s>
<s>
The	O
server	B-Application
performs	O
the	O
same	O
decryption	O
and	O
verification	O
procedure	O
as	O
the	O
client	B-Protocol
did	O
in	O
the	O
previous	O
step	O
.	O
</s>
<s>
Application	O
phase	O
:	O
at	O
this	O
point	O
,	O
the	O
"	O
handshake	B-Protocol
"	O
is	O
complete	O
and	O
the	O
application	O
protocol	B-Protocol
is	O
enabled	O
,	O
with	O
content	O
type	O
of	O
23	O
.	O
</s>
<s>
Application	O
messages	O
exchanged	O
between	O
client	B-Protocol
and	O
server	B-Application
will	O
also	O
be	O
encrypted	O
exactly	O
like	O
in	O
their	O
Finished	O
message	O
.	O
</s>
<s>
It	O
defines	O
a	O
way	O
to	O
resume	O
a	O
TLS	O
session	O
without	O
requiring	O
that	O
session-specific	O
state	O
is	O
stored	O
at	O
the	O
TLS	O
server	B-Application
.	O
</s>
<s>
When	O
using	O
session	O
tickets	O
,	O
the	O
TLS	O
server	B-Application
stores	O
its	O
session-specific	O
state	O
in	O
a	O
session	O
ticket	O
and	O
sends	O
the	O
session	O
ticket	O
to	O
the	O
TLS	O
client	B-Protocol
for	O
storing	O
.	O
</s>
<s>
The	O
client	B-Protocol
resumes	O
a	O
TLS	O
session	O
by	O
sending	O
the	O
session	O
ticket	O
to	O
the	O
server	B-Application
,	O
and	O
the	O
server	B-Application
resumes	O
the	O
TLS	O
session	O
according	O
to	O
the	O
session-specific	O
state	O
in	O
the	O
ticket	O
.	O
</s>
<s>
The	O
session	O
ticket	O
is	O
encrypted	O
and	O
authenticated	O
by	O
the	O
server	B-Application
,	O
and	O
the	O
server	B-Application
verifies	O
its	O
validity	O
before	O
using	O
its	O
contents	O
.	O
</s>
<s>
One	O
particular	O
weakness	O
of	O
this	O
method	O
with	O
OpenSSL	B-Language
is	O
that	O
it	O
always	O
limits	O
encryption	O
and	O
authentication	O
security	O
of	O
the	O
transmitted	O
TLS	O
session	O
ticket	O
to	O
AES128-CBC-SHA256	O
,	O
no	O
matter	O
what	O
other	O
TLS	O
parameters	O
were	O
negotiated	O
for	O
the	O
actual	O
TLS	O
session	O
.	O
</s>
<s>
Of	O
particular	O
concern	O
is	O
OpenSSL	B-Language
's	O
storage	O
of	O
the	O
keys	O
in	O
an	O
application-wide	O
context	O
(	O
SSL_CTX	O
)	O
,	O
i.e.	O
</s>
<s>
for	O
the	O
life	O
of	O
the	O
application	O
,	O
and	O
not	O
allowing	O
for	O
re-keying	O
of	O
the	O
AES128-CBC-SHA256	O
TLS	O
session	O
tickets	O
without	O
resetting	O
the	O
application-wide	O
OpenSSL	B-Language
context	O
(	O
which	O
is	O
uncommon	O
,	O
error-prone	O
and	O
often	O
requires	O
manual	O
administrative	O
intervention	O
)	O
.	O
</s>
<s>
This	O
field	O
identifies	O
the	O
Record	O
Layer	O
Protocol	B-Protocol
Type	O
contained	O
in	O
this	O
record	O
.	O
</s>
<s>
For	O
a	O
ClientHello	O
message	O
,	O
this	O
need	O
not	O
be	O
the	O
highest	O
version	O
supported	O
by	O
the	O
client	B-Protocol
.	O
</s>
<s>
The	O
length	O
of	O
"	O
protocol	B-Protocol
message(s )	O
"	O
,	O
"	O
MAC	B-Algorithm
"	O
and	O
"	O
padding	O
"	O
fields	O
combined	O
(	O
i.e.	O
</s>
<s>
One	O
or	O
more	O
messages	O
identified	O
by	O
