An approved security function is a cryptographic or protective operation that has been accepted for use within a defined policy or standard. It matters because unapproved functions can introduce weak, unsupported, or noncompliant controls. Security teams should inventory approved functions, block unauthorised alternatives, and ensure implementations match the intended design and validation requirements.
What “approved” changes about the security function itself
An approved security function is not just a cryptographic choice, it is a governed one. Approval means the function has been evaluated for strength, interoperability, implementation constraints, and policy fit, so teams are not relying on ad hoc algorithms or control logic that may be easy to misuse, difficult to validate, or impossible to support over time.
That matters because security assurance depends on more than mathematical strength. A function can be technically sound yet still be the wrong choice if it is obsolete in policy, incompatible with the platform, or implemented in a way that undermines the control it is meant to provide. The approval step creates a common baseline for design, review, and enforcement.
Why unapproved functions create practical security and compliance problems
Unapproved functions often appear when teams optimise for speed, compatibility, or developer convenience. The result can be weak hashing, deprecated cipher suites, inconsistent token handling, or protective logic that has never been validated against current requirements. Even when the implementation seems to work, it may fail during audit, incident response, or cross-team integration.
Approval also reduces hidden variation. If one team uses a different function than the standard build path, security testing, monitoring, and configuration review become less reliable. That makes it harder to spot downgrade paths, unsupported libraries, or control drift before they become operational weaknesses.
How security teams should operationalise approval in day-to-day control
Security teams need more than a policy statement. They need an inventory of approved functions, a way to block unauthorised alternatives, and a review process that checks whether implementation details still match the approved design. That includes library selection, configuration defaults, validation settings, and any exception process used for legacy systems.
Approval is most effective when it is tied to enforcement, not just documentation. Where possible, approved functions should be embedded in platform standards, templates, reference architectures, or build guardrails so teams cannot accidentally introduce a noncompliant option. The goal is to make the secure path the easiest path.
For teams dealing with cryptography specifically, a Cryptography Basics Guide is useful when you need to distinguish between the function that is theoretically strong and the one that is actually acceptable under policy, platform constraints, and validation requirements.
Risk and Threat Considerations
Approved functions reduce the chance that security controls quietly degrade into weak, unsupported, or noncompliant implementations. The main risk is not only direct cryptographic failure, but also configuration drift, library substitution, and compatibility workarounds that create a control the organisation thinks it has but cannot reliably trust.
Failure mechanism: Teams adopt a nonstandard function, or an approved function is implemented with insecure parameters, so the effective protection no longer matches the intended control design.
Impact: The organisation can end up with false assurance, failed audits, weaker confidentiality or integrity protection, and expensive remediation when the issue is finally discovered through review or incident response.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
NIST SP 800-53 Rev 5, CIS Controls v8 and NIST CSF 2.0 set the technical controls, while ISO/IEC 27001:2022 defines the regulatory obligations.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST SP 800-53 Rev 5 | SC-13 — Cryptographic Protection | Approved security functions directly concern governed cryptographic protection choices. |
| CM-2 — Baseline Configuration | Approval depends on maintaining a controlled baseline for supported security functions. | |
| Recommendation — Require approved cryptographic functions and validate they are implemented as designed. Maintain an approved baseline and block unapproved function substitutions. | ||
| ISO/IEC 27001:2022 | A.8.24 — Use of cryptography | The topic centers on selecting and governing cryptographic functions under policy. |
| Recommendation — Define and enforce approved cryptographic methods and implementation rules. | ||
| CIS Controls v8 | CIS-4 — Secure Configuration of Enterprise Assets and Software | Approved functions need enforced configuration to prevent insecure alternatives. |
| Recommendation — Standardise approved functions in hardened configurations and software baselines. | ||
| NIST CSF 2.0 | PR.DS-01 — Data-at-rest is protected | Approved functions are a direct means of protecting data confidentiality and integrity. |
| Recommendation — Use approved protective functions to protect data according to policy. | ||
Practitioner Guidance
What to verify: Confirm that the approved function list is actually enforced in code, configuration, and platform policy, not just published in a standard. Check that exceptions are time-bound and reviewed, because permanent exceptions usually become shadow standards.
Common mistake: Treating approval as a one-time architecture decision. The practical test is whether the deployed implementation still matches the approved design after library updates, environment changes, and vendor defaults have been applied.
Practitioner takeaway: The value of approval is control, consistency, and defensibility, so the real objective is to prevent quiet substitution of weaker or noncompliant functions before they become part of the operating baseline.