Why is it not possible to make perfect CD / DVD copies?

[Kyanzes]

Hi,

As I'm not skilled in optical storage technologies I have no clue as to why is it impossible to make a PERFECT / ABSOLUTE / 100% copy of a CD / DVD medium. Now I'm NOT asking for a solution I'm just merely wondering about it. Why does a pirated game need a crack? Obviously, if the medium could be duplicated it wouldn't be neccessary. So what's behind this? Is it an artificial restriction in burners to prevent duplication? Is it a difference in materials used for the surface? Non-linear size of sectors? Or merely the manufacturer ID on the disk?

 

[yoda291]

um...you might want to google copy protection. They generally use different techniques.

And by perfect copy, I assume you mean getting a bit perfect copy of the data, which is possible.

 

[Bassyhead]

Not exactly sure what you mean. You can make bit-for-bit duplications yourself, but you'll also duplicate the copy protection present on the media. Pirated games need cracks to bypass security features built into the software itself, not the media.

 

[kpb]

Googling copy protection or drm is probably a good idea. Each protection scheme varies but usually they focus on doing something sllightly out of spec for the cd rom specification. It also depends on what your trying to protect. Audio cd's, game cd's etc.

An early audio cd protection used the fact that cd's can be multi session and most standard cd players didn't understand that and would only see the first session or last session, i forget which now. So they put a session on the disk with intentionally incorrect information in it. Stick the disk in a computer and it would get confused trying to read the bad info from the corrupted session and not work. Put it in a "dumb" cd player and it would just read the uncorrupted session with the correct info in it and play. The problem with that of corse was cd players got more advanced and things like mp3 cd players would often understand multisession cds and would get just as confused.

One game copy protection scheme I read about relied on a spot on the cd where it was intentionally writen with errors which it would read directly and get the correct information from but a cd copying program would try and do error correction on it and would then change the information there and then the game could recognize it as a copy.

The cd standard is actually really complicated and includes things for embeding text info to have your stereo automatically display song names and all sorts of other things that people don't realize because it's not commonly done on disks and not commonly supported by players.

 

[Future Shock]

Alas, there was DVDcrypt, which was a freeware program that could bypass DVD copy protection (and selectively sqeeze 9G DVDs down into 4.5G single-sided drives) - for use in making "backups". Back when I had small children living with me, I found that to be a VERY good thing - you'd be amazed at how fast kids can destroy disks, especially when used in car DVD players.

But in reality, most people used it to make copies for their friends, which we all know is illegal, and immoral to boot. So Sony sued the coders involved, and DVDcrypter is no more. There are rumors of it still floating on the web in places, or on P2P, but some of these copies are virused badly. The only secure way to get it is to know someone who had it prior to the court order...but hey, you do want to comply with the law, so no DVDcrypter for YOU!

Future Shock

N.B.- no, don't even ask...

 

[chcarnage]

Protected CD's break the CD standard ("Red Book") and confuse CD readers, like kpb said.

DVDs have copy protection implemented right into the standard. As far as I know, film DVDs can't be copied directly because blank DVDs have prewritten headers.

Write errors on the other hand are a normal occurence in DVD burning processes, but I'm not familiar with the details.

 

[Mark R]

There are many ways of protecting discs - some better than others.

The main part of most of the methods for protecting CDs involves creating the original discs so that they do not meet CD specifications. Technically, they're not allowed to be called CDs - Philips owns the CD trademark and aggressivley protects it. Philips did sue some record companies for selling protected CDs and calling them CDs.

These non-compliant discs fool confuse some readers and/or writers. E.g. a protected disc may contain invalid data in key areas which are not normally accessed, but which will be read during a copy, and cause the reading to fail. Some writers get confused if instructed to write invalid data - many will automatically 'correct' it. The protectoin works by checking that the invalid data is present on the disc.

More modern techniques have targetted limitations in the burning technique. Because of the way the burning laser is pulsed on and off, and how burning one spot on a disc affects neighbouring areas, certain data sequences are 'weaker' than others. (Essentially, lots of minimum size burned/unburned areas lie very close and 'blur' together). Pressed master CDs are not susceptible to this effect. The protection works by including these data patterns at various areas of the disc. When a burner tries to write these patterns, they do not burn well, and reading them is unreliable. When the program loads it tries to read this data - if it can read it (and it is the correct pattern) all is fine. If it can't read it then it assumes the disc is a copy.

