DVD and Blu-ray Copy Protection
This document discusses the technical and legal issues surrounding copy protection on DVD and Blu-ray discs. We are providing this information as a service and as a means of sharing our technical and legal knowledge. Nothing in this document, however, should be considered to be actual legal advice. It is for informational purposes only.
Introduction to DVD and Blu-ray Copy Protection
Commercial pre-recorded DVD and Blu-ray discs are typically protected with some form of copy protection. There is, however, a great deal of confusion about how these copy protection schemes work and what kind of legal rights consumers may have. The purpose of this document is to clarify both the technical and the legal aspects of copy protection for DVD and Blu-ray discs.
DVD Copy Protection
There are three types of copy protection that are used on commercial pre-recorded DVD discs. These are Analog Protection System (APS) scrambling, Content Scramble System (CSS) encryption, and a system involving corrupted disc structure. Recordable DVD discs are also sometimes copy protected using Content Protection for Recordable Media (CPRM) encryption. We will go over each of these schemes in turn.
Analog Protection System (Macrovision)
The Analog Protection System, popularly known as Macrovision after the company that developed it, is a protection system that is applied to the composite analog video signal coming out of DVD players. By manipulating the signal level of the composite video, Macrovision fools the automatic gain control of most video recorders resulting in annoying shifts in color and brightness in the recorded video.
Macrovision can be defeated by passing the composite video signal through a hardware device that restores the proper video signal levels. With the demise of analog video and the widespread availability of digital decryption tools, Macrovision protection has largely become irrelevant. Macrovision Corporation renamed itself Rovi and now promotes other copy protection technologies.
Content Scramble System (CSS) Encryption
CSS is an encryption system that is the main copy protection scheme used on pre-recorded DVD discs. CSS utilizes a proprietary 40-bit cipher that is used to encrypt the data stored on the DVD disc. When the disc is inserted into a player or computer, a series of "authentication" handshake key exchanges occur between the DVD drive and the player software. At the end of the "authentication" process, the drive allows access to the encrypted DVD data and the player can use the key it has obtained to decrypt the DVD data and play the disc.
Many DVD drives have a tendency to completely lock out access to an encrypted disc until the drive has been "authenticated". In addition, many DVD drives will refuse to complete the "authentication" process and provide a decryption key if the disc and drive are not from the same region. Both of these situations can cause strange behavior and odd error messages on computer systems.
- Content Scramble System (Wikipedia)
- Crytanalysis of the CSS cipher by Frank A. Stevenson
- CSS Information Page by Dr. David S. Touretzky
DVD Disc Corruption
After the CSS protection system was cracked, the movie industry looked for a alternative copy protection scheme that would be compatible with the large number of existing DVD players in the marketplace.
Borrowing a (failed) technique from the video game industry, they settled on a scheme in which portions of DVD discs are deliberately mangled in such a way as to render them unreadable. When the disc is played, these corrupted areas of the disc are skipped. When the disc is copied sequentially, however, these corrupted areas cause the drive to hang up and get stuck.
This copy protection scheme has been marketed under a variety of names, including ARccOS (by Sony), RipGuard (by Rovi), Disney X (by Disney), etc. For cost and convenience reasons, it is not applied to all commercial DVD releases.
DVD disc corruption is a nuisance, but most of the more sophisticated DVD copy tools can handle it. Some tools maintain a database of corrupted areas on DVD discs that contain corruption, while other tools attempt to analyze the DVD structure to find areas of the disc that are never accessed.
- ARccOS Protection (Wikipedia)
- Rovi Corporation, Content Protection (Wikipedia)
- DVD Video Discs, Encrypted or Corrupted?
Content Protection for Recordable Media (CPRM)
CPRM is a copy protection scheme that is used for Secure Digital (SD) memory cards and recordable DVD discs, including DVD-R, DVD+R, DVD-RW, and DVD+RW discs. Special CPRM-compatible recordable media are required, with each disc including a unique Media ID inscribed as a bar code in the inner hub area.
When a CPRM-compliant recorder detects compatible media, it uses the unique Media ID on the disc to encrypt the data it records to the disc. The recorder will also write a block of data called the Media Key Block (MKB) which is used to decrypt the disc. If the disc is copied, the Media ID on the new disc will be different and the recorded data will not decrypt correctly.
CPRM protection has largely been restricted to the Japanese market, where it is called "Copy Guard" and used to protect broadcast HDTV programs that include a special Copy Guard flag. Japanese-market recorders that record that program are required to include CPRM protection. Depending on the Copy Guard instructions, a limited number of copies of the CPRM disc data may be permitted.
The CPRM system involves something called the Cryptomeria or C2 cipher, which uses a 56-bit key and 64 byte blocks. The majority of the cipher is published openly, but a proprietary "S-box" portion of the cipher is provided only to CPRM licensees. The licensing organization is called the 4C Entity, whose membership includes IBM, Intel, Microsoft, Panasonic and Toshiba.
