KFX Format

[Hitch]

Originally Posted by ps67

Now the limit is 65 rows, still 5 columns.

I'll be surprised if it's ever more than 5 columns, tbh.

Hitch

[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?

[HarryT]

If the book is DRM-free, that will be the case regardless of its format.

[pdurrant]

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?

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.

[HarryT]

This is easy to verify experimentally; download a DRM-free KFX book on one device, and manually copy it to another.

[jhowell]

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?

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.

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.

[JSWolf]

So basically, when an eBook is supposed to be DRM free, KFX botches that.

[darryl]

Originally Posted by JSWolf

So basically, when an eBook is supposed to be DRM free, KFX botches that.

Certainly it breaches the spirit if not the letter.succesfully

[jhowell]

Originally Posted by JSWolf

So basically, when an eBook is supposed to be DRM free, KFX botches that.

I agree. It’s a good thing that KFX is easily avoided in most cases. For now.

I do have some concerns that this may not always be true going forward. Since Amazon is adding new ebook features via KFX it may not always be avoidable. For example, interactive textbooks and kindle in motion rely on KFX. If you get one of these books in another format the new features are lost. (That may actually be a good thing in some cases.)

I have noticed that books published with the new Kindle Create program are normally delivered in KFX but fall back to MOBI on devices/apps that do not support it. A KF8 version of those books is unavailable so some formatting may be lost if KFX is avoided.

Even worse, I have found books in recently supported languages that are only available in KFX. They cannot be downloaded for transfer via USB and are unavailable to apps/devices that do not support KFX. I suspect this will be more common in the future.

[AnemicOak]

Originally Posted by jhowell

It’s a good thing that KFX is easily avoided in most cases. For now.

It is. If it ever gets to where KFX is unavoidable for the books I buy Amazon will lose that business from me (unless KFX becomes convertible, but I don't know that that's going to happen).

[darryl]

We can hope that Amazon doesn't do this. I was going to say hope that they have the sense not to, but so few people seem to care that it may make sense for them to go mostly or exclusively kfx.

Interestingly enough, if Amazon is delivering non-drm works with a public encryption key and their is hacking going on, we may be one step closer to a solution for removing the drm.

[jhowell]

Originally Posted by darryl

Interestingly enough, if Amazon is delivering non-drm works with a public encryption key and their is hacking going on, we may be one step closer to a solution for removing the drm.

As I mentioned previously, someone has already worked out a KFX DRM removal algorithm and Apprentice Harper's github repository has working code.

So far no one has bothered to integrate it into the packaged DRM tools. After all, a book in KFX format without DRM is no more useful than one with DRM at the moment.

[darryl]

Originally Posted by jhowell

As I mentioned previously, someone has already worked out a KFX DRM removal algorithm and Apprentice Harper's github repository has working code.

So far no one has bothered to integrate it into the packaged DRM tools. After all, a book in KFX format without DRM is no more useful than one with DRM at the moment.

It appears I may have misinterpreted you, in which case I am very happy. My reading was that the work in the github repository would decrypt a kfx which uses the generic key, basically files where the author/publisher chose no drm. Is it then the case that all kfx files can now be decrypted? That we know how Amazon is deriving its keys for kfx books with drm?

[JSWolf]

Originally Posted by jhowell

Even worse, I have found books in recently supported languages that are only available in KFX. They cannot be downloaded for transfer via USB and are unavailable to apps/devices that do not support KFX. I suspect this will be more common in the future.

So how is this supporting older devices that do support KF8 like the Kindle Touch and Kindle Keyboard? There are still a lot of older Kindles in use that do not support KFX. I can understand dropping Mobi because it's obsolete and doesn't help when wanting to use features that KF8 supports but Mobi does not. But to drop KF8 is wrong. A lot of people who own Kindles want to buy eBooks they can keep. KFX is not that.

[jhowell]

Originally Posted by darryl

Is it then the case that all kfx files can now be decrypted? That we know how Amazon is deriving its keys for kfx books with drm?

Yes. The sample code handles all KFX books downloaded using the latest Kindle for PC program, even those with DRM restrictions.

Originally Posted by JSWolf

So how is this supporting older devices that do support KF8 like the Kindle Touch and Kindle Keyboard?

The cases I have seen are with books that use EPUB features that are not supported by the MOBI and KF8 renderers. Rather than update those renderers to support those features Amazon is instead restricting books with those features to be KFX only.