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3.13 What about copy protection? Will it be as weak as DVD’s CSS?

One major lesson that the movie studios have learnt with DVD is that copy protection is something they should take much more seriously, and they have done just that with the next generation formats, although some would argue that there are still inherent weaknesses in the copy protection scheme chosen.

BD and HD DVD will both use AACS (Advanced Access Content System) to protect its digital data. It is very similar to the flawed CSS, but the “key” difference is in how the various decryption keys are distributed. AES encryption is to be used.

There is actually a lot of computer science behind this, including binary trees, public/private keys and what have you, so I won’t bore you with it. Basically, a key is like the normal use of the word: a device used to unlock something. All BD/HD DVD players will have sets of keys that can unlock the data on BDs/HD DVDs. Studios have the power to revoke keys, or prevent certain keys from being used to unlock the data (e.g. keys that have been posted publicly after being hacked). So far so good (or bad), as this is how CSS functions as well, although it’s much harder for CSS to revoke keys because the keys are not structured properly like with AACS. Once a key is revoked, future discs will not carry this key, and players using this key will can no longer play back these new discs. The real intention here is not to disable players, but rather, stop ripping software that uses a set of “leaked” or “hacked” keys to rip disc. There might be a situation where a particular hardware player’s keys have all been leaked, and it will no longer be able to play back new discs.

Now, there have been a lot of discussion about AACS requiring an Internet connection to update keys and so forth, as well as checking for content authorisation (pay per play, etc…), but this is not really true of standalone hardware players, at least not right now (although by launch time, this may change, but it’s hard to imagine Internet connections being required by default, as this would wipe out a huge segment of the consumer base). Only software based players will require this key update, as it isn’t really practical to implement an “Internet connection” requirement for hardware. An Internet connection might be useful if say a hardware player’s keys have all been leaked and revoked, so a new set can be issued to the player through an Internet update. Although allowing updates through the Internet opens up a whole other set of issues, like security. Besides, this kind of copy protection can be implemented without an Internet connection, as in the case of SPDC (see below).

And as long as hackers don’t post keys publicly, or produce tools which randomly generates working keys, this scheme won’t even work to provide any protection. Even if there was a large scale leak, say if all the keys of a certain hardware manufacturer are leaked, a mass revocation may not work either because this would cause big problems for existing players of said manufacturer (assuming it is an “established” name), and a lot of headaches to a lot of normal consumers (but we’ll probably have to get used to this sooner or later). If a “minor” manufacturer has its keys revoked (e.g. a small manufacturer that did not pay licensing fees), then people who have purchased this player might be in a bit of bother, but this is probably one of the intended effects of this new copy protection scheme.

Worst yet, work on AACS has been delayed meaning that a delay on the launch dates of both Blu-ray and HD DVD hardware is a strong possibility.

AACS will also feature analogue copy protection (Macrovision), a way to force lower resolution video on analogue outputs, audio watermarks to prevent non watermarked audio from being played back, and the possibility of forcing digital output only (digital output is easier to “protect” than analogue output).

Unfortunately, the Blu-Ray Disc Association has deemed AACS insufficient, and has also added support for Self-Protecting Digital Content (SPDC), or what it calls BD+, and “ROM Mark”. Starting with ROM Mark, it is a unique and undetectable identifier produced in the manufacturing phase that prevents mass piracy. Fair enough. BD+ or SPDC, on the other hand, has come under some criticism. BD+ allows discs to carry title specific security logic, basically means that each disc can contain code that can be run on a BD player to allow or disallow playback (although the player’s behaviour is not modified, and will return to normal once the disc is ejected). Whether this code can be used maliciously by hackers (e.g. a pirated disc distributed on the Internet, which can shut down a player, forcing the user to reboot and quickly eject the malicious disc before the code is run again), we can only wait to find out.

More information on SPDC can be found here: http://www.cryptography.com/technology/spdc/

As expected, the various AACS versions that have been present on discs since release have all been cracked, sometimes before the discs themselves were available for general sale. BD+ implementations have been rumoured to be hacked too with the first commercial cracking solution to be available before the end of 2007.

In November 2005, HP has requested “Managed Copy” to be added to the Blu-ray specifications as a mandatory features. That request was subsequently approved, so now both Blu-ray and HD DVD will have mandatory managed copy support. Managed copy refers to the part of the copy protection system that allows backups to be made, as well as the content to be played back remotely (eg. over a home network). Microsoft has recently cited this to be one of the main reasons for its shift of support towards HD DVD, before Blu-ray made it mandatory as well.

3.14 So why have AACS if it might not work?

The very same reasons why the (non-working) CSS and (non-working) region protection schemes are still in place today.

Licensing is the cash cow of the 21st century. By only providing working keys to manufacturers that pay you licensing fees (at your own schedule/price), every time a device capable of playing BD/HD DVD is produced, a licensing fee is paid to the founders of the formats. This is also why there are two major and two minor high definition DVD formats, as opposed to just the one (see section 2.6).

So in actual fact, AACS is more of a licensing protection scheme, than a copy protection scheme, and any inconvenience consumers have to suffer as a result is much less important, in the eye of the format founders, than the billions in income that licensing will generate in the lifetime of these high definition formats.

3.15 What about region coding?

By all accounts, region coding for DVDs should be considered a failure, with region-free hacked firmware available for DVD-ROM drives, and remote control hacks for standalones (not to mention the great number of players manufactured to be region-free). However, this is not stopping region coding to be included in Blu-ray, even if the boundaries of the regions are different to that for DVDs.

An announcement in December 2005 specified the regions for Blu-ray discs:

• Region 1: North America, South America, East Asia except for China
• Region 2: Europe and Africa
• Region 3: China, Russia and other countries

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