<s>
ISO/IEC	B-Algorithm
9797-1	I-Algorithm
Information	O
technology	O
–	O
Security	O
techniques	O
–	O
Message	B-Algorithm
Authentication	I-Algorithm
Codes	I-Algorithm
(	O
MACs	O
)	O
–	O
Part	O
1	O
:	O
Mechanisms	O
using	O
a	O
block	O
cipher	O
is	O
an	O
international	O
standard	O
that	O
defines	O
methods	O
for	O
calculating	O
a	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
(	O
MAC	O
)	O
over	O
data	O
.	O
</s>
<s>
The	O
model	O
is	O
based	O
on	O
a	O
block	O
cipher	O
with	O
a	O
secret	O
symmetric	B-Algorithm
key	I-Algorithm
.	O
</s>
<s>
Three	O
padding	B-Algorithm
methods	O
are	O
defined	O
.	O
</s>
<s>
It	O
is	O
not	O
necessary	O
to	O
transmit	O
or	O
store	O
the	O
padding	B-Algorithm
bits	O
,	O
because	O
the	O
recipient	O
can	O
regenerate	O
them	O
,	O
knowing	O
the	O
length	O
of	O
the	O
unpadded	O
data	O
and	O
the	O
padding	B-Algorithm
method	O
used	O
.	O
</s>
<s>
The	O
general	O
model	O
nominally	O
allows	O
for	O
any	O
combination	O
of	O
options	O
for	O
each	O
of	O
the	O
padding	B-Algorithm
,	O
initial	O
transformation	O
,	O
output	O
transformation	O
,	O
and	O
truncation	O
steps	O
.	O
</s>
<s>
(	O
When	O
the	O
block	O
cipher	O
is	O
DES	B-Algorithm
,	O
this	O
is	O
equivalent	O
to	O
the	O
algorithm	O
specified	O
in	O
FIPS	B-Algorithm
PUB	I-Algorithm
113	I-Algorithm
Computer	O
Data	O
Authentication	O
.	O
)	O
</s>
<s>
Algorithm	O
1	O
is	O
commonly	O
known	O
as	O
CBC-MAC	B-Algorithm
.	O
</s>
<s>
Algorithm	O
5	O
is	O
also	O
known	O
as	O
CMAC	B-Algorithm
.	O
</s>
<s>
This	O
is	O
equivalent	O
to	O
bitwise	O
exclusive-oring	O
each	O
byte	B-Application
of	O
the	O
key	O
with	O
F0	O
(	O
hex	O
)	O
.	O
</s>
<s>
To	O
completely	O
and	O
unambiguously	O
define	O
the	O
MAC	O
calculation	O
,	O
a	O
user	O
of	O
ISO/IEC	B-Algorithm
9797-1	I-Algorithm
must	O
select	O
and	O
specify	O
:	O
</s>
