Kyber

A rust implementation of the Kyber algorithm, a post-quantum KEM that is a finalist in NIST's Post-Quantum Standardization Project.

This library:

• Is no_std compatible and needs no allocator, suitable for embedded devices.
• Reference files contain no unsafe code and are written in pure rust.
• On x86_64 platforms uses an avx2 optimized version by default, which includes some assembly code taken from the C repo.
• Compiles to WASM using wasm-bindgen and has a ready-to-use binary published on NPM.

See the features section for different options regarding security levels and modes of operation. The default security setting is kyber764.

Please also read the security considerations before use.

Installation

In Cargo.toml:

[dependencies]
pqc-kyber = "0.2.0"

Usage

use pqc_kyber::*;

The higher level structs will be appropriate for most use-cases. Both unilateral or mutually authenticated key exchanges are possible.

Unilaterally Authenticated Key Exchange

let mut rng = rand::thread_rng();

// Initialize the key exchange structs
let mut alice = Uake::new();
let mut bob = Uake::new();

// Generate Keypairs
let alice_keys = keypair(&mut rng);
let bob_keys = keypair(&mut rng);

// Alice initiates key exchange
let client_init = alice.client_init(&bob_keys.public, &mut rng);

// Bob authenticates and responds
let server_send = bob.server_receive(
  client_init, &bob_keys.secret, &mut rng
)?;

// Alice decapsulates the shared secret
alice.client_confirm(server_send)?;

// Both key exchange structs now have the same shared secret
assert_eq!(alice.shared_secret, bob.shared_secret);

Mutually Authenticated Key Exchange

Mutual authentication follows the same workflow but with additional keys passed to the functions:

let mut alice = Ake::new();
let mut bob = Ake::new();

let alice_keys = keypair(&mut rng);
let bob_keys = keypair(&mut rng);

let client_init = alice.client_init(&bob_keys.public, &mut rng);

let server_send = bob.server_receive(
  client_init, &alice_keys.public, &bob_keys.secret, &mut rng
)?;

alice.client_confirm(server_send, &alice_keys.secret)?;

assert_eq!(alice.shared_secret, bob.shared_secret);

Key Encapsulation

Lower level functions for using the Kyber algorithm directly.

// Generate Keypair
let keys_bob = keypair(&mut rng);

// Alice encapsulates a shared secret using Bob's public key
let (ciphertext, shared_secret_alice) = encapsulate(&keys_bob.public, &mut rng)?;

// Bob decapsulates a shared secret using the ciphertext sent by Alice 
let shared_secret_bob = decapsulate(&ciphertext, &keys_bob.secret)?;

assert_eq!(shared_secret_alice, shared_secret_bob);

Errors

The KyberError enum handles errors. It has two variants:

• InvalidInput - One or more inputs to a function are incorrectly sized. A possible cause of this is two parties using different security levels while trying to negotiate a key exchange.

• Decapsulation - The ciphertext was unable to be authenticated. The shared secret was not decapsulated.

Features

If no security level is specified then kyber764 is used by default as recommended by the authors. It is roughly equivalent to AES-196 in terms of protection.

Testing

The run_all_tests script will traverse all possible codepaths by running a matrix of the security levels and variants.

Known Answer Tests require deterministic rng seeds, enable the KATs feature to run them, you must also specify the module as noted below. Using this feature outside of cargo test will result in a compile-time error.

# This example runs all KATs for kyber512-90s, note `--test kat` is needed here.
cargo test --test kat --features "KATs kyber512 90s"

The test vector files are quite large, you will need to build them yourself from the C reference code. There's a helper script to do this here.

See the testing readme for more comprehensive info.

Benchmarking

Uses criterion for benchmarking. If you have GNUPlot installed it will generate statistical graphs in target/criterion/.

See the benchmarking readme for information on correct usage.

Fuzzing

The fuzzing suite uses honggfuzz, installation and instructions are on the fuzzing page.

WebAssembly

This library has been compiled and published as a WASM binary package. Usage instructions are published on npm:

https://www.npmjs.com/package/pqc-kyber

Which is also located here in the wasm readme

To install:

npm i pqc-kyber

To use this library for web assembly purposes you'll need the wasm feature enabled.

[dependencies]
pqc-kyber = {version = "0.2.0", features = ["wasm"]

You will also need wasm-pack and wasm32-unknown-unknown or wasm32-unknown-emscripten toolchains installed

To build include the feature flag:

wasm-pack build -- --features wasm

Security Considerations

The NIST post quantum standardisation project is still ongoing and changes may still be made to the underlying reference code at any time.

While much care has been taken porting from the C reference codebase, this library has not undergone any third-party security auditing nor can any guarantees be made about the potential for underlying vulnerabilities in LWE cryptography or potential side-channel attacks arising from this implementation.

Please use at your own risk.

About

Kyber is an IND-CCA2-secure key encapsulation mechanism (KEM), whose security is based on the hardness of solving the learning-with-errors (LWE) problem over module lattices. It is one of the round 3 finalist algorithms submitted to the NIST post-quantum cryptography project.

The official website: https://pq-crystals.org/kyber/

Authors of the Kyber Algorithm:

• Roberto Avanzi, ARM Limited (DE)
• Joppe Bos, NXP Semiconductors (BE)
• Léo Ducas, CWI Amsterdam (NL)
• Eike Kiltz, Ruhr University Bochum (DE)
• Tancrède Lepoint, SRI International (US)
• Vadim Lyubashevsky, IBM Research Zurich (CH)
• John M. Schanck, University of Waterloo (CA)
• Peter Schwabe, Radboud University (NL)
• Gregor Seiler, IBM Research Zurich (CH)
• Damien Stehle, ENS Lyon (FR)

Contributing

Contributions welcome. For pull requests create a feature fork and submit it to the development branch. More information is available on the contributing page