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05 October 2022
Trey Li
Bolton Bailey, Andrew Miller
Aayush Jain, Huijia Lin, Ji Luo
We present the first PHFE scheme for RAMs based on the necessary assumption of FE for circuits. It achieves nearly optimal succinctness and efficiency:
* The secret keys $\mathsf{sk}_f$ are of (optimal) *constant size*, independent of the description size $|f|$ of the function tied to it.
* The ciphertexts $\mathsf{ct}_x(y)$ have (nearly optimal) *rate-2* dependency on the private input length $|y|$ and (optimal) independency of the public input length $|x|$.
* Decryption is efficient, running in time linear in the instance running time $T$ of the RAM computation, in addition to the input and function sizes, i.e., ${T_{\mathsf{Dec}}=(T+|f|+|x|+|y|)\operatorname{poly}(\lambda)}$.
Our construction significantly improves upon the asymptotic efficiency of prior schemes. As a corollary, we obtain the first ABE scheme with both constant-size keys and constant-size ciphertexts, and the best-possible decryption time matching an existing lower bound.
We show barriers to further improvement on the asymptotic efficiency of (PH-)FE. We prove the first unconditional space-time trade-off for (PH-)FE. *No* secure (PH-)FE scheme can have both key size and decryption time sublinear in the function size $|f|$, and *no* secure PHFE scheme can have both ciphertext size and decryption time sublinear in the public input length $|x|$. These space-time trade-offs apply even in the simplest selective 1-key 1-ciphertext secret-key setting. Furthermore, we show a conditional barrier towards achieving the optimal decryption time ${T_{\mathsf{Dec}}=T\operatorname{poly}(\lambda)}$ — any such (PH-)FE scheme implies a primitive called secret-key doubly efficient private information retrieval (SK-DE-PIR), for which so far the only known candidates rely on new and non-standard hardness conjectures.
Daniel Escudero, Vipul Goyal, Antigoni Polychroniadou, Yifan Song
Jakub Klemsa
Among existing FHE schemes, in this contribution we focus on the TFHE Scheme by Chillotti et al., which currently achieves the best evaluation times for generic functions. To be instantiated, TFHE however requires an extensive set of parameters. These parameters affect several aspects, including but not limited to the cleartext size, the bit-security level, the probability of errors and also the evaluation time. We propose, implement and evaluate a (semi-)automated approach to generate a set of TFHE parameters with particular respect to the evaluation time, given just the desired security level, cleartext precision, and a parameter that relates to the properties of the evaluated function $f$. With our tool, we re-generate some of the existing TFHE parameters, while achieving up to 39% better execution times in an equivalent setup.
Vincent Cheval, Cas Cremers, Alexander Dax, Lucca Hirschi, Charlie Jacomme, Steve Kremer
We develop the first methodology to systematically discover attacks on security protocols that exploit weaknesses in widely deployed hash functions. We achieve this by revisiting the gap between theoretical properties of hash functions and the weaknesses of real-world hash functions, from which we develop a lattice of threat models. For all of these threat models, we develop fine-grained symbolic models.
Our methodology's fine-grained models cannot be directly encoded in existing state-of-the-art analysis tools by just using their equational reasoning. We therefore develop extensions for the two leading tools, Tamarin and Proverif. In extensive case studies using our methodology, the extended tools rediscover all attacks that were previously reported for these protocols and discover several new variants.
