International Association
for Cryptologic Research

Yao's garbled circuits have received huge attention in both theory and practice. While garbled circuits can be constructed using minimal assumption (i.e., the existence of pseudorandom functions or one-way functions), the state-of-the-art constructions (e.g., Rosulek-Roy, Crypto 2021) are based on stronger assumptions. In particular, the ``Free-XOR'' technique (Kolesnikov-Schneider, ICALP 2008) is essential in these state-of-the-art constructions, and their security can only be proven in the random oracle model, or rely on the ``circular-correlation robust hash'' assumption.

In this paper, we aim to develop new techniques to construct efficient garbling schemes using minimal assumptions. Instead of generically replacing the Free-XOR technique, we focus on garbling schemes for specific functionalities. We successfully eliminated the need for Free-XOR in several state-of-the-art schemes, including the one-hot garbling (Heath and Kolesnikov, CCS 2021) and the garbled pseudorandom functions, and the garbled lookup tables (Heath, Kolesnikov and Ng, Eurocrypt 2024). Our schemes are based on minimal assumptions, i.e., standard pseudorandom functions (PRFs)---we resolved the need for circular security. The performance of our scheme is almost as efficient as the best results except for a small constant factor. Namely, for any lookup table $\{0,1\}^n \to \{0,1\}^m$, our scheme takes $n + (5n+9)m\lambda + 2^n \cdot m$ bits of communication, where $\lambda$ is the security parameter of PRF.

The GCM authenticated encryption (AE) scheme is one of the most widely used AE schemes in the world, while it suffers from risk of nonce misuse, short message length per encryption and an insufficient level of security. The goal of this paper is to design new AE schemes achieving stronger provable security in the standard model and accepting longer nonces (or providing nonce misuse resistance), with the design rationale behind GCM.

As a result, we propose two enhanced variants of GCM and GCM-SIV, dubbed eGCM and eGCM-SIV, respectively. eGCM and eGCM-SIV are built on top of a new CENC-type encryption mode, dubbed eCTR: using 2n-bit counters, eCTR enjoys beyond-birthday-bound security without significant loss of efficiency. eCTR is combined with an almost uniform and almost universal hash function, yielding a variable input-length variable output-length pseudorandom function, dubbed HteC. GCM and GCM-SIV are constructed using eCTR and HteC as building blocks.

eGCM and eGCM-SIV accept nonces of arbitrary length, and provide almost the full security (namely, n-bit security when they are based on an n-bit block cipher) for a constant maximum input length, under the assumption that the underlying block cipher is a pseudorandom permutation (PRP). Their efficiency is also comparable to GCM in terms of the rate and the overall speed.

Conventional Publicly Verifiable Secret Sharing (PVSS) protocols allow a dealer to share a secret among $n$ parties without interaction, ensuring that any $t + 1$ parties (where $t+1 \le n$) can recover the secret, while anyone can publicly verify the validity of both the individual shares and the reconstructed secret. PVSS schemes are shown to be a key tool in a wide range of practical applications. In this paper, we introduce Pre-constructed PVSS (PPVSS), an extension of standard PVSS schemes, highlighting its enhanced utility and efficiency in various protocols. Unlike standard PVSS, PPVSS requires the dealer to publish a commitment or encryption of the main secret and incorporates a novel secret reconstruction method. We show that these refinements make PPVSS more practical and versatile than conventional PVSS schemes. To build a PPVSS scheme, we first point out that the well-known PVSS scheme by Schoenmakers (CRYPTO'99) and its pairing-based variant presented by Heidarvand and Villar (SAC'08) can be seen as special cases of PPVSS, where the dealer also publishes a commitment to the main secret. However, these protocols are not practical for many applications due to efficiency limitations and are less flexible compared to a standard PPVSS scheme. To address this, we propose a general strategy for transforming a Shamir-based PVSS scheme into a PPVSS scheme. Using this strategy, we construct two practical PPVSS schemes in both the Random Oracle (RO) and plain models, grounded in state-of-the-art PVSS designs. Leveraging the new RO-based PPVSS scheme, we revisit some applications and present more efficient variants. Notably, we propose a new universally verifiable e-voting protocol that improves on the alternative scheme by Schoenmakers (CRYPTO'99), reducing the verification complexity with $m$ voters from $O(n^2m)$ to $O(nm)$ exponentiations--a previously unattainable goal with standard PVSS schemes. Our implementation results demonstrate that both our proposed PPVSS schemes and the new universally verifiable e-voting protocol significantly outperform existing alternatives in terms of efficiency.

