Quote:
Originally Posted by kovidgoyal
@odamizu: The algorithm used for encryption doesn't matter. Since other experiments have shown that the same encrypted KFX file collection works on multiple devices, that implies that whatever the algorithm, it is based on a key that is not device/account specific. So what is needed is to figure out what that key is and extract it. Once that is done, all KFX files will be decryptable trivially (that is assuming there is not another layer of separate device/account specific DRM underneath).
The problem is more a human one. The advantages that KFX brings are so minor and individual device specific that I doubt anyone is likely to spend the time to break the obfuscation. I know I for one am not motivated to do so.
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Agreed, more or less. The key is obviously present somewhere. So yes, it becomes a problem of who is willing to delve deep enough.
The strings in the KFX file that state the encryption algorithm and compression method are some pretty good hints, but the key could be
anywhere. Given the mention of "vouchers", and the
voucher file in the KFX metadata, that would be a good place to start. But the key could also be hard-coded into the reader software (as a default for "non-DRMed" books), or the software could use a key-derivation algorithm, using something in the file or metadata as input. The possibilities are limited only by how creative Amazon wanted to be.
So while someone could be motivated enough to crack KFX, I doubt they'd do it without prying apart the reader software itself to see what it was doing.
Quote:
Originally Posted by kovidgoyal
From what I have been able to deduce, KFX contains images and probably text that is pre-processed/changed to work for the particular device the KFX is sent to. As such it is fairly pointless as an ebook format, in that it is not suitable a source for conversion to another ebook format. About the only thing one would gain by reversing this format is the ability to generate your own KFX files to send to your particular Kindle.
EDIT: And I should say that in the long term this is likely to be a dead-end format anyway. Since the capabilities it brings are perfectly possible by just improving the text rendering engines for normal epub/azw3 files.
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What have you seen that differed between the same KFX, delivered to different devices? I don't doubt you, I'm just hungry for details.
I can see how, if that's true, then from the Calibre viewpoint KFX is not something you'd invest time in.
Quote:
Originally Posted by odamizu
 kovidgoyal and mattmc for your patient and enlightening comments. (In my next life, I want to be software developer!) |
No problem
Quote:
Originally Posted by odamizu
I'm not so interested KFX's enhanced typography. My primary concern is maintaining the ability to tweak ebooks and convert to different formats if Amazon phases out MOBI and AZW3, leaving KFX as their only format. Hopefully that won't happen any time soon, especially given kovidgoyal's comment about KFX being an unsuitable source for conversion. Yikes.
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They seem to be heading that way...