aPAKE

Augmented Password-Authenticated Key Exchange (aPAKE) is a class of password-based key exchange protocols designed to enable two parties to establish a shared secret using a memorized password, while protecting against offline password guessing even if the server storing authentication data is compromised. In an aPAKE, the password is never sent in the clear, and the stored verifier or credential data is constructed so that an attacker who gains access to the server database cannot easily determine the password or impersonate the user without interacting with a legitimate client.

How it works in brief: during registration, the user creates a password and the server stores a verifier derived from that password together with a salt or other binding to the user identity. During login, the client and server engage in a cryptographic exchange that proves knowledge of the password and results in a mutually authenticated session key. The exact mechanics vary by protocol, but the goal is mutual authentication, forward secrecy of the session key, and resistance to offline dictionary attacks even if the server data is leaked.

Notable aPAKE protocols include SRP (Secure Remote Password), which integrates verifier-based authentication with key exchange, and OPAQUE, a modern framework that decouples credential storage from the password using an encrypted credential envelope. aPAKE protocols are widely used to secure remote login, web authentication, and other password-based access scenarios while improving resilience against database breaches.