Unless you do it the other way around: Generate a list of all passwords similar to the one the user just entered and see if that matches any previous hashes. T

Unless you do it the other way around: Generate a list of all passwords similar to the one the user just entered and see if that matches any previous hashes. This is how Facebook's password check works [0] [0] https://security.stackexchange.com/a/53483 https://security.stackexchange.com/a/53483