A method for making password-based key exchange resilient to server compromise

Abstract. This paper considers the problem of password-authenticated key exchange (PAKE) in a client-server setting, where the server authenticates using a stored password file, and it is desirable to maintain some degree of security even if the server is compromised. A PAKE scheme is said to be resilient to server compromise if an adversary who compromises the server must at least perform an offline dictionary attack to gain any advantage in impersonating a client. (Of course, offline dictionary attacks should be infeasible in the absence of server compromise.) One can see that this is the best security possible, since by definition the password file has enough information to allow one to play the role of the server, and thus to verify passwords in an offline dictionary attack. While some previous PAKE schemes have been proven resilient to server compromise, there was no known general technique to take an arbitrary PAKE scheme and make it provably resilient to server compromise. This paper presents a practical technique for doing so which requires essentially one extra round of communication and one signature computation/verification. We prove security in the universal composability framework by (1) defining a new functionality for PAKE with resilience to server compromise, (2) specifying a protocol combining this technique with a (basic) PAKE functionality, and (3) proving (in the random oracle model) that this protocol securely realizes the new functionality.

Security Proof for Password Authentication in TLS-Verifier-based Three-Party Group Diffie-Hellman

The internet has grown greatly in the past decade, by some numbers exceeding 47 million active web sites and a total aggregate exceeding100 million web sites. What is common practice today on the Internet is that servers have public keys, but clients are largely authenticated via short passwords. Protecting these passwords by not storing them in the clear on institutions's servers has become a priority. This paper develops password-based ciphersuites for the Transport Layer Security (TLS) protocol that are: (1) resistant to server compromise; (2) provably secure; (3) believed to be free from patent and licensing restrictions based on an analysis of relevant patents in the area

Zero-Knowledge Password Policy Check from Lattices

Passwords are ubiquitous and most commonly used to authenticate users when logging into online services. Using high entropy passwords is critical to prevent unauthorized access and password policies emerged to enforce this requirement on passwords. However, with current methods of password storage, poor practices and server breaches have leaked many passwords to the public. To protect one's sensitive information in case of such events, passwords should be hidden from servers. Verifier-based password authenticated key exchange, proposed by Bellovin and Merrit (IEEE S\&P, 1992), allows authenticated secure channels to be established with a hash of a password (verifier). Unfortunately, this restricts password policies as passwords cannot be checked from their verifier. To address this issue, Kiefer and Manulis (ESORICS 2014) proposed zero-knowledge password policy check (ZKPPC). A ZKPPC protocol allows users to prove in zero knowledge that a hash of the user's password satisfies the password policy required by the server. Unfortunately, their proposal is not quantum resistant with the use of discrete logarithm-based cryptographic tools and there are currently no other viable alternatives. In this work, we construct the first post-quantum ZKPPC using lattice-based tools. To this end, we introduce a new randomised password hashing scheme for ASCII-based passwords and design an accompanying zero-knowledge protocol for policy compliance. Interestingly, our proposal does not follow the framework established by Kiefer and Manulis and offers an alternate construction without homomorphic commitments. Although our protocol is not ready to be used in practice, we think it is an important first step towards a quantum-resistant privacy-preserving password-based authentication and key exchange system

Efficient Two-Party Password-Based Key Exchange Protocols in the UC Framework

The original publication is available at www.springerlink.comInternational audienceMost of the existing password-based authenticated key exchange protocols have proofs either in the indistinguishability-based security model of Bellare, Pointcheval, and Rogaway (BPR) or in the simulation-based of Boyko, MacKenzie, and Patel (BMP). Though these models provide a security level that is sufficient for most applications, they fail to consider some realistic scenarios such as participants running the protocol with different but possibly related passwords. To overcome these deficiencies, Canetti et al. proposed a new security model in the universal composability (UC) framework which makes no assumption on the distribution on passwords used by the protocol participants. They also proposed a new protocol, but, unfortunately, the latter is not as efficient as some of the existing protocols in BPR and BMP models. In this paper, we investigate whether some of the existing protocols that were proven secure in BPR and BMP models can also be proven secure in the new UC model and we answer this question in the affirmative. More precisely, we show that the protocol by Bresson, Chevassut, and Pointcheval (BCP) in CCS 2003 is also secure in the new UC model. The proof of security relies in the random-oracle and ideal-cipher models and works even in the presence of adaptive adversaries, capable of corrupting players at any time and learning their internal states

Universally Composable Two-Server PAKE

Two-Server Password Authenticated Key Exchange (2PAKE) protocols apply secret shar-ing techniques to achieve protection against server-compromise attacks. 2PAKE protocols eliminate the need for password hashing and remain secure as long as one of the servers remains honest. This concept has also been explored in connection with two-server password authenticated secret sharing (2PASS) protocols for which game-based and universally composable versions have been proposed. In contrast, universally composable PAKE protocols exist currently only in the single-server scenario and all proposed 2PAKE protocols use game-based security definitions. In this paper we propose the first construction of an universally composable 2PAKE protocol, alongside with its ideal functionality. The protocol is proven UC-secure in the standard model, assuming a common reference string which is a common assumption to many UC-secure PAKE and PASS protocols. The proposed protocol remains secure for arbitrary password distributions. As one of the building blocks we define and construct a new cryptographic primitive, called Trapdoor Distributed Smooth Projective Hash Function (TD-SPHF), which could be of independent interest

Universally Composable Relaxed Password Authenticated Key Exchange

International audienceProtocols for password authenticated key exchange (PAKE) allow two parties who share only a weak password to agree on a cryptographic key. We revisit the notion of PAKE in the universal composabil-ity (UC) framework, and propose a relaxation of the PAKE functionality of Canetti et al. that we call lazy-extraction PAKE (lePAKE). Our relaxation allows the ideal-world adversary to postpone its password guess until after a session is complete. We argue that this relaxed notion still provides meaningful security in the password-only setting. As our main result, we show that several PAKE protocols that were previously only proven secure with respect to a "game-based" definition of security can be shown to UC-realize the lePAKE functionality in the random-oracle model. These include SPEKE, SPAKE2, and TBPEKE, the most efficient PAKE schemes currently known