OPAQUE Security

OPAQUE is the foundation of DarkAuth password authentication. It is a password-authenticated key exchange that lets the client authenticate without sending the password to the server.

Guarantees

In the DarkAuth model:

• The password is not posted to the server during login.
• The server stores an OPAQUE record rather than a plaintext password.
• The client receives an export key after successful authentication.
• The server-side OPAQUE login session binds the identity used to mint sessions.

This is stronger than a traditional password form plus server-side password hash because the server does not receive the password in the first place.

Export key custody

The export key belongs on the client side. DarkAuth uses it to derive material for wrapping and unwrapping user keys. The server does not receive it.

That improves custody, but it also affects recovery. If a password changes through a flow that cannot access old password-derived material, old encrypted data may need a separate recovery path.

Limits

OPAQUE does not protect against every password-related risk. It does not stop phishing, compromised devices, malicious browser extensions, malicious frontend code, weak passwords, or users entering credentials into the wrong origin.

Use OPAQUE alongside MFA, strict origins, safe deployment, clear UI, and monitoring.