Key Revocation

I wrote the CPPM section but I do have one question which I haven't been able to find the answer to: What happens if a hardware player has all its keys compromised? If the keys are revoked, new DVD-Audio discs would be rendered useless on that player, right? Do I have to get a firmware upgrade from the manufacturer? Has DRM turned my DVD-Audio player into a boat anchor? Rhobite 00:59, May 11, 2005 (UTC)

From the sound of it, if a key gets leaked, they simply stop supporting that key in new releases. So in theory all your existing music collection should continue to work. As far as firmware upgrades go, if the key was compromised by examining the old firmware it would probably be possible to extract the new key from the new firmware. It seems like releasing a new firmware would defeat the purpose of revoking keys …

Of course if the music industry did decide as a group to cut off thousands of consumers like this through no fault of their own, I'm sure they'd have a lot of law suits on their hands. For comparison, do you know of any DVD-Video players which have had their keys revoked? --James 05:03, 11 May 2005 (UTC)

I don't know if a DVD video player has ever had its key revoked. Tend to doubt it. I'm actually not too familiar with how CSS works, is that possible? I'm sure that someone has gotten their hands on a player key at some point, given the amount of DVD hacking that goes on. Since it's now trivial to decrypt CSS without a player key, it seems pointless for them to revoke keys at this point. All it would do is anger legitimate customers. Thanks for the answer, and you make a good point about firmware. Rhobite 07:24, May 11, 2005 (UTC)

With DVD Video, the content is encrypted with a disc key. This decryption key is then encrypted multiple times with different player keys and the cyphertext is stored on a special part of the disc. When you put a disc in your player, it decrypts the copy of the disc key that was encrypted with the player's key. It can then use the disc key to decrypt the content.

So when they talk of "revoking" a player's key they just mean that all new releases won't include a copy of the disc key encrypted with the player's key, which would mean that the player couldn't access the content. This is fairly similar system described for DVD Audio (the differences would be in the details of the encryption algorithms).

While CSS can be bypassed without a key, I think the analogy makes sense. Revoking a key in either case means that users of a particular device will be cut off from new content. If the general public realised that the music industry had this power, they might think twice about moving to the new format --James 03:46, 13 May 2005 (UTC)

"DVD-Audio discs employ a robust copy prevention mechanism, called Content Protection for Prerecorded Media (CPPM). CPPM, managed by the 4C Entity, prevents users from extracting audio to computers and portable media players.

Because DVD-Video's content-scrambling system (CSS) was quickly broken, DVD-Audio's developers sought a better method of blocking unauthorized duplications. They developed CPPM, which uses a media key block (MKB) to authenticate DVD-Audio players. In order to decrypt the audio, players must obtain a media key from the MKB, which also is encrypted. The player must use its own unique key to decrypt the MKB. If a DVD-Audio player's decryption key is compromised, that key can be rendered useless for decrypting future DVD-Audio discs. DVD-Audio discs also can utilize digital watermarking technology developed by the Verance Corporation."

Why is there no regional lockout, if I had developed CPPM I would have included a buit in regional lockout.144.139.89.254

Why? ROTFL! Why would you need regional lockouts? On DVD it was created to prevent people from outside USA to watch DVD movies before they hit local cinemas (as movies used to come from USA to Europe/Asia/Africa/Australia with a delay). Now - would you like to keep people in Europe waiting for new wonderful Britney Spears album, until it gets aired enough in USA?

That was the official reason. It was given away by the fact that regional coding was used on very old movies where sucha problem didn't exist. The real reason was to enforce price differentials between (mainly) the US and Europe.