Lorenzo Grassi
In this paper, we discuss the possibility to set up MPC-/HE-/ZK-friendly symmetric primitives instantiated with non-invertible weak bijective functions. With respect to one-to-one correspondence functions, any output of a weak bijective function admits at most two pre-images. The simplest example of such function is the square map over $\mathbb F_p$ for a prime $p\ge 3$, for which $x^2 = (-x)^2$. When working over $\mathbb F_p^n$ for $n\gg 1$, a weak bijective function can be set up by re-considering the recent results of Grassi, Onofri, Pedicini and Sozzi as starting point. Given a quadratic local map $F:\mathbb F_p^2 \rightarrow \mathbb F_p$, they proved that the non-linear function over $\mathbb F_p^n$ for $n\ge 3$ defined as $\mathcal S_F(x_0, x_1, \ldots, x_{n-1}) = y_0\| y_1\| \ldots \| y_{n-1}$ where $y_i := F(x_i, x_{i+1})$ is never invertible. Here, we prove that -- the quadratic function $F:\mathbb F_p^2 \rightarrow \mathbb F_p$ that minimizes the probability of having a collision for $\mathcal S_F$ over $\mathbb F_p^n$ is of the form $F(x_0, x_1) = x_0^2 + x_1$ (or equivalent); -- the function $\mathcal S_F$ over $\mathbb F_p^n$ defined as before via $F(x_0, x_1) = x_0^2 + x_1$ (or equivalent) is weak bijective.
As concrete applications, we propose modified versions of the MPC-friendly schemes MiMC, HadesMiMC, and (partially of) Hydra, and of the HE-friendly schemes Masta, Pasta, and Rubato. By instantiating them with the weak bijective quadratic functions proposed in this paper, we are able to improve the security and/or the performances in the target applications/protocols.
Trey Li
Pratish Datta, Ilan Komargodski, Brent Waters
We present the first multi-authority attribute-based encryption schemes that are provably fully-adaptively secure. Namely, our construction is secure against an attacker that may corrupt some of the authorities as well as perform key queries adaptively throughout the life-time of the system. Our main construction relies on a prime order bilinear group where the $k$-linear assumption holds as well as on a random oracle. Along the way, we present a conceptually simpler construction relying on a composite order bilinear group with standard subgroup decision assumptions as well as on a random oracle.
Prior to this work, there was no construction that could resist adaptive corruptions of authorities, no matter the assumptions used. In fact, we point out that even standard complexity leveraging style arguments do not work in the multi-authority setting.
03 October 2022
Trey Li
Matt Shams(Anis), Bingsheng Zhang
Trey Li
Vadim Lyubashevsky, Ngoc Khan Nguyen
Using these new primitives and techniques, we give instantiations of the most compact lattice-based ring and group signatures schemes. The improvement in signature sizes over prior works ranges between $25\%$ and $2$X. Perhaps of even more significance, the size of the user public keys, which need to be stored somewhere publicly accessible in order for ring signatures to be meaningful, is reduced by factors ranging from $7$X to $15$X. In what could be of independent interest, we also provide noticeably improved proofs for integer relations which, together with one-out-of-many proofs are key components of confidential payment systems.
Kazumasa Shinagawa, Koji Nuida
Trey Li
IT University of Copenhagen
The IT University of Copenhagen is searching a PhD candidate within Machine Learning for Eye Information privacy and security as part of the European Training Network EYES4ICU on Eyes for Information, Communication, and Understanding. The PhD project aims to identify sensitive eye information and develop methods for legal-compliance and safe access control and “private” data control using Eye Information. The goal is to work towards a fully GDPR (General Data Protection Regulation) compliant Eye Information pipeline that balances utility and security for everyday use of Eye information (e.g., such as in schools, and clinical settings).
The successful candidate should have a good background in one or more of the following: machine learning, statistics and computer science. Strong programming and mathematical skills Ideally also have a knowledge of and desire to work with eye tracking, human-machine interfaces, cognitive modelling, security/privacy, federated learning, and cryptographic protocols. You are enthusiastic about traveling for research conferences, PhD schools, and for internships with partners in different countries, e.g., Poland.
Benefits include: a 3-year employment contract with a competitive salary and additional family allowance (if married or having dependent children); access to high quality public education and healthcare in Denmark; budget for work-related travel, books, conferences and workshops etc.; Connections to potential employers in Europe; A rich and versatile PhD program with diverse educational modules, including mentorship, summer and winter schools, workshops... lots of fun!Closing date for applications:
Contact: Dan Witzner
More information: https://candidate.hr-manager.net/ApplicationInit.aspx?cid=119&ProjectId=181482&DepartmentId=3439&MediaId=1282
Heliax, Remote
Closing date for applications:
Contact: Christopher Goes - cwgoes@heliax.dev
More information: https://heliax.dev/jobs/zero-knowledge-cryptographer-protocol-developer/
01 October 2022
University of Waterloo, Department of Combinatorics and Optimization; Waterloo, Ontario, Canada
The Department of Combinatorics and Optimization at the University of Waterloo invites applications from qualified candidates for a 1.5-year postdoctoral fellowship appointment in cryptography under the supervision of Prof. Douglas Stebila. Expertise in cryptography is desired, particularly in the areas of cryptographic protocols, post-quantum cryptography, or digital credentials.
