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...when DRM-protected material is encrypted using the AES cipher, which there are currently no efficiently computable cracks for?

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    Usually the DRM-protected files are not traded. A copy of the DRM file is made, then the copy protection is removed from the copy. That's the way since copy protection exists. – ott-- Dec 22 '15 at 21:52
  • I don't understand what you're saying. How can you remove AES encryption from a copy of a file? – Zen Hacker Dec 22 '15 at 21:55
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    It's easy enough to exploit 'the analog hole'. Because the signal has to be converted to analog for your ears to enjoy it, that analog signal can be copied and re-digitized without the use of DRM. It won't be a 100% high fidelity copy, but it's generally good enough for people already used to listening to MP3 compressed digital music on smart phones through cheap earbuds. – John Deters Dec 23 '15 at 0:08
  • There are likely already multiple copies of DRM free music available from different sources. iTunes has mostly DRM free content and people can still easily rip CDs. – Dave Dec 23 '15 at 19:56
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when DRM-protected material is encrypted using the AES cipher

DRM solutions try to allow playback of the media, while not allowing to create a copy. To make playback possible with current hardware the media either has to decrypted at the local host or it has to be provided in decrypted form already. In the second case no decryption is needed while in the first case the decryption key must be known locally to the media player. Thus it is only a question of extracting this (usually obfuscated) key from the player while the actual strength of the encryption algorithm does not matter much.

As long as the DRM is only implemented in software the necessary keys can be extracted and thus can be used to decrypt the content and remove the DRM. To have effective DRM you would need to make any kind of reverse engineering the key impossible, i.e. implement it with fully tamper proof hardware. But the usability and other costs associated with such a hardware usually don't make this a practical option for distributing media.

  • I have considered this as a possibility for copying DRM-protected media, but then my thought was, how would you find the key? Wouldn't that require some pretty sophisticated reverse engineering? – Zen Hacker Dec 22 '15 at 22:05
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    @ZenHacker: it would probably involve sophisticated reverse engineering but this is usually only required once for all media and not for each media protected by the same type of DRM. Thus if there are enough media protected by the same DRM scheme the gain one gets from breaking the scheme as more than the efforts needed. That's why you have laws like DMCA which try to add legal costs (prison etc) for breaking the encryption. – Steffen Ullrich Dec 22 '15 at 22:15
  • Related to crypto.stackexchange.com/questions/241/… – Neil Smithline Dec 23 '15 at 1:07
  • Either way, the content will be played back. A plug-in may be able to capture and copy the streamed content. – Ajay Dec 31 '15 at 9:38
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Steffen has the technical answer regarding the protection itself, but there is one big problem that makes any DRM pretty much useless in practice: The analogue hole.

In order to play the music, you have to remove DRM - so iTunes or whatever app it is has to be able to decrypt it.

And at that point it's trivial to make a copy. A copy from Line-Out will suffer a loss of fidelity, but a copy made between application and audio driver is not going to lose much in the way of quality.

  • DRM is like a forever escalating battle: people record decrypted analogue data -> protection like HDCP gets introduced -> people breaks HDCP master key -> ... – billc.cn Dec 29 '15 at 16:34

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