Encryption protects data when everything else fails. If a laptop is stolen or a database leaks, strong cryptography can keep the information unreadable. ISO 27001 cryptography requirements make sure you use it deliberately, with approved algorithms and well-managed keys.
In the 2013 edition, cryptography was Annex A.10, with two controls. The 2022 edition merged them into a single control, 8.24 Use of cryptography. This guide explains what it requires and how to implement it.
Mapping: A.10 (2013) to ISO 27001:2022
| ISO 27001:2013 | ISO 27001:2022 |
|---|---|
| A.10.1.1 Policy on the use of cryptographic controls | 8.24 Use of cryptography |
| A.10.1.2 Key management | 8.24 Use of cryptography |
What control 8.24 requires
In plain terms, the control expects you to define and implement rules for:
- When to use cryptography, based on information classification and risk.
- Which algorithms, key lengths and protocols are approved.
- How you generate, store, distribute, rotate, revoke and destroy keys.
- Legal requirements, such as export controls or restrictions in some countries.
So the control is not just “encrypt everything”. Instead, it asks for a managed, risk-based approach.
Where to use cryptography
Typical uses include:
- Data in transit: TLS for websites, APIs, email and remote access.
- Data at rest: full-disk encryption on laptops, and encryption for databases, backups and cloud storage.
- Integrity: hashes and digital signatures for software releases and documents.
- Authentication: certificates for servers, devices and users.
Link each use to your classification scheme. For example, a policy can require encryption for all “Confidential” and “Restricted” data, both at rest and in transit.
Example of approved algorithms
Your policy should list what is allowed and what is banned. The table below reflects common current guidance. However, always check the latest NIST or national guidance before you adopt it.
| Purpose | Recommended | Avoid |
|---|---|---|
| Symmetric encryption | AES-128 or AES-256 (GCM mode) | DES, 3DES, RC4 |
| Hashing | SHA-256, SHA-384, SHA-3 | MD5, SHA-1 |
| Public key | RSA 3072+ bits, ECDSA P-256 or higher, Ed25519 | RSA under 2048 bits |
| Transport | TLS 1.2 (strong suites) and TLS 1.3 | SSL, TLS 1.0, TLS 1.1 |
| Password storage | Argon2id, bcrypt, scrypt | Plain hashes, unsalted hashes |
Also plan for post-quantum cryptography. NIST published its first post-quantum standards (FIPS 203, 204 and 205) in August 2024. Therefore, start an inventory of where you use public-key cryptography, so you can migrate when your vendors support it.
Key management
Weak key management breaks strong encryption. A key management procedure should cover the full life cycle:
- Generation: use secure random generators, ideally in an HSM or cloud KMS.
- Storage: never store keys in source code or next to the data they protect.
- Distribution: share keys only over secure channels.
- Rotation: change keys on a schedule and after any suspected compromise.
- Revocation: revoke certificates and keys quickly when needed.
- Backup and recovery: make sure you can still decrypt backups.
- Destruction: destroy keys securely when data is no longer needed.
In addition, separate duties. For instance, the people who manage keys should not also have unrestricted access to the encrypted data.
Certificates
Expired certificates cause outages, and weak ones cause risk. So keep an inventory of certificates with owners and expiry dates. Automate renewal where possible, for example with ACME. Also have a plan to replace certificates quickly if a certificate authority is distrusted.
What auditors check
- A cryptography policy, or a section in another policy, approved by management.
- An approved algorithm list that matches real configurations.
- Evidence of encryption, such as BitLocker or FileVault reports and TLS scan results.
- A key management procedure and records of key rotation.
- A certificate inventory with expiry tracking.
FAQ
Does ISO 27001 require encryption of all data?
No. It requires a risk-based decision. However, most organizations encrypt laptops, backups and all data in transit as a baseline.
Is cloud provider encryption enough?
Often it is a good start. Even so, you should decide who controls the keys, and check that encryption covers backups and replicas.
Related guides
- ISO 27001:2022 Annex A: all 93 controls and the 2013 mapping
- Free ISO 27001:2022 readiness checklist
- What is an ISMS? Concept, benefits and the PDCA cycle
Sources
- ISO/IEC 27001:2022, Information security management systems (ISO)
- ISO/IEC 27002:2022, Information security controls (ISO)
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