A Ph.D. degree and evidence of excellence in research are required. Successful applicants are expected to maintain an active program of research. The annual salary is $60,000. In addition, a travel fund of $3,000 per year is provided. The effective date of appointment is January 1, 2023 – June 30, 2024. However, dates are negotiable.
Interested individuals should apply using the MathJobs site https://www.mathjobs.org/jobs/list/20495. Applications should include a cover letter describing their interest in the position, a curriculum vitae and research statement and at least three reference letters.
Inquiries may be addressed to Douglas Stebila, Associate Professor (dstebila@uwaterloo.ca), Department of Combinatorics and Optimization, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1. The deadline for application is October 15, 2022. Late applications will be considered until the position is filled.
Closing date for applications:
Contact: Douglas Stebila (dstebila@uwaterloo.ca)
More information: https://www.mathjobs.org/jobs/list/20495
New Jersey Institute of Technology
The successful candidate will hold a faculty appointment in the department of Computer Science and is expected to lead the creation of the Institute for Cybersecurity, which builds on top of existing research and educational strengths in cybersecurity and will span multiple departments across NJIT. Exceptional organizational and communication skills, financial acumen, and the potential to fundraise are essential. As a faculty member of the Computer Science department, the successful candidate is expected to contribute to the academic life of the department, in terms of education, research and service.
NJIT is a Carnegie R1 Doctoral University (Very High Research Activity), with $166M research expenditures in FY21. The Computer Science Department has 31 tenured/tenure track faculty, with eight NSF CAREER awardees and one DARPA Young Investigator recipient. The department conducts research on real-world grand challenges in computer science and plays a key role in the NJIT Cybersecurity Research Center. The department is designated by the NSA as a National Center for Academic Excellence in Cyber Defense, and it hosts an NSF Scholarship for Service program.
To formally apply for the position, please submit your application at https://academicjobsonline.org/ajo/jobs/22924.
Applications received by December 31, 2022 will receive full consideration. However, applications are welcome until the positions are filled, and will be evaluated as they are received. Contact address for inquiries: cs-faculty-search@njit.edu.
Closing date for applications:
Contact: cs-faculty-search@njit.edu
More information: https://academicjobsonline.org/ajo/jobs/22924
New Jersey Institute of Technology
Applicants must have a Ph.D. degree by Summer 2023 in a relevant discipline, and outstanding academic credentials that demonstrate their ability to conduct independent world-class research and attract external funding. Candidates with doctorates from top worldwide institutions are especially welcome to apply. NJIT is a Carnegie R1 Doctoral University (Very High Research Activity), with $166M research expenditures in FY21. The Computer Science Department has 31 tenured/tenure track faculty, with eight NSF CAREER awardees and one DARPA Young Investigator recipient. The department conducts research to solve real-world grand challenges in computer science and plays a key role in the NJIT Cybersecurity Research Center.
Applied research, collaboration with industry, innovation and entrepreneurship are encouraged and supported. Performance and tenure expectations are aligned with those of the broader academic computing community, with an emphasis on grant funding and publishing in top conferences and journals, and contributing to our undergraduate and graduate instructional programs.
To formally apply for the position, please submit your application materials at https://academicjobsonline.org/ajo/jobs/22915.
Applications received by December 31, 2022 will receive full consideration. However, applications are welcome until the positions are filled, and will be evaluated as they are received. Contact address for inquiries: cs-faculty-search@njit.edu.
Closing date for applications:
Contact: cs-faculty-search@njit.edu
More information: https://academicjobsonline.org/ajo/jobs/22915