International Association
for Cryptologic Research

Distributed cryptography serves as a cornerstone for building trustless systems, yet existing solutions for distributed policy encryption typically require either a trusted dealer or complex interactive setup protocols. Recent advances have introduced the concept of silent setup, where users independently generate keys and a joint public key is derived deterministically. However, all current silent-setup constructions rely on bilinear pairings, leaving them vulnerable to quantum adversaries. In this work, we present the first distributed monotone-policy encryption scheme with silent setup based on lattices. Our construction supports arbitrary monotone policies represented as Disjunctive Normal Forms (DNFs) and provides a robust, post-quantum foundation for decentralized access control.

Succinct argument systems are of central importance to modern crytpography, enabling the efficient verification of computational claims. In the classical setting, Kilian (STOC 92) established that any probabilistically checkable proof for NP can be transformed into a succinct argument system for NP using only collision-resistant hash functions. In the quantum setting, recent works have established the feasibility of (classically-verifiable) succinct arguments for QMA, capturing statements that require \emph{quantum} proofs. However, known constructions all rely on the highly structured assumption of learning with errors (LWE), which stands in stark contrast with the unstructured assumptions that suffice for NP.

In this work, we develop a new framework that broadens the cryptographic foundations of succinct arguments for QMA. We assume the existence of (i) an oblivious state preparation (OSP) protocol, which in turn can be constructed from \emph{plain} trapdoor claw-free functions, and (ii) collapsing hash functions, the quantum analogue of collision-resistance. In particular, we obtain the first succinct, classically-verifiable argument system for QMA which does not rely on the hardness of LWE.

Our construction proceeds in two steps. First, we design a \emph{round-efficient} classically-verifiable argument system for QMA based only on the assumption of OSP. Second, we introduce a \emph{generalized communication compression compiler}, which, assuming collapsing hash functions, transforms any $T$-round interactive protocol with a classical verifier into one in which the communication size is bounded by $T \cdot \poly(\secp)$ for some fixed $\poly$ independent of the original size of each message. Our compiler extends a quantum rigidity-based communication compression technique of Zhang (QCrypt 25), and may be of independent interest.

Byzantine Agreement is a fundamental primitive in cryptography and distributed computing, and minimizing its round complexity is of paramount importance. The seminal works of Karlin and Yao [Manuscript'84] and Chor, Merritt and Shmoys [JACM'89] showed that any randomized $r$-round protocol must fail with probability at least $(c\cdot r)^{-r}$, for some constant $c$, when the number of corruptions is linear in the number of parties, $t = \theta(n)$. The work of Ghinea, Goyal and Liu-Zhang [Eurocrypt'22] introduced the first \emph{round-optimal BA} protocol matching this lower bound. However, the protocol requires a trusted setup for unique threshold signatures and random oracles.

In this work, we present the first round-optimal BA protocols without trusted setup: a protocol for $t 0$, assuming a bulletin-board PKI for signatures.

Anonymous credentials (AC) equip users with credentials on attested attributes, which enable them to prove verifiable yet data-minimizing statements over their attributes. However, in standard ACs, each credential presentation reveals the credential issuer, which could be more information than intended and necessary, e.g., when merely proving age or personhood. Issuer-Hiding Anonymous Credentials (IHAC) address this limitation and hide the issuer in the presentation. That is, they only reveal that the user has a credential from an issuer within a certain trust set, referred to as the policy. Recent works by Sanders and Traoré, and Katz and Sefranek show how to add issuer-hiding to PS- and BBS-based credentials while keeping presentations compact, i.e., not scaling in the number of issuers. However, both constructions require the verifier to generate dedicated policy key pairs, turning verification into a secret key operation. Managing these verifier-specific keys introduces additional complexity and affects the resulting practical privacy and security guarantees. In this work, we propose two IHAC schemes from BBS signatures that achieve compact presentations without the need of such verifier-specific keys. At the core of our schemes is a technique to randomize BBS public keys and adapt the signatures accordingly, which we believe to be of independent interest.

