So the argument of whether this increases or decreases entropy goes both ways: 1. Requiring certain characters is a limit on which characters are selected. An

So the argument of whether this increases or decreases entropy goes both ways: 1. Requiring certain characters is a limit on which characters are selected. An attacker now knows to look for at least one digit, upper case char, and one of 10 special chars. This is a smaller selection of characters than the whole of all characters that were available before, so it decreases entropy. 2. Most users choose weak simple passwords with low entropy. Requiring users to use some characters that they wouldn't otherwise increases the entropy as it increases the selection of characters in the password. I actually don't believe 2, as most users will just start with an upper case char and end with 1!, so the entropy will still decrease for most users, as they will choose easily guessable placements for these required chars.