International Association
for Cryptologic Research

Aaronson, Atia, and Susskind [Aaronson et al., 2020] established that efficiently mapping between quantum states $\ket{\psi}$ and $\ket{\phi}$ is computationally equivalent to distinguishing their superpositions $\frac{1}{\sqrt{2}}(|\psi\rangle + |\phi\rangle)$ and $\frac{1}{\sqrt{2}}(|\psi\rangle - |\phi\rangle)$. We generalize this insight into a broader duality principle in quantum computation, wherein manipulating quantum states in one basis is equivalent to extracting their value in a complementary basis. In its most general form, this duality principle states that for a given group, the ability to implement a unitary representation of the group is computationally equivalent to the ability to perform a Fourier subspace extraction from the invariant subspaces corresponding to its irreducible representations.

Building on our duality principle, we present the following applications:

* Quantum money, which captures quantum states that are verifiable but unclonable, and its stronger variant, quantum lightning, have long resisted constructions based on concrete cryptographic assumptions. While (public-key) quantum money has been constructed from indistinguishability obfuscation (iO)—an assumption widely considered too strong—quantum lightning has not been constructed from any such assumptions, with previous attempts based on assumptions that were later broken. We present the first construction of quantum lightning with a rigorous security proof, grounded in a plausible and well-founded cryptographic assumption. We extend Zhandry's construction from Abelian group actions [Zhandry, 2024] to non-Abelian group actions, and eliminate Zhandry's reliance on a black-box model for justifying security. Instead, we prove a direct reduction to a computational assumption—the pre-action security of cryptographic group actions. We show how these group actions can be realized with various instantiations, including with the group actions of the symmetric group implicit in the McEliece cryptosystem.

* We provide an alternative quantum money and lightning construction from one-way homomorphisms, showing that security holds under specific conditions on the homomorphism. Notably, our scheme exhibits the remarkable property that four distinct security notions—quantum lightning security, security against both worst-case cloning and average-case cloning, and security against preparing a specific canonical state—are all equivalent.

* Quantum fire captures the notion of a samplable distribution on quantum states that are efficiently clonable, but not efficiently telegraphable, meaning they cannot be efficiently encoded as classical information. These states can be spread like fire, provided they are kept alive quantumly and do not decohere. The only previously known construction relied on a unitary quantum oracle, whereas we present the first candidate construction of quantum fire in the plain model.

In this paper, we study multi-party non-interactive key exchange (NIKE) in the fine-grained setting. More precisely, we propose three multi-party NIKE schemes in three computation models, namely, the bounded parallel-time, bounded time, and bounded storage models. Their security is based on a very mild assumption (e.g., NC1 ⊊ ⊕L/poly) or even without any complexity assumption. This improves the recent work of Afshar, Couteau, Mahmoody, and Sadeghi (EUROCRYPT 2023) that requires idealized assumptions, such as random oracles or generic groups. Additionally, we show that all our constructions satisfy a natural desirable property that we refer to as extendability, and we give generic transformations from extendable multi-party NIKE to multi-party identity-based NIKEs in the fine-grained settings.

Service discovery is essential in wireless communications. However, existing service discovery protocols provide no or very limited privacy protection for service providers and clients, and they often leak sensitive information (e.g., service type, client’s identity and mobility pattern), which leads to various network-based attacks (e.g., spoofing, man-in-the-middle, identification and tracking). In this paper, we propose a private service discovery protocol, called PriSrv, which allows a service provider and a client to respectively specify a fine-grained authentication policy that the other party must satisfy before a connection is established. PriSrv consists of a private service broadcast phase and an anonymous mutual authentication phase with bilateral control, where the private information of both parties is hidden beyond the fact that a mutual match to the respective authentication policy occurred. As a core component of PriSrv, we introduce the notion of anonymous credential-based matchmaking encryption (ACME), which exerts dual-layer matching in one step to simultaneously achieve bilateral flexible policy control, selective attribute disclosure and multi-show unlinkability. As a building block of ACME, we design a fast anonymous credential (FAC) scheme to provide constant size credentials and efficient show/verification mechanisms, which is suitable for privacy-enhanced and highly usable service discovery in wireless networks. We present a concrete PriSrv protocol that is interoperable with popular wireless communication protocols, such as Wi-Fi Extensible Authentication Protocol (EAP), mDNS, BLE and Airdrop, to offer privacy-enhanced protection. We present formal security proof of our protocol and evaluate its performance on multiple hardware platforms: desktop, laptop, mobile phone and Raspberry Pi. PriSrv accomplishes private discovery and secure connection in less than 0.973 s on the first three platforms, and in less than 2.712 s on Raspberry Pi 4B. We also implement PriSrv into IEEE 802.1X in the real network to demonstrate its practicality.