In concretely efficient secure multiparty computation (MPC) protocols based on secret sharing, a frequent pattern is to locally multiply two shared values into some intermediate representation that is immediately and interactively translated back into sharings of the product. The intermediate representation is often still a full-fledged but different secret sharing scheme. This has been used to efficiently compute dot products by computing the sum of all intermediate products and then interactively translating only the sum instead of translating each individual product. Beyond that, the intermediate representation or secret sharing scheme has mostly been seen only as a necessary interim step, leaving most of its potential untapped.

We change that by proposing the paradigm of leveled linear secret sharing, which allows dynamic switching between the original secret sharing and the previously only intermediate one more freely, while enabling arbitrary linear computations in any of the domains. Prior multiplications are split into a non-interactive multiplication that switches from one to the other secret sharing, and an interactive upgrade back to the original secret sharing domain. The upgrade now does not necessarily follow each multiplication immediately, but just needs to be placed somewhere before the next multiplication is computed, possibly upgrading the linear aggregation of many multiplications' results. We apply this idea to improve three-party computation on replicated sharings (Araki et al., CCS'16), n-party BGW-style protocols (Ben-Or et al., STOC'88), and masked secret sharing protocols such as ABY2.0 (Patra et al., USENIX Security'21). We develop a novel optimizer that optimally selects which gate of a circuit is evaluated in which domain. With that, we improve communication by 10-37% for many circuits. Furthermore, we implement our generalization for replicated sharing, measure run time improvements of mostly 10-26% in a LAN, and make a full implementation of the protocol and our novel optimizer publicly available.

We introduce a new (amortized) functional bootstrapping framework over the CKKS homomorphic encryption (HE) scheme based on Fourier extension. While approximating the modular reduction function in CKKS bootstrapping through Fourier series is a well-known technique, how such method can be efficiently generalized to functional bootstrapping is less understood. In this work, we show that, by constructing proper Fourier extensions, any function with a bounded domain in the smoothness class $C^{\kappa}$ can be approximated by a degree-$n$ Fourier series with errors of order $O(n^{-\kappa-2})$ (except at the singularities), improving on previous results on a global error bound of $O(n^{-1})$ [AKP2025]. To achieve such bound, we propose a new way of constructing Fourier extensions, such that the extended functions appear as smooth as possible in the sense of a Fourier approximation. By implementing our functional bootstrapping over OpenFHE, we demonstrate that we can improve the data precision by $10$-$27$ bits and reduce the amortized FBS latency by $1.1$-$2\times$ over a variety of benchmarking functions.

In order to reduce size and improve efficiency, many lattice-based cryptographic schemes adopt structured variants of the Learning With Errors (LWE) problem, such as the Module-LWE and Ring-LWE. Nevertheless, when analyzing the concrete security of lattice-based schemes, these algebraic structures are usually not considered, given the absence of techniques to exploit them for accelerating known attacks.

For the widely-used polynomial ring $\mathbb{Z}_q[X]/(x^N+1)$, we first propose an enhanced hybrid decoding attack against Module/Ring-LWE by leveraging the ring structure to accelerate its guessing and decoding steps. Then, we theoretically show that compared to the prior hybrid decoding attack, our new attack can lead to a complexity improvement by a factor of $O(N)$ in sparse secret setting. Moreover, we implement our new enhanced hybrid decoding attack on the benchmark instances established by [WSM+25, S{\&}P], and achieve several new records. In particular, compared with state-of-the-art methods given by [KKN+26, EC], our approach is 17$\times$ to 114$\times$ faster on the known broken instances. Finally, we show how to estimate the concrete bit security with our new hybrid attack under the same model as in the lattice estimator, and perform the analyses of the latest sparse Ring-LWE parameter sets used in Fully Homomorphic Encryption (FHE) schemes including [JM22, EC], [CCKS23, CCS], [BCKS24, EC], [CHKS25, EC] and [AKP25, C]. The numerical results show that compared to the best-known attack, our enhanced attack can improve the attack complexity by 7-13 bits for all the considered parameter sets. In particular, under our new enhanced hybrid decoding attack, 10 out of the 16 parameter sets fall below the targeted 128-bit security level.