the	O
Protocol	B-Protocol
field	O
.	O
</s>
<s>
A	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
computed	O
over	O
the	O
"	O
protocol	B-Protocol
message(s )	O
"	O
field	O
,	O
with	O
additional	O
key	O
material	O
included	O
.	O
</s>
<s>
No	O
"	O
MAC	B-Algorithm
"	O
or	O
"	O
padding	O
"	O
fields	O
can	O
be	O
present	O
at	O
end	O
of	O
TLS	O
records	O
before	O
all	O
cipher	B-Application
algorithms	O
and	O
parameters	O
have	O
been	O
negotiated	O
and	O
handshaked	O
and	O
then	O
confirmed	O
by	O
sending	O
a	O
CipherStateChange	O
record	O
(	O
see	O
below	O
)	O
for	O
signalling	O
that	O
these	O
parameters	O
will	O
take	O
effect	O
in	O
all	O
further	O
records	O
sent	O
by	O
the	O
same	O
peer	O
.	O
</s>
<s>
Most	O
messages	O
exchanged	O
during	O
the	O
setup	O
of	O
the	O
TLS	O
session	O
are	O
based	O
on	O
this	O
record	O
,	O
unless	O
an	O
error	O
or	O
warning	O
occurs	O
and	O
needs	O
to	O
be	O
signaled	O
by	O
an	O
Alert	O
protocol	B-Protocol
record	O
(	O
see	O
below	O
)	O
,	O
or	O
the	O
encryption	B-Algorithm
mode	I-Algorithm
of	O
the	O
session	O
is	O
modified	O
by	O
another	O
record	O
(	O
see	O
ChangeCipherSpec	O
protocol	B-Protocol
below	O
)	O
.	O
</s>
<s>
Message	O
type	O
This	O
field	O
identifies	O
the	O
handshake	B-Protocol
message	O
type	O
.	O
</s>
<s>
This	O
is	O
a	O
3-byte	O
field	O
indicating	O
the	O
length	O
of	O
the	O
handshake	B-Protocol
data	O
,	O
not	O
including	O
the	O
header	O
.	O
</s>
<s>
Note	O
that	O
multiple	O
handshake	B-Protocol
messages	O
may	O
be	O
combined	O
within	O
one	O
record	O
.	O
</s>
<s>
However	O
,	O
this	O
message	O
can	O
be	O
sent	O
at	O
any	O
time	O
during	O
the	O
handshake	B-Protocol
and	O
up	O
to	O
the	O
closure	O
of	O
the	O
session	O
.	O
</s>
<s>
The	O
use	O
of	O
Alert	O
records	O
is	O
optional	O
,	O
however	O
if	O
it	O
is	O
missing	O
before	O
the	O
session	O
closure	O
,	O
the	O
session	O
may	O
be	O
resumed	O
automatically	O
(	O
with	O
its	O
handshakes	B-Protocol
)	O
.	O
</s>
<s>
Signalling	O
explicitly	O
the	O
normal	O
closure	O
of	O
a	O
secure	O
session	O
before	O
effectively	O
closing	O
its	O
transport	B-Architecture
layer	I-Architecture
is	O
useful	O
to	O
prevent	O
or	O
detect	O
attacks	O
(	O
like	O
attempts	O
to	O
truncate	O
the	O
securely	O
transported	O
data	O
,	O
if	O
it	O
intrinsically	O
does	O
not	O
have	O
a	O
predetermined	O
length	O
or	O
duration	O
that	O
the	O
recipient	O
of	O
the	O
secured	O
data	O
may	O
expect	O
)	O
.	O
</s>
<s>
FTP	B-Protocol
firewall	O
rule	O
on	O
FTPS	B-Protocol
server.21Decryption	O
failedfatalTLS	O
only	O
,	O
reserved22Record	O
overflowfatalTLS	O
only30Decompression	O
failurefatal40Handshake	O
failurefatal41No	O
certificatewarning/fatalSSL	O
3.0	O
only	O
,	O
reserved42Bad	O
certificatewarning/fatal43Unsupported	O
certificatewarning/fatale.g.	O
</s>
<s>
certificate	O
has	O
only	O
server	B-Application
authentication	O