A cryptanalysis of the C2 cipher was published in 2009 and CPRM was partially cracked in late 2009 using a crowd-sourced brute-force attack, and a set of decryption tools for Windows based on the key from this crack was distributed over the internet.
- Content Protection for Recordable Media (Wikipedia)
- CPRM base specification (PDF)
- Cryptanalysis of the C2 cipher by Julia Borghof et al. (PDF)
- Removing CPRM using relCPRM (in Japanese)
Blu-ray Disc Copy Protection
The Blu-ray Disc standard mandates that all pre-recorded discs be protected by a copy-protection scheme. The copy protection used on pre-recorded discs is in practice only applied to the stream files and not to any other files that make up the format. There are several distinct levels of copy protection for pre-recorded discs.
The first level of copy protection applied to pre-recorded discs is the Advanced Access Content System (AACS) developed by the AACS Licensing Administrator, a consortium of companies including Disney, Intel, Microsoft, Panasonic, Warner Bros., IBM, Toshiba and Sony. It is based on Advanced Encryption Standard (AES), a robust 128-bit key encryption system developed by the US government.
AACS includes a system by which the keys assigned to a particular player can be "revoked" for future Blu-ray disc releases if it is determined that those keys have been compromised. When a newer Blu-ray disc is inserted into an older drive, the drive is required to check the version of the "Media Key Block" (MKB) on the disc and, if it is newer than the one the drive has internally, to copy over to permanent non-volatile memory the newer MKB. Thus playing newer discs propagates the revoked key lists out to all drives.
AACS was broken beginning in late 2006, and numerous AACS decryption programs are available online. The key revocation system ensures, however, that the AACS licensing organization and the hacker community are constantly playing a cat-and-mouse game.
BD+ is a second level of copy protection that is optional for pre-recorded Blu-ray discs. After the stream files are encrypted using AACS encryption, they are further mangled randomly with instructions on how to repair the mangled files stored on the disc as special BD+ instructions. These instructions run in something called a "BD+ virtual machine", special software that Blu-ray players are required to include. The virtual machine on the player runs the BD+ code on the disc and retrieves something called the "Fix-up Table" (FUT) to repair all the BD+ mangled regions on the disc.
BD+ was broken in 2008 by reverse-engineering the BD+ virtual machine. Each new BD+ Blu-ray disc release brings new twists in the virtual machine programs, each of which are again reverse-engineered by the hacker community. Just as with AACS, BD+ has become a cat-and-mouse game.
Currently, the BD+ system is owned by Irdeto, which bought it from Rovi Corporation in 2011.
Cinavia, developed by a company called Verance, is a newer level of copy protection that is optional on Blu-ray discs. The system involves "steganography" or watermarking, in which a special encrypted data signal is hidden within a single audio channel in an audio track. Verance claims the Cinavia signal is inaudible, and that the signal can survive audio compression and recompression.
When a player with Cinavia support detects a Cinavia signal on a Blu-ray disc, it can verify whether playback should be allowed. The player can display one of four possible messages known as "Cinavia message codes". The most commonly viewed messages are (1) "Playback Stopped" and (3) "Audio Muted". Message (1) is supposed to stop distribution of "camcorder" recordings of first-run movies from theaters if the theaters include a Cinavia signal in the movie soundtrack. Message (3) is supposed to stop unencrypted ripped copies of movies. There is apparently no exception for consumer backup copies.
Cinavia detection became a requirement for Blu-ray players beginning in 2012. To date, the only major studio that appears to be using Cinavia is Sony Pictures, and that is not even for all releases. Most of the major studios seem to be hesitant about including Cinavia protection, perhaps because the system involves expensive royalty fees, or perhaps for fear of angering customers.
Customers have a reason to be angry, because unlike all the other protection schemes on Blu-ray and DVD discs, Cinavia protection is destructive and permanent. Audio tracks that include Cinavia have been deliberately damaged, and the damaged audio is present both for legimitate customers and for the supposed content pirates. When the audio track is protected with Cinavia, legitimate customers do not get the pristine audio content they paid for on their Blu-ray discs.
The Cinavia encoding system was broken in 2013, but it has proven very difficult to remove the protection and restore the protected audio track back to its original state. One ripper tool company claims to be able to do this, but their success rate is apparently spotty. Other ripper tool companies have figured out schemes to disable or fool Cinavia detection in players. Some stand-alone players (e.g. Panasonic, Oppo) have firmware patches available to remove Cinavia detection.