The protection of executable code in embedded systems requires efficient mechanisms that ensure confidentiality and integrity. Belkheyar \emph{et al.} recently proposed the Authenticated Code Encryption (ACE) framework, with \chilow as the first ACE-2 instantiation at EUROCRYPT~2025. \chilow-(32 + $\tau$) is a 32-bit tweakable block cipher combined with a pseudorandom function, featuring quadratic nonlinear layers called ChiChi (\dchi) and a nested tweak/key schedule optimized for low-latency \emph{decryptions} in secure code execution under strict query limits.

In this paper, we exploit the algebraic structure of \dchi and study the resistance of \chilow-(32 + $\tau$) to cube-like and integral cryptanalysis in single- and multiple-tweak settings. In the multiple-tweak setting, we present conditional attacks that can recover the full key for 5-round \chilow-(32 + $\tau$) with practical complexity, and extend the analysis to 6 rounds at a still non-trivial but purely theoretical cost below brute force.

We additionally construct borderline cube attacks on 5- and 6-round \chilow-(32 + $\tau$), each capable of recovering the full key with practical complexity. Specifically, we recover the full key for 5-round \chilow-(32 + $\tau$) using $2^{32}$ decryptions, $2^{18.58}$ chosen ciphertext data, and $2^{33.56}$ bits of memory, and for 6-round \chilow-(32 + $\tau$) using $2^{34}$ decryptions, $2^{33.58}$ chosen ciphertext data, and $2^{54.28}$ bits of memory.

We then focus on integral cryptanalysis and the challenge of extending the analysis to 7 rounds. We identify integral distinguishers in the single- and multiple-tweak models and extend suitable 2-round and 3-round integral distinguishers to build a 7-round attack. We present a nested strategy to recover all round tweaks and tackle the problem of deriving the master key from round-tweak and key information. Our key-recovery method exploits high-degree monomials that arise in the integral key-recovery phase to reduce the average number of guessed key bits and hence reduce the time complexity. As a result, we mount a 7-round key-recovery attack on \chilow-(32 + $\tau$) that requires $2^{6.32}$ chosen ciphertext data, has a time complexity of about $2^{108.55}$ encryptions, and needs negligible memory.

Notably, all our attacks remain consistent with the security claims of the design.

Zero-knowledge proofs of knowledge are a fundamental building block in many isogeny-based cryptographic protocols, such as signature schemes based on identification-to-signature transformations, or multi-party ceremonies that avoid a trusted setup, in particular for generating supersingular elliptic curves with unknown endomorphism rings.

In this paper, we construct SPRINT, an efficient polynomial IOP-based proof system that encodes the radical $2$-isogeny formulas into a system of multivariate polynomials. When combined with the recent polynomial commitment scheme (PCS) DeepFold, our construction yields substantial improvements over state-of-the-art isogeny proofs of knowledge. For the SQIsign prime $p=5 \cdot 2^{248}-1$ (giving NIST security level I), our implementation takes only a few milliseconds for proving and verification, with proof sizes around 80 kB. Compared to previous works, we achieve a $1.1$-$8\times$ speedup for the prover, a $4.4$-$24\times$ speedup for verification, and proof sizes that are $1.2$-$2.3\times$ smaller across different parameter sets.

Moreover, we study the weak simulation extractability of our proof system, which we can use as a starting point for a modular construction of signatures. We show that any Fiat–Shamir compiled interactive proof with a so-called canonical simulator is weakly simulation-extractable. We expect this general result to be widely applicable to other post-quantum proof systems and thus of independent interest.

Building on SPRINT and our wSE result, we introduce a new family of signature schemes whose security solely relies on the $\ell$-isogeny path problem, a foundational problem in isogeny-based cryptography. As a concrete instantiation, we construct a signature scheme using DeepFold as the PCS. Across the different NIST security levels, a prototype implementation of our scheme achieves performance on par with the highly optimized NIST specification for SQIsign. Even though our signatures are relatively large, our scheme relies on weaker assumptions and our framework offers flexibility for tradeoffs and optimizations – both within a given PCS and by switching to alternative PCS constructions. In particular, it will naturally inherit efficiency gains from future advances in plausibly post-quantum secure PCS constructions.

