<s>
In	O
cryptography	O
,	O
the	O
Intel	O
Cascaded	O
Cipher	O
is	O
a	O
high	O
bandwidth	O
block	O
cipher	O
,	O
used	O
as	O
an	O
optional	O
component	O
of	O
the	O
Output	O
Content	O
Protection	O
DRM	O
scheme	O
of	O
the	O
Microsoft	B-Application
Windows	I-Application
Vista	I-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
The	O
cipher	O
is	O
based	O
on	O
Advanced	B-Algorithm
Encryption	I-Algorithm
Standard	I-Algorithm
(	O
AES	B-Algorithm
)	O
operating	O
in	O
counter	O
mode	O
,	O
used	O
for	O
generating	O
keys	O
,	O
and	O
a	O
3-round	O
version	O
of	O
Serpent	B-Algorithm
for	O
encrypting	O
actual	O
content	O
.	O
</s>
<s>
The	O
Cascaded	O
Cipher	O
specifications	B-Application
are	O
not	O
currently	O
available	O
on	O
the	O
Intel	O
web	O
site	O
or	O
in	O
academic	O
journals	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
patent	O
application	O
only	O
describes	O
the	O
inventive	O
steps	O
as	O
claimed	O
by	O
its	O
inventors	O
,	O
and	O
is	O
not	O
a	O
specification	B-Application
of	O
the	O
cipher	O
as	O
it	O
is	O
intended	O
to	O
be	O
used	O
to	O
protect	O
content	O
in	O
Windows	B-Application
Vista	I-Application
.	O
</s>
<s>
In	O
the	O
counter-electronic	O
codebook	O
mode	O
,	O
the	O
Cascaded	O
Cipher	O
uses	O
full	O
strength	O
AES-128	B-Algorithm
in	O
counter	O
mode	O
to	O
generate	O
a	O
secure	O
key	O
stream	O
and	O
supplies	O
this	O
key-stream	O
to	O
a	O
reduced	O
round	O
Serpent	B-Algorithm
in	O
electronic	O
codebook	O
mode	O
to	O
encrypt	O
each	O
plaintext	O
block	O
.	O
</s>
<s>
In	O
the	O
counter-counter	O
mode	O
,	O
the	O
Cascaded	O
Cipher	O
uses	O
full-strength	O
AES-128	B-Algorithm
in	O
counter	O
mode	O
to	O
generate	O
a	O
secure	O
key	O
stream	O
and	O
supplies	O
this	O
key-stream	O
to	O
a	O
reduced	O
round	O
Serpent	B-Algorithm
also	O
operating	O
in	O
counter	O
mode	O
to	O
encrypt	O
each	O
plaintext	O
block	O
.	O
</s>
<s>
In	O
the	O
Microsoft	O
document	O
"	O
Output	O
Content	O
Protection	O
and	O
Windows	B-Application
Vista	I-Application
"	O
,	O
it	O
is	O
claimed	O
that	O
:	O
"	O
The	O
security	O
level	O
achieved	O
for	O
typical	O
video	O
data	O
is	O
estimated	O
to	O
be	O
approaching	O
that	O
of	O
regular	O
AES	B-Algorithm
.	O
</s>
<s>
The	O
security	O
of	O
the	O
system	O
requires	O
that	O
it	O
is	O
impossible	O
to	O
recover	O
the	O
currently	O
active	O
inner	O
key	O
from	O
the	O
output	O
of	O
the	O
reduced	O
round	O
Serpent	B-Algorithm
encrypted	O
video	O
stream	O
.	O
</s>
<s>
Furthermore	O
,	O
the	O
security	O
of	O
this	O
method	O
is	O
highly	O
sensitive	O
to	O
the	O
number	O
of	O
rounds	O
used	O
in	O
Serpent	B-Algorithm
,	O
the	O
mode	O
of	O
operation	O
described	O
in	O
the	O
patent	O
application	O
,	O
and	O
the	O
number	O
of	O
times	O
the	O
inner	O
key	O
is	O
reused	O
.	O
</s>
