<s>
A	O
cipher	B-Protocol
suite	I-Protocol
is	O
a	O
set	O
of	O
algorithms	O
that	O
help	O
secure	O
a	O
network	O
connection	O
.	O
</s>
<s>
Suites	O
typically	O
use	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
or	O
its	O
now-deprecated	O
predecessor	O
Secure	B-Protocol
Socket	I-Protocol
Layer	I-Protocol
(	O
SSL	O
)	O
.	O
</s>
<s>
The	O
set	O
of	O
algorithms	O
that	O
cipher	B-Protocol
suites	I-Protocol
usually	O
contain	O
include	O
:	O
a	O
key	O
exchange	O
algorithm	O
,	O
a	O
bulk	B-General_Concept
encryption	I-General_Concept
algorithm	I-General_Concept
,	O
and	O
a	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
(	O
MAC	O
)	O
algorithm	O
.	O
</s>
<s>
The	O
bulk	B-General_Concept
encryption	I-General_Concept
algorithm	I-General_Concept
is	O
used	O
to	O
encrypt	O
the	O
data	O
being	O
sent	O
.	O
</s>
<s>
In	O
addition	O
,	O
cipher	B-Protocol
suites	I-Protocol
can	O
include	O
signatures	O
and	O
an	O
authentication	O
algorithm	O
to	O
help	O
authenticate	O
the	O
server	O
and	O
or	O
client	O
.	O
</s>
<s>
Overall	O
,	O
there	O
are	O
hundreds	O
of	O
different	O
cipher	B-Protocol
suites	I-Protocol
that	O
contain	O
different	O
combinations	O
of	O
these	O
algorithms	O
.	O
</s>
<s>
Some	O
cipher	B-Protocol
suites	I-Protocol
offer	O
better	O
security	O
than	O
others	O
.	O
</s>
<s>
The	O
structure	O
and	O
use	O
of	O
the	O
cipher	B-Protocol
suite	I-Protocol
concept	O
are	O
defined	O
in	O
the	O
TLS	O
standard	O
document	O
.	O
</s>
<s>
The	O
next	O
version	O
of	O
TLS	O
(	O
TLS	O
1.3	O
)	O
includes	O
additional	O
requirements	O
to	O
cipher	B-Protocol
suites	I-Protocol
.	O
</s>
<s>
Cipher	B-Protocol
suites	I-Protocol
defined	O
for	O
TLS	O
1.2	O
cannot	O
be	O
used	O
in	O
TLS	O
1.3	O
,	O
and	O
vice	O
versa	O
,	O
unless	O
otherwise	O
stated	O
in	O
their	O
definition	O
.	O
</s>
<s>
A	O
reference	O
list	O
of	O
named	O
cipher	B-Protocol
suites	I-Protocol
is	O
provided	O
in	O
the	O
TLS	O
Cipher	B-Protocol
Suite	I-Protocol
Registry	O
.	O
</s>
<s>
The	O
use	O
of	O
ciphers	B-Application
has	O
been	O
a	O
part	O
of	O
the	O
Secure	B-Protocol
Socket	I-Protocol
Layer	I-Protocol
(	O
SSL	O
)	O
transit	O
protocol	O
since	O
its	O
creation	O
.	O
</s>
<s>
However	O
,	O
the	O
name	O
Cipher	B-Protocol
Suite	I-Protocol
was	O
not	O
used	O
in	O
the	O
original	O
draft	O
of	O
SSL	O
.	O
</s>
<s>
Instead	O
the	O
ability	O
for	O
a	O
client	O
and	O
a	O
server	O
to	O
choose	O
from	O
a	O
small	O
set	O
of	O
ciphers	B-Application
to	O
secure	O
their	O
connection	O
was	O
called	O
Cipher-Choice	O
.	O
</s>
<s>
It	O
was	O
not	O
until	O
SSL	O
v3	O
(	O
the	O
last	O
version	O
of	O
SSL	O
)	O
that	O
the	O
name	O
Cipher	B-Protocol
Suite	I-Protocol
was	O
used	O
.	O
</s>
<s>
Every	O
version	O
of	O
TLS	O
since	O
has	O
used	O
Cipher	B-Protocol
Suite	I-Protocol
in	O
its	O
standardization	O
.	O
</s>
<s>
The	O
concept	O
and	O
purpose	O
of	O
a	O
Cipher	B-Protocol
Suite	I-Protocol
has	O
not	O
changed	O
since	O
the	O
term	O
was	O
first	O
coined	O
.	O
</s>
<s>
What	O
has	O
changed	O
is	O
the	O
versions	O
of	O
the	O
algorithms	O
that	O
are	O
supported	O
in	O
the	O
cipher	B-Protocol
