ISO/IEC 23894: Security Controls Assessment

• ISO/IEC 23894 is a formal framework for systematic evaluation of information security controls in ISSH, emphasizing rigorous, risk-based, and auditable assessment practices.
• It introduces precise models and operators to quantify assurance, optimize our security testing processes, and reduce costs through automation and combinatorial techniques.
• Optimization strategies such as test consolidation and automation ensure efficient conformity assessments that align with international best practices for security assurance.

ISO/IEC 23894 defines guidance for the systematic evaluation of information security controls, emphasizing rigorous, risk-based, and auditable processes for conformity assessment, especially for Information Security Software and Hardware (ISSH). Formalized models, operators, and process optimization strategies enable quantification of assurance, reduction in test costs, and increased reproducibility of results, aligning with international best practices and standards.

1. Formal Methodological Framework for Security Test Procedures

A formal, model-driven methodology underpins conformity assessment of ISSH to regulatory and technical requirements. The methodology allows quantification of cost, time, and exhaustiveness in security testing and readily accommodates automation and optimization, supporting ISO/IEC 23894 principles.

1.1. Conceptual Model Components

• Requirements Set ($\mathbf{R}$): A finite set of explicit security requirements formulated for a specific ISSH entity $E$.
• Test Processes Set ($\mathbf{T}$): $T = \{ t_i \}$, where each $t_i$ operationalizes testing for a corresponding $r_i \in R$.
• Test Process Design Function ($\mathbf{M}$): $$M : R \times \text{Implementation Info} \rightarrow T$$. For each requirement, $M$ generates the associated test process; $M$ is commonly bijective.
• Formal Operators:
  • Requirement FulfiLLMent:

  $$FR(E, r_i) = \begin{cases} 1, & \text{if requirement } r_i \text{ is met by } E \ 0, & \text{otherwise} \end{cases}$$ - Test Process Correctness:

  $$Fc(E, t_i) = \begin{cases} 1, & \text{if } t_i \text{ is passed for } E \ 0, & \text{otherwise} \end{cases}$$

1.2. Assessment Stages

1. Planning:

   • Analyze specifications and features.
   • Confirm claimed conformity ($FR(E, r_i) = 1$ for all $r_i$).
   • Generate test processes ($T = M(R)$).
2. Testing:
   • Execute each $t_i$ and record outcomes.
3. Analysis:
   • Evaluate whether $Fc(E, t_i) = 1$ for all $i$.
   • Declare conformity if ISSH behaviors match requirements.

2. Applied Test Procedures for Information Security Controls

Distinct classes of security requirements are formalized with corresponding test procedures leveraging precise mathematical or logical models.

2.1. Discretionary Access Isolation Testing

• Model: Access matrix $M = (m_{ij})$, where $m_{ij}$ captures the set of access rights subject $S_i$ holds over object $O_j$.
• Procedure:

1. Create defined test subjects and objects.
2. Populate access matrix $M$ with intended rights.
3. Test all (subject, object) pairs for each right.
4. Compare observed outcomes with $M$.

• Acceptance Criterion:

$$\forall i, j, k: \text{actual}(S_i, O_j, R_k) = m_{ij}(R_k)$$

2.2. Mandatory Access Control Testing

• Model: Each subject and object is labeled with a security classification ($ms_i$ for subject $S_i$, $mo_j$ for object $O_j$).
• Rules:
  • Read: Allowed if $ms_i \ge mo_j$
  • Write: Allowed if $mo_j \ge ms_i$
• Operators:

$$FR_{\text{read}}(S_i, O_j) = \begin{cases} 1, & ms_i \ge mo_j \ 0, & \text{otherwise} \end{cases}$$

$$FR_{\text{write}}(S_i, O_j) = \begin{cases} 1, & mo_j \ge ms_i \ 0, & \text{otherwise} \end{cases}$$

• Procedure: Assign labels, perform read/write tests, verify according to model.

2.3. Memory Cleaning Testing

• Model: For memory area $a_j$, a sequence $S$ is inserted, the area is cleared, and then checked for presence.
• Operator:

$$F_{\text{check}}(a_j, S) = \begin{cases} 1, & S \text{ is present} \ 0, & \text{otherwise} \end{cases}$$

• Positive Outcome: Post-relocation, sequence $S$ should not be detectable ($F_{\text{check}}(a_j, S) = 0$).

2.4. Additional Requirements

Formal processes are outlined for module isolation, identification/authentication procedures, and integrity control, with specific operators and criteria structuring each step and positive decision.

3. Optimization Strategies for Security Testing

Security test procedures frequently involve exponential growth in required time and costs relative to requirements and input parameter space.

• Test Time Complexity:

$T \approx n \cdot W \cdot V$

where $n$ is the number of requirements, $W$ the number of test units (e.g., user accounts), and $V$ the number of parameter values.

• Optimization Problem Formulation:

$$\min \sum_i \tau(t_i, E) \quad \text{subject to} \quad \sum_i C(r_i, E) \leq C_M$$

with $\tau(t_i, E)$ as the execution time for test $t_i$ and $C_M$ the maximum allowed expenditure.

• Optimization Approaches:

1. Test Consolidation: Merging test activities, such as auditing logs during access control checks.
2. Combinatorial Overlapping Testing: Instead of exhaustive tests, cover parameter subsets systematically (e.g., all 2- or 3-way interactions; see NIST SP 800-142).
3. Test Automation: Adoption of automation tools to streamline or wholly automate test execution and evidence collection.

4. Conformity Assessment Principles and ISO/IEC 23894 Alignment

ISO/IEC 23894 emphasizes a risk-based, methodical approach to information security control assessment.

• Coverage: Each security control is systematically matched to explicit requirements with clear documentation.
• Process Documentation: All test procedures, results, and acceptance criteria are formally recorded, enabling auditability.
• Repeatability and Objectivity: The use of formal operators, structured models, and automation ensures consistent, objective assessment.
• Efficiency: Optimization strategies contribute to balancing thoroughness and resource constraints, as required by ISO/IEC 23894.

In practical application, these methods facilitate rigorous, auditable certification—serving regulatory compliance, product assurance, and assurance within highly secure environments. Automation and combinatorial techniques become especially important with increases in system complexity (e.g., cloud, virtualization, or multilayered platforms).

5. Summary Table: Example Operators and Process Steps

Requirement	Formal Operator/Fn	Positive Decision Criterion
Discretionary Access	$FR(L, r_i)$	Specified vs. actual permissions coinciding
Mandatory Access	$FR_{read}, FR_{write}$	Action conforms to label hierarchy rules
Memory Cleaning	$F_{check}(a_j, S)$	Test sequence removed post-cleaning
Module Isolation	–	No cross-process memory access possible
Identification/Authentication	$FU_{JS}(for)$	Only valid credentials gain access
Integrity Control	$FMOD, F_{INT}$	All integrity violations detected and logged

6. Practical Implications and Significance

The formalized and optimized approach to ISSH conformity assessment:

• Enables rigorous, transparent, and potentially automatic frameworks for security testing.
• Directly addresses ISO/IEC 23894 requirements for assurance, process auditability, and resource efficiency.
• Supports a diverse range of application contexts, including ongoing security operations, customized product evaluation, and formal certification programs.

References to automation and combinatorial testing practices place the described methodology in alignment with recognized international best practices for security conformity testing.

7. Conclusion

The systematic formalization of security controls testing, as aligned with ISO/IEC 23894, supports robust, reproducible, and efficient assessment procedures for ISSH. Explicit mathematical models, operators, and optimization strategies ensure full traceability from requirements to test outcomes, furthering both regulatory compliance and real-world assurance objectives across sectors.