Thread: Remove PDF DRM
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Old 12-13-2008, 06:43 AM   #8
wallcraft
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Quote:
Originally Posted by HarryT View Post
With respect, the DRM has not been "cracked" - that would imply the ability to remove DRM without knowing the encryption key, and that hasn't happened.

What has happened with these three formats is that, given a known encryption key (eg the PID for a Mobi file), the action of the legitimate reader for the formats has been "reverse engineered", allowing tools to be written which produce a DRM-free version of the file. The key point is, though, that in order for this to be done, the encryption key has to be known.
The term "cracked" has been commonly used for defeating DRM systems by whatever means. For example, DeCSS was said to "crack" CSS DVDs even though it was essentially "reverse engineered" DVD player software including the player key necessary for decryption. The encryption used in that case was so weak that it actually was cracked in the stronger sense, but only after DeCSS was available.

I would describe the external keys required by ebook DRM schemes as much more like public keys than private keys. You need the key for decryption, but on its own it isn't sufficient for decryption and it isn't a secret. The private keys are inside the reader software, and these are necessarily included in any DeDRM software as well. This is the sense that ebook DRM removing software "cracks" the DRM encryption.
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