I don't know much about DVD software protection, but would assume that most works similarly.

DVD videos are protected by encrypting the video data. The encryption key is stored in an area of the disc that is not burnable on recordable discs. This prevents you from making a direct 1:1 copy of an encrypted DVD. This value method is low, because the decryption method has been revealed, and there are now decryption programs that can make a exact 1:1 unencrypted copy of an encrypted DVD.

The decryption method was leaked by accident - a software company making a DVD player program accidentally released a beta version of their software, where they had forgotten to encrypt the portion of their program that decrypted the DVD (The DVD consortium required that the decryption code, be protected against reverse engineering). This unprotected beta got into the hands of one 'DVD Jon' who quickly reverse engineered it.

Future versions of DVD (HD-DVD +/- bluray) are likely to use a refinement of this system. The data on the disc will by a 2 part key - 1 part is stored on the disc, the other is given out to player manufacturers. The data will actually be encrypted to many of these keys - so that each player manufacturer gets their own personalised key. e.g. a Sony player will combine the private Sony code with the code on the disc and try to decrypt the data.
If any one company gets their player reverse engineered, and their private code leaks out - that code can be revoked and will not be included on future discs. So, if someone created a HD-DVD decryptor program by hacking their player, the publishers could identify the code it used, and not include it on new discs - these new discs could not be decrypted, nor would play on players that used the same code. This would leave the manufacturer of these players up a certain creek, so would encourage them to protect their code very well - although once the manufacturer kissed and made up (with suitable pecuniaries) they could be given a new code, and could then distribute a firmware update to customers.

 

[JEDIYoda]

Originally posted by: Future Shock
Alas, there was DVDcrypt, which was a freeware program that could bypass DVD copy protection (and selectively sqeeze 9G DVDs down into 4.5G single-sided drives) - for use in making "backups". Back when I had small children living with me, I found that to be a VERY good thing - you'd be amazed at how fast kids can destroy disks, especially when used in car DVD players.

But in reality, most people used it to make copies for their friends, which we all know is illegal, and immoral to boot. So Sony sued the coders involved, and DVDcrypter is no more. There are rumors of it still floating on the web in places, or on P2P, but some of these copies are virused badly. The only secure way to get it is to know someone who had it prior to the court order...but hey, you do want to comply with the law, so no DVDcrypter for YOU!

Future Shock

N.B.- no, don't even ask...

Thats not tue!! You can still d/l dvd decrypt and NO it is not virus laden!!!
Soumds to me like you work for one of those companies!!

 

[Kyanzes]

So basically the burners are unable to make a perfect copy of the original discs because they contain non-standard information and/or contain information in non-standard portions of the surface of the disk. Thank you all for the info and your efforts.

 

[Special K]

Originally posted by: Kyanzes
So basically the burners are unable to make a perfect copy of the original discs because they contain non-standard information and/or contain information in non-standard portions of the surface of the disk. Thank you all for the info and your efforts.

I still don't see why it would be so hard to tell a CD/DVD burner that is making a copy from a source disk "If you read a 1, write a 1. If you read a 0, write a 0", and ignore all assumptions it may be making about how the data "should" be arranged. If a bit perfect copy of a disc is made, it should function identically to the original.

Unless that's exactly what programs like Alcohol 120% accomplish. Can't A120 make a perfect copy of pretty much anything?

 

[MobiusPizza]

Originally posted by: Special K

Originally posted by: Kyanzes
So basically the burners are unable to make a perfect copy of the original discs because they contain non-standard information and/or contain information in non-standard portions of the surface of the disk. Thank you all for the info and your efforts.

I still don't see why it would be so hard to tell a CD/DVD burner that is making a copy from a source disk "If you read a 1, write a 1. If you read a 0, write a 0", and ignore all assumptions it may be making about how the data "should" be arranged. If a bit perfect copy of a disc is made, it should function identically to the original.

Unless that's exactly what programs like Alcohol 120% accomplish. Can't A120 make a perfect copy of pretty much anything?

It's not that simple. All sort of copy protection relies on all sort of tricks such as data position. CD drives cannot possiply recreate data position too accurately. And Writable CDs have a definite structure unlike CD/DVD-ROM which is molded and can take any structure. E.g. a non standard size gap in sector 1932 > 1933

hm also what you said is not 100% correct. Kyanzes said some area of the CD can contain information where the same portion in a CD-R is a non-writable region. E.g. if it contains the identifier of the CD-R such as brand, dye type, max record speed etc.

