<s>
In	O
cryptography	O
,	O
CAST-128	B-Algorithm
(	O
alternatively	O
CAST5	B-Algorithm
)	O
is	O
a	O
symmetric-key	B-Algorithm
block	O
cipher	B-Application
used	O
in	O
a	O
number	O
of	O
products	O
,	O
notably	O
as	O
the	O
default	O
cipher	B-Application
in	O
some	O
versions	O
of	O
GPG	B-Application
and	O
PGP	B-Application
.	O
</s>
<s>
Another	O
member	O
of	O
the	O
CAST	O
family	O
of	O
ciphers	B-Application
,	O
CAST-256	B-Algorithm
(	O
a	O
former	O
AES	B-Algorithm
candidate	O
)	O
was	O
derived	O
from	O
CAST-128	B-Algorithm
.	O
</s>
<s>
CAST-128	B-Algorithm
is	O
a	O
12	O
-	O
or	O
16-round	O
Feistel	B-Algorithm
network	I-Algorithm
with	O
a	O
64-bit	O
block	O
size	O
and	O
a	O
key	O
size	O
of	O
between	O
40	O
and	O
128	O
bits	O
(	O
but	O
only	O
in	O
8-bit	O
increments	O
)	O
.	O
</s>
<s>
Components	O
include	O
large	O
8×	O
32-bit	O
S-boxes	B-Algorithm
based	O
on	O
bent	O
functions	O
,	O
key-dependent	O
rotations	O
,	O
modular	O
addition	O
and	O
subtraction	O
,	O
and	O
XOR	B-Application
operations	O
.	O
</s>
<s>
There	O
are	O
three	O
alternating	O
types	O
of	O
round	O
function	O
,	O
but	O
they	O
are	O
similar	O
in	O
structure	O
and	O
differ	O
only	O
in	O
the	O
choice	O
of	O
the	O
exact	O
operation	O
(	O
addition	O
,	O
subtraction	O
or	O
XOR	B-Application
)	O
at	O
various	O
points	O
.	O
</s>
<s>
Although	O
Entrust	O
holds	O
a	O
patent	O
on	O
the	O
CAST	O
design	O
procedure	O
,	O
CAST-128	B-Algorithm
is	O
available	O
worldwide	O
on	O
a	O
royalty-free	O
basis	O
for	O
commercial	O
and	O
non-commercial	O
uses	O
.	O
</s>
