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View Full Version : DVD copying - why not bit-for-bit?


amarone
12-08-2002, 07:53 AM
I have no intention of copying DVD movies, but the subject came up in discussion with friends. One person, who works in a related industry, says that DVD movies cannot be copied because of encryption. A bit of googling tends to support this, but does find lots of people who have cracked the encryption.

My question is: why do you need to crack the encryption to do the copying? Why can you not just do an exact bit-for-bit copy of the DVD? The result would be identical to the original, so should work whether you know the encryption method or not.

Do DVD drives themselves prevent bit-level access?

Desmostylus
12-08-2002, 08:02 AM
In order to obtain a licence from the patent holders, manufacturers of DVD drives are supposed to sign an agreement that their drives will not allow such access (amongst other things).

Dreaming of Maria Callas
12-08-2002, 09:19 AM
Originally posted by Desmostylus
In order to obtain a licence from the patent holders, manufacturers of DVD drives are supposed to sign an agreement that their drives will not allow such access (amongst other things).

But that is usually based on settings in the firmware, and people who professionally make illegal copies of DVDs know how to patch firmware to let them do whatever they want.

UnuMondo

sigSEGV
12-08-2002, 11:18 AM
You can make a bit for bit copy of DVDs, no problem. The decryption only becomes involved when you try to play it.

amarone
12-08-2002, 11:21 AM
Originally posted by sigSEGV
You can make a bit for bit copy of DVDs, no problem. The decryption only becomes involved when you try to play it.
But if it is a bit-for-bit copy, the decryption should work just as it did for the original DVD.

sigSEGV
12-08-2002, 11:24 AM
I would post a link to the relevant technical details, but would probably get in trouble. :rolleyes: Lets just say, go to Google, search for DeCSS and click on the 7th link down. Scroll to the section titled DeCSS.

sigSEGV
12-08-2002, 11:26 AM
Yes, you are correct.
Originally posted by amarone
But if it is a bit-for-bit copy, the decryption should work just as it did for the original DVD.

amarone
12-08-2002, 11:31 AM
Originally posted by sigSEGV
I would post a link to the relevant technical details, but would probably get in trouble. :rolleyes: Lets just say, go to Google, search for DeCSS and click on the 7th link down. Scroll to the section titled DeCSS.
I read those types of articles before doing the OP. I still don't understand why cracking the encryption has any relevance IF you can do a bit-for-bit copy.

Let's try an analogy. I don't speak German. You could send me a document in German and I could reproduce it in many ways to create a copy that a German speaker could understand perfectly. I could scan it, photocopy it, retype it letter for letter. All of these would work and I would achieve a perfect copy without needing to understand or translate the German in any way.

The typing letter by letter is analgous to a bit-by-bit copy of a DVD (or CD or hard drive). If you can do that, then wouldn't the encryption be irrelevant - it will still be used by the decoder when playing, but that's OK. My point is that decryption would not be needed for the copying process.

amarone
12-08-2002, 11:32 AM
Oops - typed my response in after seeing your first one and before your second had appeared.

sigSEGV
12-08-2002, 11:37 AM
It doesn't have any relevance. When the DVD standard came out, it was stupidly assumed that a DVD reader that allowed bit for bit copying and a DVD burner were way off, therefore, no one would pirate. When the DeCSS software came out, all the sudden everybody assumed it was possible to copy DVDs, when it had been all along.

Originally posted by amarone
I read those types of articles before doing the OP. I still don't understand why cracking the encryption has any relevance IF you can do a bit-for-bit copy.

Let's try an analogy. I don't speak German. You could send me a document in German and I could reproduce it in many ways to create a copy that a German speaker could understand perfectly. I could scan it, photocopy it, retype it letter for letter. All of these would work and I would achieve a perfect copy without needing to understand or translate the German in any way.

The typing letter by letter is analgous to a bit-by-bit copy of a DVD (or CD or hard drive). If you can do that, then wouldn't the encryption be irrelevant - it will still be used by the decoder when playing, but that's OK. My point is that decryption would not be needed for the copying process.

Kwyjibo
12-08-2002, 11:43 AM
Originally posted by Desmostylus
In order to obtain a licence from the patent holders, manufacturers of DVD drives are supposed to sign an agreement that their drives will not allow such access (amongst other things). I believe this function is called MacroVision.

