decrypt password from aspnet_membership table

hi,

how can decrypt password like this:

 var check = from t1 in db.aspnet_Memberships
                    join t2 in db.aspnet_Users
                    on t1.UserId equals t2.UserId
                    where  t2.UserName=="test"
                    select new { t1, t2 };

Membership.GetUser("test").GetPassword();


I need to get password from membership.

Thanks