pake

PAKE stands for Password-Authenticated Key Exchange, a class of cryptographic protocols that enables two or more parties to establish a shared cryptographic key using a password as the underlying authentication factor. The core goal is to provide mutual authentication and a common session key while ensuring that an attacker who observes the communication cannot verify or guess the password offline.

In a typical PAKE protocol, parties exchange messages that depend on the password but do not reveal it. If a party uses a correct password, the protocol completes and both sides derive the same session key; if the password is incorrect, the protocol aborts. A key security objective is resistance to offline dictionary attacks, meaning an attacker cannot determine or test password guesses by simply listening to or recording the protocol run.

PAKE comes in several forms. Augmented PAKE (aPAKE) uses a verifier stored on a server rather than the plaintext password, improving security if the verifier is compromised. Classic examples of PAKE protocols include the Secure Remote Password (SRP) protocol, J-PAKE (Password Authenticated Key Exchange by Juggling), and SPEKE (Secret Password Exponential Key Exchange). OPAQUE is a newer framework that provides password-based authentication with oblivious password handling, offering strong protection even when servers store verifiers.

Common use cases include securing TLS and other network authentication, remote login, and secure messaging, where users rely on a password rather than a public-key infrastructure. While PAKE provides strong protections, its security depends on password choice and proper implementation; weak passwords or poor deployment can undermine the protocol’s guarantees.