DVD Copyright Protection Types

Region Code (RC)

DVD video discs may be encoded with a region code restricting the area of the world in which they can be played. Discs without region coding are called all region or region 0 discs.

The commercial DVD player specification requires that a player to be sold in a given place not play discs encoded for a different region (region 0 discs are not restricted). The purpose of this is to allow motion picture studios to control aspects of a release, including content, release date, and, especially, price, according to the region. Many DVD players are or can be modified to be region-free, allowing playback of all discs.

Region Code Enhanced (RCE)

Region Code Enhanced, also known as just "RCE" or "REA", this was a retroactive attempt to prevent the playing of one region's discs in another region, even if the disc was played in a region free player. The scheme was deployed on only a handful of discs. The disc contained the main programme material region coded as region 1. But it also contained a short video loop of a map of the world showing the regions, which was coded as region 2, 3, 4, 5, and 6. The idea was that when the disc was played in a non-region 1 player, the player would default to playing the material for its native region. This played the map, which was impossible to escape from, as the user controls were disabled.

However, it is easy to work around the scheme. A region-free player tries to play a disc using the last region that worked with the previously inserted disc. If it cannot play the disc, then it tries another region until one is found that works. RCE could thus be defeated by briefly playing a "normal" region 1 disc, and then inserting the RCE protected region 1 disc, which would now play. RCE caused a few problems with genuine region 1 players.

As of 2007, many "multi-region" DVD players defeat regional lockout and RCE by automatically identifying and matching a disc's region code and/or allowing the user to manually select a particular region. Some manufacturers of DVD players now freely supply information on how to disable regional lockout, and on some recent models, it appears to be disabled by default. Programs such as DVD Shrink are also capable of removing RCE protection, provided the operator knows what the region of the disk actually is. If the region is specified correctly, the copy will play in any region.

Analog Protection System (APS)

The Analog Protection System (APS), also known as Copyguard, is a DVD copy prevention system originally developed by Macrovision. Video tapes copied from DVDs encoded with APS become garbled and unwatchable. The process works by adding pulses to analog video signals to negatively impact the AGC circuit of a recording device. In digital devices changes to the analog video signal are created by a chip that converts the digital video to analog within the device. In DVD players trigger bits are created during DVD authoring to inform the APS that it should be applied to DVD players analog outputs or analog video outputs on a PC while playing back a protected DVD-Video disc. In set top boxes trigger bits are incorporated into Conditional Access Entitlement Control Messages (ECM) in the stream delivered to the STB. In VHS alterations to the analog video signal are added in a Macrovision-provided “processor box” used by duplicators.

APS can be also signaled digitally, in the CGMS-A bit field sent in the vertical blanking interval.

Content Scramble System (CSS)

Content Scramble System (CSS) is a Digital Rights Management (DRM) scheme used on almost all commercially produced DVD-Video discs. It utilizes a relatively weak, proprietary 40-bit stream cipher algorithm. The system was introduced around 1996 and has subsequently been compromised.

The CSS key sets are licensed by the DVD Copy Control Association to manufacturers who incorporate them into products such as DVD movie releases, drives & players. Most DVD players are equipped with a CSS Decryption module. CSS key is a collective term for authentication key, disc keys, player keys, title keys, secured disk key set, and/or encrypted title keys.

Some of the keys are stored on the lead-in area of the disk, which is generally only read by compliant drives. Keys can be passed from a DVD drive to a descrambler over a PC bus using a secure handshake protocol.

The purpose of CSS is twofold. First and foremost, it prevents byte-for-byte copies of an MPEG stream from being playable since such copies will not include the keys that are hidden on the lead-in area of the protected DVD disk. Second, it provides a reason for manufacturers to make compliant devices, since CSS scrambled disks will not play on noncompliant devices. Anyone wishing to build compliant devices must obtain a license, which contains the requirement that the rest of the copy-protection system be implemented.

