<s>
created	O
in	O
1998	O
by	O
a	O
group	O
of	O
researchers	O
from	O
École	O
Normale	O
Supérieure	O
,	O
CNRS	B-Application
,	O
and	O
France	O
Télécom	O
(	O
including	O
Jacques	O
Stern	O
and	O
Serge	O
Vaudenay	O
)	O
and	O
submitted	O
to	O
the	O
AES	O
competition	O
.	O
</s>
<s>
Like	O
other	O
AES	O
candidates	O
,	O
DFC	B-Algorithm
operates	O
on	O
blocks	O
of	O
128	O
bits	O
,	O
using	O
a	O
key	O
of	O
128	O
,	O
192	O
,	O
or	O
256	O
bits	O
.	O
</s>
<s>
It	O
uses	O
an	O
8-round	O
Feistel	B-Algorithm
network	I-Algorithm
.	O
</s>
<s>
The	O
round	O
function	O
uses	O
a	O
single	O
6×	O
32-bit	O
S-box	B-Algorithm
,	O
as	O
well	O
as	O
an	O
affine	B-Algorithm
transformation	I-Algorithm
mod	O
264+13	O
.	O
</s>
<s>
DFC	B-Algorithm
can	O
actually	O
use	O
a	O
key	O
of	O
any	O
size	O
up	O
to	O
256	O
bits	O
;	O
the	O
key	B-Algorithm
schedule	I-Algorithm
uses	O
another	O
4-round	O
Feistel	B-Algorithm
network	I-Algorithm
to	O
generate	O
a	O
1024-bit	O
"	O
expanded	O
key	O
"	O
.	O
</s>
<s>
The	O
arbitrary	O
constants	O
,	O
including	O
all	O
entries	O
of	O
the	O
S-box	B-Algorithm
,	O
are	O
derived	O
using	O
the	O
binary	O
expansion	O
of	O
e	O
as	O
a	O
source	O
of	O
"	O
nothing	O
up	O
my	O
sleeve	O
numbers	O
"	O
.	O
</s>
<s>
Soon	O
after	O
DFC	B-Algorithm
's	O
publication	O
,	O
Ian	O
Harvey	O
raised	O
the	O
concern	O
that	O
reduction	O
modulo	O
a	O
65-bit	O
number	O
was	O
beyond	O
the	O
native	O
capabilities	O
of	O
most	O
platforms	O
,	O
and	O
that	O
careful	O
implementation	O
would	O
be	O
required	O
to	O
protect	O
against	O
side-channel	O
attacks	O
,	O
especially	O
timing	O
attacks	O
.	O
</s>
<s>
Although	O
DFC	B-Algorithm
was	O
designed	O
using	O
Vaudenay	O
's	O
decorrelation	B-General_Concept
theory	I-General_Concept
to	O
be	O
provably	O
secure	O
against	O
ordinary	O
differential	O
and	O
linear	O
cryptanalysis	O
,	O
in	O
1999	O
Lars	O
Knudsen	O
and	O
Vincent	O
Rijmen	O
presented	O
a	O
differential	O
chosen-ciphertext	O
attack	O
that	O
breaks	O
6	O
rounds	O
faster	O
than	O
exhaustive	O
search	O
.	O
</s>
<s>
This	O
variant	O
allows	O
for	O
more	O
choice	O
in	O
the	O
cipher	O
's	O
parameters	O
,	O
and	O
uses	O
a	O
modified	O
key	B-Algorithm
schedule	I-Algorithm
to	O
eliminate	O
certain	O
weak	O
keys	O
discovered	O
by	O
Don	O
Coppersmith	O
.	O
</s>
