Secure modular password authentication for the web using channel bindings

Abstract

Secure protocols for password-based user authentication are well-studied in the cryptographic literature but have failed to see wide-spread adoption on the internet; most proposals to date require extensive modifications to the Transport Layer Security (TLS) protocol, making deployment challenging. Recently, a few modular designs have been proposed in which a cryptographically secure password-based mutual authentication protocol is run inside a confidential (but not necessarily authenticated) channel such as TLS; the password protocol is bound to the established channel to prevent active attacks. Such protocols are useful in practice for a variety of reasons: security no longer relies on users’ ability to validate server certificates and can potentially be implemented with no modifications to the secure channel protocol library. We provide a systematic study of such authentication protocols. Building on recent advances in modeling TLS, we give a formal definition of the intended security goal, which we call password-authenticated and confidential channel establishment (PACCE). We show generically that combining a secure channel protocol, such as TLS, with a password authentication or password-authenticated key exchange protocol, where the two protocols are bound together using the transcript of the secure channel’s handshake, the server’s certificate, or the server’s domain name, results in a secure PACCE protocol. Our prototypes based on TLS are available as a cross-platform client-side Firefox browser extension as well as an Android application and a server-side web application that can easily be installed on servers.