<s>
CCM	B-Algorithm
mode	I-Algorithm
(	O
counter	O
with	O
cipher	O
block	O
chaining	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
;	O
counter	O
with	O
CBC-MAC	B-Algorithm
)	O
is	O
a	O
mode	B-Algorithm
of	I-Algorithm
operation	I-Algorithm
for	O
cryptographic	O
block	O
ciphers	O
.	O
</s>
<s>
It	O
is	O
an	O
authenticated	B-Algorithm
encryption	I-Algorithm
algorithm	O
designed	O
to	O
provide	O
both	O
authentication	O
and	O
confidentiality	O
.	O
</s>
<s>
CCM	B-Algorithm
mode	I-Algorithm
is	O
only	O
defined	O
for	O
block	O
ciphers	O
with	O
a	O
block	O
length	O
of	O
128	O
bits	O
.	O
</s>
<s>
This	O
is	O
because	O
CCM	O
is	O
a	O
derivation	O
of	O
counter	O
(	O
CTR	O
)	O
mode	O
and	O
the	O
latter	O
is	O
effectively	O
a	O
stream	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
As	O
the	O
name	O
suggests	O
,	O
CCM	B-Algorithm
mode	I-Algorithm
combines	O
counter	O
(	O
CTR	O
)	O
mode	O
for	O
confidentiality	O
with	O
cipher	O
block	O
chaining	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
(	O
CBC-MAC	B-Algorithm
)	O
for	O
authentication	O
.	O
</s>
<s>
These	O
two	O
primitives	O
are	O
applied	O
in	O
an	O
"	O
authenticate-then-encrypt	O
"	O
manner	O
:	O
CBC-MAC	B-Algorithm
is	O
first	O
computed	O
on	O
the	O
message	O
to	O
obtain	O
a	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
(	O
MAC	O
)	O
,	O
then	O
the	O
message	O
and	O
the	O
MAC	O
are	O
encrypted	O
using	O
counter	O
mode	O
.	O
</s>
<s>
The	O
main	O
insight	O
is	O
that	O
the	O
same	O
encryption	O
key	O
can	O
be	O
used	O
for	O
both	O
,	O
provided	O
that	O
the	O
counter	O
values	O
used	O
in	O
the	O
encryption	O
do	O
not	O
collide	O
with	O
the	O
(	O
pre	O
-	O
)	O
initialization	B-Algorithm
vector	I-Algorithm
used	O
in	O
the	O
authentication	O
.	O
</s>
<s>
The	O
proof	O
also	O
applies	O
to	O
a	O
generalization	O
of	O
CCM	O
for	O
any	O
block	O
size	O
,	O
and	O
for	O
any	O
size	O
of	O
cryptographically	O
strong	O
pseudo-random	O
function	O
(	O
since	O
in	O
both	O
counter	O
mode	O
and	O
CBC-MAC	B-Algorithm
,	O
the	O
block	O
cipher	O
is	O
only	O
ever	O
used	O
in	O
one	O
direction	O
)	O
.	O
</s>
<s>
CCM	B-Algorithm
mode	I-Algorithm
was	O
designed	O
by	O
Russ	O
Housley	O
,	O
Doug	O
Whiting	O
and	O
Niels	O
Ferguson	O
.	O
</s>
<s>
At	O
the	O
time	O
CCM	B-Algorithm
mode	I-Algorithm
was	O
developed	O
,	O
Russ	O
Housley	O
was	O
employed	O
by	O
RSA	O
Laboratories	O
.	O
</s>
<s>
A	O
minor	O
variation	O
of	O
CCM	O
,	O
called	O
CCM*	O
,	O
is	O
used	O
in	O
the	O
Zigbee	B-Protocol
standard	O
.	O
</s>
<s>
According	O
to	O
Crypto++	B-Language
benchmarks	O
,	O
AES	O
CCM	O
requires	O
28.6	O
cycles	O
per	O
byte	O
on	O
an	O
Intel	B-Device
Core	I-Device
2	I-Device
processor	I-Device
in	O
32-bit	O
mode	O
.	O
</s>
<s>
CCM	O
is	O
not	O
an	O
"	O
on-line	O
"	O
authenticated	B-Algorithm
encryption	I-Algorithm
with	O
associated	O
data	O
(	O
AEAD	O
)	O
,	O
in	O
that	O
the	O
length	O
of	O
the	O
message	O
(	O
and	O
associated	O
data	O
)	O
must	O
be	O
known	O
in	O
advance	O
.	O
</s>
<s>
The	O
catalyst	O
for	O
the	O
development	O
of	O
CCM	B-Algorithm
mode	I-Algorithm
was	O
the	O
submission	O
of	O
offset	O
codebook	O
(	O
OCB	O
)	O
mode	O
for	O
inclusion	O
in	O
the	O
IEEE	B-Protocol
802.11i	I-Protocol
standard	O
.	O
</s>
<s>
Opposition	O
was	O
voiced	O
to	O
the	O
inclusion	O
of	O
OCB	B-Algorithm
mode	I-Algorithm
because	O
of	O
a	O
pending	O
patent	O
application	O
on	O
the	O
algorithm	O
.	O
</s>
<s>
While	O
the	O
inclusion	O
of	O
OCB	B-Algorithm
mode	I-Algorithm
was	O
disputed	O
based	O
on	O
these	O
intellectual	O
property	O
issues	O
,	O
it	O
was	O
agreed	O
that	O
the	O
simplification	O
provided	O
by	O
an	O
authenticated	B-Algorithm
encryption	I-Algorithm
system	O
was	O
desirable	O
.	O
</s>
<s>
developed	O
CCM	B-Algorithm
mode	I-Algorithm
as	O
a	O
potential	O
alternative	O
that	O
was	O
not	O
encumbered	O
by	O
patents	O
.	O
</s>
<s>
Even	O
though	O
CCM	B-Algorithm
mode	I-Algorithm
is	O
less	O
efficient	O
than	O
OCB	B-Algorithm
mode	I-Algorithm
,	O
a	O
patent	O
free	O
solution	O
was	O
preferable	O
to	O
one	O
complicated	O
by	O
patent	O
licensing	O
issues	O
.	O
</s>
<s>
Therefore	O
,	O
CCM	B-Algorithm
mode	I-Algorithm
went	O
on	O
to	O
become	O
a	O
mandatory	O
component	O
of	O
the	O
IEEE	B-Protocol
802.11i	I-Protocol
standard	O
,	O
and	O
OCB	B-Algorithm
mode	I-Algorithm
was	O
relegated	O
to	O
optional	O
component	O
status	O
,	O
before	O
eventually	O
being	O
removed	O
altogether	O
.	O
</s>
<s>
CCM	B-Algorithm
mode	I-Algorithm
is	O
used	O
in	O
IEEE	B-Protocol
802.11i	I-Protocol
(	O
as	O
CCMP	B-Protocol
,	O
the	O
CCM	O
encryption	O
protocol	O
for	O
WPA2	O
)	O
,	O
IPsec	B-Protocol
,	O
and	O
TLS	B-Protocol
1.2	O
,	O
as	O
well	O
as	O
Bluetooth	B-General_Concept
Low	I-General_Concept
Energy	I-General_Concept
(	O
as	O
of	O
Bluetooth	O
4.0	O
)	O
.	O
</s>
<s>
It	O
is	O
available	O
for	O
TLS	B-Protocol
1.3	O
,	O
but	O
not	O
enabled	O
by	O
default	O
in	O
OpenSSL	B-Language
.	O
</s>
