  The problems which are important for the effective functioning of an access
control policy in a large information system (LIS) are selected. The general
concept of a local optimization of a role-based access control (RBAC) model is
formulated. The optimization criteria are proposed. The algorithms of a local
optimization of the RBAC model are defined and justified. The developed
algorithms are used in the methods of the solution of the following problems:
the assessment of risks of the leakage of permissions in the RBAC policy, the
access control in the distributed hierarchical systems, the combining of
role-based and mandatory access control models. In the first problem the
question of the permissions distribution in the role hierarchy is researched.
The analytic hierarchy process (AHP) is applied to creation of the estimates.
The method is based on the hierarchical structure of a role set. The offered
technique can order the permissions according to the value of the risks of
their leakage. In the second problem the algorithm of the distribution of the
cryptographic keys in the system with a hierarchical arrangement of the objects
is offered. The cryptography protocols for the practical use of this algorithm
are defined. The conditions of the implementation of the discretionary and
mandatory principles of the access control on the basis of the developed
algorithm are formulated.
