ML-KEM (FIPS 203) extension for github.com/lestrrat-go/jwx.

This module adds post-quantum ML-KEM key encapsulation support to jwx, enabling ML-KEM-768, ML-KEM-1024, ML-KEM-768+A192KW, and ML-KEM-1024+A256KW algorithms for JWE key encryption. JWK representation follows draft-ietf-jose-pqc-kem using the AKP (Algorithm Key Pair) key type.

Work in progress. This module exists as a separate companion because draft-ietf-jose-pqc-kem is still an Internet-Draft (currently -05). Once the draft is published as an RFC and the bindings stabilize, ML-KEM support may move directly into jwx and this module will be deprecated. The underlying ML-KEM implementation comes from Go's standard library crypto/mlkem (Go 1.24+) — no third-party dependency.

go get github.com/jwx-go/mlkem/v4

Import this package to register ML-KEM algorithms with jwx:

import _ "github.com/jwx-go/mlkem/v4"

Note: Registration happens in init() and will panic if any of the ML-KEM algorithms, key importers, or exporters fail to register (for example, if another module has already claimed the same identifier). This is intentional: a half-registered extension would silently produce "algorithm not found" errors at encrypt or decrypt time, so the failure is raised at program start instead.

This registers:

• Key encryption algorithms: ML-KEM-768, ML-KEM-1024, ML-KEM-768+A192KW, ML-KEM-1024+A256KW
• JWK import/export for stdlib *mlkem.EncapsulationKey768/1024 and *mlkem.DecapsulationKey768/1024
• JWE encrypt/decrypt dispatch via the jwebb extension hook

import (
    "crypto/mlkem"
    jwxmlkem "github.com/jwx-go/mlkem/v4"
    "github.com/lestrrat-go/jwx/v4/jwa"
    "github.com/lestrrat-go/jwx/v4/jwe"
)

dk, _ := mlkem.GenerateKey768()
ek := dk.EncapsulationKey()

encrypted, _ := jwe.Encrypt(payload,
    jwe.WithKey(jwxmlkem.MLKEM768(), ek),
    jwe.WithContentEncryption(jwa.A256GCM()),
)

decrypted, _ := jwe.Decrypt(encrypted,
    jwe.WithKey(jwxmlkem.MLKEM768(), dk),
)

import (
    "crypto/mlkem"
    jwxmlkem "github.com/jwx-go/mlkem/v4"
    "github.com/lestrrat-go/jwx/v4/jwk"
    "github.com/lestrrat-go/jwx/v4/jwe"
)

dk, _ := mlkem.GenerateKey768()
jwkKey, _ := jwk.Import[jwk.Key](dk)

pubJWK, _ := jwkKey.PublicKey()
encrypted, _ := jwe.Encrypt(payload,
    jwe.WithKey(jwxmlkem.MLKEM768(), pubJWK),
    jwe.WithContentEncryption(jwa.A256GCM()),
)

decrypted, _ := jwe.Decrypt(encrypted, jwe.WithKey(jwxmlkem.MLKEM768(), jwkKey))

The KDF binds the algorithm identifier per draft-ietf-jose-pqc-kem using KMAC256 (NIST SP 800-185).

draft-ietf-jose-pqc-kem defines the AKP priv field as 32 bytes (the d seed component) but Go's crypto/mlkem requires the full 64-byte d || z seed. To preserve exact stdlib key identity, this module stores d in priv and the 32-byte implicit-rejection value in a companion-private z field. Private JWK round-trips emitted by this module therefore preserve the full 64-byte seed exactly, while PublicKey() drops z so public AKP JWKs do not leak it.

Legacy ML-KEM JWKs that only carry priv remain supported. When such a key is re-imported, this module derives a deterministic fallback z from d and the ML-KEM parameter set so reconstructed keys remain stable across processes and restarts. Those legacy round-trips preserve the public key and decapsulation of valid ciphertexts, but they cannot recover the original random z unless the JWK already stored it.

KDF binary format. The KMAC256 KDF input X follows draft-ietf-jose-pqc-kem-05 §5.1, which defines AlgorithmID and SuppPubInfo per RFC 7518 §4.6.2 — a length-prefixed octet string for the algorithm identifier and a big-endian 32-bit key-length-in-bits field. The draft is still an Internet-Draft and ships no KAT vectors, and as of this release no second JOSE implementation of the draft exists to cross-validate against. Treat wire-level KDF interop with other implementations as provisional until such vectors or an interoperating peer become available; any future draft revision that tightens this encoding will break wire compatibility with messages produced by earlier versions of this module.

MIT