At CRYPTO 2015, Kirchner and Fouque claimed that a carefully tuned variant of the Blum-Kalai-Wasserman (BKW) algorithm (JACM 2003) should solve the Learning with Errors problem (LWE) in slightly subexponential time for modulus $q=\mathrm{poly}(n)$ and narrow error distribution, when given enough LWE samples. Taking a modular view, one may regard BKW as a combination of Wagner's algorithm (CRYPTO 2002), run over the corresponding dual problem, and the Aharonov-Regev distinguisher (JACM 2005). Hence the subexponential Wagner step alone should be of interest for solving this dual problem - namely, the Short Integer Solution problem (SIS) - but this appears to be undocumented so far.

We re-interpret this Wagner step as walking backward through a chain of projected lattices, zigzagging through some auxiliary superlattices. We further randomize the bucketing step using Gaussian randomized rounding to exploit the powerful discrete Gaussian machinery. This approach avoids sample amplification and turns Wagner's algorithm into an approximate discrete Gaussian sampler for $q$-ary lattices. For an SIS lattice with $n$ equations modulo $q$, this algorithm runs in subexponential time $\exp(O(n/\log \log n))$ to reach a Gaussian width parameter $s = q/\mathrm{polylog}(n)$ only requiring $m = n + \omega(n/\log \log n)$ many SIS variables. This directly provides a provable algorithm for solving the Short Integer Solution problem in the infinity norm ($\mathrm{SIS}^\infty$) for norm bounds $\beta = q/\mathrm{polylog}(n)$. This variant of SIS underlies the security of the NIST post-quantum cryptography standard Dilithium. Despite its subexponential complexity, Wagner's algorithm does not appear to threaten Dilithium's concrete security.

Federated Learning (FL) has become a crucial framework for collaboratively training Machine Learning (ML) models while ensuring data privacy. Traditional synchronous FL approaches, however, suffer from delays caused by slower clients (called stragglers), which hinder the overall training process.

Specifically, in a synchronous setting, model aggregation happens once all the intended clients have submitted their local updates to the server. To address these inefficiencies, Buffered Asynchronous FL (BAsyncFL) was introduced, allowing clients to update the global model as soon as they complete local training. In such a setting, the new global model is obtained once the buffer is full, thus removing synchronization bottlenecks. Despite these advantages, existing Secure Aggregation (SA) techniques—designed to protect client updates from inference attacks—rely on synchronized rounds, making them unsuitable for asynchronous settings.

In this paper, we present Buffalo, the first practical SA protocol tailored for BAsyncFL. Buffalo leverages lattice-based encryption to handle scalability challenges in large ML models and introduces a new role, the assistant, to support the server in securely aggregating client updates. To protect against an actively corrupted server, we enable clients to verify that their local updates have been correctly integrated into the global model. Our comprehensive evaluation—incorporating theoretical analysis and real-world experiments on benchmark datasets—demonstrates that Buffalo is an efficient and scalable privacy-preserving solution in BAsyncFL environments.

Formal methods are becoming an important tool for ensuring correctness and security of cryptographic constructions. However, the support for certain advanced proof techniques, namely rewinding, is scarce among existing verification frameworks, which hinders their application to complex schemes such as multi-party signatures and zero-knowledge proofs.

We expand the support for rewinding in EasyCrypt by implementing a version of the general forking lemma by Bellare and Neven. We demonstrate its usability by proving EUF-CMA security of Schnorr signatures.