suites	I-Protocol
.	O
</s>
<s>
TLS	O
1.3	O
marks	O
a	O
change	O
in	O
how	O
cipher	B-Protocol
suites	I-Protocol
are	O
coordinated	O
between	O
machines	O
.	O
</s>
<s>
The	O
cipher	B-Protocol
suite	I-Protocol
chosen	O
for	O
two	O
communicating	O
machines	O
to	O
use	O
is	O
determined	O
by	O
the	O
handshake	O
process	O
.	O
</s>
<s>
Each	O
cipher	B-Protocol
suite	I-Protocol
has	O
a	O
unique	O
name	O
that	O
is	O
used	O
to	O
identify	O
it	O
and	O
to	O
describe	O
the	O
algorithmic	O
contents	O
of	O
it	O
.	O
</s>
<s>
Each	O
segment	O
in	O
a	O
cipher	B-Protocol
suite	I-Protocol
name	O
stands	O
for	O
a	O
different	O
algorithm	O
or	O
protocol	O
.	O
</s>
<s>
TLS	O
defines	O
the	O
protocol	O
that	O
this	O
cipher	B-Protocol
suite	I-Protocol
is	O
for	O
;	O
it	O
will	O
usually	O
be	O
TLS	O
.	O
</s>
<s>
ECDHE	B-Protocol
indicates	O
the	O
key	O
exchange	O
algorithm	O
being	O
used	O
.	O
</s>
<s>
RSA	B-Architecture
authentication	O
mechanism	O
during	O
the	O
handshake	O
.	O
</s>
<s>
AES	B-Algorithm
session	O
cipher	B-Application
.	O
</s>
<s>
128	O
session	O
encryption	O
key	O
size	O
(	O
bits	O
)	O
for	O
cipher	B-Application
.	O
</s>
<s>
GCM	O
type	O
of	O
encryption	O
(	O
cipher-block	O
dependency	O
and	O
additional	O
options	O
)	O
.	O
</s>
<s>
Indicates	O
the	O
message	B-Algorithm
authentication	I-Algorithm
algorithm	I-Algorithm
which	O
is	O
used	O
to	O
authenticate	O
a	O
message	O
.	O
</s>
<s>
To	O
use	O
cipher	B-Protocol
suites	I-Protocol
,	O
the	O
client	O
and	O
the	O
server	O
must	O
agree	O
on	O
the	O
specific	O
cipher	B-Protocol
suite	I-Protocol
that	O
is	O
going	O
to	O
be	O
used	O
in	O
exchanging	O
messages	O
.	O
</s>
<s>
Both	O
the	O
client	O
and	O
the	O
server	O
must	O
support	O
the	O
agreed	O
upon	O
cipher	B-Protocol
suite	I-Protocol
.	O
</s>
<s>
If	O
the	O
client	O
and	O
server	O
do	O
not	O
agree	O
on	O
a	O
cipher	B-Protocol
suite	I-Protocol
,	O
no	O
connection	O
will	O
be	O
made	O
.	O
</s>
<s>
TLS	O
1.3	O
includes	O
a	O
TLS	O
Handshake	O
Protocol	O
that	O
differs	O
compared	O
to	O
past	O
and	O
the	O
current	O
version	O
of	O
TLS/SSL	B-Protocol
.	O
</s>
<s>
After	O
coordinating	O
which	O
cipher	B-Protocol
suite	I-Protocol
to	O
use	O
,	O
the	O
server	O
and	O
the	O
client	O
still	O
have	O
the	O
ability	O
to	O
change	O
the	O
coordinated	O
ciphers	B-Application
by	O
using	O
the	O
ChangeCipherSpec	O
protocol	O
in	O
the	O
current	O
handshake	O
or	O
in	O
a	O
new	O
handshake	O
.	O
</s>
<s>
To	O
test	O
which	O
TLS	O
ciphers	B-Application
a	O
server	O
supports	O
,	O
an	O
SSL/TLS	B-Protocol
Scanner	O
may	O
be	O
used	O
.	O
</s>
<s>
This	O
client	O
starts	O
the	O
process	O
by	O
sending	O
a	O
clientHello	O
message	O
to	O
the	O
server	O
that	O
includes	O
the	O
version	O
of	O
TLS	O
being	O
used	O
and	O
a	O
list	O
of	O
cipher	B-Protocol
suites	I-Protocol
in	O
the	O
order	O
of	O
the	O
client	O
's	O
preference	O
.	O
</s>
<s>
In	O
response	O
,	O
the	O
server	O
sends	O
a	O
serverHello	O
message	O
that	O
includes	O
the	O
chosen	O
cipher	B-Protocol
suite	I-Protocol
and	O
the	O
session	O
ID	O
.	O
</s>
<s>
Now	O
the	O
client	O
and	O
the	O
server	O
are	O
in	O
