Crypto-agility: preparing for the algorithms after ML-KEM

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What crypto-agility means

Crypto-agility is the ability to change the cryptographic algorithms, key sizes and parameters your systems use, quickly and safely, without redesigning the systems themselves. In an agile system, swapping an algorithm is closer to changing a setting than rewriting software.

Most organisations today are the opposite. Algorithms are hard-coded across applications, embedded in devices that will run for decades, and buried in third-party products. That is why moving away from older algorithms such as SHA-1 took the industry many years.

Why post-quantum makes agility essential

New algorithms are less battle-tested

The new standards have been studied intensively, but they have far less real-world history than RSA. Cryptanalysis can move fast. In 2022, researchers broke SIKE, an algorithm that had reached the fourth round of NIST's post-quantum process, using a single ordinary computer.¹ The standardised algorithms are different and remain trusted, but the lesson stands: plan for change.

The standards themselves are still evolving

In March 2025, NIST selected HQC as an additional key-encapsulation algorithm, a backup to ML-KEM built on different mathematics (error-correcting codes rather than lattices), so that a weakness in one approach would not undermine both.² NIST said it planned to publish a draft standard about a year later and finalise it in 2027. Agile systems will be able to adopt it if needed; rigid ones will face another migration.

AI is accelerating the search for flaws

AI tools are increasingly used to find bugs in software, including cryptographic libraries and their implementations. That raises the chance that weaknesses, whether in maths or in code, are discovered faster than before. The ability to respond quickly matters more than ever.

Deadlines are fixed

The UK's NCSC expects organisations to complete migration by 2035,³ and NIST's draft transition guidance proposes disallowing widely used RSA and elliptic-curve algorithms by the same year.⁴ An agile foundation turns these from cliff edges into routine changes.

Five building blocks

1. A living cryptographic inventory. Maintain a continuously updated record of where every algorithm, key and certificate is used, sometimes called a cryptographic bill of materials (CBOM). Agility starts with visibility.
2. Abstraction instead of hard-coding. Route cryptographic operations through a small number of well-maintained libraries or services, so applications ask for "encrypt this" rather than "use RSA-2048".
3. Policy as configuration. Define approved algorithms and parameters centrally, and let systems read them, so an algorithm change can be rolled out, tested and reversed like any other configuration change.
4. Hybrid by default during the transition. Combine a classical and a post-quantum algorithm so security doesn't depend on either one alone.
5. Automated key and certificate lifecycle. Short-lived certificates and automated renewal mean new algorithms reach every system in days, not years.

Practical considerations

• Size and performance: post-quantum keys and signatures are larger than today's. Test protocols, packet sizes, constrained devices and older middleboxes that may choke on bigger handshakes.
• Interoperability: check that partners, clients and suppliers support the same hybrid modes before switching.
• Long-lived hardware: devices with fixed roots of trust need a migration plan before they are deployed, not after.
• Governance: name an owner for cryptographic policy, and review it when standards bodies publish new guidance.

A quick self-assessment

If several answers are "no", you're in good company, and the inventory is the right place to start. Aki Horizon is built to do exactly that: discover your cryptography, prioritise the risk, and plan a migration that leaves you agile for whatever comes next.