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19 October 2023
Intak Hwang, Jinyeong Seo, Yongsoo Song
ePrint ReportBar Alon, Amos Beimel, Eran Omri
ePrint ReportTo address this issue, Alon et al. [CRYPTO 20] introduced the notion of security with friends and foes (FaF security). In essence, $(t,h)$-FaF security requires that a malicious adversary corrupting up to $t$ parties cannot help a coalition of $h$ semi-honest parties to learn anything beyond what they can learn from their inputs and outputs (combined with the input and outputs of the malicious parties). They further showed that $(t,h)$-FaF security with $n$ parties is achievable for any functionality if $2t+h
In this paper, we focus on the special, yet already challenging, case of $(1,1)$-FaF security for three-party, 2-ary (two inputs), symmetric (all parties output the same value) functionalities. We provide several positive results, a lower bound on the round complexity, and an impossibility result. In particular, we prove the following. (1) we identify a large class of three-party Boolean symmetric 2-ary functionalities that can be computed with $(1,1)$-FaF full security, and (2) We identify a large class of three-party (possibly non-Boolean) symmetric 2-ary functionalities, for which no $O(\log\kappa)$-round protocol computes them with $(1,1)$-FaF full security. This matches the round complexity of our positive results for various interesting functionalities, such as equality of strings.
17 October 2023
Jianye Gao, Xinyao Li, Changhai Ou, Zhu Wang, Fei Yan
ePrint ReportShuichi Katsumata, Yi-Fu Lai, Michael Reichle
ePrint ReportIn this work, we provide a simple and novel attack on blind signatures based on identification protocols performing parallel repetition to reduce the soundness error. Our attack translates to a polynomial time break for the $\ell$-concurrent unforgeability of CSI-Otter, Blaze+, and BlindOR for $\ell = \mathsf{poly}(\lambda)$. More formally, we define an intermediate problem called Parallel Random inhomogeneities in an Overdetermined Solvable system of linear equations (pROS) problem and show that an attack against pROS implies an attack to the above blind signatures. One takeaway of our finding is that while parallel repetition allows to exponentially reduce the soundness error of an identification protocol, this has minimal effect on the resulting blind signature. Our attack is concretely very efficient and for instance breaks $4$-concurrent unforgeability of CSI-Otter in time roughly $2^{34}$ hash computations.
Alex Lombardi, Fermi Ma, John Wright
ePrint ReportTo prove this result, we formulate unitary synthesis as an efficient challenger-adversary game, which enables proving lower bounds by analyzing the maximum success probability of an adversary $A^f$. Our main technical insight is to identify a natural spectral relaxation of the one-query optimization problem, which we bound using tools from random matrix theory.
We view our framework as a potential avenue to rule out polynomial-query unitary synthesis, and we state conjectures in this direction.
Balthazar Bauer, Pooya Farshim, Patrick Harasser, Markulf Kohlweiss
ePrint ReportWe formulate the uber-knowledge (UK) assumption, a standard-model assumption that naturally extends the uber-assumption family to knowledge assumptions. We justify the soundness of the UK in both the bilinear GGM and bilinear AGM. Along the way we extend these models to incorporate hashing into groups, an adversarial capability that is available in many concrete groups. (In contrast to standard assumptions, hashing may affect the validity of knowledge assumptions.) These results, in turn, enable a modular approach to security in GGM and AGM.
As example applications, we use the UK to prove knowledge-soundness of Groth16 and KZG polynomial commitments in the standard model, where for the former we reuse the existing AGM proof without hashing.
Gaëtan Cassiers, Barbara Gigerl, Stefan Mangard, Charles Momin, Rishub Nagpal
ePrint ReportThomas Lavaur, Jérôme Lacan
ePrint ReportLéo Weissbart, Stjepan Picek
ePrint ReportAnamaria Costache, Lea Nürnberger, Tjerand Silde
ePrint ReportIn more detail, we consider the notion of circuit privacy along four dimensions: whether the adversary is internal or external (i.e. does the adversary hold the secret key or not), and in a semi-honest and malicious setting. Our starting point is Gentry’s definition, which we change from statistical to computational indistinguishability. Doing so allows us to prove that the BGV scheme is computationally circuit-private in a semi-honest setting to an external adversary out of the box.
We then propose a new definition by extending Gentry’s definition to an internal adversary. This is appropriate since the scenario that the client is the adversary (and therefore has access to the decryption key) is a realistic one. Further, we remark that our definition is strictly stronger than Gentry’s – our definition requires that a scheme be circuit private according to Gentry’s definition and additionally, the distribution of the ciphertext noise in all ciphertexts to be computationally indistinguishable. Given this new definition, and using previous results of Costache, Nürnberger and Player (CT-RSA’23), we show that slight modifications to the BGV scheme will make it fulfill this new definition. Finally, we show how to extend these results to a malicious setting if we require that the client attaches proofs of well-formedness of keys and ciphertexts.
Raja Adhithan Radhakrishnan
ePrint ReportSofia Celi, Shai Levin, Joe Rowell
ePrint ReportHannah Keller, Helen Möllering, Thomas Schneider, Oleksandr Tkachenko, Liang Zhao
ePrint ReportWe introduce efficient MPC protocols that securely realize noise sampling for several plaintext DP mechanisms that are secure against existing precision-based attacks: the discrete Laplace and Gaussian mechanisms, the snapping mechanism, and the integer-scaling Laplace and Gaussian mechanisms. Due to their inherent trade-offs, the favorable mechanism for a specific application depends on the available computation resources, type of function evaluated, and desired (epsilon,delta)-DP guarantee.
