We don't know the encryption method, the KAS is completely different but it
might be useful to record it anyway for future purposes. MID extracted from
device, Japanese NW-A35.
Change-Id: I4c4bb5b063da99003b5c316061d8c490b77428a4
There must be an evil genius in Sony's Walkman division. Someone who made sure
that each model is close enough to the previous one so that little code is needed
but different enough so that an educated guess is not enough.
Each linux-based Sony player has a model ID (mid) which is a 32-bit integer.
I was able to extract a list of all model IDs and the correspoding name of
the player (see README). This gives us 1) a nice list of all players (because
NWZ-A729 vs NWZ-A729B, really Sony?) 2) an easy way to find the name of player
programatically. It seems that the lower 8-bit of the model ID gives the storage
size but don't bet your life on it. The remaining bytes seem to follow some kind
of pattern but there are exceptions.
From this list, I was able to build a list of all Sony's series (up to quite
recent one). The only safe way to build that is by hand, with a list of series,
each series having a list of model IDs. The notion of series is very important
because all models in a series share the same firmware.
A very important concept on Sony's players is the NVP, an area of the flash
that stores data associated with keys. The README contains more information but
basically this is where is record the model ID, the destination, the boot flags,
the firmware upgrade flags, the boot image, the DRM keys, and a lot of other stuff.
Of course Sony decided to slightly tweak the index of the keys regularly over time
which means that each series has a potentially different map, and we need this map
to talk to the NVP driver. Fortunately, Sony distributes the kernel for all its
players and they contain a kernel header with this information. I wrote a script
to unpack kernel sources and parse this header, producing a bunch of nw-*.txt
files, included in this commit. This map is very specific though: it maps Sony's
3-letter names (bti) to indexes (1). This is not very useful without the
decription (bti = boot image) and its size (262144). This information is harder
to come by, and is only stored in one place: if icx_nvp_emmc.ko drivers, found
on the device. Fortunately, Sony distributes a number of firmware upgrade, that
contain the rootfs, than once extracted contain this driver. The driver is a
standard ELF files with symbols. I wrote a parsing tool (nvptool) that is able
to extract this information from the drivers. Using that, I produced a bunch
of nodes-nw*.txt files. A reasonable assumption is that nodes meaning and
size do not change over time (bti is always the boot image and is always
262144 bytes), so by merging a few of those file, we can get a complete picture
(note that some nodes that existed in older player do not exists anymore so
we really need to merge several ones from different generations).
The advantage of storing all this information in plain text files, is that it
now makes it easy to parse it and produce whatever format we want to use it.
I wrote a python script that parses all this mess and produces a C file and
header with all this information (nwz_db.{c,h}).
Change-Id: Id790581ddd527d64418fe9e4e4df8e0546117b80
