The default download method is: Private local files served by Drupal.
So when userA upload file to node. userB can't see it.
Q: How to give access to view file by entityreference(user) for userB?
I create subdomain http://filesaccess.onenglar.com/
So you can login:
Sharing access i think by entity reference field (user)
But how share access to the files of node for individual users?))