In this paper, we investigate whether the privacy mechanism of periodically changing the pseudorandom identities of Bluetooth Low Energy (BLE) beacons is sufficient to ensure privacy.

We consider a new natural privacy notion for BLE broadcasting beacons which we call ``Timed-sequence- indistinguishability'' of beacons. This new privacy definition is stronger than the well-known indistinguishability, since it considers not just the advertisements' content, but also the advertisements' broadcasting times which are observable in the physical world.

We then prove that beacons with periodically changing pseudorandom identities do not achieve timed-sequence- indistinguishability. We do this by presenting a novel privacy attack against BLE beacons, which we call the ``Battery Insertion Attack.'' This new time-based privacy attack can be executed by merely inserting or reinserting the beacon's battery at the adversary's chosen time. We performed this attack against an actually deployed beacon.

To mitigate the ``Battery Insertion Attack'' and other attacks associated with periodic signaling, we propose a new countermeasure involving quasi-periodic randomized scheduling of identity changes. We prove that our countermeasure ensures timed-sequence indistinguishability for beacons, thereby enhancing the beacon's privacy. Additionally, we show how to integrate this countermeasure in the attacked system while essentially preserving its feasibility and utility, which is crucial for practical industrial adoption.

We say there is a share conversion from a secret sharing scheme $\Pi$ to another scheme $\Pi'$ implementing the same access structure if each party can locally apply a deterministic function to their share to transform any valid secret sharing under $\Pi$ to a valid (but not necessarily random) secret sharing under $\Pi'$ of the same secret. If such a conversion exists, we say that $\Pi\ge\Pi'$. This notion was introduced by Cramer et al. (TCC'05), where they particularly proved that for any access structure (AS), any linear secret sharing scheme over a given field $\mathbb{F}$, has a conversion from a CNF scheme, and is convertible to a DNF scheme. In this work, we initiate a systematic study of convertability between secret sharing schemes, and present a number of results with implications to the understanding of the convertibility landscape. - In the context of linear schemes, we present two key theorems providing necessary conditions for convertibility, proved using linear-algebraic tools. It has several implications, such as the fact that Shamir secret sharing scheme can be neither maximal or minimal. Another implication of it is that for a broad class of access structures, a linear scheme where some party has sufficiently small share complexity, may not be minimal. - Our second key result is a necessary condition for convertibility to CNF from a broad class of (not necessarily linear) schemes. This result is proved via information-theoretic techniques and implies non-maximality for schemes with share complexity smaller than that of CNF. We also provide a condition which is both necessary and sufficient for the existence of a share conversion to some linear scheme. The condition is stated as a system of linear equations, such that a conversion exists iff. a solution to the linear system exists. We note that the impossibility results for linear schemes may be viewed as identifying a subset of contradicting equations in the system. Another contribution of our paper, is in defining and studying share conversion for evolving secret sharing schemes. In such a schemes, recently introduced by Komargodski et al. (IEEE ToIT'18), the number of parties is not bounded apriori, and every party receives a share as it arrives, which never changes in the sequel. Our impossibility results have implications to the evolving setting as well. Interestingly, that unlike the standard setting, there is no maximum or minimum in a broad class of evolving schemes, even without any restriction on the share size. Finally, we show that, generally, there is no conversion between additive schemes over different fields, however by degrading to statistical security, it may be possible to create convertible schemes.

Event date: 25 February to 26 February 2025

Applications are invited from Indian nationals for the position of Project Manager (Post-Doc) in a MeitY - funded research project with the following details:

Title of the Project FinTeQ - Quantum-Safe Financial Transaction Framework

For other details about the research group please visit - http://de.ci.phe.red and http://dhimans.in

Name of the position: Project Manager

Number of Positions: 1

Essential qualifications: PhD or ME/ MTech with a minimum of 4 years of relevant work experience, or BE/ BTech with a minimum of 7 years of relevant work experience UG/PG degrees should be in Computer Science/IT/ECE or other relevant disciplines.

Desirable: The candidate should have adequate knowledge and experience in mobile software development, particularly Android and iOS development, familiarity with concepts of Cryptography and secure software design, strong team management and leadership skills, experience in coordinating cross-functional teams, ability to work under tight deadlines and manage multiple projects simultaneously.