In October 1999, Jon Lech Johansen and two people who remained anonymous reverse engineered the algorithm and DeCSS was released. The CSS algorithm was soon revealed to be easily susceptible to a brute force attack, apart from being an example of the trusted client problem. The weakness of the protection is primarily due to US government crypto-export regulations, which, at the time, forbade the export of cryptosystems employing keys in excess of 40 bits - a key length that had already been proven to be wholly inadequate in the face of increasing processing power by the time DVD was released (see DES). In addition, structural flaws in the algorithm reduced the effective key length to only around 16 bits, which could be brute-forced by a 450 MHz processor in less than a minute. As a 450 MHz processor was the stated minimum necessary to decompress a DVD-compliant MPEG-2 videostream in realtime, it effectively meant that any computer that could play a DVD could also crack one.

The CSS algorithm has been superseded by the Cryptomeria cipher in newer DRM schemes such as CPRM/CPPM, or by AES in the AACS copy-protection scheme used by HD DVD and Blu-ray Disc.

User Operation Prohibition (UOP)

The user operation prohibition (abbreviated UOP) is a form of digital rights management used on video DVD discs. Most DVD players prohibit the viewer from performing a large majority of actions during sections of a DVD that are protected or restricted by this feature, and will display the no symbol or a message to that effect if any of these actions are attempted. It was intended for copyright notices and the ubiquitous (at least in the United States) FBI warning. Some publishers run "protected" (i.e., "unskippable") commercials on their DVDs, which is widely seen by consumers as an abuse of the feature.

Some DVD players ignore the UOP flag, allowing the user full control over DVD playback. Virtually all players that are not special-purpose DVD player hardware (for example, a player program running on a general purpose computer) ignore the flag. There are also modchips available for some standard DVD players for the same purpose, although modifying a device may be illegal in some countries. The UOP flag can be removed in DVD ripper software such as: DVD Decrypter, DVD Shrink, AnyDVD, MacTheRipper and K9Copy.

Nevertheless, removing UOP does not always provide navigation function in the restricted parts of the DVD. This is because those parts are sometimes lacking the navigation commands which allow skipping to the menu or other parts of the DVD. This has become more common in recent titles, in order to circumvent the UOP disabling that many applications or DVD players offer.

UOPs are also used for usability purposes, especially in interactive DVD content. The Next Cell, Previous Cell, and Resume features are often disabled during menus, for instance, to avoid confusing or unintended jumps between content items. DVD Games like "Scene It?" are another example of complex DVD programming in which UOPs are said to ensure a more enjoyable user experience.

Sony ARccOS Protection

ARccOS is a copy-protection system developed by Sony used on some DVDs. Designed as an additional layer to be used in conjunction with Content Scramble System (CSS), the system deliberately creates corrupted sectors on the DVD, which cause copying software to produce errors. Allegedly, "Normal" DVD players do not read these sectors since they follow a set of instructions encoded on the disc telling them to skip them. However, many users with "normal" DVD players still report unplayable discs, and in some cases total lock-up of their players. Less sophisticated DVD copying programs do not follow these instructions and instead try to read every sector on the disk sequentially, including the bad ones.

RipIt for the Mac, Slysoft's AnyDVD, Fengtao's DVDFab Decrypter, RipIt4Me + DVD Decrypter, FixVTS, DVD43, MacTheRipper, along with VLC media player, GNU ddrescue, dd_rescue and MPlayer/MEncoder (for Linux) are usually able to overcome ARccOS.

ARccOS had reportedly been discontinued by Sony in February 2006. However, several high-profile releases since then have used it, including the region 1 DVDs for Hostel, Underworld: Evolution, Running With Scissors, and Casino Royale. Many DVDs by Disney, Touchstone Pictures, and The Weinstein Company also use ARccOS including Pirates of the Caribbean: Dead Man's Chest, Cars, Flightplan, The U.S. vs. John Lennon, Lucky Number Slevin, and Ratatouille. Hairspray appears to also be encumbered with ARccOS. Many DVD rental companies are now warning users that the Sony DVDs in question may not play on their machines.