usage	O
enabled	O
and	O
is	O
presented	O
as	O
a	O
client	B-Protocol
certificate44Certificate	O
revokedwarning/fatal45Certificate	O
expiredwarning/fatalCheck	O
server	B-Application
certificate	O
expire	O
also	O
check	O
no	O
certificate	O
in	O
the	O
chain	O
presented	O
has	O
expired46Certificate	O
unknownwarning/fatal47Illegal	O
parameterfatal48Unknown	O
CA	O
(	O
Certificate	B-Architecture
authority	I-Architecture
)	O
fatalTLS	O
only49Access	O
deniedfatalTLS	O
only	O
–	O
e.g.	O
</s>
<s>
32	O
bytes	O
for	O
the	O
SHA-256-based	O
HMAC	B-Algorithm
,	O
20	O
bytes	O
for	O
the	O
SHA-1-based	O
HMAC	B-Algorithm
,	O
16	O
bytes	O
for	O
the	O
MD5-based	O
HMAC	B-Algorithm
.	O
</s>
<s>
From	O
the	O
application	O
protocol	B-Protocol
point	O
of	O
view	O
,	O
TLS	O
belongs	O
to	O
a	O
lower	O
layer	O
,	O
although	O
the	O
TCP/IP	B-Protocol
model	I-Protocol
is	O
too	O
coarse	O
to	O
show	O
it	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
TLS	O
handshake	B-Protocol
is	O
usually	O
(	O
except	O
in	O
the	O
STARTTLS	B-Protocol
case	O
)	O
performed	O
before	O
the	O
application	O
protocol	B-Protocol
can	O
start	O
.	O
</s>
<s>
In	O
the	O
name-based	O
virtual	O
server	B-Application
feature	O
being	O
provided	O
by	O
the	O
application	O
layer	O
,	O
all	O
co-hosted	O
virtual	O
servers	O
share	O
the	O
same	O
certificate	O
because	O
the	O
server	B-Application
has	O
to	O
select	O
and	O
send	O
a	O
certificate	O
immediately	O
after	O
the	O
ClientHello	O
message	O
.	O
</s>
<s>
Besides	O
the	O
loose	O
host	B-Protocol
name	I-Protocol
selection	O
that	O
might	O
be	O
a	O
problem	O
or	O
not	O
,	O
there	O
is	O
no	O
common	O
agreement	O
about	O
how	O
to	O
match	O
wildcard	O
certificates	O
.	O
</s>
<s>
Different	O
rules	O
are	O
applied	O
depending	O
on	O
the	O
application	O
protocol	B-Protocol
or	O
software	O
used	O
.	O
</s>
<s>
Add	O
every	O
virtual	O
host	B-Protocol
name	I-Protocol
in	O
the	O
subjectAltName	O
extension	O
.	O
</s>
<s>
The	O
major	O
problem	O
being	O
that	O
the	O
certificate	O
needs	O
to	O
be	O
reissued	O
whenever	O
a	O
new	O
virtual	O
server	B-Application
is	O
added	O
.	O
</s>
<s>
To	O
provide	O
the	O
server	B-Protocol
name	I-Protocol
,	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Extensions	O
allow	O
clients	O
to	O
include	O
a	O
Server	B-Protocol
Name	I-Protocol
Indication	I-Protocol
extension	O
(	O
SNI	O
)	O
in	O
the	O
extended	O
ClientHello	O
message	O
.	O
</s>
<s>
also	O
documents	O
a	O
method	O
to	O
implement	O
name-based	O
virtual	O
hosting	O
by	O
upgrading	O
HTTP	B-Protocol
to	O
TLS	O
via	O
an	O
HTTP/1.1	B-Protocol
Upgrade	I-Protocol
header	I-Protocol
.	O
</s>
<s>
Normally	O
this	O
is	O
to	O
securely	O
implement	O
HTTP	B-Protocol
over	O
TLS	O
within	O
the	O
main	O
"	O
http	B-Protocol
"	O
URI	O
scheme	O
(	O
which	O
avoids	O
forking	O
the	O
URI	O
space	O
and	O
reduces	O
the	O
number	O
of	O
