IACR News
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14 June 2024
Benny Applebaum, Kaartik Bhushan, Manoj Prabhakaran
Alexander Maximov
Xiangfu Song, Yu Zheng, Jianli Bai, Changyu Dong, Zheli Liu, Ee-Chien Chang
We propose DISCO, a simple and efficient framework for designing DSE schemes using constant client state. DISCO combines range-constrained pseudorandom functions (RCPRFs) over a global counter and leverages nice properties from the underlying primitives and index structure to simultaneously achieve forward-and-backward privacy and constant client state. To configure DISCO concretely, we identify a set of RCPRF properties that are vital for the resulting DISCO instantiations. By configuring DISCO with different RCPRFs, we resolve efficiency and usability issues in existing schemes. We further optimize DISCO's concrete efficiency without downgrading security. We implement DISCO constructions and report performance, showing trade-offs from different DISCO constructions. Besides, we compare the practical efficiency of DISCO with existing non-constant-state DSE schemes, demonstrating DISCO's competitive efficiency.
Tianpei Lu, Xin Kang, Bingsheng Zhang, Zhuo Ma, Xiaoyuan Zhang, Yang Liu, Kui Ren
13 June 2024
Maria Corte-Real Santos, Krijn Reijnders
As an example of this approach, we demonstrate that SQIsign verification can be performed completely on Kummer surfaces, and, therefore, that one-dimensional SQIsign verification can be viewed as a two-dimensional isogeny between products of elliptic curves. Curiously, the isogeny is then defined over $\mathbb{F}_p$ rather than $\mathbb{F}_{p^2}$. Contrary to expectation, the cost of SQIsign verification using Kummer surfaces does not explode: verification costs only 1.5 times more in terms of finite field operations than the SQIsign variant AprèsSQI, optimised for fast verification. Furthermore, as Kummer surfaces allow a much higher degree of parallelization, Kummer-based protocols over $\mathbb{F}_p$ could potentially outperform elliptic curve analogues over $\mathbb{F}_{p^2}$ in terms of clock cycles and actual performance.
Nuttapong Attrapadung, Junichi Tomida
Edward Eaton, Philippe Lamontagne, Peter Matsakis
Sathvika Balumuri, Edward Eaton, Philippe Lamontagne
We present a new way to build key blinding schemes form any MPC-in-the-Head signature scheme. These schemes rely on well-studied symmetric cryptographic primitives and admit short public keys. We prove a general framework for constructing key blinding schemes and for proving their security in the quantum random oracle model (QROM).
We instantiate our framework with the recent AES-based Helium signature scheme (Kales and Zaverucha, 2022). Blinding Helium only adds a minor overhead to the signature and verification time. Both Helium and the aforementioned lattice-based key blinding schemes were only proven secure in the ROM. This makes our results the first QROM proof of Helium and the first fully quantum-safe public key blinding scheme.
Navid Alamati, Varun Maram
Boneh and Zhandry (CRYPTO 2013) defined the notion of quantum CCA (qCCA) security to guarantee privacy of messages in the presence of quantum decryption queries. However, their construction is based on an exotic cryptographic primitive (namely, identity-based encryption with security against quantum queries), for which only one instantiation is known. In this work, we comprehensively study qCCA security for public-key encryption (PKE) based on both generic cryptographic primitives and concrete assumptions, yielding the following results:
* We show that key-dependent message secure encryption (along with PKE) is sufficient to realize qCCA-secure PKE. This yields the first construction of qCCA-secure PKE from the LPN assumption.
* We prove that hash proof systems imply qCCA-secure PKE, which results in the first instantiation of PKE with qCCA security from (isogeny-based) group actions.
* We extend the notion of adaptive TDFs (ATDFs) to the quantum setting by introducing quantum ATDFs, and we prove that quantum ATDFs are sufficient to realize qCCA-secure PKE. We also show how to instantiate quantum ATDFs from the LWE assumption.
* We show that a single-bit qCCA-secure PKE is sufficient to realize a multi-bit qCCA-secure PKE by extending the completeness of bit encryption for CCA security to the quantum setting.
Chaya Ganesh, Vineet Nair, Ashish Sharma
We achieve this via a combination of the following technical contributions: (i) we construct a new univariate commitment scheme in the updatable SRS setting that has better prover complexity than KZG (ii) we construct a new multilinear commitment scheme in the updatable setting that is compatible for linking with our univariate scheme (iii) we construct an argument of knowledge to prove a given linear relationship between two witnesses committed using a two-tiered commitment scheme (Pedersen+AFG) using Dory as a black-box. These constructions are of independent interest.
We implement our commitment schemes and report on performance. We also implement the version of Spartan with our dual polynomial commitment scheme and demonstrate that it outperforms Spartan in proof size and verification complexity.
Riccardo Taiello, Melek Önen, Clémentine Gritti, Marco Lorenzi
King's College London
The candidate will work alongside Prof. Martin Albrecht, Dr. Benjamin Dowling, Dr. Rikke Bjerg Jensen (Royal Holloway University of London) and Dr. Andrea Medrado (Exeter) on establishing social foundations of cryptography in protest settings. In particular, the candidate will work with a multi-disciplinary team of cryptographers (Dowling, Albrecht) and ethnographers (Jensen, Medrado) to understand the security needs of participants in protests, to formalise these needs as cryptographic security notions and to design or analyse cryptographic solutions with respect to these notions.
