IACR News
Here you can see all recent updates to the IACR webpage. These updates are also available:
03 March 2023
Vincent Grosso, Pierre-Louis Cayrel, Brice Colombier, Vlad-Florin Dragoi
Daniel Escudero, Vipul Goyal, Antigoni Polychroniadou, Yifan Song, Chenkai Weng
Practically, we also compare our work with the best concretely efficient online protocol Turbospeedz (Ben-Efraim \emph{et al}, ACNS 2019), which achieves $2(1-\epsilon)n$ field elements per multiplication gate among all parties. Our online protocol improves over Turbospeedz as $n$ grows, and as $\epsilon$ approaches $1/2$. For example, if there are $90\%$ corruptions ($\epsilon=0.1$), with $n=50$ our online protocol is $1.5\times$ better than Turbospeedz and with $n=100$ this factor is $3\times$, but for $70\%$ corruptions ($\epsilon=0.3$) with $n=50$ our online protocol is $3.5\times$ better, and for $n=100$ this factor is $7\times$.
Our circuit-dependent preprocessing can be instantiated from OLE/VOLE. The amount of OLE/VOLE correlations required in our work is a factor of $\approx \epsilon n/2$ smaller than these required by Le Mans (Rachuri and Scholl, CRYPTO 2022) leveraged to instantiate the preprocessing of Turbospeedz. Our dishonest majority protocol relies on packed secret-sharing and leverages ideas from the honest majority \textsc{TurboPack} (Escudero \emph{et al}, CCS 2022) protocol to achieve concrete efficiency for any circuit topology, not only SIMD. We implement both \textsc{SuperPack} and Turbospeedz and verify with experimental results that our approach indeed leads to more competitive runtimes in distributed environments with a moderately large number of parties.
Khashayar Barooti, Giulio Malavolta, Michael Walter
Marco Macchetti
Ecublens, Switzerland, 1 May - 3 May 2023
Simula UiB, Bergen, Norway
Project/Job description: The Ph.D. candidate will be supervised by Helger Lipmaa (https://sites.google.com/view/helgerlipmaa) on topics related to zk-SNARKs and zero-knowledge and their various applications (cryptocurrencies, verifiable computation, e-voting, to name a few). Zk-SNARKs have become excessively popular during the last few years due to their application in privacy-preserving cryptocurrencies. We expect the focus to be at least partially on post-quantum secure zk-SNARKs.
Candidate Profile: a completed MSc degree in cryptography or related areas (in particular, theoretical computer science, including algorithms and/or complexity theory, and mathematics). We will also consider applicants who are in the final phase of their MSc studies. We expect an excellent academic track record, including top grades. The student should be at home both in theory and practice: a good background in mathematics and TCS is particularly expected but having both this and an ability to read and write code is also useful. We value strong motivation with a combination of teamwork and the ability to work alone.
About Simula UiB (http://simula-uib.com): Simula UiB is a research center owned by the Simula Research Laboratory AS and the University of Bergen (UiB). Simula UiB has a large research group in cryptography and information theory, with eight faculty members who regularly publish at IACR conferences. The student will officially defend at UiB.
Simula UiB offers: modern office facilities located in downtown Bergen (“the gateway to the fjords”). A competitive salary starting from 501200 NOK (approx 45000-50000 euros, depending on the exchange rate). Emphasis on work-life balance. Numerous additional benefits.
Closing date for applications: 31.03.2023 but earlier application is encouraged
Research group homepage: https://sites.google.com/view/helgerlipmaa/research-group
Apply at: https://www.simula.no/about/job/phd-student-zero-knowledge-proofs (early application Is encouraged)
Closing date for applications:
Contact: Helger Lipmaa
More information: https://www.simula.no/about/job/phd-student-zero-knowledge-proofs
Cryptology Group, CWI Amsterdam and Mathematical Institute, Leiden University
Descryption. The CWI Cryptology group in Amsterdam and the Mathematical Institute of Leiden University offer a joint PhD position on the topic of Post-Quantum Cryptanalysis. The goal is to advance the state of the art in post-quantum cryptanalysis for the schemes that are currently being standardized. This ranges from improving our understanding in the fundamental computational problems underlying these important quantum-safe schemes, to improving the state of the art in cryptanalytic attacks, e.g., in more refined memory models.
