Here's an excerpt — unaired, I believe — from John Oliver's interview last week with Edward Snowden. In it, the discuss what's a safe password to use in the age of computers…
I don't know a lot about this topic but I do know that no matter what someone tells you would be a safe password, there's some other so-called expert who'll tell you that it would be a pushover for someone to crack. Snowden suggested "MargaretThatcheris110%SEXY." This fellow says that even leaving aside the fact that Snowden mentioned it on TV, that's not very secure at all. He says to assume that a would-be cracker would be capable of one trillion guesses a second.
I went to this site which evaluates how difficult a password is to guess and I entered Snowden's example. The site calculates that at one hundred trillion guesses per second, cracking that one could take 8.47 thousand trillion trillion centuries. If someone wants to wait that long to get into my GMail account, they're welcome to anything they can find in there.
What's interesting is that if Mr. Snowden merely added an easy-to-remember exclamation point to the end of this phrase, it becomes astronomically harder to guess. Instead of 8.47 thousand trillion trillion centuries, it would take 8.04 hundred thousand trillion trillion centuries. Two exclamation points make it 76.43 million trillion trillion centuries and five make it 65.53 trillion trillion trillion centuries. I'm sure someone will tell us that's not good enough.