Despite being promoted as "fully compatible with available DVD players and drives," movies with ARccOS cannot be played on some DVD players: Sony DVPCX995, Toshiba SD4700, Harman Kardon DVD101, Microsoft Xbox and others. Sony has announced a future firmware update for their players to fix this incompatibility issue. One revision of the ARccOS scheme used by Sony was incompatible with a higher number of players than average. Sony has offered to replace those discs for owners having problems; the replacement discs will have a newer version of ARccOS coding on them, which Sony claims is more compatible.

Analog CPS (Macrovision)

Videotape (analog) copying is prevented with a Macrovision 7.0 or similar circuit in every player. Macrovision may show up as stripes of color, distortion, rolling, black & white picture, and dark/light cycling. Macrovision creates problems for most TV/VCR combos (see 3.2.1) and some high-end equipment such as line doublers and video projectors.

The general term for a system that prevents taping is APS (Analog Protection System), also sometimes called copyguard. Computer video cards with composite or s-video (Y/C) output must also use APS. Macrovision changes the composite video and s-video output in two ways: the Colorstripe technique creates a rapidly modulated colorburst signal, and the AGC technique inserts pulses in the vertical blanking signal. This confuses the synchronization and automatic-recording-level circuitry in 95% of consumer VCRs. Unfortunately, it can degrade the picture, especially with old or nonstandard equipment. Macrovision was not present on analog component video output of early players, but is now required on component output (AGC only, since there is no burst in a component signal).

The discs themselves contain "trigger bits" telling the player whether or not to enable Macrovision AGC, with the optional addition of 2-line or 4-line Colorstripe. The triggers occur about twice a second, which allows fine control over what part of the video is protected. The producer of the disc decides what amount of copy protection to enable and then pays Macrovision royalties accordingly (several cents per disc). Just as with videotapes, some DVDs are Macrovision-protected and some aren't. (For a few Macrovision details see STMicroelectronics' NTSC/PAL video encoder datasheets at <www.st.com/stonline/books/>.)

Inexpensive devices can defeat Macrovision, although only a few work against the more recent Colorstripe feature. These devices go under names such as DVD Red, Video Clarifier, Image Stabilizer, Color Corrector, DVD Red, and CopyMaster. Or you can build your own. Some DVD players can be modified to turn off Macrovision output (see 6.4.2). Professional time-base correctors (TBCs) that regenerate line 21 also remove Macrovision. APS affects only video, not audio.

CGMS

Each disc contains information specifying if the contents can be copied. This is a serial copy generation management system (SCMS) designed to prevent initial copies or generational copies (copies of copies). The CGMS information is embedded in the outgoing video signal. For CGMS to work, the equipment making the copy must recognize and respect the CGMS information. The analog standard (CGMS-A) encodes the data on NTSC line 21 (in the XDS service) or line 20. CGMS-A is recognized by most digital camcorders and by some computer video capture cards (they will flash a message such as "recording inhibited"). Professional time-base correctors (TBCs) that regenerate lines 20 and 21 will remove CGMS-A information from an analog signal. The digital standard (CGMS-D) is included in DTCP and HDMI for digital connections such as IEEE 1394/FireWire. See subsections 6 and 7 below.

Content Protection for Prerecorded Media (CPPM)

CPPM is used only for DVD-Audio. It was developed as an improvement on CSS. Keys are stored in the lead-in area, but unlike CSS no title keys are placed in the sector headers. Each volume has a 56-bit album identifier, similar to a CSS disc key, stored in the control area. Each disc contains a media key block, stored in a file in the clear on the disc. The media key block data is logically ordered in rows and columns that are used during the authentication process to generate a decryption key from a specific set of player keys (device keys). As with CSS, the media key block can be updated to revoke the use of compromised player keys. If the device key is revoked, the media key block processing step will result in an invalid key value. The authentication mechanism is the same as for CSS, so no changes are required to existing drives. A disc may contain both CSS and CPPM content if it is a hybrid DVD-Video/DVD-Audio disc.

