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.
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What it means
In plain EnglishUse 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.
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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
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.
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.
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.
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.
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
- 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.
- 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.
- 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.
- 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.
- 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/IEC 27001: 1 mapping
This control partially meets A.8.24.
ISM-1761 requires that when ECDH is used to agree encryption session keys, organisations use specific NIST curves (P-256, P-384 or P-521), preferably P-384. Annex A 8.24 requires organisations to define and implement rules for the effective use of cryptography, including cryptographic key management. ISM-1761 is a specific, prescriptive cryptographic standard (algorithm parameter/curve selection for key agreement) that would typically be one of the rules implemented under the broader cryptography and key management governance required by Annex A 8.24.
Mappings show how controls relate across frameworks. They do not imply full equivalence or certification.




