IACR News
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07 June 2023
Kai Gellert, Kristian Gjøsteen, Håkon Jacobsen, Tibor Jager
Cohn-Gordon et al. gave a very efficient underlying protocol with weak forward secrecy having a linear security loss, and showed that this is optimal for certain reductions. However, they also claimed that full forward secrecy could be achieved by adding key confirmation messages, and without any additional loss. Our impossibility result disproves this claim, showing that their approach, in fact, has an overall quadratic loss.
Motivated by this predicament we seek to restore the original linear loss claim of Cohn-Gordon et al. by using a different proof strategy. Specifically, we start by lowering the goal for the underlying protocol with weak forward secrecy, to a selective security notion where the adversary must commit to a long-term key it cannot reveal. This allows a tight reduction rather than a linear loss reduction. Next, we show that the protocol can be upgraded to full forward secrecy using key confirmation messages with a linear tightness loss, even when starting from the weaker selective security notion. Thus, our approach yields an overall tightness loss for the fully forward-secret protocol that is only linear, as originally claimed. Finally, we confirm that the underlying protocol of Cohn-Gordon et al. can indeed be proven selectively secure, tightly.
Julia Hesse, Nitin Singh, Alessandro Sorniotti
Kelong Cong, Robin Geelen, Jiayi Kang, Jeongeun Park
We design a secure and non-interactive version of the $k$-nearest neighbors classifier, based on fully homomorphic encryption, which does not leak any information about the query to the server. Our algorithm is instantiated with the TFHE homomorphic encryption scheme, and the selection of the top-$k$ elements is done with a novel strategy based on a type of data-oblivious algorithm---sorting networks. Compared to prior work from PoPETs 2021, the asymptotic complexity is improved from $O(d^2)$ to $O(d \log^2 {k})$, where $d$ is the number of entries in the $k$-NN model. Experimental results show that the proposed protocol can be up to 16 times faster (not accounting for difference in CPU) than previous approaches for a moderately sized database.
Alex Biryukov, Je Sen Teh, Aleksei Udovenko
We illustrate our methods on block cipher families CHAM and KATAN and show best-to-date single-key differential attacks for these ciphers.
Kaiyi Zhang, Hongrui Cui, Yu Yu
As a core building block of hash-based signatures, the efficiency of one-time signature (OTS) largely dominates that of hash-based signatures. The WOTS$^{+}$ signature scheme (Africacrypt 2013) is the current state-of-the-art OTS adopted by the signature schemes standardized by NIST---XMSS, LMS and SPHINCS$^+$.
A natural question is whether there is (and how much) room left for improving one-time signatures (and thus standard hash-based signatures). In this paper, we show that WOTS$^{+}$ one-time signature, when adopting the constant-sum encoding scheme (Bos and Chaum, Crypto 1992), is size-optimal not only under Winternitz's OTS framework, but also among all tree-based OTS designs. Moreover, we point out a flaw in the DAG-based OTS design previously shown to be size-optimal at Asiacrypt 1996, which makes the constant-sum WOTS$^{+}$ the most size-efficient OTS to the best of our knowledge. Finally, we evaluate the performance of constant-sum WOTS$^{+}$ integrated into the SPHINCS$^+$ (CCS 2019) and XMSS (PQC 2011) signature schemes which exhibit certain degrees of improvement in both signing time and signature size.
Marshall Ball, Alexander Bienstock, Lisa Kohl, Pierre Meyer
In this work we move towards closing the gap between MPC and THC by presenting a protocol for THC on general graphs secure against all-but-one semi-honest corruptions from constant-round constant-overhead secure two-party computation. Our protocol is therefore the first to achieve THC on arbitrary networks without relying on assumptions with rich algebraic structure. As a technical tool, we introduce the notion of locally simulatable MPC, which we believe to be of independent interest.
Chen Qian, Yao Jiang Galteland, Gareth T. Davies
We provide three pairing-based constructions of public-key signable updatable encryption. The first scheme, $\mathsf{PSigUE}_1$, is built using a dual-mode zero-knowledge proof of knowledge system under an assumption closely related to the $k$-linear assumption. The second scheme, $\mathsf{PSigUE}_2$, provides unlinkability in addition to public authenticity. In the third scheme, $\mathsf{PSigUE}_\mathsf{T}$, we achieve the tight security with respect of number of epochs. The construction of $\mathsf{PSigUE}_\mathsf{T}$ is inspired by tag-based tightly-secure PKE schemes.