agreement	O
on	O
which	O
cipher	B-Protocol
suite	I-Protocol
to	O
use	O
to	O
communicate	O
with	O
each	O
other	O
.	O
</s>
<s>
If	O
two	O
machines	O
are	O
corresponding	O
over	O
TLS	O
1.3	O
,	O
they	O
coordinate	O
which	O
cipher	B-Protocol
suite	I-Protocol
to	O
use	O
by	O
using	O
the	O
TLS	O
1.3	O
Handshake	O
Protocol	O
.	O
</s>
<s>
The	O
handshake	O
in	O
TLS	O
1.3	O
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	O
sends	O
a	O
clientHello	O
message	O
to	O
the	O
server	O
that	O
contains	O
a	O
list	O
of	O
supported	O
ciphers	B-Application
in	O
order	O
of	O
the	O
client	O
's	O
preference	O
and	O
makes	O
a	O
guess	O
on	O
what	O
key	O
algorithm	O
is	O
being	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>
After	O
receiving	O
the	O
clientHello	O
,	O
the	O
server	O
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	O
receives	O
the	O
server	O
's	O
finished	O
message	O
it	O
now	O
is	O
coordinated	O
with	O
the	O
server	O
on	O
which	O
cipher	B-Protocol
suite	I-Protocol
to	O
use	O
.	O
</s>
<s>
In	O
addition	O
,	O
all	O
encryption	O
and	O
authentication	O
algorithms	O
are	O
combined	O
in	O
the	O
authenticated	B-Algorithm
encryption	I-Algorithm
with	I-Algorithm
associated	I-Algorithm
data	I-Algorithm
(	O
AEAD	O
)	O
encryption	O
algorithm	O
.	O
</s>
<s>
Also	O
a	O
hash	O
algorithm	O
must	O
now	O
be	O
used	O
in	O
HMAC-based	O
key	O
derivation	O
(	O
HKDF	B-Algorithm
)	O
.	O
</s>
<s>
All	O
non-AEAD	O
ciphers	B-Application
have	O
been	O
removed	O
due	O
to	O
possible	O
weaknesses	O
or	O
vulnerabilities	O
and	O
ciphers	B-Application
must	O
use	O
an	O
ephemeral	O
key	O
exchange	O
algorithm	O
so	O
that	O
new	O
key	B-Application
pairs	I-Application
are	O
generated	O
for	O
every	O
exchange	O
.	O
</s>
<s>
Datagram	B-Protocol
Transport	I-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
DTLS	B-Protocol
)	O
is	O
based	O
on	O
TLS	O
,	O
but	O
is	O
specifically	O
used	O
for	O
UDP	B-Language
connections	O
instead	O
of	O
TCP	B-Protocol
connections	O
.	O
</s>
<s>
Since	O
DTLS	B-Protocol
is	O
based	O
on	O
TLS	O
it	O
is	O
able	O
to	O
use	O
a	O
majority	O
of	O
the	O
cipher	B-Protocol
suites	I-Protocol
described	O
for	O
TLS	O
.	O
</s>
<s>
There	O
are	O
special	O
cases	O
that	O
must	O
be	O
considered	O
when	O
using	O
TLS	O
cipher	B-Protocol
suites	I-Protocol
with	O
DTLS	B-Protocol
.	O
</s>
<s>
DTLS	B-Protocol
does	O
not	O
support	O
the	O
stream	O
cipher	B-Application
RC4	B-Algorithm
which	O
means	O
that	O
no	O
TLS	O
cipher	B-Application
using	O
RC4	B-Algorithm
can	O
be	O
used	O
with	O
DTLS	B-Protocol
.	O
</s>
<s>
To	O
determine	O
if	O
a	O
TLS	O
cipher	B-Protocol
suite	I-Protocol
is	O
compatible	O
with	O
DTLS	B-Protocol
looking	O
at	O
its	O
name	O
will	O
not	O
help	O
.	O
</s>
<s>
Each	O
TLS	O
cipher	B-Protocol
suite	I-Protocol
will	O
still	O
include	O
the	O
TLS	O
identifier	O
space	O
in	O
its	O
name	O
.	O
</s>
<s>
Instead	O
,	O
all	O
TLS	O
parameter	O
registries	O
now	O
include	O
the	O
flag	O
DTLS-OK	O
to	O
signal	O
if	O
a	O
cipher	B-Protocol
suite	I-Protocol
supports	O
DTLS	B-Protocol
.	O
</s>
<s>
A	O
cipher	B-Protocol
suite	I-Protocol
is	O
as	O
