Content providers mandate the presence of protection schemes at all times when the consumers want to access their wares. For the consumer, this entails:

1. Conditional access
2. Protected transmission
3. Protected distribution
4. Protected storage

Conditional access is applicable to cases where media travels over insecure channels (such as satellite or cable). This is implemented in STBs. Protected transmission is the path to the display device, and it is usually protected by HDCP (over HDMI) or Macrovision in legacy systems. Protected storage is encountered in broadcast content, with its copy flags to allow DVR archiving. Protected distribution is enabled by the DRM mechanism in Blu-rays / DVDs. In Blu-rays, this DRM scheme is called as AACS (Advanced Access Content System). AACS also provides for protected storage through the Managed Copy feature.

A Popular Webcomic's Take on DRM (c) xkcd

AACS uses 128-bit AES for encryption. Each Blu-ray player / device has a Device Key, while discs come with a Media Key Block (MKB). The shared key generated by using these two (Media Key) is used to decrypt the Title Key, which is then used to decrypt the audio/video data in the disc. AACS also has a revocation mechanism. The MKB in each disc has a Host Revocation List for software players and a Device Revocation List for hardware drives. For PC-based playback to be successful, both the player and the drive must not be on the revocation list.

In practice, key revocation is quite rare because device keys could be shared across an entire lineup, making it hard to pinpoint which particular device was compromised. AACS does provide some sequence keys to identify a particular device as compromised if one has access to multiple pirated copies of different discs from the same drive. In addition to the MKB-Media Key-Title Key combination, PC-based players also have support to generate a Shared Bus Key to encrypt the data inbetween the drive and the software player. This ensures that any snooped data can't be used to get to the original content on the disc. AACS also has a renewal process to prevent attacks similar to those carried out on CSS (with DVDs). The net result is that we are currently at AACS v30.

In addition to AACS, the BDA mandates a BD-ROM mark, which is a physical irregularity on the disc with a 128-bit VolumeID. Blu-ray players will not play back protected content without the VolumeID, as it is essential to the decryption process. Also, the VolumeID can't be generated by consumers (BD-Recorders don't have the capability to burn a VolumeID). The process is tied to the manufacturing facility (which can obtain a license only under strict security considerations). With a counterfeit Blu-ray, it is a simple matter of using the VolumeID to trace the place where the piracy took place.

Note that AACS is based solely on cryptography and, after having been compromised, has the possibility of revoking cryptographic keys as the only means of regaining its effectiveness. So far, this method has failed. This has tempted studios to move over to other forms of DRM such as BD+ and Sony Screen Pass.

It is mandatory for players to implement support for BD+, but not all Blu-rays need to be BD+ enabled. From a player's perspective, a Security Virtual Machine (SVM) needs to be implemented. Blu-rays with BD+ have special content code which are loaded by the SVM and executed during the playback process. The content code has full control over all the components involved in playback. It can alter menus and show on-screen messages if some security breach is detected in the player.

One of the most common BD+ implementations involves storing garbled video on the disc (i.e, after AACS decryption, certain segments of the video are distorted). The content code can implement a fix for the distorted video so that licensed playback is still problem free. For example, in the recently released Contagion Blu-ray, watching the disc with an old version of AnyDVD HD (which performs only AACS decryption, say) would result in heavily distorted video in various scenes. This is because the BD+ code to fix the video wasn't being executed by AnyDVD HD. Unlike AACS, technologies such as BD+ from Irdeto (responsible for the BD+ in the Contagion Blu-ray) and Sony Screen Pass continue to evolve with each new disc.

BD+ needs a SVM to be implemented, but note that the Blu-ray specifications already include a VM requirement for the BD-Java feature. This BD-J feature can also be used to implement structural protection schemes such as Sony DADC's Screen Pass. In this scheme, BD-J code on the disc actively looks for signs of protection being in place during playback. When the BD-J code finds that the protection features are missing (say, due to playing an unprotected copy, or when ripping tools are active in the background), playback is immediately stopped along with an on-screen message. DVDFab's blog has some more details on Screen Pass.

In addition to DRMs aimed at directly protecting content by encryption, the Blu-ray developers also considered some watermarking schemes. Watermarking doesn't actually encrypt the content, but places some non-discernible (to the naked eyes/ears) information in the audio / video tracks of the stream. By serving as a digital signature, it helps the player / analyzer identify the content status. In the next section, we will be talking in detail about Cinavia, the audio watermarking scheme from Verance. Thomson's NexGuard is a type of video watermarking scheme which works with the help of the BD+ SVM. The BD+ content code embeds some invisible information in the video track which contains details of the player / drive used to decrypt the stream. If the video gets out and becomes a 'pirated copy', the watermark can be analyzed to determine the player / drive responsible for the 'piracy'. BD+ code in subsequent Blu-rays can be used to blacklist the player / add it to a revocation list.

If you are interested in learning more about content protection in Blu-rays, I strongly suggest perusing Chapter 4 of Blu-ray Disc Demystified.

Introduction Cinavia: The Lowdown
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  • ganeshts - Thursday, March 22, 2012 - link

    We are really sorry for using DailyMotion, but the fact is that there is a risk of copyright infringement or similar action notice sent to YouTube from the studios (further considering the fact that what we have written in the piece is a bitter pill to swallow for them).

