Most password managers are based on the same basic idea - you remember one password, you put that into your password manager, and it spits out your plaintext passwords for all the sites you visit. This is fine for sites you don't visit a lot and don't need high security for.
But I wanted to be able to just remember my passwords. So I created Brain Password Manager, which allows me to practice entering passwords on a schedule, so I don't forget them.
BPM doesn't actually store my passwords. Instead, it runs the passwords through a very large number of calculations (800,000 rounds of PBKDF2) to arrive at a number between 0 and 4095. This number is the only information it stores.
When you practice entering your passwords, it does the same calculations. If the resulting number is different, then your definitely typed your password wrong. But, if you enter any password at random, there is a 1 in 4096 chance that it will still say you are correct. This isn't very likely to happen due to a simple typo in your password, though.
What this means is that any attacker trying to extract your passwords will find that lots of passwords match, and has no way of proving which one is the real password, other than trying it out on the site that the password is for. In fact, BPM has a built-in feature which finds false positives for a password to demonstrate just how many passwords an attacker would have to try.
I even created a utility to bruteforce false positives, which demonstrates just how many passwords an attacker would have to try:
|All of these passwords will be accepted as correct.|
I still use a regular password manager for sites which I rarely log into. BPM is mainly for passwords that I enter frequently enough that a password manager is a hassle, but not frequently enough that I don't forget the password.