Age limit: 50 years

Monthly Salary: INR 80,000/- (Indian Rupees Eighty Thousand)

Duration: 5 Months (Extendable based on performance)

Closing date for applications:

Contact: Principal Investigator:
Dr. Dhiman Saha
Assistant Professor
Department of Computer Science and Engineering
IIT Bhilai, Chhattisgarh, INDIA - 491002
Email - dhiman@iitbhilai.ac.in

More information: https://iitbhilai.ac.in/index.php?pid=adv_oct24_30_1

The Young Investigator Group “COSYS - Control Systems and Cyber Security Lab” at the Chair of IT Security at the Brandenburg University of Technology Cottbus-Senftenberg has an open PhD/Postdoc position in the following areas:

• AI-based Network Attack Detection and Simulation.
• AI-enabled Penetration Testing.
• Privacy-Enhancing Technologies in Cyber-Physical Systems.

The available position is funded as 100% TV-L E13 tariff in Germany and limited until 31.07.2026, with possibility for extension. Candidates must hold a Master’s degree (PhD degree for Postdocs) or equivalent in Computer Science or related disciplines, or be close to completing it. If you are interested, please send your CV, transcript of records from your Master studies, and an electronic version of your Master's thesis (if possible), as a single pdf file. Applications will be reviewed until the position is filled.

Closing date for applications:

Contact: Ivan Pryvalov (ivan.pryvalov@b-tu.de)

PhD Studentship in Security for Smart Manufacturing and Digital Twin
(University of Sheffield, UK)

Are you ready to explore the forefront of securing smart manufacturing systems and digital twins? Join the University of Sheffield's research team through a 3.5-year PhD studentship focused on enhancing security within advanced manufacturing environments, specifically in applications involving digital twins and robotic arms.

Project Overview:
This project addresses critical security challenges within smart manufacturing environments, focusing on the protection and resilience of digital twin frameworks. The research aims to fortify systems against cyber threats to ensure safe, secure, and efficient operation in industrial settings. Key areas of study include vulnerability analysis, digital twin security, and developing defence mechanisms to protect interconnected manufacturing components, including robotic arms.

Research Themes Include:

• Identifying and analysing vulnerabilities in digital twins and robotic arm systems
• Designing robust digital twin models with enhanced resistance to cyber threats
• Implementing advanced security protocols for smart manufacturing infrastructure
• Collaborating with industry partners to establish new security standards for digital twin and robotic systems

Position Details:

• Starting Date: Flexible, with preferred start dates in January 2025 or September 2025.
• Location: Department of Computer Science, University of Sheffield, UK.
• Duration: 3 years and 6 months

Candidate Requirements:
The ideal candidate should have an excellent academic track record at both Bachelor’s and Master’s levels and a strong background in research, demonstrated by relevant publications. This opportunity is available for UK home students only.

Note: Only UK-based candidates are eligible to apply.

Closing date for applications:

Contact:

Application Process:
To apply, please send your CV, research statement, letter of motivation, and academic transcripts to aryan.pasikhani@sheffield.ac.uk. Be sure to include [PhD-SmartMfgSec] in the subject line

More information: https://www.linkedin.com/posts/aryanphd_phdopportunity-smartmanufacturing-digitaltwin-activity-7257849433168470016-AsDw?utm_source=share&utm_medium=member_desktop

At the Centre for Cyber Security and Privacy at the University of Birmingham, we are looking for a PhD student in low-level security topics, for example confidential computing, embedded & firmware security, GPU security, side channels, and/or mobile network security.

Studentship: The studentship covers a stipend and tuition fees based on home student rates. The stipend provides an annual maintenance allowance of £19,237. The allowance is paid as a (usually) tax-free stipend and its rate is usually incremented on 1 October each following year.

We provide personal laptops and travel funding to attend conferences (subject to prior approval) and one summer school (or equivalent). Students will also be given the chance to participate in teaching activities, including creating and grading exercises as well as conducting laboratory and tutorial sessions, which are compensated separately.

Eligibility: Candidates from most countries are welcome to apply. Candidates should have a good background in system-level programming (e.g. using C, C++, Assembly, and/or Rust) and/or embedded systems/hardware. We also expect a first-class UG or PG degree in a relevant subject (e.g. computer science or electrical engineering).

Apply: Applications are accepted until 5 Dec 2024, see https://www.birmingham.ac.uk/schools/computer-science/postgraduate-research/applying-for-phd-in-computer-science.

Closing date for applications:

Contact: Feel free to informally discuss with David Oswald (d.f.oswald (at) bham.ac.uk) and Marius Münch (m.muench (at) bham.ac.uk) before putting in a full application.