Requirements. Candidates are required to have a master’s degree in mathematics or in computer science. Experience in one or more of these relevant background areas is an advantage: cryptography, algorithms, number theory, coding theory, and quantum algorithms. Some programming skills are expected. Candidates are expected to have an excellent command of English.
Information and application. All applications should include a detailed resume and motivation letter. The application deadline is 31 March 2023. Please visit the vacancy page (click the title) for more information about our terms of employment.
Closing date for applications:
Contact: Marc Stevens (stevens@cwi.nl), Peter Bruin (p.j.bruin@math.leidenuniv.nl)
More information: https://www.cwi.nl/en/jobs/vacancies/983536/
01 March 2023
Eleni Agathocleous, Vishnupriya Anupindi, Annette Bachmayr, Chloe Martindale, Rahinatou Yuh Njah Nchiwo, Mima Stanojkovski
Brandon Goodell, Aaron Feickert
Léo Ducas, Ludo Pulles
However, from a theoretical perspective, all of these works are painfully specific to Learning with Errors, while the principle of the Dual-Sieve attack is more general (Laarhoven & Walter, CT-RSA 2021). More critically, all of these works are based on heuristics that have received very little theoretical and experimental attention.
This work attempts to rectify the above deficiencies of the literature. We first propose a generalization of the FFT trick by Guo and Johansson to arbitrary Bounded Distance Decoding instances. This generalization offers a new improvement to the attack.
We then theoretically explore the underlying heuristics and show that these are in contradiction with formal, unconditional theorems in some regimes, and with well-tested heuristics in other regimes. The specific instantiations of the recent literature fall into this second regime.
We confirm these contradictions with experiments, documenting several phenomena that are not predicted by the analysis, including a ``waterfall-floor'' phenomenon, reminiscent of Low-Density Parity-Check decoding failures.
We conclude that the success probability of the recent Dual-Sieve-FFT attacks are presumably significantly overestimated. We further discuss the adequate way forward towards fixing the attack and its analysis.
Kamil Kluczniak, Giacomo Santato
A desirable property for homomorphic encryption is circuit privacy, which requires that a ciphertext leaks no information on the computation performed to obtain it. Despite numerous improvements, directed toward improving efficiency, the question of circuit privacy for approximate homomorphic encryption remains open.
In this paper, we give the first formal study of circuit privacy for homomorphic encryption over approximate arithmetic. We introduce formal models that allow us to reason about circuit privacy. Then, we show that approximate homomorphic encryption can be made circuit private using tools from differential privacy with appropriately chosen parameters. In particular, we show that by applying an exponential (in the security parameter) Gaussian noise on the evaluated ciphertext, we remove useful information on the circuit from the ciphertext. Crucially, we show that the noise parameter is tight, and taking a lower one leads to an efficient adversary against such a system.
We expand our definitions and analysis to the case of multikey and threshold homomorphic encryption for approximate arithmetic. Such schemes allow users to evaluate a function on their combined inputs and learn the output without leaking anything on the inputs. A special case of multikey and threshold encryption schemes defines a so-called partial decryption algorithm where each user publishes a ``masked'' version of its secret key, allowing all users to decrypt a ciphertext. Similarly, in this case, we show that applying a proper differentially private mechanism gives us IND-CPA-style security where the adversary additionally gets as input the partial decryptions. This is the first security analysis of approximate homomorphic encryption schemes that consider the knowledge of partial decryptions. We show lower bounds on the differential privacy noise that needs to be applied to retain security. Analogously, in the case of circuit privacy, the noise must be exponential in the security parameter. We conclude by showing the impact of the noise on the precision of CKKS-type schemes.
Hu Xiaobo, Xu Shengyuan, Tu Yinzi, Feng Xiutao
28 February 2023
Yonglin Hao, Qingju Wang, Lin Jiao, Xinxin Gong
To show the utility of our method, we propose boomerang attacks on the keyed permutations of three ARX hash functions of BLAKE. For the first time we mount an attack on the full 7 rounds of BLAKE3, with the complexity as low as $2^{180}$. Our best attack on BLAKE2s can improve the previously best result by 0.5 rounds but with lower complexity. The attacks on BLAKE-256 cover the same 8 rounds with the previous best result but with complexity $2^{16}$ times lower. All our results are verified practically with round-reduced boomerang quartets.
