jumust on "Hide relationship user / post in database tables - sensitive data"

Hi,
in case of external attack to the website I need to hide in the database the relationship between custom post type and users, since I'm working with sensitive data.

Let's say that I have a CPT "A" and a User role "Patient". One Patient is assigned to One post.

I need to hide (in the DB) that Patient "x" is associated to post "y".

Basically in the database I need to hide the user_id (coming from the wp_users table) in the field "post_author" of the wp_customposttype table.

I was thinking to create an interim table to link both tables above, this table should do the following: USER_ID * 100 = POST_AUTHOR

Obviously the math operation (* 100) is not known, so only administrator can gain the User_id by doing: Post_author/100 = User_id

What would be your approach?

Thanks