International Association
for Cryptologic Research

The transition of cryptographic primitives to the post-quantum era necessitates the rigorous translation of asymptotic security proofs into concrete parameter instantiations. This paper evaluates the practical realizability of the Decentralized Multi-Authority Attribute-Based Encryption (MA-ABE) scheme by Datta, Komargodski, and Waters (Eurocrypt 2021), a seminal construction relying exclusively on the Learning With Errors (LWE) assumption. While DKW21 eliminates the reliance on bilinear maps, offering resilience against quantum adversaries, our comprehensive numerical audit reveals a profound dichotomy between its theoretical soundness and practical feasibility. We demonstrate that the convergence of constraints derived from LWE hardness and the noise flooding technique required for simulation-based security forces the modulus-to-noise ratio into a super-polynomial regime. Consequently, the requisite parameters---particularly the smudging bound $\hat{B}$---scale astronomically ($\approx 10^{47}$), rendering the scheme unimplementable on existing computational substrates. Beyond identifying this "Parameter Wall," this work proposes a radical architectural reconfiguration to bridge the gap between theory and practice. We introduce novel optimization strategies including the transition to non-commutative Module-LWE structures, the invention of Coset-Restricted Lattice Hashing to minimize pre-image norms, and the adoption of Entropic Smudging via Lossy Trapdoors. Furthermore, we explore Isospectral Lattice Deformations and Learning With Rounding (LWR) transformations to decouple security constraints from decryption correctness, outlining a viable roadmap for practical post-quantum access control.

We study the problem of constructing Boolean garbling schemes that are both succinct$-$with garbled circuit size significantly smaller than the original circuit$-$and have low-depth garbling algorithms, where the garbling process runs in parallel time logarithmic in the circuit size. Prior schemes achieve one but not the other, unless relying on indistinguishability obfuscation ($\mathsf{iO}$), which is prohibitively inefficient, relies on a combination of multiple assumptions, and achieves only polynomial garbling depth $\mathsf{poly}(\lambda,\log |C|)$.

We resolve this tension by presenting the first garbling schemes that are both succinct and admit garbling algorithms in $\mathsf{NC}^1$, based only on standard group and lattice assumptions. Our main results include: • $\textbf{One-bit-per-gate garbling}$ with logarithmic garbling depth based on DDH or RLWE and the existence of a local PRG. • $\textbf{Succinct privacy-free garbling}$ of size linear in the circuit depth $D$ (and sublinear in the circuit size $|C|$), based on DDH or RLWE. • $\textbf{Reusable, fully succinct garbling}$ with logarithmic garbling depth, based on decomposable LWE.

The DDH-based one-bit-per-gate scheme has tunably small inverse polynomial correctness and privacy errors, which can be made negligible at the cost of increasing garbling depth to $\mathsf{poly}(\lambda)$.

As further extension, we also obtain the first attribute-based encryption schemes with succinct keys and low-depth key generation.

At a conceptual level, our constructions are derived from a unified framework that subsumes all prior approaches to succinct garbling. It identifies the common source of high-depth garbling, and provides a general methodology for reducing garbling depth without sacrificing succinctness, applicable across different techniques and assumptions.

We present the first construction of attribute-based laconic function evaluation (AB-LFE) from the decisional composite residuosity (DCR) assumption. This yields the first example of computationally succinct secure computation from a group-based assumption, avoiding reliance on noisy lattice assumptions such as LWE. Our construction builds on recent work in fully homomorphic MACs and homomorphic secret sharing by Ishai, Li and Lin (FOCS 2025) and Meyer, Orlandi, Roy, and Scholl (Crypto 2025), which we extend by constructing a fully homomorphic MAC for packed vector operations, where the evaluation time of one party is independent of the vector length.

As applications, we obtain full-fledged laconic function evaluation (LFE) from the combination of DCR and standard LWE, avoiding the need for sub-exponential modulus-to-noise ratio LWE used in previous work. We also obtain the first constrained pseudorandom function whose master evaluation key is succinct in the constraint.

These results highlight the unexplored power of group-based cryptography for succinct secure computation.