06 June 2023
University of Surrey
The Surrey Centre for Cyber Security (SCCS) at the University of Surrey is seeking to recruit a full-time Research Fellow in Data Resilience, Security and Privacy. The post is available with the opportunity for hybrid working – some time on campus and some from home. We welcome applicants who wish to pursue the role through flexible working patterns.
The successful candidate will be expected to conduct research within the context of the Defence Data Research Centre https://ddrc.uk/, funded by DSTL, in which SCCS is a partner, alongside the Universities of Exeter and Liverpool, and the Digital Catapult. The Centre is focusing on problems related to the use of data for Artificial Intelligence applications, particularly around the challenges of bringing raw data to the state where it can be used. We consider these problems within a defence context, such as logistics support, object tracking and data wrangling. SCCS is focused on the area of data resilience, security and privacy, considering problems such as the trustworthiness and resilience of data and issues around anonymisation.
The post holder will benefit from the research environment provided by the Surrey Centre for Cyber Security, an Academic Centre of Excellence in Cyber Security Research recognised by the National Cyber Security Centre. The Centre’s broader research agenda is in the areas of trusted computing, data privacy, privacy preserving security, applied cryptography, and a range of cyber security topics.
Closing date for applications:
Contact: Steve Schneider.
s.schneider@surrey.ac.uk
More information: https://jobs.surrey.ac.uk/Vacancy.aspx?id=13336
The University of Manchester, Department of Computer Science
The postdoc will be hosted by Bernardo Magri at the Systems and Software Security group at the CS department of the University of Manchester, located in the Northwest of England (https://www.cs.manchester.ac.uk/research/expertise/systems-and-software-security/).
The ideal candidate should have a PhD degree in Computer Science or related areas, and a proven record of publications in cryptography and/or security venues such as Crypto, Eurocrypt, Asiacrypt, TCC, PKC, CCS, S&P, USENIX, ACNS, ESORICS, etc. Experience with protocol composition frameworks (such as the UC framework) is a plus, but not required.
The position is at grade 7 (salary between £43k-53k/year depending on experience) and it lasts for 2 years. Positions can be filled from September 1st to December 1st, 2023, and will remain open until filled.
To apply, please send an email with the subject "SECCOM application" to bernardo.magri@manchester.ac.uk with:
Closing date for applications:
Contact: Bernardo Magri
Edoardo Persichetti, Paolo Santini
Giacomo Fenzi, Ngoc Khanh Nguyen
In this paper, we propose a lattice-based polynomial commitment that achieves succinct proof size and verification time in the degree $d$ of the polynomial. Extractability of our scheme holds in the random oracle model under a natural ring version of the BASIS assumption introduced by Wee and Wu (EUROCRYPT 2023). Unlike recent constructions of polynomial commitments by Albrecht et al. (CRYPTO 2022), and by Wee and Wu, we do not require any expensive preprocessing steps, which makes our scheme particularly attractive as an ingredient of a PIOP compiler for succinct arguments.
We further instantiate our polynomial commitment, together with the Marlin PIOP (Eurocrypt 2020), to obtain a publicly-verifiable trusted-setup succinct argument for Rank-1 Constraint System (R1CS). Performance-wise, we achieve 26 MB proof size for $2^{20}$ constraints, which is 10X smaller than currently the only publicly-verifiable lattice-based SNARK proposed by Albrecht et al.
Maxime Bombar, Geoffroy Couteau, Alain Couvreur, Clément Ducros
In this work, we construct new programmable PCG's for the OLE correlation, that overcome both limitations. To this end, we introduce the quasi-abelian syndrome decoding problem (QA-SD), a family of assumptions which generalises the well-established quasi-cyclic syndrome decoding assumption. Building upon QA-SD, we construct new programmable PCG's for OLE's over any field $\mathbb{F}_q$ with $q>2$. Our analysis also sheds light on the security of the ring-LPN assumption used in Boyle $\textit{et al.}$ (Crypto 2020). Using our new PCG's, we obtain the first efficient N-party silent secure computation protocols for computing general arithmetic circuit over $\mathbb{F}_q$ for any $q>2$.
