More Like this

1. Quantifying the Security Cost of Migrating Protocols to Practice

   https://doi.org/10.1007/978-3-030-56784-2_4  

   Patton, Christopher; Shrimpton, Thomas (August 2020, Advances in Cryptology -- CRYPTO 2020)

   We give a framework for relating the concrete security of a “reference” protocol (say, one appearing in an academic paper) to that of some derived, “real” protocol (say, appearing in a cryptographic standard). It is based on the indifferentiability framework of Maurer, Renner, and Holenstein (MRH), whose application has been exclusively focused upon non-interactive cryptographic primitives, e.g., hash functions and Feistel networks. Our extension of MRH is supported by a clearly defined execution model and two composition lemmata, all formalized in a modern pseudocode language. Together, these allow for precise statements about game-based security properties of cryptographic objects (interactive ornot) at various levels of abstraction. As a real-world application, we design and prove tight security bounds for a potential TLS 1.3 extension that integrates the SPAKE2 password-authenticated key-exchange into the handshake. 

   more » « less
2. Two-factor Password-authenticated Key Exchange with End-to-end Security

   https://doi.org/10.1145/3446807  

   Jarecki, Stanislaw; Jubur, Mohammed; Krawczyk, Hugo; Saxena, Nitesh; Shirvanian, Maliheh (August 2021, ACM Transactions on Privacy and Security)

   null (Ed.)

   We present a secure two-factor authentication (TFA) scheme based on the user’s possession of a password and a crypto-capable device. Security is “end-to-end” in the sense that the attacker can attack all parts of the system, including all communication links and any subset of parties (servers, devices, client terminals), can learn users’ passwords, and perform active and passive attacks, online and offline. In all cases the scheme provides the highest attainable security bounds given the set of compromised components. Our solution builds a TFA scheme using any Device-enhanced Password-authenticated Key Exchange (PAKE), defined by Jarecki et al., and any Short Authenticated String (SAS) Message Authentication, defined by Vaudenay. We show an efficient instantiation of this modular construction, which utilizes any password-based client-server authentication method, with or without reliance on public-key infrastructure. The security of the proposed scheme is proven in a formal model that we formulate as an extension of the traditional PAKE model. We also report on a prototype implementation of our schemes, including TLS-based and PKI-free variants, as well as several instantiations of the SAS mechanism, all demonstrating the practicality of our approach. Finally, we present a usability study evaluating the viability of our protocol contrasted with the traditional PIN-based TFA approach in terms of efficiency, potential for errors, user experience, and security perception of the underlying manual process. 1 

   more » « less
3. Universally Composable Relaxed Password Authenticated Key Exchange

   https://doi.org/10.1007/978-3-030-56784-2_10  

   Abdalla, Michel; Barbosa, Manuel; Bradley, Tatiana; Jarecki, Stanislaw; Katz, Jonathan; Xu, Jiayu (August 2020, Lecture notes in computer science)

   Micciancio, Daniele; Ristenpart, Thomas (Ed.)

   Protocols 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 composability (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. 

   more » « less
4. Password-Protected Threshold Signatures

   https://doi.org/10.1007/978-981-96-0891-1_6  

   Dziembowski, Stefan; Jarecki, Stanislaw; Kedzior, Pawel; Krawczyk, Hugo; Ngo, Chan Nam; Xu, Jiayu (December 2024, Springer Nature Singapore)

   Chung, KM; Sasaki, Y (Ed.)

   We witness an increase in applications like cryptocurrency wallets, which involve users issuing signatures using private keys. To protect these keys from loss or compromise, users commonly outsource them to a custodial server. This creates a new point of failure, because compromise of such a server leaks the user’s key, and if user authentication is implemented with a password then this password becomes open to an offline dictionary attack (ODA). A better solution is to secret-share the key among a set of servers, possibly including user’s own device(s), and implement password authentication and signature computation using threshold cryptography. We propose a notion of augmented password-protected threshold signature (aptSIG) scheme which captures the best possible security level for this setting. Using standard threshold cryptography techniques, i.e. threshold password authentication and threshold signatures, one can guarantee that compromising up to t out of n servers reveals no information on either the key or the password. However, we extend this with a novel property, that compromising even all n servers also does not leak any information, except via an unavoidable ODA attack, which reveals the key only if the attacker guesses the password. We define aptSIG in the Universally Composable (UC) framework and show that it can be constructed very efficiently, using a black-box composition of any UC threshold signature [13] and a UC augmented Password-Protected Secret Sharing (aPPSS), which we define as an extension of prior notion of PPSS [30]. As concrete instantiations we obtain secure aptSIG schemes for ECDSA (in the case of t=n-1) and BLS signatures with very small overhead over the respective threshold signature. Finally, we note that both the notion and our generic solution for augmented password-protected threshold signatures can be generalized to password-protecting MPC for any keyed functions. 

   more » « less
5. Don't Forget the Stuffing! Revisiting the Security Impact of Typo-Tolerant Password Authentication

   https://doi.org/10.1145/3460120.3484791  

   Sahin, Sena; Li, Frank (November 2021, ACM SIGSAC Conference on Computer and Communications Security)

   To enhance the usability of password authentication, typo-tolerant password authentication schemes permit certain deviations in the user-supplied password, to account for common typographical errors yet still allow the user to successfully log in. In prior work, analysis by Chatterjee et al. demonstrated that typo-tolerance indeed notably improves password usability, yet (surprisingly) does not appear to significantly degrade authentication security. In practice, major web services such as Facebook have employed typo-tolerant password authentication systems. In this paper, we revisit the security impact of typo-tolerant password authentication. We observe that the existing security analysis of such systems considers only password spraying attacks. However, this threat model is incomplete, as password authentication systems must also contend with credential stuffing and tweaking attacks. Factoring in these missing attack vectors, we empirically re-evaluate the security impact of password typo-tolerance using password leak datasets, discovering a significantly larger degradation in security. To mitigate this issue, we explore machine learning classifiers that predict when a password's security is likely affected by typo-tolerance. Our resulting models offer various suitable operating points on the functionality-security tradeoff spectrum, ultimately allowing for partial deployment of typo-tolerant password authentication, preserving its functionality for many users while reducing the security risks. 

   more » « less