secure	O
as	O
the	O
algorithms	O
that	O
it	O
contains	O
.	O
</s>
<s>
If	O
the	O
version	O
of	O
encryption	O
or	O
authentication	O
algorithm	O
in	O
a	O
cipher	B-Protocol
suite	I-Protocol
have	O
known	O
vulnerabilities	O
the	O
cipher	B-Protocol
suite	I-Protocol
and	O
TLS	O
connection	O
may	O
then	O
vulnerable	O
.	O
</s>
<s>
Therefore	O
,	O
a	O
common	O
attack	O
against	O
TLS	O
and	O
cipher	B-Protocol
suites	I-Protocol
is	O
known	O
as	O
a	O
downgrade	B-Protocol
attack	I-Protocol
.	O
</s>
<s>
However	O
,	O
it	O
is	O
possible	O
for	O
an	O
adversary	O
to	O
take	O
advantage	O
of	O
this	O
feature	O
and	O
make	O
it	O
so	O
that	O
a	O
client	O
will	O
automatically	O
downgrade	O
to	O
a	O
version	O
of	O
TLS	O
or	O
SSL	O
that	O
supports	O
cipher	B-Protocol
suites	I-Protocol
with	O
algorithms	O
that	O
are	O
known	O
for	O
weak	O
security	O
and	O
vulnerabilities	O
.	O
</s>
<s>
This	O
has	O
resulted	O
in	O
attacks	O
such	O
as	O
POODLE	B-Protocol
.	O
</s>
<s>
If	O
SSL	O
3.0	O
support	O
is	O
needed	O
for	O
legacy	O
hardware	O
,	O
there	O
is	O
an	O
approved	O
TLS_FALLBACK_SCSV	O
cipher	B-Protocol
suite	I-Protocol
which	O
verifies	O
that	O
downgrades	O
are	O
not	O
triggered	O
for	O
malicious	O
intentions	O
.	O
</s>
<s>
To	O
provide	O
security	O
to	O
constrained	O
devices	O
with	O
limited	O
processing	O
power	O
,	O
memory	O
,	O
and	O
battery	O
life	O
such	O
as	O
those	O
powering	O
the	B-Operating_System
Internet	I-Operating_System
of	I-Operating_System
things	I-Operating_System
there	O
are	O
specifically	O
chosen	O
cipher	B-Protocol
suites	I-Protocol
.	O
</s>
<s>
Each	O
of	O
these	O
cipher	B-Protocol
suites	I-Protocol
has	O
been	O
implemented	O
to	O
run	O
on	O
devices	O
with	O
constraints	O
in	O
processing	O
power	O
and	O
memory	O
.	O
</s>
<s>
Implementations	O
of	O
the	O
pre-shared	O
key	O
cipher	B-Protocol
suite	I-Protocol
used	O
only	O
1889	O
bytes	O
of	O
RAM	O
and	O
38266	O
of	O
flash	O
ROM	O
which	O
is	O
very	O
resource-conscious	O
compared	O
to	O
most	O
encryption	O
and	O
security	O
algorithms	O
.	O
</s>
<s>
This	O
low	O
memory	O
usage	O
is	O
due	O
to	O
these	O
cipher	B-Protocol
suites	I-Protocol
using	O
proven	O
efficient	O
algorithms	O
that	O
are	O
secure	O
,	O
but	O
maybe	O
not	O
as	O
secure	O
as	O
more	O
resource-required	O
algorithms	O
;	O
exp	O
:	O
Using	O
128	O
bit	O
encryption	O
vs	O
256	O
bit	O
encryption	O
.	O
</s>
<s>
In	O
addition	O
they	O
use	O
pre-shared	O
key	O
or	O
raw	O
public	B-Application
key	I-Application
which	O
requires	O
less	O
memory	O
space	O
and	O
processing	O
power	O
compared	O
to	O
using	O
traditional	O
public	B-Application
key	I-Application
infrastructure	O
(	O
PKIX	O
)	O
.	O
</s>
<s>
In	O
programming	O
,	O
a	O
cipher	B-Protocol
suite	I-Protocol
is	O
referred	O
to	O
in	O
both	O
plural	O
and	O
non-plural	O
forms	O
.	O
</s>
<s>
CipherSuite	B-Protocol
cipher_suites	O
a	O
list	O
of	O
the	O
cryptographic	O
options	O
supported	O
by	O
the	O
client	O
.	O
</s>
<s>
CipherSuite	B-Protocol
cipher_suite	O
the	O
cipher	B-Protocol
suite	I-Protocol
selected	O
by	O
the	O
server	O
from	O
the	O
client	O
's	O
cipher_suites	O
.	O
</s>
