Kyber

A rust implementation of the Kyber algorithm, a KEM selected by the long-running NIST Post-Quantum Standardization Project.

This library: * Is nostd compatible and needs no allocator, suitable for embedded devices. * Reference files contain no unsafe code and are written in pure rust. * On x8664 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 kyber768.

It is recommended to use Kyber in a hybrid system alongside a traditional key exchange algorithm such as X25519.

Please also read the security considerations before use.

Installation

In Cargo.toml:

toml [dependencies] pqc_kyber = "0.2.0"

Usage

rust use pqc_kyber::*;

For optimisations enable the following RUSTFLAGS on x86_64 systems when building:

shell export RUSTFLAGS="-C target-cpu=native -C target-feature=+aes,+avx2,+sse2,+sse4.1,+bmi2,+popcnt"

The higher level key exchange structs will be appropriate for most use-cases.

Unilaterally Authenticated Key Exchange

```rust let mut rng = rand::thread_rng();

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

// Generate Bob's Keypair let bob_keys = keypair(&mut rng);

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

// Bob authenticates and responds let serverresponse = bob.serverreceive( clientinit, &bobkeys.secret, &mut rng )?;

// Alice decapsulates the shared secret alice.clientconfirm(serverresponse)?;

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

Mutually Authenticated Key Exchange

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

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

let alicekeys = keypair(&mut rng); let bobkeys = keypair(&mut rng);

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

let serverresponse = bob.serverreceive( clientinit, &alicekeys.public, &bob_keys.secret, &mut rng )?;

alice.clientconfirm(serverresponse, &alice_keys.secret)?;

asserteq!(alice.sharedsecret, bob.shared_secret); ```

Key Encapsulation

Lower level functions for using the Kyber algorithm directly. ```rust // Generate Keypair let keys_bob = keypair(&mut rng);

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

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

asserteq!(sharedsecretalice, sharedsecret_bob); ```

Errors

The KyberError enum 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 kyber768 is used by default as recommended by the authors. It is roughly equivalent to AES-196. Apart from the two security levels, all other features can be combined as needed. For example:

toml [dependencies] pqc_kyber = {version = "0.2.0", features = ["kyber512", "90s", "reference"]}

| Feature | Description | |-----------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | kyber512 | Enables kyber512 mode, with a security level roughly equivalent to AES-128. | | kyber1024 | Enables kyber1024 mode, with a security level roughly equivalent to AES-256. A compile-time error is raised if more than one security level is specified. | | 90s | Uses SHA2 and AES in counter mode as a replacement for SHAKE. This can provide hardware speedups in some cases. | | reference | On x86_64 platforms the optimized version is used by default. Enabling this feature will force usage of the reference codebase. This flag is redundant on other architectures and has no effect. | | wasm | For compiling to WASM targets. |

Testing

The runalltests 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.

```bash

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.

toml [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:

shell wasm-pack build -- --features wasm

Security Considerations

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.

Kyber is relatively new, it is advised to use it in a hybrid key exchange system alongside a traditional algorithm like X25519 rather than by itself.

For further reading the IETF have a draft construction for hybrid key exchange in TLS 1.3:

https://www.ietf.org/archive/id/draft-ietf-tls-hybrid-design-04.html

You can also see how such an system is implemented here in C by OpenSSH

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 the final standardised algorithm resulting from 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