So you create a
.kbdx file, protected by a password.
AFAIK in asymmetric key schemes and in WPA-AES brute-forcing consists of:
- try a random password on the private key / on the router
- if it doesn’t log you in, try another.
So you immediately know did you hit the correct password.
What about a password manager’s database? You know nothing about the content of the file. How do you know you did manage to crack it?