Encoding::UndefinedConversionError on uploading a key with UTF8

While trying to upload the attached keyfile (as downloaded from schleuder-web), the keys_controller barfs with:

F, [2018-04-11T16:54:38.726388 #6289] FATAL -- :
Encoding::UndefinedConversionError ("\xC3" from ASCII-8BIT to UTF-8):
  app/controllers/keys_controller.rb:39:in `create'

8DC901CE64146C048AD50FBB792152527B75921E.asc

Edited by ng