The OPAQUE key exchange protocol

OPAQUE is an augmented password-authenticated key exchange protocol. It allows a client to authenticate to a server using a password, without ever having to expose the plaintext password to the server.

This implementation is based on RFC 9807.

Background

Augmented Password Authenticated Key Exchange (aPAKE) protocols are designed to provide password authentication and mutually authenticated key exchange without relying on PKI (except during user/password registration) and without disclosing passwords to servers or other entities other than the client machine.

OPAQUE is a PKI-free aPAKE that is secure against pre-computation attacks and capable of using a secret salt.

Documentation

The API can be found here along with an example for usage. More examples can be found in the examples directory.

Installation

Add the following line to the dependencies of your Cargo.toml:

opaque-ke = "4.1.0-pre.2"

Minimum Supported Rust Version

Rust 1.87 or higher.

Audit

This library was audited by NCC Group in June of 2021. The audit was sponsored by WhatsApp for its use in enabling end-to-end encrypted backups.

The audit found issues in release v0.5.0, and the fixes were subsequently incorporated into release v1.2.0. See the full audit report here.

Resources

• OPAQUE academic publication, including formal definitions and a proof of security
• RFC 9807, containing a detailed (byte-level) specification for OPAQUE
• “Let’s talk about PAKE”, an introductory blog post written by Matthew Green that covers OPAQUE
• @serenity-kit/opaque, a WebAssembly package for this library
• opaque-wasm, a WebAssembly package for this library. A comparison between @serenity-kit/opaque and opaque-wasm can be found here
• react-native-opaque, a React Native package for this library matching the API of @serenity-kit/opaque

Contributors

The authors of this code are Kevin Lewi (@kevinlewi) and François Garillot (@huitseeker). To learn more about contributing to this project, see this document.

Acknowledgments

Special thanks go to Hugo Krawczyk and Chris Wood for helping to clarify discrepancies and making suggestions for improving this implementation. Additional credit goes to @daxpedda for adding no_std support, p256 support, and making other general improvements to the library.

License

This project is dual-licensed under either the MIT license or the Apache License, Version 2.0. You may select, at your option, one of the above-listed licenses.