This position is part of the EPSRC-funded project “Social Foundations of Cryptography” and more information is available at https://social-foundations-of-cryptography.gitlab.io/.
In brief, ethnography is a social science method involving prolonged fieldwork, i.e. staying with the group under study, to observe not only what they say but also what their social reality and practice is. In this project, we are putting cryptography at the mercy of ethnographic findings, allowing them to shape what we model.
Closing date for applications:
Contact: Martin Albrecht <martin.albrecht@kcl.ac.uk>
More information: https://martinralbrecht.wordpress.com/2024/06/11/cryptography-postdoc-position-in-social-foundations-of-cryptography/
12 June 2024
Xuanming Liu, Jiawen Zhang, Yinghao Wang, Xinpeng Yang, Xiaohu Yang
In this paper, several potential attacks are identified when applying the ZKCP protocol in a practical public data marketplace. To address these issues, we propose SmartZKCP, an enhanced solution that offers improved security measures and increased performance. The protocol is formalized to ensure fairness and secure against potential attacks. Moreover, SmartZKCP offers efficiency optimizations and minimized communication costs. Evaluation results show that SmartZKCP is both practical and efficient, making it applicable in a data exchange marketplace.
Xuanming Liu, Zhelei Zhou, Yinghao Wang, Jinye He, Bingsheng Zhang, Xiaohu Yang, Jiaheng Zhang
In this work, we address this problem by extending the existing zk-SNARKs Libra (Crypto'19) and HyperPlonk (Eurocrypt'23) into scalable collaborative zk-SNARKs. Crucially, our collaborative proof generation does not require a powerful server, and all servers take up roughly the same proportion of the total workload. In this way, we achieve privacy and scalability simultaneously for the first time in proof outsourcing. To achieve this, we develop an efficient MPC toolbox for a number of useful multivariate polynomial primitives, including sumcheck, productcheck, and multilinear polynomial commitment, which can also be applied to other applications as independent interests. For proof outsourcing purposes, when using $128$ servers to jointly generate a proof for a circuit size of $2^{24}$ gates, our benchmarks for these two collaborative proofs show a speedup of $21\times$ and $24\times$ compared to a local prover, respectively. Furthermore, we are able to handle enormously large circuits, making it practical for real-world applications.
A. Telveenus
Zoë Ruha Bell, Shafi Goldwasser, Michael P. Kim, Jean-Luc Watson
(1) We introduce two new notions: Certified Probabilistic Mechanisms (CPM) and Random Variable Commitment Schemes (RVCS). A CPM is an interactive protocol that forces a prover to enact a given probabilistic mechanism or be caught; importantly, the interaction does not reveal secret parameters of the mechanism. An RVCS—a key primitive for constructing CPMs—is a commitment scheme where the verifier is convinced that the commitment is to an RV sampled according to an agreed-upon distribution, but learns nothing else.
(2) We instantiate the general notion of CPM for the special case of Certifying DP. We build a lightweight, doubly-efficent interactive proof system to certify arbitrary-predicate counting queries released via the DP Binomial mechanism. The construction relies on a commitment scheme with perfect hiding and additive homomorphic properties that can be used to release a broad class of queries about a committed database, which we construct on top of Pedersen commitments.
(3) Finally, we demonstrate the immediate feasibility of Certified DP via a highly-efficient and scalable prototype implementation to answer counting queries of arbitrary predicates. The mechanism is composed of an offline and online stage, where the online phase allows for non-interactive certification of queries. For example, we show that CDP queries over a US Census Public Use Microdata Sample (PUMS) ($n=7000$) can be completed in only 1.6 ms and verified in just 38 $\mu \text{s}$. Our implementation is available in open source at https://github.com/jlwatson/certified-dp.
Keyu Ji, Bingsheng Zhang, Hong-Sheng Zhou, Kui Ren
Recently, Servan-Schreiber et al. (S&P 2023) investigate the access control problem for DPF; namely, the DPF evaluators can ensure that the DPF dealer is authorized to share the given function with privacy assurance. In this work, we revisit this problem, introducing a new notion called DPF with constraints; meanwhile, we identify that there exists a subtle flaw in their privacy definition as well as a soundness issue in one of their proposed schemes due to the lack of validation of the special output value $\beta$. Next, we show how to reduce both the storage size of the constraint representation and the server's computational overhead from $O(N)$ to $O(\log N)$, where $N$ is the number of authorized function sets. In addition, we show how to achieve fine-grained private access control, that is, the wildcard-style constraint for the choice of the special output $\beta$. Our benchmarks show that the amortized running time of our logarithmic storage scheme is $2\times$ - $3\times$ faster than the state-of-the-art when $N=2^{15}$. Furthermore, we provide the first impossibility and feasibility results of the DPF with constraints where the evaluators do not need to communicate with each other.
James Bell-Clark, Adrià Gascón, Baiyu Li, Mariana Raykova, Phillipp Schoppmann
Matteo Scarlata, Matilda Backendal, Miro Haller
We show that the MFKDF constructions proposed by Nair and Song fall short of the stated security goals. Underspecified cryptographic primitives and the lack of integrity of the MFKDF state lead to several attacks, ranging from full key recovery when an HOTP factor is compromised, to bypassing factors entirely or severely reducing their entropy. We reflect on the different threat models of key-derivation and authentication, and conclude that MFKDF is always weaker than plain PBKDF and multi-factor authentication in each setting.