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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  • haukionkannel - Wednesday, March 21, 2012 - link

    Good point!

    I allso hate those extras and I have paid for that movie! And if pirate can get the movie without those "extra" features... I am really pissed off...
    I allso byumy movies but every time I watch again those extra warning screens I wonder why... I want that movies studio gets my money, thats ok, but I don't want to give up my sanity, by watching all those extras
    Reply
  • Swirlser - Wednesday, March 21, 2012 - link

    http://www.lauexplorer.com/2010/03/10/products/leg...

    Want me to cough-up for that TV series Im watching atm? Extremely simply answer! Match the convenience level of the above pic (link) coupled with a sane price tag.

    No fancy tech or laws required.

    This coming from a pretty straight laced fellow, who pays his taxes and bills and I think Ive 2 audio tracks out of many, many thousands that were pirated (before the preview extension I pirated to see if I liked, then actually bought it legitimately if I did, deleted if I didnt - the 2 which I didnt pay for are from a certain artist - initials JB >.< - who I couldnt live with myself if I gave him a cent, hes got a *stupid* amount of money already)

    Aside from a certain percent of people who simply refuse to pay for anything they can possibly get for free, I think the vast majority of people would fall into line if you price it sensibly and make it as simple and convenient as possible. Music is there now, films arent far off (speaking more so of streaming, but even physical BDs are coming to a more reasonable price level.) My main beef is TV, the time gap between regions (US content specifically) to view my fav shows is immense and you just cant get up to the minute anything via paid for services (in Ireland), if you could, I'd be all over it.
    Reply
  • jnmfox - Wednesday, March 21, 2012 - link

    LOL, great minds think alike! Reply
  • Swirlser - Wednesday, March 21, 2012 - link

    Lol! Yeah, thats exactly what I thought of when I read this article.

    Such a shame, the time and money wasted (in vain!) trying to get a small percent and ultimately punishing the legitimate customer is all thats going on here.

    Instead, understand there is a percent (a greater percent I'd be willing to bet good money on) of people who don't enjoy getting shafted and paying crazy money for a film or watch things weeks (or more) after they have been aired else-where and then go about getting it by whatever means necessary, most know a friend or a friend-of-a-friend that has damn near everything and will stream it to you for nothing.

    If Netflix (AFAIK in the US have a better selection - I'm hoping it advances here) or Lovefilm or whoever else runs services here actually had the content (rather than largely ancient stuff which accounts for the bulk on offer currently), I'd subscribe!

    Sadly I know only too well that there are layers of BS at work preventing this to happen, rather than just a greedy A-hole. But the platform is there, the devices are there, the infrastructure is widely available (needs to be expanded further), but it can be done. The obstacles lie entirely with some snotty out of touch publishers and advertisers who seem hell bent on throwing good money after bad. They wont win!
    Reply
  • ssj3gohan - Wednesday, March 21, 2012 - link

    I haven't viewed a single DRM-protected video in probably over 6 years (I became so incredibly annoyed with VHS/DVD and television advertising/unskippable content and all that) but since my last endeavor with that things have only seem to have gotten worse. I honestly didn't know that there were things like regional restrictions (what the hell?) and the necessity for approved screens (WHAT THE HELL?!?!) to view certain copyright. It just seems really, really out of this world. Cinavia really just seems to be a logical step on the way. I am already calling it: somewhere in a future BD specification they will require physical bd stores to knife any and every customer who buys protected content. The revision after that ensures that this indeed results in death. What the hell are those consumers thinking, buying our stuff? We don't want that, go away! RRRAAaaAAaarghhh!

    If I want to see something, I type it into youtube and I usually get a good idea of the content. I can skip advertising within a couple of seconds, get HD resolution and if I like it, I can subsequently download it legally or, if it's not available in my region for some arbitrary reason (this really seems to be much the norm these days) I can pirate it. That way I don't waste any time on frankly something I am not entertained by in the slightest, I have full control over my own purchases and my viewing behaviour. Just like I had with earlier VHS releases (which had maybe 2 minutes of pre-roll stuff) and subscription VOD services like a lot of starcraft (or in general: gaming-related) stuff.
    Reply
  • Sanctusx2 - Wednesday, March 21, 2012 - link

    Matroskas, really? I don't understand why the article seems to imply this is the dominant format. MKV is mainly the format you only see with anime, where subtitles and multiple audio streams are much more relevant. The broader video scene has favored avi containers with h.264/xvid encoding for years for everything from cams to blu-ray rips.

    Everytime I read MKV in this article I had to cringe and question the credibility of the author.
    Reply
  • Spivonious - Wednesday, March 21, 2012 - link

    Why would I sacrifice quality when ripping (which is what h.264/xvid is doing)?

    MKV is perfect if I want to grab just the movie and the main audio track from the disc. No quality loss, and smaller than if I did an ISO or folder structure rip.

    DRM hurts nobody except legitimate consumers. As this article explains, any DRM the providers can come up with is cracked within two weeks.

    The music industry is finally coming around to selling DRM-free tracks. Why can't the movie studios do the same?
    Reply
  • ganeshts - Wednesday, March 21, 2012 - link

    High definition stuff in AVI? The only ones I have seen are the XViD encodes of Blu-rays and they are very rare compared to H.264 in MKVs.. I will leave it to the other readers to judge for themselves, but my research indicates that MKV is the most common container for high definition stuff and AVIs are suited for standard definition TV recordings and DVDRips / BDRips of 1 and 2CD sizes. Reply
  • iamezza - Wednesday, March 21, 2012 - link

    mkv is definitely the most dominant format for HD content.
    avi is the most dominant for SD content.
    Reply
  • Iketh - Wednesday, March 21, 2012 - link

    MKV is the future... you sir, are outdated Reply

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