Hey Daniel.

""VT100 Pseudographic Mode" is a feature of Plymouth which is usually toggled 
by pressing Escape."
I can reproduce this behavior without pressing ESC and am quite certain I did 
not repeatedly entered VT100 by accidentally pressing ESC every time I 
encountered this issue as the key is far away and obviously not used for 
anything in the passphrase - in addition, I can be more than certain as it is 
impossible I hit ESC by accident 30 times in a row in the particular event I 
stated where I restarted the machine 30 times to finally decrypt it.

I have stated how to reproduce this behavior:
VT100 can be entered with AltGr + Q, and AltGr + Shift - atleast with a german 
keyboard layout. The evidence is the linked jpeg file that clearly proofs that 
VT100 mode is activated after performing the @ Symbol on a german keyboard 
layout by AltGr + Q. And this particular photo was created when testing, and 
while that I performed every key stroke carefully and "slow" (slow as in 
dedicated and not rushing from Key to Key like with conventional typing).

So Im not sure what you mean by "So it's possible you've hit a combination that 
emits the escape sequence ^["
I was not pressing anything other than AltGr + Q in the particular linked jpeg. 
In that scenario I was far away from the ^ key or the AltGr + 8 combination to 
perform a [ symbol.
I am also far away from these keys in my daily routine where I encounter this 
issue persistently.
As stated, while testing to debug this behavior, I tried various C0/C1 control 
codes, like ^[, and non of them exited VT100 mode in the "initramfs" 
environment (the environment you see in the linked jpeg).

I was not able to exit VT100 except of using AltGr + Shift: But this
method is not 100% reproducible for me as it requires proper timing.
Additionally, within the actual LUKS passphrase, you do not know if you
are in VT100 or not due to the * characters in plymouth - so one can not
assume after AltGr+Q/AltGr+Shift if he entered VT100 and needs to exit
again before continuing with the passphrase.

As mentioned, I have this issue with 2 machines and at least 3 different 
keyboards (internal and external), since Ubuntu 18!, with various fresh 
installs. So this behavior is reproducible and not some user error of 
accidentally having the unlikely combination of keys to enter VT100 or some 
altered system that causes the behavior.
To repeat myself: It always occurs for me when AltGr + Q or (accidental) AltGr 
+ Shift is involved.

The later, AltGr + Shift, on the other hand is an "unlikely" accident of 
holding the Shift Key for too long as I need to capitalize the letter of my 
passphrase before of the @ symbol.
Cheers

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https://bugs.launchpad.net/bugs/2097231

Title:
  LUKS Passphrase: AltGr + Shift Triggers VT100 Pseudographic Mode

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