Why can't CSS-protected DVDs be copied?

Well, I know they CAN be copied with the approrpiate software, but I am
just curious why that is even necessary. As far as I can tell, CSS just
encrypts the data, so that my copy (like the original) can only be played
on authorized DVD players. But when I try to do a whole disc copy with
Nero, it tells me "This DVD is copy-protected and canot be read". The only
thing I can think of is that Nero checks for the copy protection, and
willingly refuses to copy it. Or am I missing something?

Note that I am not asking for HOW to copy a DVD; I can manage that with all
of the decrypting utilities out there. I am just curious as to why, if I
just want to make a byte-for-byte copy of a DVD, Nero does not let me.

David () wrote in alt.video.dvd:
> Well, I know they CAN be copied with the approrpiate software, but I am
> just curious why that is even necessary. As far as I can tell, CSS just
> encrypts the data, so that my copy (like the original) can only be played
> on authorized DVD players. But when I try to do a whole disc copy with
> Nero, it tells me "This DVD is copy-protected and canot be read". The only
> thing I can think of is that Nero checks for the copy protection, and
> willingly refuses to copy it. Or am I missing something?

A simplified explanation:

A DVD-ROM (which is what a DVD-Video disc is based on, just with a
specific place to put the files) is like any other disc in that it has
sectors of data. And, like any other disc, in addition to the data,
there is extra space in each sector for error correction. The error
correction on a DVD (or a CD, for that matter) is a form of cyclic
redundancy check (CRC)...basically, a checksum of the data. There are
other error correction methods used on DVDs as well, and you can do more
research if you want find out more.

What CSS does is take the *entire* sector that was on the master data
(including the error correction) and encrypts it. This data is then
what ends up on the master DVD, and gets pressed to every copy. The
trouble is that the CRC is no longer valid, and every time the drive
reads it, it thinks that the sector is bad.

So, unless you decyrpt the data, you can't know if the data is accurate,
and many DVD drives won't even return the "error-filled" data unless the
programmer is doing some very low-level calls. Even then, there is
still no way to know if the data is accurate without decryption, and
since there is a "soft" error (that is, one that can be corrected by the
drive because of the extra data on the disc) on about 1 in 10 sectors,
you basically end up with garbage without error correction.

As for how Nero tells it is copy-protected, I suspect there is just a
byte in one of the files that says it is. I haven't looked that deep
into that part of CSS.

But, even if this wasn't set, Nero (or any other program) couldn't copy
the disc without some sort of CSS decrypter.


--
Jeff Rife | "The old guy was leading a 'Simon Says' game
| when he collapsed. On the way down he yelled
| 'call an ambulance!', but no one moved."
| -- Wings

"David" <> wrote in message
news:Xns9776DB36C69ABdaveinnyc@24.29.109.206...
> Well, I know they CAN be copied with the approrpiate software, but I am
> just curious why that is even necessary. As far as I can tell, CSS just
> encrypts the data, so that my copy (like the original) can only be played
> on authorized DVD players. But when I try to do a whole disc copy with
> Nero, it tells me "This DVD is copy-protected and canot be read". The only
> thing I can think of is that Nero checks for the copy protection, and
> willingly refuses to copy it. Or am I missing something?
>
> Note that I am not asking for HOW to copy a DVD; I can manage that with
> all
> of the decrypting utilities out there. I am just curious as to why, if I
> just want to make a byte-for-byte copy of a DVD, Nero does not let me.


"As far as I can tell, CSS just encrypts the data, so that my copy (like the
original) can only be played
on authorized DVD players."

No that is not the reason and has nothing to do with region coding or
'authorised players whatever that is?. CSS is there to try to stop you from
copying the DVD at all. Not very effective since decrypters but it stops
dead a lot of casual computer users, the so called 'moms and dads' user's.
Nero and most other legit burning programs detects the presence of
encryption and stops the copying process, it's both a legal and commercial
requirement. Of course these days there are several levels of copy
protection apart from CSS. So called 'fair use' provisions don't apply in
many countries, for example it is technically illegal in Australia to even
record a TV program on a VHS recorder and no fair use provision exists. It's
going to be changed this year I believe not that any one takes any notice.

