What is OPAQUE?

OPAQUE is a modern protocol for secure password login. Unlike traditional login methods where the server stores a hashed version of your password, OPAQUE uses advanced cryptography so that the server never sees your actual password in plaintext.

Private.Ki uses OPAQUE for login authentication. So the password which you set up when creating your Private.Ki account is 100% yours - it is never sent to the server in any form. We don't know it, and we can't recover it for you. (But you can reset it securely.)

How does login work with OPAQUE?

When you log in to your Private.Ki account, a special cryptographic exchange occurs between your device and the server. This exchange allows the server to verify that you entered the correct password without learning what your password is. The server ends up storing only an encrypted “credential envelope” derived from your password (combined with a server secret key), rather than a usable password hash or the password itself.

That means that even if someone were to steal the login database from Private.Ki’s servers or a rogue employee gets access to it, they still could not recover your actual password from what’s stored. An attacker would be forced to perform expensive guessing attacks for each individual account - and if your password is strong and Private.Ki implements rate-limiting on login attempts, guessing becomes impractical.

In simpler terms, OPAQUE gives you a form of zero-knowledge password proof: you prove you know your secret to the server, but the server gains zero knowledge of the secret itself. This greatly strengthens account security and privacy.