The XKCD comic uses the entropy of common words assuming an informed cracker is using the best tools at their disposal, that being a dictionary attack. That’s why the entroy per character of the passphrase is so low compared to that of the special character password, but the passphrase can be much longer because it’s easier to remember, so that’s what gives it its higher total entropy.
The XKCD comic uses the entropy of common words assuming an informed cracker is using the best tools at their disposal, that being a dictionary attack. That’s why the entroy per character of the passphrase is so low compared to that of the special character password, but the passphrase can be much longer because it’s easier to remember, so that’s what gives it its higher total entropy.
Explain XKCD goes into more detail about how the calculation was done: https://www.explainxkcd.com/wiki/index.php/936:_Password_Strength