Zero-knowledge proofs (ZKPs) are cryptographic protocols that enable a prover to convince a verifier of a statement's truth without revealing any details beyond its validity. Typically, the statement is encoded as an arithmetic circuit, and allows the prover to demonstrate that the circuit evaluates to true without revealing its inputs. Despite their potential to enhance privacy and security, ZKPs are difficult to write and optimize, limiting their adoption in machine learning and data science. To address these challenges, we introduce Zinnia, a zero-knowledge programming framework with high utility, expressiveness and efficiency for tensor-oriented computation. Zinnia provides a high-level programming language that enables developers to easily write ZKP programs, and it employs a novel symbolic execution-inspired approach to extracting semantics from these programs to generate arithmetic circuits. Zinnia supports tensor-oriented computations and provides a rich set of programming constructs, optimizations, and a powerful static type system for expressing and optimizing complex logic. We evaluate Zinnia across 25 real-world programming tasks and a user study, comparing it to existing solutions, including DSLs and zkVMs (Halo2, SP1, and RISC0). Our results demonstrate that Zinnia outperforms these baselines in utility, expressiveness, and efficiency, with a statistically significant reduction in development time, $2-3\times$ shorter code length, 19.3% smaller circuit size, and up to $245\times$ faster proving time compared to zkVMs, paving the way for practical ZKP applications in various domains.

Password-Authenticated Key Exchange (PAKE) establishes a secure channel between two parties who share a password. Asymmetric PAKE is a variant of PAKE, where one party stores a hash of the password to preserve security under the situation that the party is compromised. The security of PAKE and asymmetric PAKE is often analyzed in the framework of universal composability (UC). Abdalla et al. (CRYPTO '20) relaxed the UC security of PAKE and showed that the relaxed security still guarantees reasonable properties. This relaxation makes it possible to prove the security in the UC framework for several PAKE protocols. In this paper, we propose a relaxed functionality of asymmetric PAKE by following the approach of Abdalla et al. We prove that the SPAKE2+ protocol UC-realizes this functionality. We also define a more relaxed functionality and prove that a variant of the AuCPace protocol UC-realizes it.

Embedded devices can be exposed to a wide range of attacks. Some classes of attacks can be mitigated using security features or dedicated countermeasures. Examples include Trusted Execution Environments, and masking countermeasures against physical side-channel attacks. However, a system that incorporates such secure components is not automatically a secure system. Partial Key Overwrite attacks are one class of attacks that specifically target the interface between different components of the security system. These attacks may allow an adversary to extract otherwise protected cryptographic keys through careful manipulation of memory-mapped registers. So far this powerful class of attacks has received little attention in the academic literature. In this work, we provide an overview of known Partial Key Overwrite vulnerabilities and how they were used in real-world attacks. Additionally, we evaluated 31 common microcontrollers and embedded microprocessors from eleven distinct vendors and detail our findings. Based on a first high-level evaluation we selected 15 SoCs and performed an in-depth evaluation. This evaluation revealed that at least eight of these SoCs are vulnerable to partial key overwrite attacks.

Issuing tokens on Bitcoin remains a highly sought-after goal, driven by its market dominance and robust security. However, Bitcoin's limited on-chain storage and functionality pose significant challenges. Among the various approaches to token issuance on Bitcoin, client-side validation (CSV) has emerged as a prominent solution. CSV delegates data storage and functionalities beyond Bitcoin’s native capabilities to off-chain clients, while leveraging the blockchain to validate tokens and prevent double-spending. Nevertheless, these protocols require participants to maintain token ownership and transactional data, rendering them vulnerable to data loss and malicious data withholding. In this paper, we propose UTxO binding, a novel framework that achieves both robust data availability and enhanced functionality compared to existing CSV designs. This approach securely binds a Bitcoin UTxO, which prevents double-spending, to a UTxO on an auxiliary blockchain, providing data storage and programmability. We formally prove its security and implement our design using Nervos CKB as the auxiliary blockchain.