    YouTube's policy is 3 strikes and channel closed (no questions entertained). We can't take the risk of endangering the official YouTube channel for this purpose. However, I have taken the risk of uploading the videos on YouTube from another account after reading your comment. The links are here:

    Cinavia - Message Code 01 - The Wolfman.MTS :

    Cinavia - Message Code 03 - Battlefield LA - 20 Minutes Delay.ts :

    Cinavia - Message Code 03 - The Losers.MTS :
  • strangevil - Thursday, March 22, 2012 - link

    Cinavia is one of the main reasons why I stopped using my PS3 as a media playback device and have moved to the 360. I loved the UI of the PS3 as it lets you skip by looking at frames, but I bought my PS3 from the US and I live in UK, so every time I buy an official Blu-Ray, it doesn't work due to some stupid region restrictions. and for the ones that do work, I have to sit through 10-15 min of commercials and stupid warnings. So every time the warning pops up, I just plug my HDD out of the PS3 and pop it into my 360 and continue watching.

    I do what most other 'sane' people do... I pirate sh!t off the internet now. I tried to go the official route... I really tried, but you get treated like some garbage and have to sit through 10 min of studios flashing warnings that I'll go in jail if I pirate this even though I just legally bought it. Fu*k that sh!t.
  • cjs150 - Thursday, March 22, 2012 - link

    I am a legitimate customer. I buy Blu-rays. What I want to do is as follows:

    Rip down to NAS and watch them anywhere in house or portable player (Tablet, Laptop, PSP). That means I also need to have a SD version for some of the smaller screens.

    I do not want all the health warnings etc.

    Scrub regional coding

    Does that make me someone who is ripping off artists - no it does not.

    And finally the price is way too high in the UK
  • khory - Thursday, April 5, 2012 - link

    This describes my situation perfectly.
  • Willhouse - Thursday, March 22, 2012 - link

    Is this article about the downfalls of DRM or a gripe about how Blu-ray discs contain too many difficult-to-skip trailers? If there were no trailers, why would one bother stripping the DRM? Further, what does anybody care if there is DRM if it can simply be stripped off and the content then streamed? Is the argument that spending money on DRM ultimately raises the cost of Blu-ray discs.

    If so, just vote with your wallet. We're not talking about bread here folks.

    Ah well, I guess it's not my issue. I'm fine just renting Blu-rays.
  • fuzzymath10 - Thursday, March 22, 2012 - link

    Agreed. I don't think I've ever had a BD fail to play, and it takes seconds to skip the previews after pressing [>|] a handful of times (yes, a bit inconvenient but we have remote controls and it sure beats fast forwarding a VHS tape).

    The crux of the problem is "why get something for $X when you can get it for free?", where X>0. Of course more people would pay $2 vs $20, but not 10x as many, and there will still be plenty of folks who won't even pay $2 even if they could afford it.

    What I don't understand is that part of the argument is that the movies offered are "crappy", i.e. not worth paying for. Yet once it's free, it's worth wasting 2 hours watching/having on a hard disk. Pirated crap is still crap.

    Unfortunately, neither side is willing to give the other the benefit of a doubt.
  • colonelciller - Wednesday, March 28, 2012 - link

    the point is that DRM = Pain in the @ for the person who purchases the product

    DRM has ZERO impact on piracy and as such is an abject failure.
    What is the point of DRM since all it accomplishes is forcing legitimate folk to suffer and stare confusedly as their home entertainment system that is talking about firmware upgrades... I can guarantee you my parents haven't got a f'n clue what firmware is.
  • lundman - Thursday, March 22, 2012 - link

    I do occasionally buy Blurays, as it is currently my only way to support movies I like. I never play the actual retail disk though. One of my recent purchases was The Thing (2011) bluray, which comes with UltraViolet.

    Curiosity over-powering me, I thought to check out UltraViolet. I typed in the WWW address, and the numbers, and in less than a second, I was told that "UltraViolet is not available in your country". With no option to do anything else, but close the browser. The disk is not region protected either, just not for "my kind".

    Why is it *my* money is no good anyway? What is it about my cash that stinks so much :)

    I would even be happy with a system where I can just "donate" money to the movie makers directly, and only get a receipt back (for legal defence). I'll get the movies by other means...
  • otbricki - Friday, March 23, 2012 - link

    Netflix and Hulu are non-starters for anyone who cares enough about the fidelity of what they are watching to want a BD. The user experience is awful by comparison. The fidelity is crummy, sound is barely passable, and the content choices very limited.

    And guess what - the studios will keep it that way because they want to preserve their optical disk market.

    Throw monthly bandwidth caps on top of this, plus the fact that studios can (and do) pull content from streaming distribution you have a situation that clearly points to the fact that physical media are going to be with us for the forseeable future.

    Personally I'm fine with that because I want something that gives ME control over what I can watch. Not some studio or streaming service executive.
  • Sasparilla - Friday, March 23, 2012 - link

    "...and the content choices very limited. And guess what - the studios will keep it that way because they want to preserve their optical disk market."


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