Information
Defines the minimum number of characters that are required in a new password which were not in the old password.
In setting the mindiff attribute, it ensures that users are not able to reuse the same or similar passwords.
Solution
In /etc/security/user, set the default user stanza mindiff attribute to be greater than or equal to 4-
chsec -f /etc/security/user -s default -a mindiff=4
This means that when a user password is set it needs to comprise of at least 4 characters not present in the previous password.