Blog | G5 Cyber Security

Access Control Matrix to BLP Lattice

G5 Cyber Security

TL;DR

This guide shows how to build a Bell-LaPadula (BLP) lattice structure from an Access Control Matrix. This is useful for implementing mandatory access control in systems where you need fine-grained security policies.

Building the BLP Lattice

  1. Understand Your Access Control Matrix: The matrix defines who can do what to which resources. Rows represent subjects (users, processes), columns represent objects (files, databases). Cells contain permissions (read, write, execute).
  2. Identify Security Levels: Assign a security level to each subject and object. These levels should be hierarchical – think of them as classifications like ‘Top Secret’, ‘Secret’, ‘Confidential’, ‘Unclassified’.
  3. Create the Lattice Nodes: Each unique security level becomes a node in your BLP lattice.
  4. Define Dominance Relation: This is crucial. A security level A dominates security level B if all information flowing from B to A does not compromise the system’s security. Typically, higher levels dominate lower levels. For example:
    • Top Secret dominates Secret
    • Secret dominates Confidential
    • Confidential dominates Unclassified
  5. Representing Dominance: You can represent this with a graph. Draw arrows from higher-level nodes to lower-level nodes indicating dominance.
  6. No Read Upwards Rule: Subjects at level L cannot read objects at levels above L. In the lattice, this means no edges point *up* from an object’s node to a subject’s node. 
    # Example (Python): Check if a subject can read an object
def can_read(subject_level, object_level):
  return subject_level >= object_level # Dominates or equal
  7. No Write Downwards Rule: Subjects at level L cannot write to objects at levels below L. No edges point *down* from a subject’s node to an object’s node. 
    # Example (Python): Check if a subject can write to an object
def can_write(subject_level, object_level):
  return subject_level <= object_level # Dominated or equal
  8. Apply the Rules to Your Matrix: Go through each cell in your Access Control Matrix. If a permission exists that violates either the 'No Read Upwards' or 'No Write Downwards' rule, you need to adjust the permissions or security levels.
    • If Subject A at level X has read access to Object B at level Y and X < Y, deny the read permission.
    • If Subject A at level X has write access to Object B at level Y and X > Y, deny the write permission.
  9. Example Matrix Adjustment: Let's say your matrix initially allows a 'Confidential' user to read a 'Secret' file. You would remove that read permission.
  10. Implement Enforcement: Integrate the lattice structure and rules into your system’s access control mechanism. This might involve modifying kernel-level security checks, using a policy engine, or implementing custom authorization logic in your application code.

Important Considerations

Exit mobile version