"Jeff Rife" <> wrote in message
news:...
> David () wrote in alt.video.dvd:
>> Well, I know they CAN be copied with the approrpiate software, but I am
>> just curious why that is even necessary. As far as I can tell, CSS just
>> encrypts the data, so that my copy (like the original) can only be played
>> on authorized DVD players. But when I try to do a whole disc copy with
>> Nero, it tells me "This DVD is copy-protected and canot be read". The
>> only
>> thing I can think of is that Nero checks for the copy protection, and
>> willingly refuses to copy it. Or am I missing something?
>
> A simplified explanation:
>
> A DVD-ROM (which is what a DVD-Video disc is based on, just with a
> specific place to put the files) is like any other disc in that it has
> sectors of data. And, like any other disc, in addition to the data,
> there is extra space in each sector for error correction. The error
> correction on a DVD (or a CD, for that matter) is a form of cyclic
> redundancy check (CRC)...basically, a checksum of the data. There are
> other error correction methods used on DVDs as well, and you can do more
> research if you want find out more.
>
> What CSS does is take the *entire* sector that was on the master data
> (including the error correction) and encrypts it. This data is then
> what ends up on the master DVD, and gets pressed to every copy. The
> trouble is that the CRC is no longer valid, and every time the drive
> reads it, it thinks that the sector is bad.
>
> So, unless you decyrpt the data, you can't know if the data is accurate,
> and many DVD drives won't even return the "error-filled" data unless the
> programmer is doing some very low-level calls. Even then, there is
> still no way to know if the data is accurate without decryption, and
> since there is a "soft" error (that is, one that can be corrected by the
> drive because of the extra data on the disc) on about 1 in 10 sectors,
> you basically end up with garbage without error correction.
>
> As for how Nero tells it is copy-protected, I suspect there is just a
> byte in one of the files that says it is. I haven't looked that deep
> into that part of CSS.
>
> But, even if this wasn't set, Nero (or any other program) couldn't copy
> the disc without some sort of CSS decrypter.

Thank you for the good explanation, Jeff. I have always wondered why it
could not just "clone" the disc.

>
>
> --
> Jeff Rife | "The old guy was leading a 'Simon Says' game
> | when he collapsed. On the way down he yelled
> | 'call an ambulance!', but no one moved."
> | -- Wings

What do you mean, Netmask, that no-one takes any notice. I've been
telling people for years here in Australia that it's illegal to use a
video-recorder to tape your favourite shows. Instead I've been setting
up my old Leica on a tripod in front of the telly and taking a snap
every five to 10 seconds. Mount those pics in an album and flick
through them once in a while, and you get a pretty fair idea of what a
program was all about. And you can go to sleep easy knowing you haven't
broken the law.
And speaking of law, have you noticed that our glorious leader JH has,
as part of the Free Trade Agreement, let us be suckered into signing up
for the American 'protect Walt Disney products' 70-year Copyright
legislation, replacing our own very reasonable 50-year legislation? The
new tougher law came into effect at the start of Feb.

"anthony" <> wrote in message
news: oups.com...
> What do you mean, Netmask, that no-one takes any notice. I've been
> telling people for years here in Australia that it's illegal to use a
> video-recorder to tape your favourite shows. Instead I've been setting
> up my old Leica on a tripod in front of the telly and taking a snap
> every five to 10 seconds. Mount those pics in an album and flick
> through them once in a while, and you get a pretty fair idea of what a
> program was all about. And you can go to sleep easy knowing you haven't
> broken the law.
> And speaking of law, have you noticed that our glorious leader JH has,
> as part of the Free Trade Agreement, let us be suckered into signing up
> for the American 'protect Walt Disney products' 70-year Copyright
> legislation, replacing our own very reasonable 50-year legislation? The
> new tougher law came into effect at the start of Feb.
>

You have probably infringed somebodies copyright by posting that comment or
maybe the SMH will sue for plagiarism from an article written 10 years ago
speculating on the future of copyright law because you used 3 consecutive
identical words....... the pollies and their advisors are so out of touch
with the real world not to realise if you can see and hear it on a TV
monitor or computer screen, or hear it on the radio then you can record it
by a dozen or so different methods. Bah and humbug