Comment 10 for bug 1621367

I've recently installed Ubuntu 14.04 LTS server on two different computers when I ran across this issue. (For legitimate reasons newer versions of Ubuntu was not an option).

One one computer I was able to enter the password and on the other I was not able to enter the password.

The difference is the keyboard and the problem follows the keyboard being used.

When you use a Logitech USB keyboard you'll notice that the USB subsystem only recognizes the "Logitech USB Receiver" but does NOT register the mouse and keyboard. Hence the keyboard is non functional at the "Enter passphrase:" to unlock the encrypted partition. It's surprising because the keyboard will work at the Grub screen.

But using a different brand keyboard it'll get registered as a recognized input device and viola you can enter the password.

Once you enter the password then you can switch back to the Logitech keyboard because it'll eventually get picked up as a valid input device.