<s>
In	O
cryptography	O
,	O
MacGuffin	B-Algorithm
is	O
a	O
block	O
cipher	O
created	O
in	O
1994	O
by	O
Bruce	O
Schneier	O
and	O
Matt	O
Blaze	O
at	O
a	O
Fast	O
Software	O
Encryption	O
workshop	O
.	O
</s>
<s>
It	O
was	O
intended	O
as	O
a	O
catalyst	O
for	O
analysis	O
of	O
a	O
new	O
cipher	O
structure	O
,	O
known	O
as	O
Generalized	O
Unbalanced	B-Algorithm
Feistel	I-Algorithm
Networks	I-Algorithm
(	O
GUFNs	O
)	O
.	O
</s>
<s>
Schneier	O
and	O
Blaze	O
based	O
MacGuffin	B-Algorithm
on	O
DES	B-Algorithm
,	O
their	O
main	O
change	O
being	O
that	O
the	O
data	O
block	O
is	O
not	O
split	O
into	O
equal	O
halves	O
in	O
the	O
Feistel	B-Algorithm
network	I-Algorithm
.	O
</s>
<s>
The	O
algorithm	O
was	O
experimental	O
,	O
intended	O
to	O
explore	O
the	O
security	O
properties	O
of	O
unbalanced	B-Algorithm
Feistel	I-Algorithm
networks	I-Algorithm
.	O
</s>
<s>
The	O
adjacent	O
diagram	O
shows	O
one	O
round	O
of	O
MacGuffin	B-Algorithm
.	O
</s>
<s>
They	O
are	O
then	O
fed	O
through	O
eight	O
S-boxes	B-Algorithm
,	O
each	O
of	O
which	O
takes	O
six	O
bits	O
of	O
input	O
and	O
produces	O
two	O
bits	O
of	O
output	O
.	O
</s>
<s>
MacGuffin	B-Algorithm
's	O
key	B-Algorithm
schedule	I-Algorithm
is	O
a	O
modified	O
version	O
of	O
the	O
encryption	O
algorithm	O
itself	O
.	O
</s>
<s>
Since	O
MacGuffin	B-Algorithm
is	O
a	O
Feistel	B-Algorithm
network	I-Algorithm
,	O
decryption	O
is	O
easy	O
;	O
simply	O
run	O
the	O
encryption	O
algorithm	O
in	O
reverse	O
.	O
</s>
<s>
Schneier	O
and	O
Blaze	O
recommended	O
using	O
32	O
rounds	O
,	O
and	O
specified	O
MacGuffin	B-Algorithm
with	O
a	O
128-bit	O
key	O
.	O
</s>
<s>
At	O
the	O
same	O
workshop	O
where	O
MacGuffin	B-Algorithm
was	O
introduced	O
,	O
Rijmen	O
and	O
Preneel	O
showed	O
that	O
it	O
was	O
vulnerable	O
to	O
differential	O
cryptanalysis	O
.	O
</s>
<s>
They	O
showed	O
that	O
32	O
rounds	O
of	O
MacGuffin	B-Algorithm
is	O
weaker	O
than	O
16	O
rounds	O
of	O
DES	B-Algorithm
,	O
since	O
it	O
took	O
"	O
a	O
few	O
hours	O
"	O
to	O
get	O
good	O
differential	O
characteristics	O
for	O
DES	B-Algorithm
with	O
good	O
starting	O
values	O
,	O
and	O
the	O
same	O
time	O
to	O
get	O
good	O
differential	O
characteristics	O
for	O
MacGuffin	B-Algorithm
with	O
no	O
starting	O
values	O
.	O
</s>
<s>
They	O
found	O
that	O
it	O
is	O
possible	O
to	O
get	O
the	O
last	O
round	B-Algorithm
key	I-Algorithm
with	O
differential	O
cryptanalysis	O
,	O
and	O
from	O
that	O
reverse	O
the	O
last	O
round	O
and	O
repeat	O
the	O
attack	O
for	O
the	O
rest	O
of	O
the	O
rounds	O
.	O
</s>
<s>
Rijmen	O
and	O
Preneel	O
tried	O
attacking	O
MacGuffin	B-Algorithm
with	O
different	O
S-boxes	B-Algorithm
,	O
taken	O
directly	O
from	O
DES	B-Algorithm
.	O
</s>
