A super s e c u r e account creation system. /r/badUIbattles submission.
Just clone it. I'm pretty sure that's it.
By creating an account, the password is saved to the database without being encrypted. If you try to create an account with an email that's already being used, you'll get notified about so and it won't create. However, if someone tries to create an account with the same password of another account, they'll be notified that password is already being used by the user with the email [the account that is using that password's email].