The interest in verifiable credential systems has gained traction as eIDAS 2.0 Regulation has been published. This regulation instructs EU member states to provide their citizens with digital identity wallets (EUDI Wallet) that must store the credentials and enable privacy-preserving presentation of identity information to relying parties. This new digital identity system requires defining new protocols and procedures to perform tasks involving the disclosure of identity information. One of such procedures is the delegation of attestation, as is reported in the EUDI Wallet Reference Implementation Roadmap.

In this work, we address the problem of constructing secure processes for the delegation of verifiable presentations derived from both verifiable and anonymous credentials. Our goal is to enable a credential holder (the delegator) to securely delegate another party (the delegatee) to present a credential on their behalf. We introduce the notion of a verifiable presentation delegation scheme, formalizing the core algorithms, namely delegation issuance, delegated presentation, and presentation verification, and defining the relevant security properties that such a scheme should satisfy: the correctness, the unforgeability, and, when the scheme is built on top of anonymous credentials, even the unlinkability. We present two concrete instantiations of delegation schemes: the first is built on top of mdoc verifiable credentials, the credential format currently supported by the EUDI Wallet Architecture and Reference Framework (EUDI ARF), while the second is built on top of BBS anonymous credentials. Finally, we discuss and analyze the security of our constructions in terms of the security properties we have introduced.

Secure multi-party computation (MPC) enables $N$ parties to jointly evaluate any function over their private inputs while preserving confidentiality. While decades of research have produced concretely efficient protocols for small to moderate numbers of participants, scaling MPC to thousands of parties remains a central challenge. Most of the existing approaches either incur per-party costs linear in $N$, due to pairwise computations, or rely on heavy cryptographic tools such as homomorphic encryption, which introduces prohibitive overheads when evaluating Boolean circuits.

In this work, we introduce a new lightweight approach to designing semi-honest MPC protocols with per-party, per-gate computation and communication costs that are independent of $N$. Our construction leverages the Sparse Learning Parity with Noise (Sparse LPN) assumption in the random oracle model to achieve per-gate costs of $O(k^2 \cdot c(\lambda))$ computation and $O(c(\lambda))$ communication, where $k$ is the sparsity parameter for the Sparse LPN assumption and $c(\lambda)$ is an arbitrarily small super-constant in the security parameter $\lambda$. Assuming Sparse LPN remains hard for any super-constant sparsity, this yields the first semi-honest MPC protocol in the dishonest-majority setting with per-party per-gate costs bounded by an arbitrarily small super-constant overhead in $\lambda$.

Structurally, our MPC instantiates a Beaver style MPC with the required correlations generated efficiently. Departing from prior approaches that generate Beaver triples silently (Boyle et al., 2019; 2020; 2022) or using homomorphic computation (Damgård et al., 2012) for Beaver style MPC, the focus of this work rests on efficiently generating a weaker correlation. In particular, using Sparse LPN we show that if we relax the correctness requirement in generating random Beaver triples to permit a tunably small inverse-polynomial error probability, such triples can be silently generated with arbitrarily small super-constant per-party computation. We then show that such correlations can be used in an efficient online phase similar to Beaver's protocol (with a tiny super-constant factor blow-up in communication).

Collecting statistics from users of software and online services is crucial to improve service quality, yet obtaining such insights while preserving individual privacy remains a challenge. Recent advances in function secret sharing (FSS) make it possible for scalable privacy-preserving measurement (PPM), which leads to ongoing standardization at the IETF. However, FSS-based solutions still face several challenges for streaming analytics, where messages are continuously sent, and secure computation tasks are repeatedly performed over incoming messages. We introduce a new cryptographic primitive called streaming function secret sharing (SFSS), a new variant of FSS that is particularly suitable for secure computation over streaming messages. We formalize SFSS and propose concrete constructions, including SFSS for point functions, predicate functions, and feasibility results for generic functions. SFSS powers several promising applications in a simple and modular fashion, including conditional transciphering, policy-hiding aggregation, and attribute-hiding aggregation. In particular, our SFSS formalization and constructions identify security flaws and efficiency bottlenecks in existing solutions, and SFSS-powered solutions achieve the expected security goal with asymptotically and concretely better efficiency and/or enhanced functionality.

