<s>
In	O
cryptography	O
,	O
LOKI97	B-Algorithm
is	O
a	O
block	O
cipher	O
which	O
was	O
a	O
candidate	O
in	O
the	O
Advanced	B-Algorithm
Encryption	I-Algorithm
Standard	I-Algorithm
competition	O
.	O
</s>
<s>
It	O
is	O
a	O
member	O
of	O
the	O
LOKI	B-Device
family	O
of	O
ciphers	O
,	O
with	O
earlier	O
instances	O
being	O
LOKI89	B-Algorithm
and	O
LOKI91	B-Algorithm
.	O
</s>
<s>
LOKI97	B-Algorithm
was	O
designed	O
by	O
Lawrie	O
Brown	O
,	O
assisted	O
by	O
Jennifer	O
Seberry	O
and	O
Josef	O
Pieprzyk	O
.	O
</s>
<s>
Like	O
DES	B-Algorithm
,	O
LOKI97	B-Algorithm
is	O
a	O
16-round	O
Feistel	B-Algorithm
cipher	I-Algorithm
,	O
and	O
like	O
other	O
AES	B-Algorithm
candidates	O
,	O
has	O
a	O
128-bit	O
block	O
size	O
and	O
a	O
choice	O
of	O
a	O
128-	O
,	O
192	O
-	O
or	O
256-bit	O
key	O
length	O
.	O
</s>
<s>
It	O
uses	O
16	O
rounds	O
of	O
a	O
balanced	B-Algorithm
Feistel	I-Algorithm
network	I-Algorithm
to	O
process	O
the	O
input	O
data	O
blocks	O
(	O
see	O
diagram	O
right	O
)	O
.	O
</s>
<s>
The	O
key	B-Algorithm
schedule	I-Algorithm
is	O
also	O
a	O
Feistel	B-Algorithm
structure	I-Algorithm
–	O
an	O
unbalanced	O
one	O
unlike	O
the	O
main	O
network	O
—	O
but	O
using	O
the	O
same	O
F-function	B-Algorithm
.	O
</s>
<s>
The	O
LOKI97	B-Algorithm
round	O
function	O
(	O
shown	O
right	O
)	O
uses	O
two	O
columns	O
each	O
with	O
multiple	O
copies	O
of	O
two	O
basic	O
S-boxes	B-Algorithm
.	O
</s>
<s>
These	O
S-boxes	B-Algorithm
are	O
designed	O
to	O
be	O
highly	O
non-linear	O
and	O
have	O
a	O
good	O
XOR	O
profile	O
.	O
</s>
<s>
The	O
permutations	O
before	O
and	O
between	O
serve	O
to	O
provide	O
auto-keying	O
and	O
to	O
diffuse	O
the	O
S-box	B-Algorithm
outputs	O
as	O
quickly	O
as	O
possible	O
.	O
</s>
<s>
The	O
authors	O
have	O
stated	O
that	O
,	O
"	O
LOKI97	B-Algorithm
is	O
a	O
non-proprietary	O
algorithm	O
,	O
available	O
for	O
royalty-free	O
use	O
worldwide	O
as	O
a	O
possible	O
replacement	O
for	O
the	O
DES	B-Algorithm
or	O
other	O
existing	O
block	O
ciphers.	O
"	O
</s>
<s>
It	O
was	O
intended	O
to	O
be	O
an	O
evolution	O
of	O
the	O
earlier	O
LOKI89	B-Algorithm
and	O
LOKI91	B-Algorithm
block	O
ciphers	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
published	O
candidate	O
in	O
the	O
Advanced	B-Algorithm
Encryption	I-Algorithm
Standard	I-Algorithm
competition	O
,	O
and	O
was	O
quickly	O
analysed	O
and	O
attacked	O
.	O
</s>
<s>
An	O
analysis	O
of	O
some	O
problems	O
with	O
the	O
LOKI97	B-Algorithm
design	O
,	O
which	O
led	O
to	O
its	O
rejection	O
when	O
shortlisting	O
candidates	O
,	O
is	O
given	O
in	O
a	O
paper	O
(	O
Rijmen	O
&	O
Knudsen	O
1999	O
)	O
.	O
</s>
