PAS-TA-U: PASsword-based Threshold Authentication with PASsword Update

A single-sign-on (SSO) is an authentication system that allows a user to log in with a single identity and password to any of several related, yet independent, server applications. SSO solutions eliminate the need for users to repeatedly prove their identities to different applications and hold different credentials for each application. Token-based authentication is commonly used to enable an SSO experience on the web, and on enterprise networks. A large body of work considers distributed token generation which can protect the long-term keys against a subset of breached servers. A recent work (CCS\u2718) introduced the notion of Password-based Threshold Authentication (PbTA) with the goal of making password-based token generation for SSO secure against server breaches that could compromise both long-term keys and user credentials. They also introduced a generic framework called PASTA that can instantiate a PbTA system. The existing SSO systems built on distributed token generation techniques, including the PASTA framework, do not admit password-update functionality. In this work, we address this issue by proposing a password-update functionality into the PASTA framework. We call the modified framework PAS-TA-U. As a concrete application, we instantiate PAS-TA-U to implement in Python a distributed SSH key manager for enterprise networks (ESKM) that also admits a password-update functionality for its clients. Our experiments show that the overhead of protecting secrets and credentials against breaches in our system compared to a traditional single server setup is low (average 119 ms in a 10-out-of-10 server setting on Internet with 80 ms round trip latency)

Distributed Smooth Projective Hashing and its Application to Two-Server PAKE

Smooth projective hash functions have been used as building block for various cryptographic applications, in particular for password-based authentication. In this work we propose the extended concept of distributed smooth projective hash functions where the computation of the hash value is distributed across $n$ parties and show how to instantiate the underlying approach for languages consisting of Cramer-Shoup ciphertexts. As an application of distributed smooth projective hashing we build a new framework for the design of two-server password authenticated key exchange protocols, which we believe can help to explain the design of earlier two-server password authenticated key exchange protocols

Threshold password-authenticated key exchange

Abstract. In most password-authenticated key exchange systems there is a single server storing password verification data. To provide some resilience against server compromise, this data typically takes the form of a one-way function of the password (and possibly a salt, or other public values), rather than the password itself. However, if the server is compromised, this password verification data can be used to perform an offline dictionary attack on the user’s password. In this paper we propose an efficient password-authenticated key exchange system involving a set of servers, in which a certain threshold of servers must participate in the authentication of a user, and in which the compromise of any fewer than that threshold of servers does not allow an attacker to perform an offline dictionary attack. We prove our system is secure in the random oracle model under the Decision Diffie-Hellman assumption against an attacker that may eavesdrop on, insert, delete, or modify messages between the user and servers, and that compromises fewer than that threshold of servers.

Provably secure threshold password-authenticated key exchange

We present two protocols for threshold password authenticated key exchange. In this model for password authentication, the password is not stored in a single authenticating server but rather shared among a set of n servers so that an adversary can learn the password only by breaking into t + 1 of them. The protocols require n> 3t servers to work. The goal is to protect the password against hackers attacks that can break into the authenticating server and steal password information. All known centralized password authentication schemes are susceptible to such an attack. Ours are the first protocols which are provably secure in the standard model (i.e. no random oracles are used for the proof of security). Moreover our protocols are reasonably efficient and implementable in practice. In particular a goal of the design was to avoid costly zero-knowledge proofs to keep interaction to a minimum