Modular reduction over binary extension fields $\mathbb{F}_{2^m}$ is a fundamental operation in cryptographic implementations, including GCM and Elliptic Curve Cryptography. Traditional reduction algorithms (e.g., linear LFSR-based methods) are highly sensitive to the algebraic structure of the defining polynomial. This sensitivity is especially acute for trinomials $P(x) = x^m + x^t + 1$, where cryptographic standards have historically mandated the use of ``friendly'' polynomials (with small $t$) to avoid the linear performance degradation associated with ``random'' or ``unfriendly'' parameters. In this paper, we challenge this constraint by introducing Suwako, a novel reduction algorithm. By exploiting the self-similar algebraic structure of the reduction map, Suwako transforms the reduction process from a serial iterative chain (dependent on the degree gap $\Delta = m-t$) into a logarithmic-depth binary-doubling structure. We theoretically prove that Suwako achieves $O(\log m)$ folding depth for arbitrary trinomials, regardless of the position of the middle term $t$. Furthermore, unlike window-based or Montgomery/Barrett reduction methods, Suwako requires no pre-computation, making it optimal for dynamic environments.

We present the first power side-channel analysis of a Hybrid Homomorphic Encryption (HHE) tailored symmetric encryption scheme. HHE combines lightweight client-side Symmetric Encryption (SE) with server-side homomorphic evaluation, enabling efficient privacy-preserving computation for the client and minimizing the communication overhead. Recent integer-based HHE designs such as PASTA, MASTA, HERA, and Rubato rely on prime-field arithmetic, but their side-channel security has not been studied. This gap is critical, as modular arithmetic and large key spaces in integer-based schemes introduce new leakage vectors distinct from those in conventional Boolean symmetric ciphers. In this work, we close this gap by presenting the first power side-channel analysis of an HHE-tailored scheme - HERA.

Our results demonstrate a successful key recovery from as few as 40 power traces using Correlation Power Analysis. In addition to showing that such attacks are feasible, we develop the first masking framework for integer-based SE schemes to mitigate them. Our design integrates PINI-secure gadgets with assembly-level countermeasures to address transition leakage, and we validate its effectiveness using the Test Vector Leakage Assessment. Our experiments confirm both the practicality of the attack and the strength of the proposed countermeasures. We also demonstrate that the framework extends to other integer-based HHE schemes, by applying our technique to PASTA. Thus, we provide leakage models, identify relevant attack targets, and define evaluation benchmarks for integer-based HHE-tailored SE schemes, thereby filling a longstanding gap and laying the foundation for side-channel-resilient design in this area.

We present the first high-performance SIMD software implementation of Spielman codes for their use in polynomial commitment schemes and zero-knowledge proofs. Spielman codes, as used in the Brakedown framework, are attractive alternatives to Reed-Solomon codes and benefit from linear-time complexity and field agnosticism. However, the practical deployment of Spielman codes has been hindered by a lack of research on efficient implementations. The involved costly finite-field arithmetic and random memory accesses operate on large volumes of data, typically exceeding gigabytes; these pose significant challenges for performance gains. To address these challenges, we propose several computational and memory-related optimizations that together reach an order-of-magnitude performance improvement in software. On the computation side, we propose SIMD optimizations using the AVX-512-IFMA instruction set and introduce a lazy reduction method to minimize the modular arithmetic cost. On the memory side, we implement a cache-friendly memory layout and a slicing technique, which exploit the CPU memory hierarchy. Finally, we present our multithreading approach to improve throughput without saturating memory bandwidth. Compared to prior Spielman software, our optimizations achieve speedups of up to 26.7x and 20.6x for single- and multi-threaded execution, respectively. In addition, instantiating our software with 64 threads on a high-end CPU even outperforms a recent FPGA accelerator by up to 4.3x for small and mid-sized polynomials. Our improvements make Spielman codes competitive with well-optimized Reed-Solomon codes on software platforms.

