Quote:
Originally Posted by JSWolf
If you buy a Kindle eBook from Tor and you get a KFX, is the KFX DRM free so it can be loaded on any Kindle that supports KFX?
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Quote:
Originally Posted by pdurrant
I beleive that to be the case. It is encrypted, but with a universal key. That is, a key that is already on every device from Amazon that can display KFX files.
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I agree with pdurrant that books that are intended to be DRM-free are all encrypted with the same generic key. You can copy a book to another device of the same type running the same level of firmware and it should work. This has been shown to work between e-ink Kindle devices.
However, that does not mean that it will work on every device from Amazon that can display KFX files. There are a few problem with that.
1. Different devices and apps use different naming conventions and directory layouts for the multiple files that make up a KFX book. In some cases a book can be made to work by renaming and rearranging the files.
In other cases, such as the iOS and Android apps, it appears that the book has to be downloaded from Amazon for the files that make up a book to be properly associated with each other. Sideloading a KFX book composed of multiple files does not seem to work for these apps.
This problem can be overcome by removing the encryption from the book and combining the KFX files that make up the book into a single monolithic KFX file. Apprentice Harper's github repository has some work toward this, but it has not yet be made into an easily usable tool.
2. KFX was designed by Amazon to be incrementally improved. Newer apps and firmware support more KFX features than older ones. Each book has a set of metadata, called "content features", that indicates which KFX features are used by the book. When Amazon delivers a book in KFX format to an app or device it first checks the app version or firmware level and verifies that that it is capable of handling all of the features used by the book. If a book requires features that are missing from the app/device then Amazon delivers that book in KF8 or MOBI format instead.
If you sideload a KFX book you bypass this check and run the risk that it will not display properly if it uses a feature that the destination device does not support. The actual apps and devices do not check for supported content features.
3. KFX books delivered to an e-ink Kindle have covers and internal images in gray scale. This doesn't prevent the book from displaying on a color device, but it is an annoyance.