ISO 27001 A.8.24

ISO/IEC 27001:2022 Annex A control 8.24, "Use of cryptography," is the clause of an information security management system (ISMS) that governs how an organization uses encryption. It is deliberately standard-agnostic: it names no algorithms and no key lengths, and it says nothing about post-quantum cryptography. Its role in a PQC programme is different and increasingly load-bearing: it is the governance hook under which a certification auditor now asks whether you actually know where your cryptography lives and whether you have a plan for the quantum transition. The detailed implementation guidance lives in ISO/IEC 27002:2022 §8.24; in the 2013 edition this same material sat under A.10.1.

Why it matters

A crypto policy written a decade ago typically says "use AES-256 and RSA-2048" and stops. That is no longer sufficient evidence. The RSA- and ECDH-protected data being harvested today can be decrypted retroactively once a cryptographically relevant quantum computer exists, so an ISMS that cannot say which systems, protocols, and third parties depend on quantum-vulnerable algorithms cannot manage the risk it is certified to manage. Auditors have begun probing quantum readiness directly under A.8.24, and a two-line approved-algorithm list is now a finding waiting to happen.

What the control requires

A.8.24 rests on two normative pillars: a policy on the use of cryptographic controls, a documented and risk-based statement of which controls apply where, and key management across the full lifecycle. Read forward for PQC, both pillars now have to account for algorithm change rather than a fixed set of primitives:

• A crypto policy that addresses algorithm selection, deprecation, and crypto-agility: swapping primitives without re-architecting, not just a static approved-algorithm list.
• Key management covering generation, distribution, storage, rotation, archival, and retirement/destruction, sized for larger post-quantum keys and longer transition windows.
• A maintained cryptographic inventory: the evidence that you know what you run, ideally exported as a machine-readable CBOM.
• A documented algorithm-transition plan aligned to external drivers such as the federal inventory mandate and the NIST migration timeline.

Answering the auditor's cryptography question

We turn A.8.24 from a paragraph in your ISMS into defensible evidence. Our audit produces the cryptographic inventory and the quantum-risk assessment auditors ask for; our migration engineering delivers the documented transition plan and the crypto-agility to execute it without breaking production; and our certification work verifies that the implementations you actually ship match the policy you wrote. The result is a control that survives scrutiny rather than one that reads well until someone asks for the inventory behind it.