Rocket.Chat is a group chat platform widely deployed in industries and national organizations, with over 15 million users across 150 countries. One of its main features is an end-to-end encryption (E2EE) protocol; however, no cryptographic security analysis has been conducted. We conduct an in-depth cryptographic analysis of Rocket.Chat's E2EE protocol and identify multiple significant flaws that allow a malicious server or even an outsider to break the confidentiality and integrity of the group chat. Specifically, we formally model and analyze the protocol using ProVerif under the Dolev-Yao model, uncovering multiple theoretical weaknesses and verifying that some of them lead to practical attacks. Furthermore, through meticulous manual analysis, we identify additional vulnerabilities, including implementation flaws and cryptographic weaknesses such as CBC malleability, and demonstrate how they are exploitable in practical attack scenarios. To validate our findings, we develop Proof-of-Concept implementations, highlighting the real-world feasibility of these attacks. We also propose mitigation techniques and discuss the implications of our attacks.

FPGAs rely on highly dense and symmetric internal routing networks to interconnect their configurable logic ele- ments. In standard applications, these interconnects are used solely for digital signal transfer within the device, leaving many routing paths idle. We study the surprising ability of configurable FPGA routing fabrics to act as intentional radiators when struc- tured and driven coherently. Building on prior near-field demon- strations (few centimeters), we (i) present a practical toolchain and methodology for synthesizing “fabric-only” antennas using constrained placement/routing; (ii) demonstrate reliable far-field reception for extremely long ranges (≤ 100 m) and quantified bit-error performance at meter-scale ranges using ASK/FSK modulation and simple ECC; and (iii) analyze the security implications by formalizing adversary capabilities, enumerating novel multi-tenant attack vectors, and outlining detection and mitigation strategies. Our work bridges implementation engineer- ing, complex physical-layer measurement (with a set of complex Far-Field measurement apparatus), and security analysis, and highlights the urgent need for screening and runtime monitoring in shared FPGA environments. We have systematically shaped and combined unused paths into a contiguous structure, such as {Fractal, loop, Dipole, Snake, Spiral, Array}-Antennas, which required building an automation tool-chain. When energized, this embedded structure emits measurable electromagnetic energy that can serve as a stealth communication channel. We’ve extended this concept far beyond previous near-field demonstra- tions, achieving reliable reception in the Far-Field, demonstrated rigorously with various measurements setups - a first for this class of long-range FPGA-based antennas without any external radiating RF hardware from a tiny ∼ 1x1 cm2 device. We further show a Trojan example while triggering it with rare events attacking a Decryption Oracle model

Secure three-party computation (3PC) with semi-honest security under an honest majority offers notable efficiency in computation and communication; for Boolean circuits, each party sends a single bit for every AND gate, and nothing for XOR. However, round complexity remains a significant challenge, especially in high-latency networks. Some works can support multi-input AND and thereby reduce online round complexity, but they require \textit{exponential} communication for generating the correlations in either preprocessing or online phase. How to extend the AND gate to multi-input while maintaining high correlation generation efficiency is still not solved.

To address this problem, we propose a round-efficient 3PC framework ALKAID for Boolean circuits through improved multi-input AND gate. By mixing correlations and redundancy, we propose a concretely efficient correlation generation approach for small input bits $N<4$ and shift the correlation generation to the preprocessing phase. Building on this, we create a round-efficient AND protocol for general cases with $N>4$. Exploiting the improved multi-input AND gates, we design fast depth-optimized parallel prefix adder and share conversion primitives in 3PC, achieved with new techniques and optimizations for better concrete efficiency. We further apply these optimized primitives to enhance the efficiency of secure non-linear functions in machine learning. We implement ALKAID and extensively evaluate its performance. Compared to state of the arts like ABY3 (CCS'2018), Trifecta (PoPETs'2023), and METEOR (WWW'2023), ALKAID enjoys $1.5\times$--$2.5\times$ efficiency improvements for boolean primitives and non-linear functions, with better or comparable communication.

BEANIE is a 32-bit tweakable block cipher, published in ToSC 2025.4, designed for memory encryption of microcontroller units. In this paper, we propose its first third-party analysis and present a key recovery against the full 5+5 rounds of BEANIE using a yoyo distinguisher. The attack has a cost close to the security claim of $2^{80}$ time and $2^{40}$ data.

