Clatter 🔊

no_std compatible, pure Rust implementation of the Noise protocol framework with support for Post Quantum (PQ) extensions as presented by Yawning Angel, Benjamin Dowling, Andreas Hülsing, Peter Schwabe, and Fiona Johanna Weber.

Main targets of this crate are correctness, extensibility, and strict no_std compatibility and those come with the small drawback of more verbose user experience with some boilerplate. If you don't need PQ functionality and are developing for a regular target, you probably are better off using these instead:

• snow
• noise-rust

Basis of this implementation relies heavily on the abovementioned crates and I'm extending huge thanks to the developers for their effort!

⚠️ Warning ⚠️

• This library has not received any formal audit
• While we enable some cryptographic providers by default, it is up to you to get familiar with those and decide if they meet your security and integrity requirements
• Post-Quantum cryptography generally is not as established and mature as classical cryptography. Users are encouraged to implement hybrid encryption schemes with classical crypto primitives incorporated to provide additional security in case of a catastrophic flaw in the post-quantum algorithms. Clatter provides DualLayerHandshake for this purpose.

Noise Protocol

This crate tracks Noise protocol framework revision 34. As of now we omit support for the following features:

• Handshake pattern parsing support - Handshakes have to instantiated with the correct primitives compile-time
• Curve 448 DH support - No suitable Rust implementation exists for our requirements
• Deferred pattern support - can be implemented by the user
• Fallback pattern support - Can be implemented by the user

Basics

From user perspective, everything in this crate is built around three types:

• NqHandshake - Classical, non-post-quantum Noise handshake
• PqHandshake - Post-quantum Noise handshake
• DualLayerHandshake - Dual layer handshake, which combines two Noise handshakes and allows a naive hybrid encryption approach

Users will pick and instantiate the desired handshake state machine with the crypto primitives they wish to use (supplied as generic parameters) and complete the handshake using the methods provided by the common Handshaker trait:

• write_message(...) - Write next handshake message
• read_message(...) - Read next handshake message
• is_finished() - Is the handshake ready?
• finalize() - Move to transport state

Once the handshake is complete, the handshake state machine can be moved to transport state by calling .finalize(). This finishes the handshake and the returned TransportState can be used for encrypting and decrypting communication with the peer. Voilà!

As already mentioned, this crate is quite verbose due to no_std compatibility requirements, so it's a good idea to take a look at the examples for a better view of the handshake process.

Example

Simplified example with the most straightforward (and most unsecure) interactive PQ handshake pattern and no handshake payload data at all:

use clatter::crypto::cipher::ChaChaPoly;
use clatter::crypto::hash::Sha512;
use clatter::crypto::kem::rust_crypto_kyber::Kyber512;
use clatter::handshakepattern::noise_pqnn;
use clatter::traits::Handshaker;
use clatter::PqHandshake;

fn main() {
    let mut rng_alice = rand::thread_rng();

    // Instantiate initiator handshake
    let mut alice = PqHandshake::<Kyber512, Kyber512, ChaChaPoly, Sha512, _>::new(
        noise_pqnn(),   // Handshake pattern
        &[],            // Prologue data
        true,           // Are we the initiator
        None,           // Pre-shared keys..
        None,           // ..
        None,           // ..
        None,           // ..
        &mut rng_alice, // RNG instance
    ).unwrap();

    let mut buf_alice_send = [0u8; 4096];
    let mut buf_alice_receive = [0u8; 4096];

    // Write handshake message and deliver to peer
    let n = alice.write_message(&[], &mut buf_alice_send).unwrap();
    my_send_function(&buf_alice_send[..n]);

    // Receive handshake message and process it
    let n = my_receive_function(&mut buf_alice_receive);
    let _ = alice.read_message(&buf_alice_receive[..n], &mut[]).unwrap();

    assert!(alice.is_finished());

    // Move to transport state
    let mut alice = alice.finalize().unwrap();

    // All done! Use .send() and .receive() on the transport state to encrypt
    // and decrypt communication with the peer
    let n = alice.send(b"Hello from Alice", &mut buf_alice_send).unwrap();
    my_send_function(&buf_alice_send[..n]);   
}

Selectable Features

Clatter allows user to pick the crypto primitives they wish to use via feature flags. Below is a table of all the configurable features supported by Clatter:

Feature flag	Description	Default	Details
use-25519	Enable X25519 DH	yes
use-aes-gcm	Enable AES-GCM cipher	yes
use-chacha20poly1305	Enable ChaCha20-Poly1305 cipher	yes
use-sha	Enable SHA-256 and SHA-512 hashing	yes
use-blake2	Enable BLAKE2 hashing	yes
use-rust-crypto-kyber	Enable Kyber KEMs by RustCrypto	yes
use-pqclean-kyber	Enable Kyber KEMs by PQClean	yes
std	Enable standard library support	no	Enables std for supported dependencies
alloc	Enable allocator support	no

PQ? NQ? Why should I care?

This crate refers to classical Noise handshakes as NQ handshakes (non-post-quantum). But what does a PQ (post-quantum) handshake actually mean?

Key encapsulation mechanism or KEM is a public-key encryption system that allows a sender to securely transmit a short shared secret to a receiver using the receivers public key. This shared secret can then be used as a basis for further symmetric encrypted communication.

Classical Noise uses Diffie-Hellman or DH key exchanges to establish a shared secret between the parties. During a DH key exchange the shared secret is generated by both parties through mutual computations on the publicly transmitted data - whereas KEMs are used to transmit the shared secret directly.

The motivation to use KEMs lies in the fact that there are KEM algorithms that are currently though to be secure against cryptoanalytic attacks by quantum computers. The DH algorithms used by Noise rely on the difficulty of mathematical problems that can be easily solved on a powerful quantum computer. Such quantum computers do not exist yet, but the world is already shifting towards quantum-safe cryptography.

Post Quantum Noise by Yawning Angel et al. introduced methods and rules for substituting DH key exchanges from classical Noise with KEMs, while maintaining a similar level of secrecy. This crate provides a safe Rust based implementation for the post-quantum handshakes proposed by PQNoise - so that we can keep on benefitting from the clarity and formal security guarantees of Noise even in post-quantum era.

PQ Handshake Notation

Noise uses a simple pattern language for defining the handshake patterns. PQ patterns follow these same rules, only substituting DH tokens with ekem and skem operations, which indicate sending of a ciphertext that was encapsulated to the ephemeral/static key of the receiving party.

Differences to PQNoise paper

• PQNoise presents the possibility to use different KEMs for ephemeral, initiator, and responder. With Clatter the same KEM is used for both initiator and responder operations, while it is still possible to configure a separate KEM for ephemeral use.
• PQNoise presents SEEC, a method for improving RNG security in bad randomness settings. Clatter does not currently implement SEEC.

Verification

Caltter is verified by:

• Unit tests
• Integration tests
• Fuzzing
• Cacophony and Snow test vectors
  • Supported pre-made handshake patterns verified
  • Test harness in vectors/