used	O
ports	O
)	O
,	O
however	O
,	O
few	O
implementations	O
currently	O
support	O
this	O
.	O
</s>
<s>
:	O
"	O
The	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Protocol	B-Protocol
Version	O
1.3	O
"	O
.	O
</s>
<s>
:	O
"	O
The	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Protocol	B-Protocol
Version	O
1.2	O
"	O
.	O
</s>
<s>
:	O
"	O
The	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Protocol	B-Protocol
Version	O
1.1	O
"	O
.	O
</s>
<s>
:	O
"	O
The	O
TLS	B-Protocol
Protocol	I-Protocol
Version	O
1.0	O
"	O
.	O
</s>
<s>
:	O
"	O
The	O
Secure	B-Protocol
Sockets	I-Protocol
Layer	I-Protocol
(	O
SSL	O
)	O
Protocol	B-Protocol
Version	O
3.0	O
"	O
.	O
</s>
<s>
:	O
"	O
AES	B-Algorithm
Galois	I-Algorithm
Counter	I-Algorithm
Mode	I-Algorithm
(	O
GCM	B-Algorithm
)	O
Cipher	B-Protocol
Suites	I-Protocol
for	O
TLS	O
"	O
.	O
</s>
<s>
:	O
"	O
TLS	O
Elliptic	O
Curve	O
Cipher	B-Protocol
Suites	I-Protocol
with	O
SHA-256/384	O
and	O
AES	B-Algorithm
Galois	I-Algorithm
Counter	I-Algorithm
Mode	I-Algorithm
(	O
GCM	B-Algorithm
)	O
"	O
.	O
</s>
<s>
:	O
"	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Renegotiation	O
Indication	O
Extension	O
"	O
.	O
</s>
<s>
:	O
"	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Authorization	O
Extensions	O
"	O
.	O
</s>
<s>
:	O
"	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Extensions	O
:	O
Extension	O
Definitions	O
"	O
,	O
includes	O
Server	B-Protocol
Name	I-Protocol
Indication	I-Protocol
and	O
OCSP	B-Protocol
stapling	I-Protocol
.	O
</s>
<s>
:	O
"	O
Using	O
OpenPGP	O
Keys	O
for	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Authentication	O
"	O
.	O
</s>
<s>
:	O
"	O
Prohibiting	O
Secure	B-Protocol
Sockets	I-Protocol
Layer	I-Protocol
(	O
SSL	O
)	O
Version	O
2.0	O
"	O
.	O
</s>
<s>
:	O
"	O
Addition	O
of	O
the	O
ARIA	B-Algorithm
Cipher	B-Protocol
Suites	I-Protocol
to	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
"	O
.	O
</s>
<s>
:	O
"	O
Datagram	B-Protocol
Transport	I-Protocol
Layer	I-Protocol
Security	I-Protocol
Version	O
1.2	O
"	O
.	O
</s>
<s>
:	O
"	O
Addition	O
of	O
the	O
Camellia	B-Algorithm
Cipher	B-Protocol
Suites	I-Protocol
to	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
"	O
.	O
</s>
<s>
:	O
"	O
Suite	O
B	O
Profile	O
for	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
"	O
.	O
</s>
<s>
:	O
"	O
AES-CCM	O
Cipher	B-Protocol
Suites	I-Protocol
for	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
"	O
.	O
</s>
<s>
:	O
"	O
Elliptic	O
Curve	O
Cryptography	O
(	O
ECC	O
)	O
Brainpool	O
Curves	O
for	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
"	O
.	O
</s>
<s>
:	O
"	O
AES-CCM	O
Elliptic	O
Curve	O
Cryptography	O
(	O
ECC	O
)	O
Cipher	B-Protocol
Suites	I-Protocol
for	O
TLS	O
"	O
.	O
</s>
<s>
:	O
"	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Application-Layer	B-Protocol
Protocol	I-Protocol
Negotiation	I-Protocol