The Nintendo DSi is a handheld gaming console released by Nintendo in 2008. In Nintendo's line-up the DSi served as a successor to the DS and was later succeeded by the 3DS. The security systems of both the DS and 3DS have been fully analysed and defeated. However, for over 14 years the security systems of the Nintendo DSi remained standing and had not been fully analysed. To that end this work builds on existing research and demonstrates the use of a second-order fault injection attack to extract the ROM bootloaders stored in the custom system-on-chip used by the DSi. We analyse the effect of the induced fault and compare it to theoretical fault models. Additionally, we present a security analysis of the extracted ROM bootloaders and develop a modchip using cheap off-the-shelf components. The modchip allows to jailbreak the console, but more importantly allows to resurrect consoles previously assumed irreparable.

Current DAG-based BFT protocols face a critical trade-off: certified DAGs provide strong security guarantees but require additional rounds of communication to progress the DAG construction, while uncertified DAGs achieve lower latency at the cost of either reduced resistance to adversarial behaviour or higher communication costs.

This paper presents Starfish, a partially synchronous DAG-based BFT protocol that achieves the security properties of certified DAGs, the efficiency of uncertified approaches and linear amortized communication complexity. The key innovation is Encoded Cordial Dissemination, a push-based dissemination strategy that combines Reed-Solomon erasure coding with Data Availability Certificates (DACs). Each of the $n=3f+1$ validators disseminates complete transaction data for its own blocks while distributing encoded shards for others' blocks, enabling efficient data reconstruction with just $f+1$ shards. Building on the previous uncertified DAG BFT commit rule, Starfish extends it to efficiently verify data availability through committed leader blocks serving as DACs. For large enough transaction data, this design allows Starfish to achieve $O(n)$ amortized communication complexity per committed transaction byte. The average and worst-case end-to-end latencies for Starfish are rigorously proven to be bounded by $7.5\delta$ and $11\delta$ in the steady state, where $\delta$ denotes the actual network delay.

Experimental evaluation against state-of-the-art DAG BFT protocols demonstrates Starfish's robust performance under steady-state and Byzantine scenarios. Our results show that strong Byzantine fault tolerance, high performance, and low communication complexity can coexist in DAG BFT protocols, making Starfish particularly suitable for large-scale distributed ledger deployments.

We are seeking motivated and dedicated Research Assistant to join our team. The details are as follows:

Key Responsibilities:

• Design and implement user interfaces for web and mobile applications
• Create wire frames, prototypes, and user flows
• Conduct user research and usability testing
• Collaborate with product managers and researchers
• Develop and maintain design systems
• Optimize user journeys and experiences
• Create responsive designs for multiple platforms
• Perform any other duties as assigned by the project leader, the Head of Unit or their delegates

Technical Requirements:

• Bachelor's degree in Design, Computer Science, or related field
• 3+ years experience in UI/UX design
• Proficient in design tools: Figma, Adobe XD, Sketch
• Experience with prototyping tools
• Knowledge of HTML, CSS, and basic JavaScript
• Portfolio demonstrating UI/UX projects
• Strong understanding of user-centered design principles
• Experience with responsive design

Preferred Skills:

• Experience with web3 or blockchain products
• Knowledge of user research methodologies
• Familiarity with agile development processes
• Experience with motion design/Adobe After Effects
• Understanding of accessibility standards

For more details and to apply, please visit: https://jobs.polyu.edu.hk/job_detail.php?job=250306003

Closing date for applications:

Contact: Elaine Chow (blockchain.rcbt@polyu.edu.hk)

We are seeking motivated and dedicated Research Assistant to join our team. The details are as follows:

Key Responsibilities:

• Develop and maintain web applications using modern frameworks
• Write clean, maintainable, and efficient code
• Work on both frontend and backend development tasks
• Collaborate with senior researchers and product teams
• Participate in code reviews and technical discussions
• Assist in database design and management
• Debug and fix software issues
• Perform any other duties as assigned by the project leader, the Head of Unit or their delegates

Technical Requirements:

• Bachelor's degree in Computer Science, Engineering, or related field
• Knowledge of JavaScript/TypeScript
• Experience with frontend frameworks (React.js, Vue.js)
• Basic understanding of backend development (Node.js, Java, or Python)
• Familiarity with HTML5, CSS3
• Basic knowledge of SQL databases
• Version control with Git

Preferred Skills:

• Experience with REST APIs
• Understanding of web security principles
• Knowledge of cloud services (AWS, Azure, or GCP)
• Basic understanding of CI/CD pipelines
• Experience with agile development methodology

For more details and to apply, please visit: https://jobs.polyu.edu.hk/job_detail.php?job=250306002

Closing date for applications:

Contact: Elaine Chow (blockchain.rcbt@polyu.edu.hk)

Do you want to contribute to making our increasingly digitised world safer and more private by diving into the exciting field of privacy-enhancing cryptography? This research topic will influence how data can be shared and processed in the future, with major ramifications for the use of AI and machine learning.

The successful applicant will have the opportunity to explore and contribute to groundbreaking research questions, for instance focusing on its efficient implementation and deployment. While specific research questions will be discussed with the successful applicant, they may include techniques such as fully homomorphic encryption (FHE), multi-party computation (MPC) and zero-knowledge protocols (ZK). This is not just an opportunity to develop and shape your own research project, but also to help shape the future of cryptography and privacy.

Simula UiB currently has 11 early career researchers working on a range of research problems in cryptography and information theory. We can offer a vibrant, stimulating, and inclusive working environment to successful candidates. The position is for three years, with a possible extension of one year.

Read more and apply here: https://www.simula.no/careers/job-openings/postdoctoral-fellow-in-privacy-enhancing-cryptography

Closing date for applications:

Contact:

Martijn Stam (martijn@simula.no)

or Simula UiB (bergen@simula.no)

About the Project
We are seeking a highly motivated PhD candidate to join our DFG-funded project on privacy-preserving rare disease analysis. This interdisciplinary research initiative focuses on developing secure and efficient methods for variant filtering, prioritization, and rare-variant association studies.

Responsibilities

• Conduct research on secure algorithms and protocols for privacy-preserving analysis of genomic and clinical data.
• Develop and integrate methods for variant filtering, prioritization, and rare-variant association studies in a federated environment.
• Implement and evaluate methods as part of an open-source software framework for privacy-preserving rare variant analyses.
• Present findings in peer-reviewed publications and international conferences.

Requirements

• Master’s degree (or equivalent) in Computer Science, Bioinformatics, Mathematics, or a related field.
• Background or interest in cryptography (e.g., secure multi-party computation), machine learning (e.g., federated learning, data privacy), or bioinformatics (e.g., variant analysis).
• Solid programming skills in at least one language commonly used in research (Python, C/C++, Java, etc.).
• Strong analytical and problem-solving capabilities.
• Excellent communication and teamwork skills.

How to Apply
Please email a single PDF to [Contact Email Address] with:

1. Cover Letter (your motivation and relevant experience)
2. CV (academic background, technical skills, publications)
3. Transcript(s) (BSc, MSc or equivalent)
4. References(contact details)

Application Deadline: [30.04.2025]

Closing date for applications:

Contact: Dr. Mete Akgün

More information: https://mdppml.github.io/downloads/PhD_Student_in_Privacy_Preserving_Rare_Disease_Analysis.pdf

