Post-Quantum Cryptography in Rust

This repository is parameter selection and lightweight wrapper around a number of Rust cryptographic libraries. Its purpose isn't to implement primitives, rather to unify the API surface of existing libraries; limited to the tiny subset needed by the Dark Bio project.

The library is opinionated. Parameters and primitives were selected to provide matching levels of security in a post-quantum world. APIs were designed to make the library easy to use and hard to misuse. Flexibility will always be rejected in favor of safety.

• Digital signatures
  • xDSA (RFC-DRAFT): MLDSA, EdDSA, SHA512
    • EdDSA (RFC-8032): Ed25519
    • MLDSA (RFC-9881): Security level 3 (ML-DSA-65)
  • RSA (RFC-8017): 2048-bit, SHA256
• Encryption
  • xHPKE (RFC-9180): X-WING, HKDF, SHA256, ChaCha20, Poly1305, dark-bio-v1: domain prefix
    • X-WING (RFC-DRAFT): MLKEM, ECC
      • ECC (RFC-7748): X25519
      • MLKEM (FIPS-203): Security level 3 (ML-KEM-768)
  • STREAM (RFC N/A, Rage): ChaCha20, Poly1305, 16B tag, 64KB chunk
• Key derivation
  • Argon2 (RFC-9106): id variant
  • HKDF (RFC-5869): SHA256
• Serialization
  • CBOR (RFC-8949): restricted to bool,null, integer, text, bytes, array, map[int], option
  • COSE (RFC-9052): COSE_Sign1, COSE_Encrypt0, dark-bio-v1: domain prefix
• Credential / Attestation
  • CWT (RFC-8392): xDSA, xHPKE
    • EAT (RFC-9711)

All functionality is WASM ready. Targeting wasm32-unknown-unknown needs the getrandom_backend="wasm_js" config passed to rustc, as this repository does in its own .cargo/config.toml.

The entire library is hidden behind feature flags to allow selectively depending on it from the firmware, cloud and mobile app, each cherry-picking only what's needed.

Quick start

Signatures come from xdsa, encryption from xhpke, and cose wraps both into COSE envelopes using the Dark Bio wire profile documented in the cose module. Enabling the three pulls in everything they need.

[dependencies]
darkbio-crypto = { version = "0.18", features = ["cose", "xdsa", "xhpke"] }

COSE signing and verification and xHPKE encryption and decryption use an application domain that both sides must agree on. It is prefixed with dark-bio-v1: internally and binds the operation to one purpose. Choose distinct domains for distinct purposes. Raw xdsa signatures carry no such application domain, which is why the cose envelopes are the recommended entry point.

# #[cfg(feature = "cose")] {
use darkbio_crypto::{cose, xdsa, xhpke};

// Long term identities, one for signing and one for receiving
let signer = xdsa::SecretKey::generate();
let recipient = xhpke::SecretKey::generate();

// A detached signature over a message that travels separately
let signature = cose::sign_detached("payload", &signer, b"example").unwrap();
cose::verify_detached(&signature, "payload", &signer.public_key(), b"example", Some(60)).unwrap();

// Sign and encrypt a payload to the recipient, then open and verify it back.
// The second argument is authenticated but must be supplied separately.
let sealed = cose::seal("payload".to_string(), "metadata", &signer, &recipient.public_key(), b"example").unwrap();
let opened: String = cose::open(&sealed, "metadata", &recipient, &signer.public_key(), b"example", Some(60)).unwrap();
assert_eq!(opened, "payload");
# }

Each module's documentation opens with a runnable example of its own primitives.

Feature gates

As a starting point, you will most probably want xdsa for digital signatures, xhpke for asymmetric encryption and cose for proper enveloping. For the remainder for the features, please consult the list below:

Derive Cbor

The cbor feature provides a #[derive(Cbor)] macro that generates encoders and decoders for structs. By default, structs are represented as maps, with the possibility of requesting array encoding.

In map encoding mode, all keys are integers. This is a deliberate restriction to support maps but still force non-wasteful encoding. Each field requires #[cbor(key = N)]. To encode a struct as an array, use #[cbor(array)].

Siblings

This is a sibling package with the Go github.com/dark-bio/crypto-go; as in, both repositories implement the same feature sets and API surfaces at the same version points. This naturally means PRs merged into one project necessarily have to have a counter-PR in the other project.

Bindings

This package currently has a Flutter binding github.com/dark-bio/crypto-fl that exposes the same API surface and versioning; implemented by wrapping the Rust code via FFI rather than reimplementing it.

This package also has a TypeScript binding github.com/dark-bio/crypto-ts that also exposes the same API surface and versioning; implemented by wrapping the Rust code via WASM rather than reimplementing it.

Acknowledgements

Shoutout to Filippo Valsorda (@filosottile) for lots of tips and nudges on what kind of cryptographic primitives to use and how to combine them properly; and also for his work in general on cryptography standards.

Naturally, many thanks to the authors of all the libraries this project depends on.

License

This library is licensed under the BSD 3-Clause License.