How to do backups and updates properly with full device encryption? I think about the following use cases:


'Perfectly' reverse encryption without losing settings
Update ROMs. Even if /system, /data, /sdcard (internal) are encrypted
Low level Backups with CWM. When SDCARD partition is also encrypted.
Emergency access to my data (screen broken, soft bricked...)
How to mount crypted dumps on linux (knowing the passphrase)


Is there some salt value going into the key together with the passphrase stored on the device?

I currently use a tmpfs mount to /sdcard and 'adb push update.zip' on my Nexus S to update the ROM. I've been told that the Galaxy Nexus also has an encrypted /system which would prevent all that (see Nexus S solution here: Broken screen while debug mode was disabled. How can I re-enable adb? )
I don't know of any implementation for non-android devices for accessing the data, although it should be fairly easy to port / implement. For an explanation how the encryption works I recommend reading the following article:

http://nelenkov.blogspot.de/2014/10/revisiting-android-disk-encryption.html

I really doubt the Galaxy Nexus has an encrypted /system. And starting from Android 5.0 it could be almost impossible to read the data on other devices than the android device itself because parts of the key are stored in otherwise unaccessible DRM areas of the system board / SoC --- not the eMMC flash (on Qualcomm devices and possibly also Intel).