- Cinavia (Wikipedia)
- Cinavia technology summary (Cinavia official site)
- Ultimate Cinavia Guide (myce)
- DVD-Ranger CinEx Cinavia Removal Whitepaper (PDF, Pixbyte DVD-Ranger)
Removing DVD and Blu-ray Copy Protection
The removal of copy-protection schemes from DVD and Blu-ray discs involves both legal issues and technical issues. On the legal side, efforts by the movie industry have made defeating copy protection a bit of a legal gray area. On the technical side, ripping programs are widely available, but efforts by the movie industry have made them into essentially subscription services. Each update to the copy protection schemes results in an update to the ripper programs.
In the US, a controversial law called the Digital Millennium Copyright Act (DMCA) has criminalized any attempt to decrypt protected content, even if the consumer has legally purchased the content. The problem is that this "anti-circumvention" provision of the DMCA conflicts with the long-standing "Fair Use" provision of copyright law. The courts have yet to rule on which portion of the law should prevail.
Because of this legal uncertainly, it is legally risky for any software company to market DVD or Blu-ray disc-related tools that include decryption capabilities. Commercial software companies that attempt to sell decryption or ripping products have been threatened with legal action, or in some cases taken to court. The same situation holds whether in the US, Europe, or Japan after great efforts by the movie industry to put in place similar laws to the DMCA in the US. The companies with the most success in avoiding legal action have been those based in countries with weak copyright protection laws, including China, Russia, Antigua, and Panama.
Many believe that removing DVD and Blu-ray disc encryption is reasonable and lawful because they feel the "fair use" provision of copyright law should override any provisions against removing encryption. In fact, to our knowledge no individual has ever been prosecuted for removing DVD or Blu-ray disc copy protection.
In 2010, the US Librarian of Congress specified several exemptions from the anti-circumvention provision of the DMCA law. These are described as:
- The incorporation of short portions of motion pictures into new works for the purpose of criticism or comment
- Educational uses by college and university professors and by college and university film and media studies students
- Documentary filmmaking
- Noncommercial videos
Individuals that meet these exemptions are permitted to circumvent the copy protection on DVD discs. Whether this applies in the case of Blu-ray discs is unclear. In most aspects, however, these exemptions follow the standard "fair use" provisions of traditional copyright law.
Copy Protection Removal Tools
For those with the legal rights to use them, there are a number of DVD and Blu-ray copy-protection removal tools available. Here we will divide them into two broad classes, ripping tools and on-the-fly tools.
Ripping tools were the first type of copy-protection removal utilities to appear. The idea is that the ripping tool will first determine the appropriate keys to use to decode the protected data, then the tool will make a clean copy of the entire disc with all the copy protection removed. At that point the user can make a backup copy of the disc on recordable media, play the unprotected content without the original disc present, extract out content, modify the disc data, etc.
The ripping process requires allocating a large chunk of free space on the user hard drive in order to save the unprotected data, up to 9 GB for DVDs and up to 50 GB for Blu-ray discs. Depending on the level of protection on the original disc, the ripping process can take upwards of 20-30 minutes for a DVD or 1-2 hours for a Blu-ray disc.
For Windows systems, popular DVD ripping tools include DVDDecrypter, DVDShrink, DVD Cloner, and DVDFab. Popular Blu-ray ripping tools include MakeMKV and DVDFab Blu-ray Copy. The gold standard decryption tool is, however, the on-the-fly tool AnyDVD HD (see below).
In order to use MakeMKV as a ripping tool, users should follow the MakeMKV FAQ and select "Backup" from the File menu or click Backup on the toolbar. Make sure that "decrypt video files" is selected in the next dialog.
It is important to note that some DVD ripper tools can handle removal of disc corruption and "Region Control Enhanced" (RCE) protection, while others cannot. Likewise, some Blu-ray ripper tools can remove BD+ protection while others cannot.
On-the-fly tools work by installing a background process to monitor the any discs that are mounted on the user’s computer. When the user inserts a copy-protected disc, the on-the-fly tool will intercept the mounting of the disc. It will first perform an analysis of the disc to determine all details of the copy protection (e.g. decryption keys, corrupted sectors, etc.). Then, the tool will mount the disc in a special way so that it appears to the operating system as an unprotected disc.
Any time the operating system or any application reads data off of the disc, the on-the-fly tool will first remove any copy-protection and before proceeding to deliver the unprotected data. For all intents and purposes, the disc appears to be unprotected. The user may play the disc, copy all or part of it, or manipulate the disc in any way without worrying about the copy protection.
Since it is not necessary to rip the entire disc, no block of hard drive space is required for the unprotected data and no initial ripping time is necessary. The user may begin using the unprotected disc data immediately. All the copy-protection removal takes place gradually and on-the-fly as the data are read off of the protected disc.
For Macintosh systems, the best on-the-fly DVD tool is Fairmount. The Fairmount source code was uploaded to GitHub and slightly modified. There are no on-the-fly Blu-ray tools currently available for the Macintosh.
For Windows systems, the best on-the-fly tool for both DVD and Blu-ray discs is AnyDVD HD.