[OPAQUE](https://eprint.iacr.org/2018/163.pdf) is an asymmetric 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 the [Internet Draft for OPAQUE](https://github.com/cfrg/draft-irtf-cfrg-opaque).
Background
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Asymmetric 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.
The API can be found [here](https://docs.rs/opaque-ke/) along with an example for usage. More examples can be found in the [examples](./examples) directory.
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](https://engineering.fb.com/2021/09/10/security/whatsapp-e2ee-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](https://research.nccgroup.com/2021/12/13/public-report-whatsapp-opaque-ke-cryptographic-implementation-review/).
- [draft-irtf-cfrg-opaque-08](https://datatracker.ietf.org/doc/draft-irtf-cfrg-opaque/08/), containing a detailed (byte-level) specification for OPAQUE
- ["Let's talk about PAKE"](https://blog.cryptographyengineering.com/2018/10/19/lets-talk-about-pake/), an introductory blog post written by Matthew Green that covers OPAQUE
