<s>
Offset	O
codebook	O
mode	O
(	O
OCB	B-Algorithm
mode	I-Algorithm
)	O
is	O
an	O
authenticated	B-Algorithm
encryption	I-Algorithm
mode	B-Algorithm
of	I-Algorithm
operation	I-Algorithm
for	O
cryptographic	O
block	O
ciphers	O
.	O
</s>
<s>
OCB	B-Algorithm
mode	I-Algorithm
was	O
designed	O
by	O
Phillip	O
Rogaway	O
,	O
who	O
credits	O
Mihir	O
Bellare	O
,	O
John	O
Black	O
,	O
and	O
Ted	O
Krovetz	O
with	O
assistance	O
and	O
comments	O
on	O
the	O
designs	O
.	O
</s>
<s>
It	O
is	O
based	O
on	O
the	O
integrity-aware	B-Algorithm
parallelizeable	I-Algorithm
mode	I-Algorithm
(	O
IAPM	B-Algorithm
)	O
of	O
authenticated	B-Algorithm
encryption	I-Algorithm
by	O
Charanjit	O
S	O
.	O
Jutla	O
.	O
</s>
<s>
OCB	B-Algorithm
mode	I-Algorithm
was	O
designed	O
to	O
provide	O
both	O
message	B-Error_Name
authentication	I-Error_Name
and	O
privacy	O
.	O
</s>
<s>
It	O
is	O
essentially	O
a	O
scheme	O
for	O
integrating	O
a	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
(	O
MAC	O
)	O
into	O
the	O
operation	O
of	O
a	O
block	O
cipher	O
.	O
</s>
<s>
In	O
this	O
way	O
,	O
OCB	B-Algorithm
mode	I-Algorithm
avoids	O
the	O
need	O
to	O
use	O
two	O
systems	O
:	O
a	O
MAC	O
for	O
authentication	O
and	O
encryption	O
for	O
confidentiality	O
.	O
</s>
<s>
OCB2	O
improves	O
on	O
OCB1	O
by	O
allowing	O
associated	O
data	O
to	O
be	O
included	O
with	O
the	O
message	O
,	O
providing	O
authenticated	B-Algorithm
encryption	I-Algorithm
with	O
associated	O
data	O
(	O
AEAD	O
;	O
that	O
is	O
,	O
data	O
that	O
are	O
not	O
encrypted	O
but	O
should	O
be	O
authenticated	O
)	O
and	O
a	O
new	O
method	O
for	O
generating	O
a	O
sequence	O
of	O
offsets	O
.	O
</s>
<s>
OCB2	O
was	O
first	O
published	O
in	O
2003	O
,	O
originally	O
named	O
authenticated-encryption	O
mode	O
,	O
or	O
advanced	O
encryption	B-Algorithm
mode	I-Algorithm
(	O
AEM	O
)	O
and	O
was	O
shown	O
to	O
be	O
completely	O
insecure	O
in	O
2019	O
.	O
</s>
<s>
OCB	B-Algorithm
mode	I-Algorithm
is	O
listed	O
as	O
an	O
optional	O
method	O
in	O
the	O
IEEE802.11	O
wireless	O
security	O
standard	O
as	O
an	O
alternative	O
to	O
counter	B-Algorithm
with	I-Algorithm
CBC-MAC	I-Algorithm
mode	O
(	O
CCM	O
)	O
.	O
</s>
<s>
For	O
comparison	O
,	O
CCM	B-Algorithm
mode	I-Algorithm
offering	O
similar	O
functionality	O
requires	O
twice	O
as	O
many	O
block	O
cipher	O
operations	O
per	O
message	O
block	O
(	O
associated	O
data	O
requires	O
one	O
,	O
as	O
in	O
OCB	O
)	O
.	O
</s>
<s>
Two	O
U.S.	O
patents	O
have	O
been	O
issued	O
for	O
OCB	B-Algorithm
mode	I-Algorithm
.	O
</s>
<s>
However	O
,	O
a	O
special	O
exemption	O
is	O
granted	O
allowing	O
OCB	B-Algorithm
mode	I-Algorithm
to	O
be	O
used	O
in	O
software	O
licensed	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
without	O
cost	O
,	O
as	O
well	O
as	O
for	O
any	O
non-commercial	O
,	O
non-governmental	O
application	O
.	O
</s>
