<s>
In	O
cryptography	O
,	O
ICE	O
(	O
Information	B-Algorithm
Concealment	I-Algorithm
Engine	I-Algorithm
)	O
is	O
a	O
symmetric-key	B-Algorithm
block	O
cipher	O
published	O
by	O
Kwan	O
in	O
1997	O
.	O
</s>
<s>
The	O
algorithm	O
is	O
similar	O
in	O
structure	O
to	O
DES	B-Algorithm
,	O
but	O
with	O
the	O
addition	O
of	O
a	O
key-dependent	O
bit	O
permutation	O
in	O
the	O
round	O
function	O
.	O
</s>
<s>
ICE	O
is	O
a	O
Feistel	B-Algorithm
network	I-Algorithm
with	O
a	O
block	O
size	O
of	O
64	O
bits	O
.	O
</s>
<s>
ICE	O
is	O
a	O
16-round	O
Feistel	B-Algorithm
network	I-Algorithm
.	O
</s>
<s>
Each	O
round	O
uses	O
a	O
32	O
→	O
32	O
bit	O
F	B-Algorithm
function	I-Algorithm
,	O
which	O
uses	O
60	O
bits	O
of	O
key	O
material	O
.	O
</s>
<s>
The	O
structure	O
of	O
the	O
F	B-Algorithm
function	I-Algorithm
is	O
somewhat	O
similar	O
to	O
DES	B-Algorithm
:	O
The	O
input	O
is	O
expanded	O
by	O
taking	O
overlapping	O
fields	O
,	O
the	O
expanded	O
input	O
is	O
XORed	O
with	O
a	O
key	O
,	O
and	O
the	O
result	O
is	O
fed	O
to	O
a	O
number	O
of	O
reducing	O
S-boxes	O
which	O
undo	O
the	O
expansion	O
.	O
</s>
<s>
(	O
These	O
are	O
much	O
larger	O
than	O
DES	B-Algorithm
's	O
8	O
6	O
→	O
4	O
bit	O
S-boxes	O
.	O
)	O
</s>
<s>
Like	O
DES	B-Algorithm
,	O
a	O
software	O
implementation	O
would	O
typically	O
store	O
the	O
S-boxes	O
pre-permuted	O
,	O
in	O
4	O
1024×32	O
bit	O
lookup	O
tables	O
.	O
</s>