 

[digiram]

Originally posted by: Future Shock
Alas, there was DVDcrypt, which was a freeware program that could bypass DVD copy protection (and selectively sqeeze 9G DVDs down into 4.5G single-sided drives) - for use in making "backups". Back when I had small children living with me, I found that to be a VERY good thing - you'd be amazed at how fast kids can destroy disks, especially when used in car DVD players.

But in reality, most people used it to make copies for their friends, which we all know is illegal, and immoral to boot. So Sony sued the coders involved, and DVDcrypter is no more. There are rumors of it still floating on the web in places, or on P2P, but some of these copies are virused badly. The only secure way to get it is to know someone who had it prior to the court order...but hey, you do want to comply with the law, so no DVDcrypter for YOU!

Future Shock

N.B.- no, don't even ask...

Haha, it's funny how Sony sells dvd/cd rw drives and media, but don't want you to use them for what they are intended for. I guess that's kind of like buying a ferrari to drive around the neighborhood. LOL

 

[bobdole369]

till don't see why it would be so hard to tell a CD/DVD burner that is making a copy from a source disk "If you read a 1, write a 1. If you read a 0, write a 0",

Its not that simple. Take Safedisc protected games for instance (Battlefield Vietnam, The Sims 2, etc.) They use "unreadable data" in certain portions of the disc. Its neither a 0 nor a 1. Its garbage. In fact from what I understand the software looks for the raw ERROR from the disc to get its indication that the CD is genuine. So how exactly do you write NOT a 0 OR a 1? thats the hard part. Most burners cannot. Lots can.

 

[Marthisdil]

Originally posted by: JEDIYoda

Originally posted by: Future Shock
Alas, there was DVDcrypt, which was a freeware program that could bypass DVD copy protection (and selectively sqeeze 9G DVDs down into 4.5G single-sided drives) - for use in making "backups". Back when I had small children living with me, I found that to be a VERY good thing - you'd be amazed at how fast kids can destroy disks, especially when used in car DVD players.

But in reality, most people used it to make copies for their friends, which we all know is illegal, and immoral to boot. So Sony sued the coders involved, and DVDcrypter is no more. There are rumors of it still floating on the web in places, or on P2P, but some of these copies are virused badly. The only secure way to get it is to know someone who had it prior to the court order...but hey, you do want to comply with the law, so no DVDcrypter for YOU!

Future Shock

N.B.- no, don't even ask...

Thats not tue!! You can still d/l dvd decrypt and NO it is not virus laden!!!
Soumds to me like you work for one of those companies!!

If people wouldn't pirate movies and music, then the industry would have no reason to go after companies that provide software that allow people to pirate. Funny how that works,

 

[Mir96TA]

Originally posted by: Mark R
.
If any one company gets their player reverse engineered, and their private code leaks out - that code can be revoked and will not be included on future discs. So, if someone created a HD-DVD decryptor program by hacking their player, the publishers could identify the code it used, and not include it on new discs - these new discs could not be decrypted, nor would play on players that used the same code. This would leave the manufacturer of these players up a certain creek, so would encourage them to protect their code very well - although once the manufacturer kissed and made up (with suitable pecuniaries) they could be given a new code, and could then distribute a firmware update to customers.

That is not gonnna Fly
cause let say me and my father buy a same dvd player. I hacked into mine and reverse eng the codes and realse on WWW. New DVD came out with different SONY coed on it.
It wouldn't work on my dvd and my father dvd player. Basically what he bought become useless.
With that fear no DVD player ever catch the market
That is one of the concept why Dvix (sp) fail. Cicuit City really try to push it

 

[tinyabs]

Originally posted by: bobdole369

till don't see why it would be so hard to tell a CD/DVD burner that is making a copy from a source disk "If you read a 1, write a 1. If you read a 0, write a 0",

Its not that simple. Take Safedisc protected games for instance (Battlefield Vietnam, The Sims 2, etc.) They use "unreadable data" in certain portions of the disc. Its neither a 0 nor a 1. Its garbage. In fact from what I understand the software looks for the raw ERROR from the disc to get its indication that the CD is genuine. So how exactly do you write NOT a 0 OR a 1? thats the hard part. Most burners cannot. Lots can.

That's the same way floppy copy protection was implemented. For StarForce 3, you need to buy special CD from them.