When I first used a DVD player, it was at work and we were watching the Matrix. I wanted to see what happened why you tried to copy it as I had heard it some how knows and scrambles the signal.

MacroVision kicked in and it did just that.

sailor
12-08-2002, 12:08 PM
I believe Macrovision was for VCRs.

>> Do DVD drives themselves prevent bit-level access?

The answer is much more complex than you may realise at first. Say you have a file and want to store it. The first thing you (or rather your computer) do is to break it up in blocks of (say) 512 bytes, but now each block has its own header, CRC, and other overhead. Now you want to record this on a CDrom but it is further encoded at a lower level with more error correcting codes etc. In other words, if you record the same file on a CDR there are going to be multiple differences but the error correction at read time, done by the drive, will be able to reconstruct the original block and return it. So, only the drive itself has access to the lowest level and will return the next upper level which in turn will be decoded and the file reconstructed.

At any rate, you are right that if I copy a file bit for bit at the file level, I should get the same result. The problem is if the drive which I am asking to do the job will not cooperate because there is some bit somewhere telling it not to.

I remember a couple years ago, I believe IBM and MS were cooperating on a new kind of hard disks which would not allow copying of copyrighted materials. I never heard agin. I guess not many people were interested in buying these drives.

Kwyjibo
12-08-2002, 12:18 PM
Originally posted by sailor
I believe Macrovision was for VCRs.Possibly. But I do know that my DVD player had MacroVision on it.

Kwyjibo
12-08-2002, 12:20 PM
(Add a ;) to that. I just realised that might have sounded snooty.;) )

neutron star
12-08-2002, 12:22 PM
I believe Macrovision was for VCRs.

According to this (http://reoc.keyservice.co.uk/a3/macrovision), Macrovision and CSS are one and the same.

From that link:
Macrovison is a property of the DVD and not the player and not all DVD's contain macrovision but a large percentage do.

A little more on this (http://www.apexmodchip.com/macrovision.html) page:
A standard DVD player contains a special Macrovision-enabled digital-analog conversion chip that is activated when a DVD is played. The activated chip applies copy protection to the analog output and causes copies made on most VCRs to be substantially degraded.

sailor
12-08-2002, 12:31 PM
>> Macrovison is a property of the DVD and not the player and not all DVD's contain macrovision but a large percentage do.

>> A standard DVD player contains a special Macrovision-enabled digital-analog conversion chip that is activated when a DVD is played. The activated chip applies copy protection to the analog output and causes copies made on most VCRs to be substantially degraded.

The two above statements can be interpreted to contradict each other. The main thing is that "A standard DVD player contains a special Macrovision-enabled digital-analog conversion chip that is activated when a DVD is played". In other words, the player is cooperating in preventing the copying and in that sense the player "has" macrovision. Then certain DVDs may or may not have macrovision enabled.

handy
12-08-2002, 06:25 PM
Ah, when I put a copy protected dvd in the drive the Nero software says the dvd is copyrighted. But then it does that when I make my own dvds too. Odd.

Dvds are basically just a VIDEO_TS & a AUDIO_TS folder with their associated files. Look at one yourself.

happyheathen
12-08-2002, 07:11 PM
I have equipment which will copy all known video formats.

The CR does not like discussion of the details, so I won't go there.

I will say this: I seriously doubt that bit-copy will defeat the DVD encryption - I have an old bit-copy CD burner, and it can be beaten by modern CD's.

Desmostylus
12-08-2002, 07:31 PM
happyheathen: Bit copy and encryption are different issues.

A pirate can make a bit-copy of a DVD. The resulting copy is still encrypted, but that's not a problem for the pirate. All DVD players contain the necessary decryption algorithms.

The point of the OP was whether DVD drives will allow bit-copying, and the answer is that they won't. The pirate has to hack the drive's firmware first.

Servo
12-08-2002, 07:57 PM
I don't know if this has been answered or not, but the whole point of breaking the encryption was not to be able to copy the disc, but being able to view it.

If I remember the whole DeCSS thing correctly, someone wanted a DVD player for Linux but there were none available. So in order to write a program that could play back the video and audio stored on a DVD he needed to break the encryption. It wasn't about copying, it was about viewing.

