DRM
Blu-ray uses complex DRM schemes to protect their discs from unauthorized copying. DRM has been a controversial subject since the DVD-era.
It's uncommon for commercial BD discs to be unencrypted or DRM-free, but it's up to the studio/developer if they want to publish a DRM-free disc*. Here are the DRM schemes that Blu-ray uses, each one is very unique and many individuals have been successful at cracking these.
Advanced Access Content System (AACS) is part of the Blu-ray DRM and it's an advanced and complex cryptic DRM that works by encrypting the content on the disc using a combination of symmetric and asymmetric key cryptography. The AACS cryptic system is overwhelmingly complex to explain, so I'll just cut it short. The system also employs digital signatures and a key revocation system to protect against unauthorized copying and distribution. It encrypts content under one or more title keys using the Advanced Encryption Standard (AES). To view a BD movie, the player must first decrypt the content on the disc. The decryption process is somewhat complex. The disc contains 4 items—the Media Key Block (MKB), the Volume ID, the Encrypted Title Keys, and the Encrypted Content. Think of the keys like the offline activation keys for DVD-ROM games, except the player is the one reading and activating them, not you.
AACS decryption process |
There have been several successful unauthorized cracks on it, including the very famous AACS encryption key controversy and PS3's compromised private key in 2007. AACS was created by a consortium of companies known as the AACS Licensing Authority (AACS LA), which includes major players in the entertainment and tech industry, such as Sony, Disney, Warner Bros. Intel, Microsoft, Panasonic, IBM, and Toshiba.
Each year new keys are regularly published which makes this a game of cat and mouse for hackers. Here's the famous encryption key, one of the most banned numbers back in the day: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0 .
A compromised player can still be used to view old discs, but not newer releases without encryption keys for a compromised player. If other players become cracked, revoking access could result in legitimate users of compromised players needing to upgrade or replace their software or firmware to be able to watch new discs.
Many individuals who wish to watch BD-ROMs on their computer typically use either Windows or Linux in conjunction with the VLC player. Although the VLC player can successfully play older physical BD-ROMS (or unencrypted ISO files) with the use of older keys, it is unable to play newer ones without obtaining new keys. The process of obtaining these new keys can prove to be quite challenging.
Volume IDs are unique identifiers or serial numbers that are stored on pressed pre-recorded discs with special hardware. They cannot be physically duplicated on consumers' recordable media. The point of this is to prevent simple bit-by-bit copies since the Volume ID is required (though not sufficient) for decoding content. On Blu-ray discs, the Volume ID is stored in the BD-ROM Mark.
Here's an example of a BD-ROM title with unique keys for the 2007 U.S. release of Robocop:
- CPS Unit Key (Title Key): 2CC3A36907E90C22E0B0B16856DB12AD121991EA
- Volume Unit Key: 98B02655F0A387AFDF636352875E0AB6
- Media Key: 5B90FE346BBF4CA41570D3F25CAD9B4A
AACS: Directory containing the Blu-ray's DRM AACS decryption files.
- MKB_RW.inf file: Read/Write Media Key Block.
- Content001.cer
- Content002.cer
- ContentHash001.tbl
- ContentHash002.tbl
- ContentRevocation.lst
- CPSUnit0000x.cci: CPS Unit Usage files.
- mcmf.xml
- MKB_RO.inf
- MKB_RW.inf
- SKBx.inf
- Unit_Key_RO.inf: AACS CPS Unit Key.
- DUPLICATE: Directory of duplicated AACS files.
See: List of AACS and Certificate files
You can find more info about ACCS at the Doom9 forums.
BD-ROM Mark is a serialization technology designed to protect against mass production piracy or the mass replication and sale of unauthorized copies of "pressed" Blu-ray Discs. Only licensed BD-ROM manufacturers have access to the equipment that can make these unique ROM Marks, thus allowing genuine BD-ROM media like movies and music to be identified. A unique and authentic digital signature is buried in the recording which can identify whether an individual disc was pressed by an authorized glass master.
High-bandwidth Digital Content Protection (HDCP) is a form of digital copy protection developed by Intel Corporation to prevent the copying of digital audio and video content as it travels across digital connections including HDMI. Any device associated with this type of DRM will often have an HDCP transmitter chip. It uses the Image Constraint Token (ICT). This protocol flag can cause the downsampling of high-definition video content on Blu-ray to DVD quality video and not be able to enjoy high-definition video from such discs. It faced several breaches including a 2010 master key leak.
BD+ is an additional but optional component of the Blu-ray DRM. It was developed by Cryptography Research Inc. and is based on their concept of Self-Protecting Digital Content (SPDC). It is owned by BD+ Technologies LLC. It uses a small virtual machine embedded in authorized players (unrelated to the HDMV/BDJ virtual machine). This DRM program which can be found inside the BDSVM directory of a BD+-protected disc is called "content code". The content code is executed on a virtual big endian DLX-like processor interfacing with 4MB of memory. This special processor supports 59 different instructions and a register set consisting of 32 general-purpose registers and three special-purpose registers for the instruction ο¬lter, the clock cycle counter, and the program counter. It may look simple, but the I/O between the virtual machine and the player is somewhat more complex. BD+ mainly works by adding errors to the video stream, not enough to make it unwatchable but enough to make it unpleasant to watch due to near-constant artifacts. There have been several reverse engineering attempts. Pre- 2019 20th Century Fox is a well-known user of BD+. Online forum, Doom9, discovered its technological specifications.
This is what happens when you rip a BD+ encrypted disc, turn it into an ISO, and try to play it. The BD+'s Java Xlet will detect that BD+ is not present and will prevent you from playing the disc. |
Cinavia is an analog watermarking and steganography system under development by Verance. In conjunction with the existing AACS DRM, the inclusion of Cinavia watermarking detection support became mandatory for all consumer Blu-ray Disc players in 2012. It is not required to have Cinavia DRM on the disc. Sony is a well-known user of Cinavia and there's been a decrease in releases from other studios in recent years.
You can mostly bypass most of these DRM schemes by just ripping the discs, modifying the directory files, decrypting the files, and compiling them into an ISO file thus defeating the purpose. However, it's better said than done, as it is not easy. But Cinavia and BD+ are the most difficult to crack.
Footnotes
*Only for BD-Rs or ISO files. It is mandatory for officially licensed BD-ROMs to have at least the minimum AACS DRM encryption.Sources
Author(s) : Γ Firestone
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