Federated Learning (FL) is an advancement in Machine Learning motivated by the need to preserve the privacy of the data used to train models. While it effectively addresses this issue, the multi-participant paradigm on which it is based introduces several challenges. Among these are the risks that participating entities may behave dishonestly and fail to perform their tasks correctly. Moreover, due to the distributed nature of the architecture, attacks such as Sybil and collusion are possible. Recently, with advances in Verifiable Computation (VC) and Zero-Knowledge Proofs (ZKP), researchers have begun exploring how to apply these technologies to Federated Learning aiming to mitigate such problems. In this Systematization of Knowledge, we analyze the first, very recent works that attempt to integrate verifiability features into classical FL tasks, comparing their approaches and highlighting what is achievable with the current state of VC methods.

Secret sharing schemes represent a crucial cryptographic protocol, with linear codes serving as a primary tool for their construction. This paper systematically investigates the construction of ideal secret sharing schemes for complete $t$-partite $k$-uniform hypergraph access structures using linear codes as the tool. First, it is proved that the generator matrix $G$ of an ideal linear code realizing a complete $t$-partite $2$-uniform hypergraph access structure must have a rank of $2$. Simultaneously, a novel method for constructing an ideal secret sharing scheme that realizes such access structures is proposed. Building on this foundation, the case of complete $t$-partite $2$-uniform hypergraphs is extended to complete $t$-partite $k$-uniform hypergraphs, and a method for constructing ideal secret sharing schemes to realize them is provided. Compared with existing approaches, both Shamir’s method and the scheme proposed by Brickell et al. are special cases of our proposed approach.

We introduce new {Distributed Multi-Point Function} (DMPF) constructions that make multi-point sharing as practical as the classic single-point (DPF) case. Our main construction, {Reverse Cuckoo}, replaces the ``theoretical'' cuckoo insertions approach to DMPFs with a MPC-friendly linear solver that circumvents the concrete inefficiencies. Combined with our new sparse DPF construction, we obtain the first fully distributed and efficient DMPF key generation that avoids trusted dealers and integrates cleanly with standard two-party MPC.

Applied to pseudorandom correlation generators (PCGs), our DMPFs remove the dominant “sum of $t$ DPFs'' bottleneck. In Ring-LPN and Stationary-LPN pipelines (Crypto 2020, 2025), this translates to {an order of magnitude more Beaver triples per second} with {an order of magnitude less communication} compared to the status quo by Keller et al (Eurocrypt 2018). The gains persist across fields and rings ($\mathbb{F}_{p^k}$, $\mathbb{Z}_{2^k}$ for $k\geq 1$) and are complementary to existing PCG frameworks: our constructions drop in as a black-box replacement for their sparse multi-point steps, accelerating {all} PCGs that rely on such encodings.

We provide a complete protocol suite (deduplication, hashing, linear solver, sparse DPF instantiation) with a semi-honest security proof via a straight-line simulator that reveals only hash descriptors and aborts with negligible (cuckoo-style) probability. A prototype implementation validates the asymptotics with strong concrete performance improvements.

The standardization of CRYSTALS-Kyber (ML-KEM) by NIST represents a milestone in post-quantum security, yet its substantial communication overhead remains a critical bottleneck for resource-constrained environments. This paper introduces LAKE (Lattice-Code Accelerated Kyber Encapsulation), a novel cryptographic framework that symbiotically integrates coding theory into the Module-LWE structure. Unlike previous concatenation approaches, LAKE embeds density-optimized Construction-A lattices derived from Polar codes directly into the public matrix generation. This structural innovation yields a 15–25% reduction in ciphertext size while simultaneously improving the Decryption Failure Rate (DFR) from \(2^{-139}\) to \(2^{-156}\), leveraging innate coding gains to suppress noise. We provide a rigorous reduction of LAKE's IND-CCA2 security to the hardness of the Structured Module-LWE problem. Although LAKE introduces a modest 8–15% computational overhead, it optimizes the critical "Compute-for-Bandwidth" trade-off, exploiting the asymmetry between low-cost local processing and high-cost transmission. Consequently, LAKE significantly enhances deployment viability in high-latency, energy-sensitive domains such as Satellite Communications (SatCom), Narrowband-IoT (NB-IoT), and tactical edge networks, where transmission efficiency is the dominant performance metric.