Desmostylus
12-08-2002, 09:10 PM
Servo: Whilst DeCSS may have ostensibly been about viewing, once you've broken the encryption, you can do other things with the content, like remove copyright notices, transmit it over the internet, etc.

Whatever the intended purpose, breaking the encryption contravenes the DMCA, i.e., it's illegal.

Kalt
12-08-2002, 09:56 PM
Whatever the intended purpose, breaking the encryption contravenes the DMCA, i.e., it's illegal.

Only here in america (the land of the free). In Sweden (or wherever it was) where the guy wrote DeCSS, it was not illegal for him to do so. Must be nice living in a free country. I wouldn't know.

Servo
12-08-2002, 10:00 PM
Desmostylus,

I understand that. I realize I wasn't very clear.

What I should have said:

Breaking the encryption is about getting at the content [and doing things to it that you wouldn't be able to do with a licensed player]. It's not about just making copies of the media.

I was really answering this question in the OP: "why do you need to crack the encryption to do the copying?"

If the encryption we're talking about is CSS, the answer is, "you don't." The encryption isn't there to prevent making copies of the media, it's to prevent free access to the content. But, if you break CSS then you can make a copy of the content, and you don't need to make a bit-level copy of the media. You can write [or download] software that reads the data from the DVD, decrypts it, and writes it to an mpeg file on a hard disk. Which is much scarier from a copyright holder's point of view, because now you don't need special equipment, and you can make changes to the content [like you pointed out].

Alereon
12-09-2002, 05:00 AM
The reason you cannot make a bit-for-bit copy is that you cannot burn the decryption keys onto writable media. The decryption keys must be written to a special section of a special disk using a special drive that consumers do NOT have access to. A standard DVD-R drive you buy at Best Buy cannot write to this special area, and even if it could, the discs you buy along with the drive cannot be written to in that special area. Thus, you end up burning encrypted content with no decryption key, which is quite useless.

Firmware is not an issue. The only access control mechanism having to do with firmware is the Region Coding, which insures that you can only play a DVD from your geographical region in your DVD-ROM drive or DVD player. And also, Macrovision and CSS are different. Macrovision doesn't affect the data on the DVD, its supposed to be activated and applied by the DVD player. CSS is actual encryption of the DVD data.

Popup
12-09-2002, 05:38 AM
Originally posted by Kalt
Only here in america (the land of the free). In Sweden (or wherever it was) where the guy wrote DeCSS, it was not illegal for him to do so.
Wrong on both accounts.
Jon Johansen (http://www.eff.org/IP/Video/DeCSS_prosecutions/Johansen_DeCSS_case/) was actually prosecuted in Norway.

It was heavily publiced by EFF last spring, but I haven't heard the results.

Desmostylus
12-09-2002, 05:41 AM
FDISK: No one is claiming that pirates use off-the-shelf equipment to do the bit-copy. To tell the truth, I hadn't even considered using DVD-R discs as the output medium, I was thinking of print runs in the thousands that get sold in markets (in same countries).

Nevertheless, you point is well taken, the writing question is implicit in the OP.

Macrovision is an irrelevant side-issue that seems to have confused some of the posters. Your interpretation of the Macrovision/CSS issue is the correct one, however.

I don't accept your "firmware is not an issue" claim. Firmware in a DVD drive implements more than the region coding. Region coding is just one of the "amongst other things" I referred to in my first post.

Alereon
12-09-2002, 06:09 AM
If a pirate has access to professional DVD authoring equipment and DVD authoring discs, he can do a bit-for-bit copy of DVDs until the cows come home. There's nothing standing in his way besides the law. I'll wager that thats how any major bootlegging outfit does it, except I'd think they'd use pressed discs and much more expensive pressing machines instead of DVD-Rs.

As for the firmware, I've never encountered nor heard of the firmware on a DVD-ROM drive preventing bit-for-bit data extraction. In fact, I don't know how this would be possible. I believe what you are thinking of is the requirement that hardware or software that implements CSS decryption LEGALLY is required to insure that the decrypted data stream isn't sent anywhere unprotected. In a computer, this restriction would apply to the DVD playing software or DVD decoder card, not the DVD-ROM drive. On a DVD player, this requirement will be satisfied by the employment of Macrovision protection.

Desmostylus
12-09-2002, 06:43 AM
FDISK: Your first paragraph is spot on.

In your second paragraph, I'm not sure what you are saying.