Need help to design model with multiple rights
Since my question I have now a great concept.
Security, rights and access are handled by an ownership table.
Each row contains :

booleans access for create, delete, read &amp; update
Link to table Element wich contains all manageable elements in my website
Link to table OwnershipType wich tells me if it's an access on ownership, for all ressources or only a specific ressource ID
Link to table User
An ID in case OwnershipType is only a specific ressource

To manage groups, I didn't want to create more tables, what I found clever was to consider a group as a user and assign it some ownerships. To add a user to a group, I have a Parent table wich link a user to another (in this case that user is in fact a 'group'). It explains why I have a UserType table. It tells me if it's a group or a normal user.
In my code I just have to check if a user has a parent and if so add its ownership to the user's ones.
That concept let me having some global ownership on many user who are linked to a group and still have really specific ownership on certain user.
If people are interested I can explain how I implemented that concept in my website, it's quite simple and clean.
My model :