In view of today’s XKCD:
I thought it would be useful to again mention the post by Jeff over at the Agile Bits Blog. That post discusses making a password by choosing 5 or 6 random words for your passwords. That’s what Randall Munroe is talking about in the XKCD comic.
As I was writing this post, I popped over to Agile Bits to get the URL for the link to the Blog. There I found that Jeff had written a followup article also based on the comic. In it he deconstructs the comic and shows how Munroe arrived at his estimation of the entropy of the two systems. As usual, there is a lot more going on in the comic than you might think. This is a really great post and everyone who uses a password for anything nontrivial should read it. Really.