Content Protection for Recordable Media (CPRM)

CPRM is a mechanism that ties a recording to the media on which it is recorded. It is supported by some DVD recorders, but not by many DVD players. Each blank recordable DVD has a unique 64-bit media ID etched in the BCA (see 3.11). When protected content is recorded onto the disc, it can be encrypted with a 56-bit C2 (Cryptomeria) cipher derived from the media ID. During playback, the ID is read from the BCA and used to generate a key to decrypt the contents of the disc. If the contents of the disc are copied to other media, the ID will be absent or wrong and the data will not be decryptable.

Digital Copy Protection System (DCPS)

In order to provide digital connections between components without allowing perfect digital copies, five digital copy protection systems were proposed to the CEA. The frontrunner is DTCP (digital transmission content protection), which focuses on IEEE 1394/FireWire but can be applied to other protocols. The draft proposal (called 5C, for the five companies that developed it) was made by Intel, Sony, Hitachi, Matsushita, and Toshiba in February 1998. Sony released a DTCP chip in mid 1999. Under DTCP, devices that are digitally connected, such as a DVD player and a digital TV or a digital VCR, exchange keys and authentication certificates to establish a secure channel. The DVD player encrypts the encoded audio/video signal as it sends it to the receiving device, which must decrypt it. This keeps other connected but unauthenticated devices from stealing the signal. No encryption is needed for content that is not copy protected. Security can be "renewed" by new content (such as new discs or new broadcasts) and new devices that carry updated keys and revocation lists (to identify unauthorized or compromised devices). A competing proposal, XCA (extended conditional access), from Zenith and Thomson, is similar to DTCP but can work with one-way digital interfaces (such as the EIA-762 RF remodulator standard) and uses smart cards for renewable security. Other proposals have been made by MRJ Technology, NDS, and Philips. In all five proposals, content is marked with CGMS-style flags of "copy freely", "copy once," "don't copy," and sometimes "no more copies". Digital devices that do nothing more than reproduce audio and video will be able to receive all data (as long as they can authenticate that they are playback-only devices). Digital recording devices are only able to receive data that is marked as copyable, and they must change the flag to "don't copy" or "no more copies" if the source is marked "copy once." DCPSes are designed for the next generation of digital TVs, digital receivers, and digital video recorders. They require new DVD players with digital connectors (such as those on DV equipment). These new products began to appear in 2003. Since the encryption is done by the player, no changes are needed to existing discs.

High-Bandwidth Digital Content Protection (HDCP, DVI, and HDMI)

HDCP is similar to DTCP, but it was designed for digital video monitor interfaces. In 1998, the Digital Display Working Group (DDWG) was formed to create a universal interface standard between computers and displays to replace the analog VGA connection standard. The resulting Digital Visual Interface (DVI) specification, released in April 1999, was based on Silicon Image's PanelLink technology, which at 4.95 Gbps can support 1600×1200 (UXGA) resolution, which covers all the HDTV resolutions. Intel proposed HDCP as a security component for DVI. A new connection standard called HDMI combines DVI and HDCP. DVD players with DVI or HDMI digital video output appeared in spring 2003. Many new HDTV displays are likely to have both IEEE 1394 and HDMI connections.

HDCP provides authentication, encryption, and revocation. Specialized circuitry in the playback device and in the display monitor encrypts video data before it is sent over the link. When an HDMI output senses that the connected monitor does not support HDCP, it lowers the image quality of protected content. The HDCP key exchange process verifies that a receiving device is authorized to display or record video. It uses an array of forty 56-bit secret device keys and a 40-bit key selection vector -- all supplied by the HDCP licensing entity. If the security of a display device is compromised, its key selection vector is placed on the revocation list. The host device has the responsibility of maintaining the revocation list, which is updated by system renewability messages (SRMs) carried by newer devices and by video content. Once the authority of the receiving device has been established, the video is encrypted by an exclusive-or operation with a stream cipher generated from keys exchanged during the authentication process. If a display device with no decryption ability attempts to display encrypted content, it appears as random noise.

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