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Cryptography
ASD ISMISM-1761

ASD ISM 1761 Use NIST curves for ECDH encryption

What it says

When using ECDH for agreeing on encryption session keys, NIST P-256, P-384 or P-521 curves are used, preferably the NIST P-384 curve.

Quoted as published. Everything else on this page is written by Control Stack.

What it means

In plain English

Use specific NIST curves for secure encryption key exchanges, with P-384 preferred.

When we talk about securing sensitive communications online, it's a bit like making sure your personal diary is under lock and key. This control recommends using specific mathematical techniques (NIST curves) for protecting data exchanges, with a preference for one type called P-384. If these techniques are not used, there's a heightened risk that hackers could intercept and understand sensitive information intended to be private.

Why it matters

Using non‑NIST curves for ECDH can weaken key agreement, enabling attackers to derive session keys and decrypt sensitive traffic.

How to implement

  1. The IT team should ensure that their encryption software is configured to use the NIST P-384 curve when setting up secure communications.

    They can do this by checking the settings in their encryption tools or consulting with their software vendors to confirm that these settings are available and enabled.

  2. System owners should collaborate with their IT providers to ensure that any new systems they procure include support for NIST curves, particularly P-384, for encrypting data.

    This involves having detailed discussions before purchase and verifying the encryption capabilities with the vendor.

  3. Managers should oversee staff training sessions about secure communications and why using specific encryption settings, like NIST P-384, can protect against data breaches.

    This can be achieved through a one-hour interactive workshop using simple, relatable analogies to explain complex concepts.

  4. The procurement team should update their purchasing checklists to require that any encryption product supports NIST P-384 or higher.

    They can implement this by creating a new section on the checklist specifically for technical compliance and ticking it off during vendor evaluations.

  5. Executives should set a policy that mandates the use of recommended NIST curves across all levels of the organisation where sensitive information is being communicated.

    This can be done by formalising it in the organisation's cyber security policy documents and ensuring everyone, from managers to employees, adheres to it.

Keep it running

Audit TLS/ECDH configurations so only NIST P‑256, P‑384 or P‑521 curves are enabled; prefer P‑384 and remove all others.

Evidence and audit

  1. Check 1 of 5What an auditor asks for

    Ask for

    The encryption product documentation: Request to see manuals or specification sheets for encryption tools being used.

    Look at

    The section that details supported NIST curves, ensuring P-384 is listed.

    Good evidence

    Shows clear support for P-384 and others.

  2. Check 2 of 5What an auditor asks for

    Look at

    The organisation's cyber security policy regarding encryption. Check if it mandates the use of NIST P-384 for secure communications.

    Good evidence

    Includes specific mention of P-384 as a standard requirement.

  3. Check 3 of 5What an auditor asks for

    Ask for

    System configuration reports: Request a report or demonstration on how encryption settings are configured.

    Look at

    Settings that specify enabled NIST curves, verifying that P-384 is active.

    Good evidence

    Is a printout or screen capture showing P-384 active.

  4. Check 4 of 5What an auditor asks for

    Ask for

    Training materials or attendance records from sessions on secure communications.

    Look at

    Content covering the importance and usage of NIST P-384.

    Good evidence

    Includes a training schedule and materials referencing P-384.

  5. Check 5 of 5What an auditor asks for

    Ask for

    To see the procurement checklists used for evaluating new encryption tools.

    Look at

    Sections that require compliance with NIST curves, particularly P-384.

    Good evidence

    Is a checklist showing this requirement ticked off.

Mappings

Closest match in ISO/IEC 27001: A.8.24, Effective use of cryptography and key management, which this control partially meets.

ISO 27001

ISO/IEC 27001: 1 mapping

Mappings show how controls relate across frameworks. They do not imply full equivalence or certification.