<s>
In	O
cryptography	O
,	O
COCONUT98	B-Algorithm
(	O
Cipher	O
Organized	O
with	O
Cute	O
Operations	O
and	O
N-Universal	O
Transformation	O
)	O
is	O
a	O
block	O
cipher	O
designed	O
by	O
Serge	O
Vaudenay	O
in	O
1998	O
.	O
</s>
<s>
It	O
was	O
one	O
of	O
the	O
first	O
concrete	O
applications	O
of	O
Vaudenay	O
's	O
decorrelation	B-General_Concept
theory	I-General_Concept
,	O
designed	O
to	O
be	O
provably	O
secure	O
against	O
differential	O
cryptanalysis	O
,	O
linear	O
cryptanalysis	O
,	O
and	O
even	O
certain	O
types	O
of	O
undiscovered	O
cryptanalytic	O
attacks	O
.	O
</s>
<s>
Its	O
basic	O
structure	O
is	O
an	O
8-round	O
Feistel	B-Algorithm
network	I-Algorithm
,	O
but	O
with	O
an	O
additional	O
operation	O
after	O
the	O
first	O
4	O
rounds	O
,	O
called	O
a	O
decorrelation	O
module	O
.	O
</s>
<s>
This	O
consists	O
of	O
a	O
key-dependent	O
affine	B-Algorithm
transformation	I-Algorithm
in	O
the	O
finite	O
field	O
GF(264 )	O
.	O
</s>
<s>
The	O
round	O
function	O
makes	O
use	O
of	O
modular	O
multiplication	O
and	O
addition	O
,	O
bit	O
rotation	O
,	O
XORs	B-Application
,	O
and	O
a	O
single	O
8×	O
24-bit	O
S-box	B-Algorithm
.	O
</s>
<s>
The	O
entries	O
of	O
the	O
S-box	B-Algorithm
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>
Despite	O
Vaudenay	O
's	O
proof	O
of	O
COCONUT98	B-Algorithm
's	O
security	O
,	O
in	O
1999	O
David	O
Wagner	O
developed	O
the	O
boomerang	O
attack	O
against	O
it	O
.	O
</s>
<s>
The	O
same	O
team	O
has	O
also	O
developed	O
what	O
they	O
call	O
a	O
related-key	O
boomerang	O
attack	O
,	O
which	O
distinguishes	O
COCONUT98	B-Algorithm
from	O
random	O
using	O
one	O
related-key	O
adaptive	O
chosen	O
plaintext	O
and	O
ciphertext	O
quartet	O
under	O
two	O
keys	O
.	O
</s>
