ISO 27001 Annex A 8.24: Use of cryptography

What Control 8.24 means in practice

Govern cryptographic use, algorithms, certificates and keys according to information and service risk. Test the control through the organisation's actual scope, decisions, ownership and operating records rather than relying on a policy reference alone.

For use of cryptography, proportional design depends on the affected services, information, people and dependencies. The evidence below should be adapted to that real boundary.

Implementation steps

1. Step 1. Define ownership, scope and operating criteria for use of cryptography.
2. Step 2. Implement cryptographic standard that fits the organization’s risks, services and working practices.
3. Step 3. Integrate the activity with relevant change, exception and review processes.
4. Step 4. Review performance and improve the arrangement when risks, technology or obligations change.

What good implementation looks like

• recent samples show use of cryptography operating across the intended scope
• exceptions and adverse results have accountable decisions and verified closure
• review results lead to measurable correction or improvement

Implementation evidence and effectiveness evidence

How an auditor may test Control 8.24

1. Select a representative in-scope service, asset or process.
2. Confirm the accountable owner and expected operation.
3. Trace a recent example: A sensitive data flow is sampled to confirm approved cryptographic use, key ownership, configuration and lifecycle controls.
4. Inspect the operating record and corroborating technical evidence.
5. Compare the design with evidence that the control operated effectively.
6. Follow an exception or adverse result through decision and closure.
7. Review trends, metrics and improvement decisions.

Questions to prepare for

• How is use of cryptography implemented in practice?
• Who owns the activity and how are decisions approved?
• Show me a recent example from operation through review.
• How are exceptions, changes or overdue actions handled?

Practical examples

Illustrative decision and evidence record

Reviewer note: Test use of cryptography with a recent real example; a current operating record normally reveals more than policy wording alone.

Useful performance and coverage measures

• in-scope coverage for use of cryptography
• overdue exceptions or actions by age
• repeat findings identified through review

Approach for smaller and mature organizations

Smaller organization

Use a clear owner, a proportionate working record, built-in platform capability and a scheduled review. Sample real activity instead of creating duplicate paperwork for use of cryptography.

Mature or complex organization

Define service-level ownership, automated coverage reporting, integrated workflow, risk-based exceptions and independent assurance across business units and technology platforms.

Practical implementation checklist

• □ Define ownership, scope and operating criteria for use of cryptography.
• □ Implement cryptographic standard that fits the organization’s risks, services and working practices.
• □ Integrate the activity with relevant change, exception and review processes.
• □ Review performance and improve the arrangement when risks, technology or obligations change.
• □ Sample evidence has been checked for operation and effectiveness.
• □ Exceptions have owners, rationale, review dates and closure evidence.

Common implementation mistakes

• documenting use of cryptography without consistent operation
• unclear ownership or review frequency
• evidence that does not cover the full ISMS scope
• exceptions accepted without risk-based approval or follow-up

Related controls, clauses and resources