<s>
The	O
Content	B-Algorithm
Scramble	I-Algorithm
System	I-Algorithm
(	O
CSS	O
)	O
is	O
a	O
digital	O
rights	O
management	O
(	O
DRM	O
)	O
and	O
encryption	O
system	O
employed	O
on	O
many	O
commercially	O
produced	O
DVD-Video	O
discs	O
.	O
</s>
<s>
CSS	O
utilizes	O
a	O
proprietary	B-Application
40-bit	O
stream	B-Algorithm
cipher	I-Algorithm
algorithm	O
.	O
</s>
<s>
It	O
has	O
been	O
superseded	O
by	O
newer	O
DRM	O
schemes	O
such	O
as	O
Content	O
Protection	O
for	O
Recordable	O
Media	O
(	O
CPRM	O
)	O
,	O
or	O
by	O
Advanced	B-Algorithm
Encryption	I-Algorithm
Standard	I-Algorithm
(	O
AES	B-Algorithm
)	O
in	O
the	O
Advanced	O
Access	O
Content	O
System	O
(	O
AACS	O
)	O
DRM	O
scheme	O
used	O
by	O
HD	B-Operating_System
DVD	I-Operating_System
and	O
Blu-ray	O
Disc	O
,	O
which	O
have	O
56-bit	O
and	O
128-bit	O
key	O
sizes	O
,	O
respectively	O
,	O
providing	O
a	O
much	O
higher	O
level	O
of	O
security	O
than	O
the	O
less	O
secure	O
40-bit	O
key	O
size	O
of	O
CSS	O
.	O
</s>
<s>
The	O
content	B-Algorithm
scramble	I-Algorithm
system	I-Algorithm
(	O
CSS	O
)	O
is	O
a	O
collection	O
of	O
proprietary	B-Application
protection	O
mechanisms	O
for	O
DVD-Video	O
discs	O
.	O
</s>
<s>
The	O
license	O
,	O
which	O
binds	O
the	O
licensee	O
to	O
a	O
non-disclosure	O
agreement	O
,	O
would	O
not	O
permit	O
the	O
development	O
of	O
open-source	B-Application
software	I-Application
for	O
DVD-Video	O
playback	O
.	O
</s>
<s>
Instead	O
,	O
there	O
is	O
libdvdcss	B-Language
,	O
a	O
reverse	O
engineered	O
implementation	O
of	O
CSS	O
.	O
</s>
<s>
Libdvdcss	B-Language
is	O
a	O
source	O
for	O
documentation	O
,	O
along	O
with	O
the	O
publicly	O
available	O
DVD-ROM	O
and	O
MMC	O
specifications	O
.	O
</s>
<s>
The	O
content	B-Algorithm
scramble	I-Algorithm
system	I-Algorithm
deals	O
with	O
three	O
participants	O
:	O
the	O
disc	O
,	O
the	O
drive	O
and	O
the	O
player	O
.	O
</s>
<s>
The	O
drive	O
may	O
also	O
support	O
Regional	B-Device
Playback	I-Device
Control	I-Device
(	O
RPC	O
)	O
to	O
limit	O
the	O
playback	O
of	O
DVD-Video	O
content	O
to	O
specific	O
regions	O
of	O
the	O
world	O
( §	O
3.3.26	O
)	O
.	O
</s>
<s>
CSS	O
employs	O
a	O
stream	B-Algorithm
cipher	I-Algorithm
and	O
mangles	O
the	O
keystream	B-Algorithm
with	O
the	O
plain-text	O
data	O
to	O
produce	O
the	O
cipher	O
text	O
.	O
</s>
<s>
The	O
stream	B-Algorithm
cipher	I-Algorithm
is	O
based	O
on	O
two	O
linear-feedback	B-Architecture
shift	I-Architecture
register	I-Architecture
(	O
LFSR	B-Architecture
)	O
and	O
set	O
up	O
with	O
a	O
40-bit	O
seed	O
.	O
</s>
<s>
At	O
the	O
time	O
CSS	O
was	O
introduced	O
,	O
it	O
was	O
forbidden	O
in	O
the	O
United	O
States	O
for	O
manufacturers	O
to	O
export	O
cryptographic	O
systems	O
employing	O
keys	O
in	O
excess	O
of	O
40	O
bits	O
,	O
a	O
key	O
length	O
that	O
had	O
already	O
been	O
shown	O
to	O
be	O
wholly	O
inadequate	O
in	O
the	O
face	O
of	O
increasing	O
computer	O
processing	O
power	O
(	O
see	O
Data	B-Algorithm
Encryption	I-Algorithm
Standard	I-Algorithm
)	O
.	O
</s>
<s>
A	O
correlation	O
attack	O
enables	O
the	O
recovery	O
of	O
a	O
keystream	B-Algorithm
's	O
seed	O
at	O
complexity	O
of	O
216	O
.	O
</s>
<s>
Libdvdcss	B-Language
uses	O
such	O
a	O
list	O
of	O
generated	O
player-keys	O
.	O
</s>
