<s>
In	O
cryptography	O
,	O
Lucifer	B-Algorithm
was	O
the	O
name	O
given	O
to	O
several	O
of	O
the	O
earliest	O
civilian	O
block	O
ciphers	O
,	O
developed	O
by	O
Horst	O
Feistel	O
and	O
his	O
colleagues	O
at	O
IBM	O
.	O
</s>
<s>
Lucifer	B-Algorithm
was	O
a	O
direct	O
precursor	O
to	O
the	O
Data	B-Algorithm
Encryption	I-Algorithm
Standard	I-Algorithm
.	O
</s>
<s>
Lucifer	B-Algorithm
uses	O
a	O
combination	O
of	O
transposition	O
and	O
substitution	O
crypting	O
as	O
a	O
starting	O
point	O
in	O
decoding	O
ciphers	O
.	O
</s>
<s>
The	O
cipher	O
is	O
a	O
substitution	B-Algorithm
–	I-Algorithm
permutation	I-Algorithm
network	I-Algorithm
and	O
uses	O
two	O
4-bit	O
S-boxes	B-Algorithm
.	O
</s>
<s>
The	O
key	O
selects	O
which	O
S-boxes	B-Algorithm
are	O
used	O
.	O
</s>
<s>
Another	O
variant	O
by	O
John	O
L	O
.	O
Smith	O
from	O
the	O
same	O
year	O
uses	O
a	O
64-bit	O
key	O
operating	O
on	O
a	O
32-bit	O
block	O
,	O
using	O
one	O
addition	O
mod	O
4	O
and	O
a	O
singular	O
4-bit	O
S-box	B-Algorithm
.	O
</s>
<s>
described	O
a	O
later	O
Lucifer	B-Algorithm
as	O
a	O
16-round	O
Feistel	B-Algorithm
network	I-Algorithm
,	O
also	O
on	O
128-bit	O
blocks	O
and	O
128-bit	O
keys	O
.	O
</s>
<s>
IBM	O
submitted	O
the	O
Feistel-network	O
version	O
of	O
Lucifer	B-Algorithm
as	O
a	O
candidate	O
for	O
the	O
Data	B-Algorithm
Encryption	I-Algorithm
Standard	I-Algorithm
(	O
compare	O
the	O
more	O
recent	O
AES	O
process	O
)	O
.	O
</s>
<s>
It	O
became	O
the	O
DES	B-Algorithm
after	O
the	O
National	O
Security	O
Agency	O
reduced	O
the	O
cipher	O
's	O
key	O
size	O
to	O
56	O
bits	O
,	O
reduced	O
the	O
block	O
size	O
to	O
64	O
bits	O
,	O
and	O
made	O
the	O
cipher	O
resistant	O
against	O
differential	O
cryptanalysis	O
,	O
which	O
was	O
at	O
the	O
time	O
known	O
only	O
to	O
IBM	O
and	O
the	O
NSA	O
.	O
</s>
<s>
The	O
name	O
"	O
Lucifer	B-Algorithm
"	O
was	O
apparently	O
a	O
pun	O
on	O
"	O
Demon	O
"	O
.	O
</s>
<s>
The	O
variant	O
described	O
by	O
has	O
16	O
Feistel	B-Algorithm
rounds	I-Algorithm
,	O
like	O
DES	B-Algorithm
,	O
but	O
no	O
initial	O
or	O
final	O
permutations	B-Algorithm
.	O
</s>
<s>
The	O
Feistel	B-Algorithm
function	I-Algorithm
operates	O
on	O
a	O
64-bit	O
half-block	O
of	O
data	O
,	O
together	O
with	O
a	O
64-bit	O
subkey	O
and	O
8	O
"	O
interchange	O
control	O
bits	O
"	O
(	O
ICBs	O
)	O
.	O
</s>
<s>
Each	O
byte	O
is	O
then	O
operated	O
on	O
by	O
two	O
4×	O
4-bit	O
S-boxes	B-Algorithm
,	O
denoted	O
S0	O
and	O
S1	O
S0	O
operates	O
on	O
the	O
left	O
4-bit	O
nibble	O
and	O
S1	O
operates	O
on	O
the	O
right	O
.	O
</s>
<s>
This	O
is	O
followed	O
by	O
a	O
permutation	B-Algorithm
operation	O
in	O
two	O
stages	O
;	O
the	O
first	O
permutes	O
each	O
byte	O
under	O
a	O
fixed	O
permutation	B-Algorithm
.	O
</s>
<s>
Initially	O
,	O
the	O
128	O
key	O
bits	O
are	O
loaded	O
into	O
a	O
shift	B-General_Concept
register	I-General_Concept
.	O
</s>
