Usage Clarification

[CocoroBlue]

Hi,

Could you clarify if I'm using this correctly and advise me please?

I am running Kindle 2.7.1.

I run the command inside the install directory as shown below. I have confirmed that the KRFDyanmic.dll's md5 matches the notes.

The script seems to be successful after a few minutes as it scans through my library, then it gives me the keys and creates the file as shown below.

Is the k4i file then imported via "Kindle for Mac/PC ebooks" in Calibre? I get this error message below when attempting it. In the above screenshot, it mentions that I can copy the keys into a text file, but where would I use/import that into Calibre?

Thanks in advance

[Satsuoni]

In the config above, there should be a different text field with a button, like so:

It is not a k4i file, so please don't try to put it into "Kindle for MAC/PC ebooks"

Edit: The last three lines, starting with "device_serial_number", can be copied into separate text file and used instead of Kindle.dmp, speeding up scan, since it does not have to go through 700mb of binary.

[ElleKayEm]

You need to run KRFExtractor each time you download books.

[l-l-l-l-l-l]

You need to run KRFExtractor each time you download books.

I meant get a new dump. Can I run KRFExtractor with this txt file (device serial number + working secrets) instead of a dump every time I download books and only make a new dump when a book fails decrypting or do I have to make a new dump each and every time?

[ElleKayEm]

Yes, new books, new keys.

[Satsuoni]

You can use it instead of DMP file to get new book keys, since your client secret only changes rarely (usually with new version). In some cases, you have two active client secrets (one left over from previous updates) and the dump only picks up one, though. The flow would be roughly: use the text file with DSN/secret, to try and get new book key, of that does not work, open book in K4PC, dump memory, try with that dump and see if there are different secrets that you can then add to the text file.
Note that there is often a spurious "secret" caused by the fact that some books do not use secret for encryption, so any random string works.

[Satsuoni]

I feel a bit like going into unnecessary detail, so here goes: From our understanding, every book is converted to several formats/variants depending on device and resolution. Each of those is encrypted with a separate key per book variant, but not per customer, since that would be incredibly wasteful (imagine keeping a copy of book per customer?) (might not be true for older formats). Then, when customer buys a book, the key of the appropriate version is encrypted with another key derived from device data. That can include device serial number (older kindles use only that), device secret (that is created at login/registration), and, in newer version, it also includes salt per book, so the keys are no longer the same for every book per device.

Older version of deDRM derived the last key from the data, and also extracted DSN/secret from k4pc settings file, but with newer obfuscation, that is no longer feasible, at least for me. Further, they altered the derivation process to no longer use AES256 in the middle, as far as I can tell. So I went the simpler route of dumping the actual keys for book variants from memory, but unfortunately, I cannot fold that into python script, one of the reasons being bitness (my calibre is 64 bit, kindle is 32bit). Hence the separate utility that runs decryption procedure provided by Kindle using every hex string from the memory dump as a secret candidate (since I cannot read .kinf2024). (And hence the ability to put those strings that opened books successfully into separate file)

In theory, book keys (16bytes) would work across accounts, until key rotation at least. One would still need to download the book first, of course, which no longer works for all books for K4PC, and only works on accounts that bought the book anyway. And yes, one key per book variant (I assume the high-resolution books have different keys but cannot confirm).

[CocoroBlue]

Thanks, makes sense now, I got it working! Thanks for the work