<s>
In	O
cryptography	O
key	B-Algorithm
feedback	I-Algorithm
mode	I-Algorithm
(	O
KFB	O
)	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>
KFB	B-Algorithm
mode	I-Algorithm
outputs	O
m	O
bits	O
(	O
typically	O
m	O
=	O
8	O
)	O
at	O
a	O
time	O
and	O
uses	O
a	O
constant	O
bitstring	O
p	O
as	O
block	O
cipher	O
input	O
,	O
a	O
key	O
k	O
of	O
n	O
bit	O
length	O
,	O
and	O
a	O
n	O
×	O
m	O
matrix	O
with	O
non-zero	O
rows	O
as	O
IV	O
.	O
</s>
<s>
The	O
speed	O
of	O
KFB	O
is	O
a	O
bit	O
lower	O
than	O
for	O
other	O
modes	B-Algorithm
of	I-Algorithm
operation	I-Algorithm
like	O
OFB	O
,	O
mainly	O
because	O
the	O
key	O
schedule	O
has	O
to	O
be	O
done	O
for	O
each	O
key	O
.	O
</s>
<s>
This	O
property	O
allows	O
many	O
error	B-Error_Name
correcting	I-Error_Name
codes	I-Error_Name
to	O
function	O
normally	O
even	O
when	O
applied	O
before	O
encryption	O
.	O
</s>
<s>
The	O
concept	O
of	O
KFB	O
has	O
already	O
been	O
mentioned	O
1982	O
by	O
Hellman	O
and	O
Reyneri	O
,	O
but	O
only	O
as	O
a	O
theoretical	O
construct	O
to	O
analyse	O
the	O
cycle	O
length	O
of	O
random	O
functions	O
with	O
the	O
purpose	O
of	O
comparing	O
DES	B-Algorithm
to	O
a	O
truly	O
random	O
function	O
.	O
</s>