The benchmarks of our protocols implemented in the state-of-the-art MPC framework MOTION (Braun et al., TOPS'22) demonstrate highly efficient online runtimes of less than 32 ms/query and down to about 1ms/query with batching in the two-party setting. Also the respective offline phases are practical, requiring only 51 ms to 5.6 seconds/query depending on the batch size.
Quang Dao, Yuval Ishai, Aayush Jain, Huijia Lin
ePrint ReportIn this work, we give the first construction of a multi-party HSS scheme for a non-trivial function class, from an assumption not known to imply FHE. In particular, we construct an HSS scheme for an arbitrary number of parties with an arbitrary corruption threshold, supporting evaluations of multivariate polynomials of degree $\log / \log \log$ over arbitrary finite fields. As a consequence, we obtain a secure multiparty computation (MPC) protocol for any number of parties, with (slightly) sub-linear per-party communication of roughly $O(S / \log \log S)$ bits when evaluating a layered Boolean circuit of size $S$.
Our HSS scheme relies on the Sparse Learning Parity with Noise assumption, a standard variant of LPN with a sparse public matrix that has been studied and used in prior works. Thanks to this assumption, our construction enjoys several unique benefits. In particular, it can be built on top of any linear secret sharing scheme, producing noisy output shares that can be error-corrected by the decoder. This yields HSS for low-degree polynomials with optimal download rate. Unlike prior works, our scheme also has a low computation overhead in that the per-party computation of a constant degree polynomial takes $O(M)$ work, where $M$ is the number of monomials.
Zhengjun Cao, Lihua Liu
ePrint ReportYanyi Liu, Rafael Pass
ePrint ReportUnder standard derandomization assumptions, we can show the same result also w.r.t. the standard notion of time-bounded Kolmogorov complexity, K^t.
Guillaume Goy, Julien Maillard, Philippe Gaborit, Antoine Loiseau
ePrint Report16 October 2023
Florida Atlantic University, Department of Mathematics; Boca Raton, Florida, USA.
Job PostingThe candidate will conduct research in cryptography/cryptanalysis. Strong candidates from all areas of cryptology are encouraged to apply. Preference will be given to candidates with several broad areas of interest including, but not limited to, symmetric and public-key cryptography, post-quantum cryptography, quantum algorithms in cryptography, mathematical cryptography, or a closely related area. The candidate should have a strong record of research accomplishments, demonstrated potential for extramural funding, and a commitment to excellence in education. FAU possesses a culture that fosters internal collaboration and innovation as well as partnerships with local, national, and international agencies, and thus candidates must display strong collaborative potential and the ability to conduct transformative externally funded research within their area of specialization.
The Department of Mathematical Sciences is a collegial and research-active department demonstrating excellence in teaching, research, and service. The department has an established national and international reputation for research innovation through our Center for Cryptology and Information Security (CCIS). FAU is also recognized as a National Center of Academic Excellence in Cybersecurity for Cyber Research (CAE-R) for academic years 2012-2024. More information about the department can be found at: http://www.math.fau.edu/
Application Deadline: 2024-01-03.
Closing date for applications:
Contact: Informal inquiries can be made to Shi Bai (sbai@fau.edu), formal applications must be submitted through: https://fau.wd1.myworkdayjobs.com/FAU/job/Boca-Raton/Assistant-Professor--Cryptology_REQ17017
More information: https://fau.wd1.myworkdayjobs.com/FAU/job/Boca-Raton/Assistant-Professor--Cryptology_REQ17017
Shield Lab, Huawei France Research Center, Paris, France
Job PostingClosing date for applications:
Contact: Prof. Houda Labiod (houda.labiod@huawei.com) and Dr. Guilin Wang (wang.guilin@huawei.com)
University of South Florida
Job PostingThe Department of Mathematics & Statistics of the University of South Florida seeks to fill a nine-month, full-time and tenure-earning Assistant Professor position in Applied Algebra to begin August 7, 2024. A Ph.D. in Mathematics or a closely-related field is required, with preference for applications of algebra to Cryptography, Coding Theory, and Quantum Computing.
The Department is home to the USF Center for Cryptographic Research (usf-crypto.org), which is run in collaboration with the Department of Computer Science & Engineering. The Department of Mathematics & Statistics offers vertically-integrated programs in Applied Algebra at all levels: postdoctoral supervision in Applied Algebra, a graduate sequence in Applied Algebra, an undergraduate certificate in Cryptography, a Research Undergraduate Experience ( REU Site : usf-crypto.org/reu-program) program in Cryptography and Coding Theory, as well as a K–12 summer program in cybersecurity (codebreakhers.org).
Applications from individuals who are ABD will be accepted, but the degree must be conferred by the start date of the appointment. We seek applicants with a strong record of research productivity, the potential to secure external funding, and experience teaching university undergraduates. Special consideration will be given to candidates who possess experience beyond the Ph.D. level and the potential for excellence in teaching at the graduate level. Applications from women and minorities are encouraged. Salary is negotiable. To receive consideration, applications must be submitted no later than November 15, 2023.
To apply, please follow the instructions on the Mathjob advertisement for this position: https://www.mathjobs.org/jobs/list/23078
Closing date for applications:
Contact: Jean-François Biasse
More information: https://www.mathjobs.org/jobs/list/23078