Extension	O
"	O
.	O
</s>
<s>
:	O
"	O
Encrypt-then-MAC	O
for	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
and	O
Datagram	B-Protocol
Transport	I-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
DTLS	B-Protocol
)	O
"	O
.	O
</s>
<s>
:	O
"	O
Prohibiting	O
RC4	B-Algorithm
Cipher	I-Algorithm
Suites	O
"	O
.	O
</s>
<s>
:	O
"	O
TLS	O
Fallback	O
Signaling	O
Cipher	B-Protocol
Suite	I-Protocol
Value	O
(	O
SCSV	O
)	O
for	O
Preventing	O
Protocol	B-Protocol
Downgrade	I-Protocol
Attacks	I-Protocol
"	O
.	O
</s>
<s>
:	O
"	O
Deprecating	O
Secure	B-Protocol
Sockets	I-Protocol
Layer	I-Protocol
Version	O
3.0	O
"	O
.	O
</s>
<s>
:	O
"	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Session	O
Hash	B-Algorithm
and	O
Extended	O
Master	O
Secret	O
Extension	O
"	O
.	O
</s>
<s>
:	O
"	O
A	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
ClientHello	O
Padding	O
Extension	O
"	O
.	O
</s>
<s>
:	O
"	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Extensions	O
"	O
describes	O
both	O
a	O
set	O
of	O
specific	O
extensions	O
and	O
a	O
generic	O
extension	O
mechanism	O
.	O
</s>
<s>
:	O
"	O
Elliptic	O
Curve	O
Cryptography	O
(	O
ECC	O
)	O
Cipher	B-Protocol
Suites	I-Protocol
for	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
"	O
.	O
</s>
<s>
:	O
"	O
TLS	O
Handshake	B-Protocol
Message	O
for	O
Supplemental	O
Data	O
"	O
.	O
</s>
<s>
:	O
"	O
Pre-Shared	B-Protocol
Key	I-Protocol
(	O
PSK	B-Protocol
)	O
Ciphersuites	B-Protocol
with	O
NULL	O
Encryption	O
for	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
"	O
.	O
</s>
<s>
:	O
"	O
Using	O
the	O
Secure	B-Protocol
Remote	I-Protocol
Password	I-Protocol
(	O
SRP	B-Protocol
)	O
Protocol	B-Protocol
for	O
TLS	O
Authentication	O
"	O
.	O
</s>
<s>
Defines	O
the	O
TLS-SRP	B-Protocol
ciphersuites	B-Protocol
.	O
</s>
<s>
:	O
"	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Session	O
Resumption	O
without	O
Server-Side	O
State	O
"	O
.	O
</s>
<s>
:	O
"	O
Using	O
OpenPGP	O
Keys	O
for	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Authentication	O
"	O
,	O
obsoleted	O
by	O
.	O
</s>
<s>
Specifies	O
an	O
extension	O
to	O
the	O
IMAP	O
,	O
POP3	O
and	O
ACAP	O
services	O
that	O
allow	O
the	O
server	B-Application
and	O
client	B-Protocol
to	O
use	O
transport-layer	B-Architecture
security	O
to	O
provide	O
private	O
,	O
authenticated	O
communication	O
over	O
the	O
Internet	O
.	O
</s>
<s>
:	O
"	O
Addition	O
of	O
Kerberos	B-Protocol
Cipher	B-Protocol
Suites	I-Protocol
to	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
"	O
.	O
</s>
<s>
The	O
40-bit	O
cipher	B-Protocol
suites	I-Protocol
defined	O
in	O
this	O
memo	O
appear	O
only	O
for	O
the	O
purpose	O
of	O
documenting	O
the	O
fact	O
that	O
those	O
cipher	B-Protocol
suite	I-Protocol
codes	O
have	O
already	O
been	O
assigned	O
.	O
</s>
<s>
:	O
"	O
Upgrading	O
to	O
TLS	O
Within	O
HTTP/1.1	B-Protocol
"	O
,	O