Mihir Bellare, Hannah Davis, Zijing Di
Simone Colombo, Kirill Nikitin, Henry Corrigan-Gibbs, David J. Wu, Bryan Ford
Ethan Heilman, Lucie Mugnier, Athanasios Filippidis, Sharon Goldberg, Sebastien Lipman, Yuval Marcus, Mike Milano, Sidhartha Premkumar, Chad Unrein
OpenPubkey is transparent to users and OpenID Providers. An OpenID Provider can not even determine that OpenPubkey is being used. This makes OpenPubkey fully compatible with existing OpenID Providers. In fact a variant of OpenPubkey is currently deployed and used to authenticate signed messages and identities for users with accounts on Google, Microsoft, Okta, and Onelogin. OpenPubkey does not add new trusted parties to OpenID Connect and reduces preexisting trust assumptions. If used in tandem with our MFA-cosigner, OpenPubkey can maintain security even against a malicious OpenID Provider (the most trusted party in OpenID Connect).
Bruno Freitas Dos Santos, Yanqi Gu, Stanislaw Jarecki
We propose an IC relaxation called a (Randomized) Half-Ideal Cipher (HIC), and we show that HIC on a group can be realized by a modified 2-round Feistel (m2F), at a cost of 1 hash-onto-group operation, which beats existing IC constructions in versatility and computational cost. HIC weakens IC properties by letting part of the ciphertext be non-random, but we exemplify that it can be used as a drop-in replacement for IC by showing that EKE [10] and aPAKE of [40] realize respectively UC PAKE and UC aPAKE even if they use HIC instead of IC. The m2F construction can also serve as IC domain extension, because m2F constructs HIC on domain D from an RO-indiferrentiable hash onto D and an IC on 2κ-bit strings, for κ a security parameter. One application of such extender is a modular lattice-based UC PAKE using EKE instantiated with HIC and anonymous lattice-based KEM.
Qian Guo, Denis Nabokov, Alexander Nilsson, Thomas Johansson
In this paper, we propose a framework to be used in key-recovery side-channel attacks on CCA-secure post-quantum encryption schemes. The basic idea is to construct chosen ciphertext queries to a plaintext checking oracle that collects information on a set of secret variables in a single query. Then a large number of such queries is considered, each related to a different set of secret variables, and they are modeled as a low-density parity-check code (LDPC code). Secret variables are finally determined through efficient iterative decoding methods, such as belief propagation, using soft information. The utilization of LDPC codes offers efficient decoding, source compression, and error correction benefits. It has been demonstrated that this approach provides significant improvements compared to previous work by reducing the required number of queries, such as the number of traces in a power attack.
The framework is demonstrated and implemented in two different cases. On one hand, we attack implementations of HQC in a timing attack, lowering the number of required traces considerably compared to attacks in previous work. On the other hand, we describe and implement a full attack on a masked implementation of Kyber using power analysis. Using the ChipWhisperer evaluation platform, our real-world attacks recover the long-term secret key of a first-order masked implementation of Kyber-768 with an average of only 12 power traces.
Diana Maimut, Evgnosia-Alexandra Kelesidis, Ilona Teodora Ciocan
Cybersecurity Group, TU Delft, The Netherlands
Post-doc positions:
Responsibilities:
Requirements:
PhD positions:
Responsibilities:
Requirements:
Please send your CV, PhD/MSc transcripts, PhD/MSc certificate, English test certificate and a publication list to kaitai.liang@tudelft.nl.
We provide our PhDs and Post-Docs: (1) International academic and industrial collaborations, e.g., working with other top ranking universities, renown companies. (2) Opportunities of participating into various domestic and international cybersecurity projects. (3) Being trained to deliver world-leading research works and publish them to top-tier venues. (4) Flexible and supportive working surroundings. (5) Competitive salary and benefits package, relocation supports, summer and end-year bonus, free academic trainings.
Closing date for applications:
Contact: K. Liang (kaitai.liang@tudelft.nl)