BackupHDDVD

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BackupHDDVD
BackupHDDVD-GUI 1.0
Stable release:	None _[+/-]
Preview release:	1.0.3 / January 25, 2007 _[+/-]
OS:	Windows
License:	None (Public domain)

BackupHDDVD is a small open source utility available in both command line and GUI-based versions which aids in the decryption of AACS copy-protected commercial HD DVD discs, intended to be used for backing up a film the user has purchased.

The software, written by an anonymous programmer using the handle Muslix64, is distributed in a manner which the author feels neither violates the Digital Millenium Copyright Act nor infringes on any copyrights. Largely an implementation of Java-based sample code made freely available by the entity which oversees AACS licensing, the utility by itself cannot be used to decrypt AACS-protected content.^[1] Users wanting to use the software to decrypt a protected disc's contents would need to have obtained either a disc's volume or title key separately, a task which BackupHDDVD's author provides no assistance with.^[2]^[3]

Newer, unofficial versions of BackupHDDVD include several with a basic Java Swing GUI and one with support for automatically obtaining volume keys from internet-based repositories. The original code has since been ported to C and C++ and used to create native x86 applications, some of which feature more sophisticated GUIs and multi-threading capability, among other features.

1 History
2 Background
3 Limitations
4 Reaction
5 Future
6 See also
7 Notes
8 External links

[edit] History

On December 18, 2006 a video which claimed to show BackupHDDVD being used to decrypt and copy the film Full Metal Jacket to a hard drive was uploaded to YouTube.^[4] This video has since been removed at the request of Warner Brothers Entertainment, citing copyrighted material being used without permission.^[5] Two days after the video was uploaded, the initial version of the utility along with its source code and documentation was uploaded to a file hosting service. A link to the file was then posted by the utility's creator on the forums of Doom9, a website devoted to DVD backup.

The utility's documentation, along with the forum post, contained little information as to how keys necessary for a successful decryption could be extracted. The author elaborated in another post, claiming that keys could be obtained by exploiting the necessity for them to be held in memory in order to facilitate playback in the PowerDVD software. Cyberlink, the company which sells PowerDVD, has since denied claims that their software could be used to obtain title keys.^[6]^[7]

On January 2, 2007 the author posted the 1.0 version of the BackupHDDVD utility, which included support for the decoding of disks using volume keys among several other new features.^[8]

Further development of BackupHDDVD was being hosted on SourceForge until the site received a DMCA takedown notice alleging a violation in late February. In compliance with the notice, the project was immediately removed.^[9]

[edit] Background

Main article: Advanced Access Content System

AACS LA assigns a series of 253 unique device keys to each licensed device manufacturer. When a protected disk is manufactured, a series of title keys is generated and the video content on the disc is encrypted using these keys. The title keys are stored on the disk and themselves encrypted with the disk's volume unique key. The volume unique key is calculated by all authorized devices using a media key, which is stored in encrypted form as a media key block on each disk. Authorized devices use one or more of the manufacturer's assigned device keys to decrypt the media key block, yielding the media key and enabling further decryption of the volume and title keys, and finally the content. If a device key is to be revoked, the media key blocks on all future disks are encrypted in a way which does not enable the revoked device to successfully decrypt the media key.^[10]^[11]

While a compromised device or media key could potentially be used to decrypt a large number of disks, these keys are easily be revoked by AACS LA, thereby limiting their usefulness as a long-term backup solution. Because the AACS revocation system works by preventing a given device or player from calculating a valid volume unique key, BackupHDDVD circumvents the system entirely by relying on high-level AACS keys (title, volume) being obtained separately by users. With these keys BackupHDDVD is able to decrypt the content directly, bypassing the key exchange and verification process.^[11]

A small text file included with BackupHDDVD hinted at the method Muslix had used to extract keys, but for several weeks following the utility's release no success using this key extraction technique was reported.^[12]^[13] In mid-January of 2007, a volume key was published by another member of the Doom9 forum along with an explanation of the technique used to obtain it. Other forum members quickly discovered keys for different titles and keys for many disks are now readily available on the internet.

[edit] Limitations

Early versions of BackupHDDVD were not able to properly decrypt disks which used the in-movie experience technology. A workaround has since been found and was automated in a later, unofficial version of BackupHDDVD. The utility cannot reproduce the navigation functions of HD DVD EVOBs. Arguably a limitation, users must have either obtained appropriate keys themselves or have found them elsewhere in order for most versions of BackupHDDVD to work.

[edit] Reaction

Reaction to the utility by Doom9 forum members, bloggers, and mainstream media has ranged from supportive to intensely hostile. By some, the circumvention of AACS was seen as as a reaffirmation of fair use.^[14] Others felt that the utility was no more than a piracy tool and would bring about group punishment against consumers in the form of player revocation. One article compared proponents of BackupHDDVD to terrorists.^[15] Initially, it was feared that the compromise of HD DVD's security would entice some studios into adopting the competing Blu-Ray format, but Blu-Ray's AACS implementation has since been circumvented using a similar method. Blu-Ray offers BD+, an additional layer of protection which could make the format more desirable to content creators, but BD+ has yet to be finalized or implemented in commercial releases. The consortium behind the HD DVD format and the studios delivering films on the format did not release an official statement beyond that they were investigating the utility's claims.^[16]

When the release of the tool was publicized, several articles claimed that AACS had been cracked.^[14]^[1]^[4] However no cryptographic weaknesses have yet been found in AES, the underlying cryptographic system of AACS. Keys are actually obtained through a side-channel attack.

Initially, there was speculation that the device key belonging to the version of PowerDVD then-believed to have been used by the utility's author to extract AACS keys would be added to revocation lists in future HD DVD titles, preventing the obtainment of valid keys for any disks not already released.^[14] Cyberlink has since claimed that PowerDVD could not have been used to obtain any of the needed keys.^[17] In the case of player revocation, users trying to view newly released films would be forced to upgrade the revoked HD DVD player software to a version in which the exploit is not possible, thereby theoretically limiting the exploit's damage to disks released before the flaw was found in the player software.^[18]^[19]

On January 24 AACS-LA issued a statement acknowledging that AACS had been compromised while urging software vendors to limit the availability of keys in memory. It remains unknown whether or not compromised players will have their keys revoked.^[20]

[edit] Future

Several unofficial versions of BackupHDDVD have been released, including ones with a GUI and the ability to locate keys on the internet or scan for them in memory automatically. HDDecrypter, a port of BackupHDDVD to C with a native Windows GUI is also available. This version supports multiple CPU threads and is purported to run faster that its Java counterparts.

Future versions or ports of BackupHDDVD may use the recently compromised AACS processing or media keys to enable one click backup for less experienced users,^[21]^[22] similar to the multitude of DVD backup tools available now.