Kindle Watermarking format

[sasq]

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?

-- Sasq

[Serpentine]

First 16 might be an MD5, I imagine the last block will be some sort of hash reference to download logs stored server side. Shouldn't be an actual device ID in there tho.

[Dylan Tomorrow]

FYI, I just noticed that on my Kindle Touch this watermark is stored in the SQLITE Collections Database at /var/local/cc.db in column p_watermark in table entries not just for DRMed books (p_isDRMProtected=1) but for one purchased book where I removed the DRM as well (p_isDRMProtected=0).

When I unpack said book with MobiUnpack the same watermark shows up in the BookName/mobi7/BookName.opf as

<meta name="Watermark" content="[...]" />

and is reported as an EXTH header when unpacking.

The cc.db also lists such a watermark for one mobi that I let Readability.com email to my Kindle. Strange ...