Kindle Watermarking format
So I just explored the watermark tag found in AZW files a bit, and this is what I found so far;
The tag has the format
atv:kin:1:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX=:YYYYYYYYYYYYYYYYY YYYYYYYYYY=
where X and Y are base64 encoded numbers, the first 1024bit long and the second 160bit.
X has the following components
16 bytes Unknown
48 bytes Book ID (ie same for all copies of this book)
32 bytes User ID (ie same for all books downloaded to this user/device)
32 bytes Unknown
I have not compared different devices yet, that may change things.
Anyone found out anything else?