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the blu-ray is encrypted and the player requires a key to decrypt it if you want your blu-ray player to be able to read blu-ray disks you sign a contract that

the blu-ray is encrypted and the player requires a key to decrypt it if you want your blu-ray player to be able to read blu-ray disks you sign a contract that says you will respect the revocation list if you change your mind later: your player key will be revoked and new blu-rays won't play on your device (it's actually more sophisticated than this... they can block specific players too)

tshaddox 3y ago
That doesn't quite sound right to me. I don't think a new Blu-ray disc could be released that continues to be readable by some old readers but is no longer readable by other old readers.
- blibble 3y ago
  > I don't think a new Blu-ray disc could be released that continues to be readable by some old readers but is no longer readable by other old readers. you can obviously think whatever you want, but you'd be completely wrong DVD supported this 20 years ago, blu-ray's system is far more sophisticated and can even block individual players The approach of AACS provisions each individual player with a unique set of decryption keys which are used in a broadcast encryption scheme. This approach allows licensors to "revoke" individual players, or more specifically, the decryption keys associated with the player. Thus, if a given player's keys are compromised and published, the AACS LA can simply revoke those keys in future content, making the keys/player useless for decrypting new titles. (from https://en.wikipedia.org/wiki/Advanced_Access_Content_System https://en.wikipedia.org/wiki/Advanced_Access_Content_System) the spec also supports a persistent CRL so a new disk can also stop your old disks from working
  - AnthonyMouse 3y ago
    The problem, of course, being that some players will just read the raw bytes from the disc without even attempting to decrypt them, and then anyone can decrypt them in software using any other keys even if the player used to read the disc was revoked. Then every time another player's keys are published it allows anyone to use the older player to read discs using the newer player's leaked keys. And some players are cracked but the keys aren't published, instead they use them to extract the disc key for every new disc and then publish all the disc keys, which can be used in the same way without revealing which player was cracked.
  - tshaddox 3y ago
    For CSS and AACS, yes. I was referring specifically to HDCP, which involves negotiation between source and sink devices and AFAIK has nothing like broadcast encryption.

tshaddox 3y ago

That doesn't quite sound right to me. I don't think a new Blu-ray disc could be released that continues to be readable by some old readers but is no longer readable by other old readers.

blibble 3y ago
> I don't think a new Blu-ray disc could be released that continues to be readable by some old readers but is no longer readable by other old readers. you can obviously think whatever you want, but you'd be completely wrong DVD supported this 20 years ago, blu-ray's system is far more sophisticated and can even block individual players The approach of AACS provisions each individual player with a unique set of decryption keys which are used in a broadcast encryption scheme. This approach allows licensors to "revoke" individual players, or more specifically, the decryption keys associated with the player. Thus, if a given player's keys are compromised and published, the AACS LA can simply revoke those keys in future content, making the keys/player useless for decrypting new titles. (from https://en.wikipedia.org/wiki/Advanced_Access_Content_System https://en.wikipedia.org/wiki/Advanced_Access_Content_System) the spec also supports a persistent CRL so a new disk can also stop your old disks from working
- AnthonyMouse 3y ago
  The problem, of course, being that some players will just read the raw bytes from the disc without even attempting to decrypt them, and then anyone can decrypt them in software using any other keys even if the player used to read the disc was revoked. Then every time another player's keys are published it allows anyone to use the older player to read discs using the newer player's leaked keys. And some players are cracked but the keys aren't published, instead they use them to extract the disc key for every new disc and then publish all the disc keys, which can be used in the same way without revealing which player was cracked.
- tshaddox 3y ago
  For CSS and AACS, yes. I was referring specifically to HDCP, which involves negotiation between source and sink devices and AFAIK has nothing like broadcast encryption.