[Bug 1541649] Re: Plymouth needs a safe method to unlock the device on boot without a physical keyboard.

Harrison Smith harrisonts at gmail.com
Mon May 16 01:11:12 UTC 2016

This affects the practicality of Ubuntu as an operating system on my
Dell Venue 8 Pro. Encrypting just the home directory is not really a
satisfactory alternative, nor is carrying a USB keyboard at all times. I
found this:


as a rudimentary example of what could be implemented as a quick hack. I
don't have the experience to modify it in a very helpful way, but in my
tests, if I set MOUSEFILE in osk_mouse.c to "/dev/input/mice", I am able
to _somewhat_ control it via the touchscreen – emphasis on "somewhat".

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  Plymouth needs a safe method to unlock the device on boot without a
  physical keyboard.

Status in plymouth package in Ubuntu:

Bug description:
  My tablet is encrypted, and I'm presented with the plymouth decryption
  screen during every boot.  However, there is no onscreen keyboard,
  causing me to have to dig out a keyboard just to start the machine.

  I'd imagine as this goes along we're going to get more and more
  keyboardless devices.  Windows has already solved this.

  I disagree with the comments in bug
  https://bugs.launchpad.net/ubuntu/+source/plymouth/+bug/1239004 which
  is closely related to this.

  The simplest way is to implement an onscreen keyboard.  Obviously, it
  would have to support everything that could be in a physical keyboard,
  tho, or people could lock it with a physical keyboard and then find
  they can't unlock it with an onscreen one due to a missing symbol.

  Another idea would be not to use a keyboard at all.  We could instead use:
  (a) a USB key (which has the (dis)advantage of being crackable programmatically)
  (b) a sequence of vectors, like phones do (but there's a security risk since on some screens you can see the mark where it's been done repeatedly)
  (c) a voice print (fakeable)
  (d) a voice password (security risk due to being heard)
  (e) a camera image (also fakeable)
  (f) randomised visual word ordering with decoys and fail2ban scenarios.

  I believe that the safest and most reliable way is simply to use an
  onscreen keyboard, however, creating an encryption hook into plymouth
  could allow other methods to be used.  (f) could also work, tho and
  may be considerably easier to implement.

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