Contributing new schemes to PQClean

Why contribute to PQClean

PQClean hopes to provide your scheme to people who want to integrate post-quantum cryptography into their own libraries and applications. But our extensive testing framework might also help you catch bugs in your implementation, that might have otherwise gone unnoticed. We run our builds on (emulated) ARMv7, ARMv8, 32-bit PowerPC, x86 and amd64. Also, we apply static and dynamic analysis tools.

Adding your scheme

For this text, we will assume that you want to contribute a key encapsulation mechanism (KEM) to PQClean. For a signature scheme, these steps are equivalent, but the API is slightly different. See the section API below.

Fork our repository. You will be creating a pull request soon.
- Tip: Do not wait until you think you have gotten everything perfect, before you open the pull request. We set up things so Github and the CI environment will give you feedback and guidance on the steps to follow.
Create the following folder structure: crypto_kem/yourschemename/clean. We follow the SUPERCOP layout, so please create a separate folder under crypto_kem for each parameter set.

For now, we only accept pure, portable C code. Our coding conventions impose certain constraints on the C code -- C99 code, fixed sized integer types (e.g., uint64_t rather than unsigned long long), and more. See README.md for more information.

Create a META.yml file in crypto_(kem|sign)/yourschemename following this template:

name: Name
type: <kem|signature>
claimed-nist-level: <N>
claimed-security: IND-CPA/IND-CCA2  # KEM only
length-public-key: <N>          # KEM and signature
length-secret-key: <N>          # KEM and signature
length-ciphertext: <N>          # KEM only
length-shared-secret: <N>       # KEM only
length-signature: <N>           # Signature only
nistkat-sha256: sha256sum of 1st NIST KAT test case # KEM and signature
testvectors-sha256: sha256sum of output of testvectors # Signature only
principal-submitters:
  - Alice
  - Bob
  - ...
auxiliary-submitters: # optional
  - Alice
  - Bob
  - ...
implementations:
  - name: clean
    version: <some version indicator>

This file needs to be valid YAML.

Put your scheme's C source code into crypto_kem/yourschemename/clean.
1. Make sure all symbols are prefixed with PQCLEAN_YOURSCHEME_CLEAN_.
2. Include api.h into your scheme with the symbols specified in the section API. Make sure it does not include other files.
3. We use astyle to format code. You may consider running the following command on your submission:
```
astyle --project crypto_kem/yourschemename/clean/*.[ch]
```
1. You may run the tests in the tests/ folder. See the README for how to run the test suite.
2. Migrate your use of AES, SHA-2, and SHA-3 to the API in the common directory. Note that if you use the AES API, you must use the aes128_ecb_keyexp or aes128_ctr_keyexproutines (or 192 or 256) to expand the key into a key schedule object, then useaes128_ctx_releaseto release the key schedule object once you're finished with it. For the SHAKE API, use the appropriate_ctx_releasefunctions. For fixed-output functions SHA-2 and SHA-3, the_finalize` function will free the state. If you need to make copies of any of the states of these primitives, use the appropriate functions.
Create Makefile and Makefile.Microsoft_nmake files to compile your scheme as static library.
- We suggest you copy these from crypto_kem/kyber768/clean and modify them to suit your scheme.
Add a LICENSE file to your implementation folder.
Commit everything and push it to your fork.
Open a pull request on our Github repository and process the feedback given to you by the CI environment. The pull request will also set up a checklist for you and us to follow. Feel free to ask us questions via the pull request.

Generating implementations

It may sometimes be helpful to generate the implementations from a shared code base. You can find an example of how this can be done for SPHINCS+, Dilithium or Kyber

Testing your implementations locally using the PQClean test environment

It can be helpful to debug issues if you run the testing environment locally. This allows you to solve, for example, endianness problems or 32-bit problems much quicker, without waiting for the full CI runs to complete.

You will need Docker on your computer.

To run the ARM and powerpc containers you will need to run the following from a Linux computer:

docker pull multiarch/qemu-user-static:register
docker run --rm --privileged multiarch/qemu-user-static:register --reset

Then, to launch a specific testing environment, we suggest the following command:

docker run \
    --rm --tty --interactive \
    --volume $PWD:/pqclean \
    --user $(id -u):$(id -g) \
    --workdir /pqclean \
    pqclean/ci-container:ARCHITECTURE \
    /bin/bash

Replace ARCHITECTURE by one of the following:

armhf*
arm64*
i386
amd64
unstable-ppc*

Items marked with * require the multiarch/qemu-user-static registation step.

API

These items should be available in your api.h file.

KEMs

Functions:

int PQCLEAN_YOURSCHEME_IMPLEMENTATION_crypto_kem_keypair(
    uint8_t *pk, uint8_t *sk);
int PQCLEAN_YOURSCHEME_IMPLEMENTATION_crypto_kem_enc(
    uint8_t *ct, uint8_t *ss, const uint8_t *pk);
int PQCLEAN_YOURSCHEME_IMPLEMENTATION_crypto_kem_dec(
    uint8_t *ss, const uint8_t *ct, const uint8_t *sk);

#define macros:

CRYPTO_SECRETKEYBYTES
CRYPTO_PUBLICKEYBYTES
CRYPTO_CIPHERTEXTBYTES
CRYPTO_BYTES
CRYPTO_ALGNAME

Signature schemes

Functions:

int PQCLEAN_YOURSCHEME_IMPLEMENTATION_crypto_sign_keypair(
    uint8_t *pk, uint8_t *sk);
int PQCLEAN_YOURSCHEME_IMPLEMENTATION_crypto_sign(
    uint8_t *sm, size_t *smlen,
    const uint8_t *msg, size_t len,
    const uint8_t *sk);
int PQCLEAN_YOURSCHEME_IMPLEMENTATION_crypto_sign_open(
    uint8_t *m, size_t *mlen,
    const uint8_t *sm, size_t smlen,
    const uint8_t *pk);
int PQCLEAN_YOURSCHEME_IMPLEMENTATION_crypto_sign_signature(
    uint8_t *sig, size_t *siglen,
    const uint8_t *m, size_t mlen,
    const uint8_t *sk);
int PQCLEAN_YOURSCHEME_IMPLEMENTATION_crypto_sign_verify(
    const uint8_t *sig, size_t siglen,
    const uint8_t *m, size_t mlen,
    const uint8_t *pk);

#define macros:

PQCLEAN_YOURSCHEME_IMPLEMENTATION_CRYPTO_SECRETKEYBYTES
PQCLEAN_YOURSCHEME_IMPLEMENTATION_CRYPTO_PUBLICKEYBYTES
PQCLEAN_YOURSCHEME_IMPLEMENTATION_CRYPTO_ALGNAME
PQCLEAN_YOURSCHEME_IMPLEMENTATION_CRYPTO_BYTES

for KEMs, additionally define:

PQCLEAN_YOURSCHEME_IMPLEMENTATION_CRYPTO_CIPHERTEXTBYTES

Please make sure your api.h file does not include any other files.

Return codes

Your schemes should return 0 on success, or a negative value on failure. Notably, crypto_sign_open should return -1 if signature verification failed.

Contributing to the framework of PQClean

We also welcome contributions to the testing framework. Open an issue or pull request on Github and we will review your suggestion. In general, we are always looking to improve the experience of submitters of schemes and of people consuming the implementations collected by this project.

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