explains	O
how	O
to	O
use	O
the	O
Upgrade	B-Protocol
mechanism	I-Protocol
in	I-Protocol
HTTP/1.1	I-Protocol
to	O
initiate	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
over	O
an	O
existing	O
TCP	B-Protocol
connection	O
.	O
</s>
<s>
This	O
allows	O
unsecured	O
and	O
secured	O
HTTP	B-Protocol
traffic	O
to	O
share	O
the	O
same	O
well	O
known	O
port	O
(	O
in	O
this	O
case	O
,	O
http:	O
at	O
80	O
rather	O
than	O
https	B-Protocol
:	O
at	O
443	O
)	O
.	O
</s>
<s>
:	O
"	O
HTTP	B-Protocol
Over	O
TLS	O
"	O
,	O
distinguishes	O
secured	O
traffic	O
from	O
insecure	O
traffic	O
by	O
the	O
use	O
of	O
a	O
different	O
'	O
server	B-Application
port	O
 '	O
.	O
</s>
<s>
:	O
"	O
SMTP	B-Protocol
Service	O
Extension	O
for	O
Secure	B-Protocol
SMTP	I-Protocol
over	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
"	O
.	O
</s>
<s>
Specifies	O
an	O
extension	O
to	O
the	O
SMTP	B-Protocol
service	O
that	O
allows	O
an	O
SMTP	B-Protocol
server	I-Protocol
and	O
client	B-Protocol
to	O
use	O
transport-layer	B-Architecture
security	O
to	O
provide	O
private	O
,	O
authenticated	O
communication	O
over	O
the	O
Internet	O
.	O
</s>
<s>
:	O
"	O
AES	B-Algorithm
Ciphersuites	B-Protocol
for	O
TLS	O
"	O
.	O
</s>
<s>
Adds	O
Advanced	B-Algorithm
Encryption	I-Algorithm
Standard	I-Algorithm
(	O
AES	B-Algorithm
)	O
cipher	B-Protocol
suites	I-Protocol
to	O
the	O
previously	O
existing	O
symmetric	B-Algorithm
ciphers	I-Algorithm
.	O
</s>
<s>
:	O
"	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Extensions	O
"	O
,	O
adds	O
a	O
mechanism	O
for	O
negotiating	O
protocol	B-Protocol
extensions	O
during	O
session	O
initialisation	O
and	O
defines	O
some	O
extensions	O
.	O
</s>
<s>
:	O
"	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
Protocol	I-Protocol
Compression	B-General_Concept
Methods	O
"	O
,	O
specifies	O
the	O
framework	O
for	O
compression	B-General_Concept
methods	O
and	O
the	O
DEFLATE	B-Algorithm
compression	B-General_Concept
method	O
.	O
</s>
<s>
:	O
"	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
Protocol	B-Protocol
Compression	B-General_Concept
Using	O
Lempel-Ziv-Stac	O
(	O
LZS	O
)	O
"	O
.	O
</s>
<s>
:	O
"	O
Addition	O
of	O
Camellia	B-Algorithm
Cipher	B-Protocol
Suites	I-Protocol
to	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
"	O
.	O
</s>
<s>
:	O
"	O
Addition	O
of	O
SEED	B-Algorithm
Cipher	B-Protocol
Suites	I-Protocol
to	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
"	O
.	O
</s>
<s>
:	O
"	O
Securing	O
FTP	B-Protocol
with	I-Protocol
TLS	I-Protocol
"	O
.	O
</s>
<s>
:	O
"	O
Pre-Shared	B-Protocol
Key	I-Protocol
Ciphersuites	B-Protocol
for	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
"	O
,	O
adds	O
three	O
sets	O
of	O
new	O
cipher	B-Protocol
suites	I-Protocol
for	O
the	O
TLS	B-Protocol
protocol	I-Protocol
to	O
support	O
authentication	O
based	O
on	O
pre-shared	O
keys	O
.	O
</s>
