If you want the absolute highest levels of password security, consider using Strongbox. One neat thing about Strongbox is that it comes with a built-in Diceware ... Or even 6 times! · Or 5 times. · Roll the Dice 4 times. · 4 dice rolls
This Diceware web app is based on the original proposal wherein virtual dice are rolled 5 times, and the 5 digit number used against a lookup table of words.
Diceware generates passphrases, albeit ones composed of random words. You're talking about 'natural language passphrases' when you describe passphrases.
Create strong passphrases with EFF's new random number generators! This page includes information about passwords, different wordlists, and EFF's suggested ...