Adding CSS Copy Protection to DVD
Introduction
CSS stands for Content Scrambling System. It is the copy protection scheme being used for DVD. The protection uses a relative week algorithm and it has long been cracked since 1996. Nevertheless CSS is still used by content owners who want to minimize the loss due to illegal DVD copying. The rationale is: If you cannot stop everyone, try to stop some ones.
DVD authoring software such as ULead DVD Workshop, Apple DVD Studio Pro and FinalCut, Sony Vegas+DVD all allow the enabling of CSS. But they also require the authored content be output to DLT tapes instead of DVD-R. Most DVD authors find this to be a frustrated nuisance as DLT tape drive is not a common peripheral on most computers.
This article briefly explains what CSS is, how it works, and the problems faced by DVD authors who want to add CSS to their DVDs. We then provide solutions to the problem by making it an authoring stage problem to be solved at the mastering stage.
CSS - A butt of all the jokes
Besides the Clinton Sex Scandal (CSS), Content Scrambling System has been a laughing stock since its release and later cracked by a 16 year-old kid in Norway. CSS uses a very simple encryption algorithm that revolves among three keys; i.e. the player key, the disc key, and the title key. The idea is: Every DVD player in the world is assigned with a unique player key. For example, a Sony DVD player will have a Sony key, an HP player will have an HP key. When a DVD is encrypted with CSS, the lead-in area of the disc will have maximum 409 encrypted keys and one of them will work with the player key to retrieve the disk key. Once the disc key is found, the player key is used again with the disc key to find the title key. The title key is the final key to decrypt the scrambled digital content.
In case you don't know what the keys are all about, they are analogous to a physical key which allow you to open the door and get access to the content behind the door. With a key you can unlock the secrecy and make the content clear and legible.
CSS in action
The following pictures illustrate what happens when you try to copy a CSS protected DVD.
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Nero, the most common disc copying software on personal computers, will display a warning dialog. Nero will refuse the copying. Other famous disc copying software such as Roxio Easy Media Creator and Toast on the Mac will refuse the copying too. |
| If you try to copy a CSS protected DVD using a duplicator tower, the firmware of the duplicator tower will detect the CSS information and refuse the copying as well. The pictures below show what is displayed on an ACard and Smarrcopy control cards. | ||
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How to add CSS
There is a misconception that CSS can be added to a DVD-R or DVD+R. The fact is: CSS can only be added to replicated disc from glass master. The reason being the disc key is stored on tracks where DVD-R or DVD+R is not recordable, i.e. DVD writers cannot write information on those tracks. DLT tapes, though an old technology, have been used as source for replication even before the use of DVD-R. If you own a DLT tape drive then adding CSS is no brainer. Just enable the CSS check box before output your project to one or two DLT tapes.
Ooooops, I don't have a DLT Tape Drive
Two solutions: Get a DLT Tape drive or let someone do the DVD to DLT for you.
If you are pretty computer savvy, try to buy a used DLT tape drive from eBay. You will also need an old SCSI card to connect your DLT tape drive to your computer. Your total investment should be around $500, $300 ~ $400 for the drive and $100 ~ $200 for the SCSI card. Make sure your authoring software supports the drive you intend to buy before making your purchase decision. Be warned though: Getting a DLT tape drive to work is not as straightforward as what you might have thought. Also, writing to DLT tapes will be at 1x speed. If you are used to writing DVD-R at 8x then expect it will take 8 times longer to write on DLT tapes, or 16 times longer if you also need data verification.
Another solution is to output your project to a DVD-R without CSS enabled and send it to your replicator for replication. Your replicator should be able to add CSS at the mastering stage. Company such as New Cyberian can accept a complete authored DVD-R as source for adding CSS without the need for re-authoring. Many replicators still think adding CSS is an authoring task but it can actually be added at the mastering stage.
Conclusion
If you want your DVD be copy protected, think twice. People who have the ill-intention to copy your DVD will find the tool to do it anyway. Software such as DVD Decrypter and Alcohol can copy any copy-protected DVDs in a snap. But if for whatever reasons you still need to add copy protection, CSS is the cheapest way to do it without losing player compatibility. CSS can be added after the DVD is authored for replication. Your replicator needs to have to know-how to add it during the mastering stage without the need for re-authoring.
Glossary
CSS
Content Scrambling System
DeCSS
A computer program capable of decrypting content on a DVD video disc encrypted using the Content-Scrambling System (CSS)
Disc Key
The key to decrypt title keys on DVD discs
DLT
Digital Linear Tape
Duplicator
A stacking up of CD/DVD writers to form a tower that can copy multiple discs in one batch.
Encryption
A way to obscure information to make it unreadable without special knowledge, sometimes referred to as scrambling.
Nero
A popular disc copying software on desktop and laptop computers.
Player Key
The key to decrypt disc keys on DVD disc
Replicator
A company that can press CD/DVD using glass master.
Title Key
The key to scramble and descramble actual data on DVD discs called titles. A title could be a complete motion picture, a trailer or similar self-contained unit.