Data Availability Sampling (DAS) has emerged as a key scalability technique for blockchain systems, enabling light clients to verify that block data have been fully published without downloading them in entirety. We introduce FRIVail, a new DAS construction built on top of the FRI-Binius polynomial commitment scheme, designed for datasets composed of many independent single-row payloads that together form a block’s data blob. FRIVail exploits the intrinsic Reed–Solomon structure of FRI, wherein each commitment naturally encodes a codeword that light clients can sample directly.

Each row of the blob is assigned an independent FRI proof. These row-level proofs are then combined into a global availability certificate using one of three aggregation strategies. The first constructs a succinct zero-knowledge proof attesting to the correct verification of all row-level FRI proofs, yielding a compact proof of proofs that enables constant-size global verification while preserving row independence. The second is a fully post-quantum construction that recursively applies FRI-Binius to build a proof of proofs. In this setting, global verification relies on FRI proximity checks, but reconstruction of the aggregated proof polynomial is required to recover embedded row-level information. The third is a hybrid aggregation based on KZG polynomial commitments, where the aggregated polynomial admits direct algebraic openings but relies on pairing-based assumptions and a trusted setup, and is therefore not post-quantum.

In all variants, light clients verify availability via a small number of local opening checks against the header commitment, without downloading entire rows or the full blob. We formalize DAS security in this multi-row, multi-proof setting and show that FRIVail achieves sublinear verification complexity, strong robustness against adversarial row withholding, and resistance to correlated sampling attacks. FRIVail provides a modular foundation for next-generation blockchain data availability protocols, supporting zero-knowledge-based, fully post-quantum, and hybrid cryptographic deployments.

The construction of building beyond-birthday-bound secure pseudorandom functions (PRFs) from the Xor-sum of 2 pseudorandom permutations (PRPs) has been known since EUROCRYPT 1998. However, the first concrete instance was only published recently at FSE 2022: the low latency PRF Orthros. Subsequently, at ASIACRYPT 2024, Flórez-Gutiérrez et al. proposed the general framework of ZIP ciphers, where a block cipher $E_{1} \circ E_{0}$ is used to construct the PRF $E_{0} \oplus E_{1}^{-1}$. This allows re-using some of the cryptanalysis of the underlying block cipher. They propose the PRF ZIP-AES, as the Xor sum of 5 AES encryption rounds and 5 decryption rounds. They discuss differential, linear, and integral distinguishers for this construction, but provide no concrete key recovery attacks. Furthermore, they propose ZIP-GIFT as a 64-bit PRF but leave cryptanalysis as future work. In this work, we provide the first third-party analysis of ZIP-AES and ZIP-GIFT. We focus our efforts on the unique challenges of performing key recovery attacks for ZIP ciphers and propose new techniques to overcome these challenges. We show differential, linear, and integral key recovery attacks for both PRFs. We develop new techniques for integral key recovery attacks and show how to extend differential characteristics by some rounds for key recovery.

Despite their simplicity and quantum-resistant security properties, the deployment of hash chains in distributed settings through secure multi-party computation (MPC) has been demonstrated to be impractical when employing traditional hash functions (i.e., SHA2/SHA3) due to their high number of non-linear gates which lead to heavy computational costs. In this work, we present a comprehensive evaluation of hash chain computations over MPC using arithmetization-oriented (AO) primitives, specifically focusing on the Poseidon2 family of hash functions. We systematically analyze the MPC-friendliness of various Poseidon2 instantiations across different prime fields and parameter choices to minimize both multiplicative depth and preprocessing requirements. We conduct extensive benchmarks using the MP-SPDZ framework across three state-of-the-art MPC protocols under varying network conditions and adversarial models. We further explore practical applications to threshold cryptography, presenting optimized implementations of threshold hash-based signatures that achieve signing times less than 1 second in a 3-party setting for practical parameter sets. Specifically, we demonstrate how structural parallelism in hash-based signatures can be exploited to batch independent hash chains within a single MPC execution, and introduce a time-memory trade-off that enables non-interactive online signature generation through systematic precomputation of all chain intermediates. Our work suggests the practical viability of moderate length AO-based hash chains for MPC applications.