Do you have a git repo or blog post with code/info about your Beaglebone passthrough setup? I wanted to do something similar a while ago but never got to it.
I may have written a tiny script to automate part of it at the time but I probably just did it all manually as it's quite simple. I haven't setup a blog for this sort of thing yet, but the minimum steps required to make it work is just a few high level commands:
1) Create a LUKS volume on a connected USB stick/drive (cryptsetup luksFormat /dev/sda1)
2) Open the LUKS volume with a standard name for step 3 to use (cryptsetup luksOpen /dev/sda1 securestick)
3) Load the g_mass_storage USB gadget module and point it at that LUKS device (modprobe g_mass_storage file=/dev/mapper/securestick)
That's basically it, for testing it can be done very easily without scripting.
The end result is a transparent encryption device for USB drives. Plug the beaglebone in to a laptop's USB port and it will show a standard USB mass storage device available for formatting and mounting, unaware that the actual storage is encrypted, and neither the password or LUKS master key will ever be in the laptops RAM (a useful property of this setup).
This could of course be automated with some scripting, and made quite fancy (touchscreen keyboard to unlock the LUKS stick at boot time and load that gadget module properly).
Some beaglebone distros load a gadget module at boot time with their own scripts, but it should be possible to automatically unload it where that is the case.