Diana Maimut, George Teseleanu
To begin with, we introduce an approach for solving the previously mentioned problem using Lagrange interpolation for the evaluation of univariate polynomials. This method is well-established for determining univariate polynomials that satisfy a specific set of points. Moreover, we propose a second approach based on modular knapsack resolution algorithms. These algorithms are designed to address optimization problems where a set of objects with specific weights and values is involved. Finally, we give recommendations on how to run our algorithms in order to obtain better results in terms of precision.
Gareth T. Davies, Sebastian Faller, Kai Gellert, Tobias Handirk, Julia Hesse, Máté Horvárth, Tibor Jager
Mingxun Zhou, Mengshi Zhao, T-H. Hubert Chan, Elaine Shi
In Zhou et al.'s basic composition theorem for NPDO, the privacy loss is linear in $k$ for $k$-fold composition. In comparison, for standard differential privacy, we can enjoy roughly $\sqrt{k}$ loss for $k$-fold composition by applying the well-known advanced composition theorem. Therefore, a natural question left open by their work is whether we can also prove an analogous advanced composition for NPDO.
In this paper, we answer this question affirmatively. As a key step in proving an advanced composition theorem for NPDO, we define a more operational notion called symmetric NPDO which we prove to be equivalent to NPDO. Using symmetric NPDO as a stepping stone, we also show how to generalize NPDO to more general notions of divergence, resulting in Rényi-NPDO, zero-concentrated NPDO, Gassian-NPDO, and $g$-NPDO notions. We also prove composition theorems for these generalized notions of NPDO.
Dylan Rowe, Joachim Breitner, Nadia Heninger
Aldo Gunsing, Ritam Bhaumik, Ashwin Jha, Bart Mennink, Yaobin Shen
Alexander Bienstock, Daniel Escudero, Antigoni Polychroniadou
In this work we present alternative Fluid MPC solutions that require $O(n)$ communication per gate for both the information-theoretic honest majority setting and the information-theoretic dishonest majority setting with preprocessing. Our solutions also achieve maximal fluidity where parties only need to be online for a single communication round. Additionally, we show that a protocol in the information-theoretic dishonest majority setting with sub-quadratic $o(n^2)$ overhead per gate requires for each of the $N$ parties who may ever participate in the (later) execution phase, $\Omega(N)$ preprocessed data per gate.
Benny Applebaum, Oded Nir, Benny Pinkas
We resolve the question in the affirmative and present such a near-threshold secret sharing scheme that provides privacy against unauthorized sets of density at most $\tau_p$, and correctness for authorized sets of density at least $\tau_c$, for any given arbitrarily close constants $\tau_p<\tau_c$. Reconstruction can be computed by making at most $O(n)$ additions and, in addition, (1) the share size is constant, (2) the sharing procedure also makes $O(n)$ additions, and (3) the scheme is a blackbox secret-sharing scheme, i.e., the sharing and reconstruction algorithms work universally for all finite abelian groups $\mathbb{G}$. Prior to our work, no such scheme was known even without features (1)--(3) and even for the ramp setting where $\tau_p$ and $\tau_c$ are far apart. As a by-product, we derive the first blackbox near-threshold secret-sharing scheme with linear-time sharing. We also present several concrete instantiations of our approach that seems practically efficient (e.g., for threshold discrete-log-based signatures).
Our constructions are combinatorial in nature. We combine graph-based erasure codes that support ``peeling-based'' decoding with a new randomness extraction for low dimensional sub-space that is based on inner-product with a small-integer vector. By combining these tools with the blueprint of Cramer et al. (EUROCRYPT 2015), we derive efficient secret-sharing scheme with far-apart thresholds. We then introduce a general concatenation-like transform for secret-sharing schemes that allows us to arbitrarily shrink the privacy-correctness gap with a minor overhead. Our techniques enrich the secret-sharing toolbox and, in the context of blackbox secret sharing, provide a new alternative to existing number-theoretic approaches.