More information: https://www.birmingham.ac.uk/schools/computer-science/postgraduate-research/applying-for-phd-in-computer-science

Oxford University’s Computer Science Department is hiring four new faculty members. Most of the positions are open to all areas of computer science. The closing date for the Associate Professor and Professor of Computer Science positions is 12 noon on 18 December 2024. There is also a Chair in Computer Science and a joint faculty position with philosophy in AI ethics. For more information, see here: https://www.cs.ox.ac.uk/aboutus/vacancies/vacancy-faculty-hiring.html

Closing date for applications:

Contact: Jo Francis, Computer Science Department, Oxford Univeristy.

More information: https://www.cs.ox.ac.uk/aboutus/vacancies/vacancy-faculty-hiring.html

e present a key-policy attribute-based encryption (ABE) scheme for circuits based on the Learning With Errors (LWE) assumption whose key size is independent of the circuit depth. Our result constitutes the first improvement for ABE for circuits from LWE in almost a decade, given by Gorbunov, Vaikuntanathan, and Wee (STOC 2013) and Boneh, et al. (EUROCRYPT 2014) -- we reduce the key size in the latter from $\mathsf{poly}(\mbox{depth},\lambda)$ to $\mathsf{poly}(\lambda)$. The starting point of our construction is a recent ABE scheme of Li, Lin, and Luo (TCC 2022), which achieves $\mathsf{poly}(\lambda)$ key size but requires pairings and generic bilinear groups in addition to LWE; we introduce new lattice techniques to eliminate the additional requirements.

The enormous potential of Attribute-Based Encryption (ABE) in the context of IoT has driven researchers to propose pairing-free ABE schemes that are suitable for resource-constrained devices. Unfortunately, many of these schemes turned out to be insecure. This fact seems to reinforce the point of view of some authors according to which instantiating an Identity-Based Encryption (IBE) in plain Decision Diffie-Hellman (DDH) groups is impossible. In this paper, we provide a generic AND gate access structured Ciphertext-Policy ABE (CP-ABE) scheme with secret access policy from Inner-Product Functional Encryption (IPFE). We also propose an instantiation of that generic CP-ABE scheme from the DDH assumption. From our generic CP-ABE scheme we derive an IBE scheme by introducing the concept of Clustered Identity-Based Encryption (CIBE). Our schemes show that it is indeed possible to construct practical and secure IBE and ABE schemes based on the classical DDH assumption.

Yu et al. described an algorithm for conducting computational searches for quadratic APN functions over the finite field $\mathbb{F}_{2^n}$, and used this algorithm to give a classification of all quadratic APN functions with coefficients in $\mathbb{F}_{2}$ for dimensions $n$ up to 9. In this paper, we speed up the running time of that algorithm by a factor of approximately $\frac{n \times 2^n}{n^3}$. Based on this result, we give a complete classification of all quadratic APN functions over $\mathbb{F}_{2^{10}}$ with coefficients in $\mathbb{F}_{2}$. We also perform some partial computations for quadratic APN functions over $\mathbb{F}_{2^{11}}$ with coefficients in $\mathbb{F}_{2}$ , and conjecture that they form 6 CCZ-inequivalent classes which also correspond to known APN functions.

Digital signature schemes based on multivariate- and code-based hard problems are promising alternatives for lattice-based signature schemes, due to their smaller signature size. Hence, several candidates in the ongoing additional standardization for quantum secure digital signature (DS) schemes by the National Institute of Standards and Technology (NIST) rely on such alternate hard problems. Gaussian Elimination (GE) is a critical component in the signing procedure of these schemes. In this paper, we provide a masking scheme for GE with back substitution to defend against first- and higher-order attacks. To the best of our knowledge, this work is the first to analyze and propose masking techniques for multivariate- or code-based DS algorithms. We propose a masked algorithm for transforming a system of linear equations into row-echelon form. This is realized by introducing techniques for efficiently making leading (pivot) elements one while avoiding costly conversions between Boolean and multiplicative masking at all orders. We also propose a technique for efficient masked back substitution, which eventually enables a secure unmasking of the public output. We evaluate the overhead of our countermeasure for several post-quantum candidates and their different security levels at first-, second-, and third-order, including UOV, MAYO, SNOVA, QR-UOV, and MQ-Sign. Notably, the operational cost of first-, second-, and third-order masked GE is 2.3$\times$ higher, and the randomness cost is 1.2$\times$ higher in MAYO compared to UOV for security levels III and V. In contrast, these costs are similar in UOV and MAYO for one version of level I. We also show detailed performance results for masked GE implementations for all three security versions of UOV on the Arm Cortex-M4 and compare them with unmasked results. Our first-order implementations targeting UOV parameters have overheads of factor 6.5$\times$, 5.9$\times$, and 5.7$\times$ compared to the unprotected implementation for NIST security level I, III, and V.

