<s>
One-key	B-Algorithm
MAC	I-Algorithm
(	O
OMAC	B-Algorithm
)	O
is	O
a	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
constructed	O
from	O
a	O
block	O
cipher	O
much	O
like	O
the	O
CBC-MAC	B-Algorithm
algorithm	O
.	O
</s>
<s>
Officially	O
there	O
are	O
two	O
OMAC	B-Algorithm
algorithms	O
(	O
OMAC1	O
and	O
OMAC2	O
)	O
which	O
are	O
both	O
essentially	O
the	O
same	O
except	O
for	O
a	O
small	O
tweak	O
.	O
</s>
<s>
OMAC1	O
is	O
equivalent	O
to	O
CMAC	B-Algorithm
,	O
which	O
became	O
an	O
NIST	O
recommendation	O
in	O
May	O
2005	O
.	O
</s>
<s>
In	O
cryptography	O
,	O
CMAC	B-Algorithm
is	O
a	O
block	O
cipher-based	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
algorithm	O
.	O
</s>
<s>
This	O
mode	B-Algorithm
of	I-Algorithm
operation	I-Algorithm
fixes	O
security	O
deficiencies	O
of	O
CBC-MAC	B-Algorithm
(	O
CBC-MAC	B-Algorithm
is	O
secure	O
only	O
for	O
fixed-length	O
messages	O
)	O
.	O
</s>
<s>
The	O
core	O
of	O
the	O
CMAC	B-Algorithm
algorithm	O
is	O
a	O
variation	O
of	O
CBC-MAC	B-Algorithm
that	O
Black	O
and	O
Rogaway	O
proposed	O
and	O
analyzed	O
under	O
the	O
name	O
XCBC	O
and	O
submitted	O
to	O
NIST	O
.	O
</s>
<s>
The	O
XCBC	O
algorithm	O
efficiently	O
addresses	O
the	O
security	O
deficiencies	O
of	O
CBC-MAC	B-Algorithm
,	O
but	O
requires	O
three	O
keys	O
.	O
</s>
<s>
Iwata	O
and	O
Kurosawa	O
proposed	O
an	O
improvement	O
of	O
XCBC	O
and	O
named	O
the	O
resulting	O
algorithm	O
One-Key	O
CBC-MAC	B-Algorithm
(	O
OMAC	B-Algorithm
)	O
in	O
their	O
papers	O
.	O
</s>
<s>
They	O
later	O
submitted	O
OMAC1	O
,	O
a	O
refinement	O
of	O
OMAC	B-Algorithm
,	O
and	O
additional	O
security	O
analysis	O
.	O
</s>
<s>
The	O
OMAC	B-Algorithm
algorithm	O
reduces	O
the	O
amount	O
of	O
key	O
material	O
required	O
for	O
XCBC	O
.	O
</s>
<s>
CMAC	B-Algorithm
is	O
equivalent	O
to	O
OMAC1	O
.	O
</s>
<s>
To	O
generate	O
an	O
ℓ-bit	O
CMAC	B-Algorithm
tag	O
(	O
t	O
)	O
of	O
a	O
message	O
(	O
m	O
)	O
using	O
a	O
b-bit	O
block	O
cipher	O
(	O
E	O
)	O
and	O
a	O
secret	O
key	O
(	O
k	O
)	O
,	O
one	O
first	O
generates	O
two	O
b-bit	O
sub-keys	O
(	O
k1	O
and	O
k2	O
)	O
using	O
the	O
following	O
algorithm	O
(	O
this	O
is	O
equivalent	O
to	O
multiplication	O
by	O
x	O
and	O
x2	O
in	O
a	O
finite	O
field	O
GF(2b )	O
)	O
.	O
</s>
<s>
The	O
CMAC	B-Algorithm
tag	O
generation	O
process	O
is	O
as	O
follows	O
:	O
</s>
