One (devastatingly bad) way to do that is to store hashed subsets of your password string, say the first and second half, and if one matches then your new passw

One (devastatingly bad) way to do that is to store hashed subsets of your password string, say the first and second half, and if one matches then your new password is considered too similar to the old password Note that this demolishes the security protection of hashing because brute forcing two (n/2) length password hashes is much easier than brute forcing a length n password hash.