Hash-based Signatures: An illustrated Primer
I think this focuses on the wrong reason for why signatures are important.  Sometimes, you can't or don't care to secure the channel you are using to communicate.  A signature doesn't hide the messages, so it is unsecured, but it does give a guarantee of who it came from.<p>I know this is touched at the beginning.  But the odd shift at the end to "quantum will break all crypto" seems out of nowhere and makes this sound like a hypothetical tool.