Why, and how to increase 16-character lockscreen password limit?

From Android Security Internals: An In-Depth Guide to Android's Security :

Android doesn’t have a dedicated setting to manage the encryption pass-
word after the device is encrypted, and changing the screen lock password or
PIN will also silently change the device encryption password. This is most
probably a usability-driven decision: most users would be confused by having
to remember and enter two different passwords at different times and would
probably quickly forget the less frequently used, and possibly more complex,
disk encryption password. While this design is good for usability, it effectively
forces users to use a simple disk encryption password, because they have to
enter it each time they unlock the device, usually dozens of times a day. No
one wants to enter a complex password that many times, and thus most users
opt for a simple numeric PIN (unless a device policy requires otherwise)

Additionally, passwords are limited to
16 characters (a limit that is hardwired
in the framework and not configurable), so using a passphrase is not an
option

(Emphasis supplied)

I don't know more about this limitation and would be glad if somebody can amplify (Edit: Andrew T has clarified here to an extent)

So, that rules out increasing password length to beyond 16 ( how to increase, Androids 16 character lockscreen password limit )

Since you are on Lollipop , you may like to related pitfall (claimed to be fixed) of long passwords here Android lockscreen can be bypassed by overloading with massive password

Note:

• For earlier versions (Lollipop and below), Cryptfs Password by Nikolay Elenkov, allows you to set a separate password for disk encryption or if your device is rooted

  
  
  

  su -c vdc cryptfs changepw new where new is your new password.

  
  
  

  Source: http://nelenkov.blogspot.be/2012/08/changing-androids-disk-encryption.html




• Nikolay Elenkov is the author of the book Android Security Internals: An In-Depth Guide to Android's Security and runs a blog here