mlkem-c-aarch64 is a collection of MLKEM implementations for CPUs based on the Armv8-A and Armv9-A architectures.

Goals of mlkem-c-aarch64

The primary goals of this project are as follows:

• Assurance: Offer code that's extensively tested and amenable for audit and verification
• Ease of use: Permissive licensing, modularity, adaptability, few dependencies
• Performance: Competitive performance for most Armv8-A/Armv9-A platforms

There are tensions between these goals:

• Optimal code is target-specific, but a large variety of CPU-specific implementations makes a library harder to both use and maintain.
• Optimal code is complex (e.g. relying on handwritten assembly and extensive interleaving), impeding maintainenance and amenability for audit, and potentially hardening verification efforts.

In doubt, mlkem-c-aarch64 chooses assurance and ease of use over performance: We only include implementations into mlkem-c-aarch64 which are manually auditable or (ideally and) for which we see a path towards formal verification. All assembly should be as readable as possible and micro-optimization ideally deferred to automated tooling such as SLOTHY. Ultimately, mlkem-c-aarch64 strives for constant-time implementations for which the C-code is, at minimum, verified to be free of undefined behaviour, and where all assembly is functionally verified.

mlkem-c-aarch64 aims to provide a portfolio of implementations jointly providing competitive performance for most Armv8-A/Armv9-A microarchitectures. For some specific microarchitectures of particular interest, mlkem-c-aarch64 may also provide CPU-specific implementations. Initially, our benchmarking platforms are:

• Arm Cortex-A55
• Arm Cortex-A72 (as used in the Raspberry Pi4)
• Arm Cortex-A76 (as used in the Raspberry Pi5) / Neoverse N1 (as used in AWS Graviton2/c6g instances)
• Arm Neoverse V1 (as used in the AWS Graviton3/c7g instances)
• Apple M1

Please reach out to the mlkem-c-aarch64 maintainers or open an issue if you would like to see benchmarking on other microarchitectures.

Non-goals

At this point, we do not provide implementations optimized for memory usage (code / RAM). If you need a memory-optimized implementation and the implementation provided by MLKEM-C-Generic is not of sufficient performance to your application, please contact us.

Relation to MLKEM-C-Generic

Eventually, we aim to unify the (shared) C-part of the implementations provided by mlkem-c-aarch64 with the implementations in mlkem-c-generic. Initially, however, we will allow some divergence, e.g. to explore interfaces to 2-/4-/8-way parallel Keccak implementations which are essential for high-performance implementations of MLKEM.

Current state

mlkem-c-aarch64 is currently a work in progress and we do not recommend relying on it at this point. WE DO NOT CURRENTLY RECOMMEND RELYING ON THIS LIBRARY IN A PRODUCTION ENVIRONMENT OR TO PROTECT ANY SENSITIVE DATA. Once we have the first stable version, this notice will be removed.

The current code is compatible with the standard branch of the official MLKEM repository.

Development

Environment Setup

All the development and build dependencies are specified in flake.nix. We recommend installing them using nix.

• Setup with nix

  • Running nix develop will execute a bash shell with the development environment specified in flake.nix.

  • Alternatively, you can enable direnv by using direnv allow, allowing it to handle the environment setup for you.

  • As flake is still an experimental feature of nix, --experimental-features 'nix-command flakes' is needed when running the nix command. Alternatively, add the following to your ~/.config/nix/nix.conf or /etc/nix/nix.conf:

    experimental-features = nix-command flakes

• If you are not using nix, please ensure you have installed the same versions as specified in flake.nix.

Development scripts

After running nix develop you should automatically have a number of support scripts in your PATH:

• format formats all files. The format is enforced by our CI, so you should run this script prior to committing.
• tests run functional, kat tests natively or emulate them using QEMU. For information on how to use the script, please refer to the --help option.

Call for contributors

We are actively seeking contributors who can help us build mlkem-c-aarch64. If you are interested, please contact us, or volunteer for any of the open issues.

Call for potential consumers

If you are a potential consumer of mlkem-c-aarch64, please reach out to us. We're interested in hearing the way you are considering using mlkem-c-aarch64 and could benefit from additional features. If you have specific feature requests, please open an issue.