md5 based passwords
Often you need a key or password of some type that needs to be complex, easily shared, but rarely used. For example, the key to access your local WiFi network. Instead of attempting to memorize or write down your code, pick a word... any word...
Edit a simple text file, for this example a file called test.txt, containing nothing but that word. Not even a carriage return! Then, run the md5sum command against that file.
$ md5sum test.txt dd02c7c2232759874e1c205587017bed test $
Take as many letters as you need for your password. In fact, if you wanted to make the password nine characters long, use the word nine!
$ echo nine > file.txt $ md5sum file.txt e84f745eb89b85ddef70c48ef6f8b411 file.txt $
Thus, your real password would be e84f745eb. Delete the file and recreate it whenever you need the password.
In actuality, it doesn't really matter how much or how little text is in the file, or even that it is a text file. It simply needs to be a file that is easily reproduced or found, whenever you need to use the password.