Fruit-F is a lightweight short-state stream cipher designed by Ghafari et al. The authors designed this version of the cipher, after earlier versions of the cipher viz. Fruit 80/v2 succumbed to correlation attacks. The primary motivation behind this design seemed to be preventing correlation attacks. Fruit-F has a Grain-like structure with two state registers of size 50 bits each. In addition, the cipher uses an 80-bit secret key and an 80-bit IV. The authors use a complex key-derivation function to update the non-linear register which prevents the same key-bit alignment across fixed-length window of keystream bits, which is essentially what stops the correlation attacks. In this paper, we first present two attacks against Fruit-F. The first attack stems from the fact that the key-derivation can be rewritten as the Boolean xor of two key-dependent terms one of which is the Boolean OR of two bits of the key. Using this we show that the cipher does not offer 80-bit security: the effective key space of Fruit-F is slightly less than $2^{80}$, i.e. a simple brute force attack costs around $2^{80}-2^{49}$ time. The second is a differential attack using the cipher's complex initialization process. We show that under some given conditions, it is possible to have two initial vectors $V_1$ and $V_2$ that produce identical keystream vectors with any given key. Using this as a distinguisher, it is possible to collect enough linear and quadratic equations of the secret key to find it in practical time with very few keystream bits.

We demonstrate an attack on the soundness of a widely known optimization of the Gemini multilinear Polynomial Commitment Scheme (PCS). The attack allows a malicious prover to falsely claim that a multilinear polynomial takes a value of their choice, for any input point. We stress that the original Gemini multilinear PCS and HyperKZG, an adaptation of Gemini, are not affected by the attack.

Both masking and shuffling are very common software countermeasures against side-channel attacks. However, exploring possible combinations of the two countermeasures to increase and fine-tune side-channel resilience is less investigated. With this work, we aim to bridge that gap by both concretising the security guarantees of several masking and shuffling combinations presented in earlier work and additionally investigating their randomness cost. We subsequently implement these approaches to also analyse their performance. In this context, we present five different protected implementations of the new standard for lightweight cryptography, Ascon, on a 32-bit RISC-V architecture: A 3rd-order masked, unshuffled implementation and three combined 3rd-order masked and shuffled implementations. Additionally, we present a levelled implementation where only the particularly vulnerable keyed initialisation and finalisation of the permutation are masked and shuffled, while the rest is only shuffled. To further improve the security and performance of our implementations we make use of the Probe Isolating Non-Interference (PINI) masked AND gadget, coupled with techniques like bit-slicing and bit-interleaving. Utilising benchmarking and an MI-shortcut security analysis, we pinpoint the best masking-shuffling combinations that maximize security at reasonable overheads.

Since the selection of the National Institute of Standards and Technology (NIST) Post-Quantum Cryptography (PQC) standardization algorithms, research on integrating PQC into security protocols such as TLS/SSL, IPSec, and DNSSEC has been actively pursued. However, PQC migration for Internet of Things (IoT) communication protocols remains largely unexplored. Embedded devices in IoT environments have limited computational power and memory, making it crucial to optimize PQC algorithms for efficient computation and minimal memory usage when deploying them on low-spec IoT devices. In this paper, we introduce KEM-MQTT, a lightweight and efficient Key Encapsulation Mechanism (KEM) for the Message Queuing Telemetry Transport (MQTT) protocol, widely used in IoT environments. Our approach applies the NIST KEM algorithm Crystals-Kyber (Kyber) while leveraging MQTT’s characteristics and sensor node constraints. To enhance efficiency, we address certificate verification issues and adopt KEMTLS to eliminate the need for Post-Quantum Digital Signatures Algorithm (PQC-DSA) in mutual authentication. As a result, KEM-MQTT retains its lightweight properties while maintaining the security guarantees of TLS 1.3. We identify inefficiencies in existing Kyber implementations on 8-bit AVR microcontrollers (MCUs), which are highly resource-constrained. To address this, we propose novel implementation techniques that optimize Kyber for AVR, focusing on high-speed execution, reduced memory consumption, and secure implementation, including Signed LookUp-Table (LUT) Reduction. Our optimized Kyber achieves performance gains of 81%,75%, and 85% in the KeyGen, Encaps, and DeCaps processes, respectively, compared to the reference implementation. With approximately 3 KB of stack usage, our Kyber implementation surpasses all state-of-the-art Elliptic Curve Diffie-Hellman (ECDH) implementations. Finally, in KEM-MQTT using Kyber-512, an 8-bit AVR device completes the handshake preparation process in 4.32 seconds, excluding the physical transmission and reception times.