In 2020, Castryck-Decru-Smith constructed a hash function, using the (2,2)-isogeny graph of superspecial principally polarized abelian surfaces. In their construction, the initial surface was chosen from vertices very "close" to the square of a supersingular elliptic curve with a known endomorphism ring. In this paper, we introduce an algorithm for detecting a collision on their hash function. Under some heuristic assumptions, the time complexity and space complexity of our algorithm are estimated to be $\widetilde{O}(p^{3/10})$ which are smaller than the complexity $\widetilde{O}(p^{3/2})$ the authors claimed to be necessary to detect a collision, where $p$ is the characteristic of the base field. In particular case where $p$ has a special form, then both the time and space complexities of our algorithm are polynomial in $\log{p}$. We implemented our algorithm in Magma, and succeeded in detecting a collision in 17 hours (using 64 parallel computations) under a parameter setting which the authors had claimed to be 384-bit secure.

In this paper, we introduce zkMarket, a privacy-preserving fair trade system on the blockchain. zkMarket addresses the challenges of transaction privacy and computational efficiency. To ensure transaction privacy, zkMarket is built upon an anonymous transfer protocol. By combining encryption with zero-knowledge succinct non-interactive arguments of knowledge (zk-SNARK), both the seller and the buyer are enabled to trade fairly. Furthermore, by encrypting the decryption key, we make the data registration process more concise and improve the seller's proving time by leveraging commit-and-prove SNARK (CP-SNARK) and our novel pseudorandom generator, the matrix-formed PRG (MatPRG).

Our evaluation demonstrates that zkMarket significantly reduces the computational overhead associated with traditional blockchain solutions while maintaining robust security and privacy. The seller can register 1MB of data in 3.2 seconds, while the buyer can generate the trade transaction in 0.2 seconds, and the seller can finalize the trade in 0.4 seconds.

Approximate nearest neighbor search (ANNS), also known as vector search, is an important building block for varies applications, such as databases, biometrics, and machine learning. In this work, we are interested in the private ANNS problem, where the client wants to learn (and can only learn) the ANNS results without revealing the query to the server. Previous private ANNS works either suffers from high communication cost (Chen et al., USENIX Security 2020) or works under a weaker security assumption of two non-colluding servers (Servan-Schreiber et al., SP 2022). We present Panther, an efficient private ANNS framework under the single server setting. Panther achieves its high performance via several novel co-designs of private information retrieval (PIR), secretsharing, garbled circuits, and homomorphic encryption. We made extensive experiments using Panther on four public datasets, results show that Panther could answer an ANNS query on 10 million points in 23 seconds with 318 MB of communication. This is more than 6× faster and 18× more compact than Chen et al..

Adaptor signatures (AS) extend the functionality of traditional digital signatures by enabling the generation of a pre-signature tied to an instance of a hard NP relation, which can later be turned (adapted) into a full signature upon revealing a corresponding witness. The recent work by Liu et al. [ASIACRYPT 2024] devised a generic AS scheme that can be used for any NP relation---which here we will refer to as universal adaptor signatures scheme, in short UAS---from any one-way function. However, this generic construction depends on the Karp reduction to the Hamiltonian cycle problem, which adds significant overhead and hinders practical applicability.

In this work, we present an alternative approach to construct universal adaptor signature schemes relying on the multi-party computation in the head (MPCitH) paradigm. This overcomes the reliance on the costly Karp reduction, while inheriting the core property of the MPCitH---which makes it an invaluable tool in efficient cryptographic protocols---namely, that the construction is black-box with respect to the underlying cryptographic primitive (while it remains non-black-box in the relation being proven). Our framework simplifies the design of UAS and enhances their applicability across a wide range of decentralized applications, such as blockchain and privacy-preserving systems. Our results demonstrate that MPCitH-based UAS schemes offer strong security guarantees while making them a promising tool in the design of real-world cryptographic protocols.

ARADI is a low-latency block cipher proposed by the NSA (National Security Agency) in 2024 for memory encryption. Bellini et al. experimentally demonstrated that in specific cubes of 5-round ARADI, the cube sums are byte-wise equal, for example, to 0x9d9dc5c5. This paper modifies the MILP-based division property algorithm to prove this and observes that the rotation amount of 8 in ARADI causes cancellations of monomials, allowing us to extend the byte-wise equal property up to 8 rounds. As a result, we obtained distinguishers for rounds 6 and 7 with lower data complexities of $2^{77}$ and $2^{112}$, respectively, compared to previous methods.