Fully Homomorphic Encryption (FHE) is a modern cryptographic technique that allows performing computations directly over encrypted data. This makes FHE an indispensable method for privacy-preserving applications, where users' data are encrypted and processed by a potentially untrusted third party. Nevertheless, FHE computations are computationally expensive, often rendering them less practical for realistic scenarios. Notably, a major performance bottleneck for FHE is an operation called bootstrapping that allows refreshing the inherent noise of an FHE ciphertext so it could support more computations. In this work, we introduce LazyArc, a versatile lightweight dynamic Out-of-Order (OoO) engine that supports higher-throughput FHE computations expressed as a sequence of instructions. Notably, LazyArc encapsulates a hybrid engine capable of evaluating both arithmetic and Boolean instructions in the same program. Moreover, our proposed OoO paradigm improves the runtime performance by masking the latency of bootstrapping by executing of independent instructions in an FHE application. To enable LazyArc, we introduce a novel data structure, dubbed RegisterMap, which performs static analysis on FHE arithmetic circuits and tracks the noise of each ciphertext to allow proactive bootstrapping scheduling. Our approach is evaluated using linear algebra benchmarks and can achieve about 10% performance improvement over baselines.

Homomorphic Encryption (HE) enables secure cloud computing through computations on encrypted data, yet the physical security of these implementations on shared hardware accelerators remains a critical challenge. While Graphics Processing Units (GPUs) offer the massive parallelism required for HE workloads, their Single Instruction Multiple Thread (SIMT) architecture amplifies side-channel vulnerabilities. Standard implementations of polynomial multiplication and relinearization often exhibit data-dependent control flows and irregular memory access patterns that leak sensitive information through variable timing behavior. In this paper, we present Janus-FHE, a GPU-based framework for BFV ciphertext multiplication and relinearization designed with intrinsic side-channel resistance. We reformulate polynomial multiplication as large-integer arithmetic via Kronecker substitution, executing it using a Schonhage-Strassen algorithm based on the Discrete Galois Transform (DGT). Critically, we compute these transforms using the Stockham algorithm, which enforces strictly deterministic, input-independent memory access patterns, effectively mitigating cache-timing vulnerabilities. Furthermore, we implement a constant-time relinearization strategy that replaces conditional branching with masked arithmetic to prevent warp divergence. Our experimental evaluation confirms that Janus-FHE eliminates the control-flow leakage observed in state-of-the-art libraries like HEonGPU, extending the computational reach of GPU-based FHE by successfully computing multiplications for polynomial degrees up to $2^{18}$.

Fully Homomorphic Encryption (FHE) offers strong cryptographic guarantees for secure outsourced computation, yet the performance of modern schemes like TFHE remains a barrier for complex applications. Existing TFHE approaches relying on programmable bootstrapping (PBS) are inefficient for large circuits, as they are limited to evaluating small (3-4 bit) lookup tables (LUTs).

Our work introduces a novel compiler framework that overcomes this limitation by integrating circuit bootstrapping (CBS) and vertical packing (VP) to enable the evaluation of circuits composed of LUTs up to 12 bits. Our framework, built upon MLIR, introduces new dialects for CBS and VP and leverages Yosys for circuit synthesis, automating the translation from high-level programs to optimized TFHE circuits. Furthermore, we propose bespoke optimization passes that combine shared LUTs to minimize the overall cryptographic operations required. Experimental results demonstrate that our CBS-based design achieves execution times several times faster than the baseline PBS-only approach, highlighting the practical benefits of combining CBS and VP with compiler-driven circuit-level optimizations.

First, we correct certain omissions in the literature on the complexity analysis of Crossbred and give a full analysis of this algorithm. Secondly, we propose a criterion to reduce the number of polynomials generated in the preprocessing step for a set of admissible parameters $D$, $d$ and $k$, whenever this step of the algorithm produces more polynomials than necessary. We conclude by applying this criterion to the security of MQOM.

Folding is a powerful technique for constructing efficient succinct proof systems, especially for computations that are expressed in a streaming fashion. In this work, we present Cyclo, a new lattice-based folding protocol that improves upon LatticeFold+ [Boneh and Chen '25] in multiple dimensions and which incorporates, among others, the pay-per-bit techniques from Neo when folding constraints expressed over a field $\mathbb{F}_q$ [Nguyen and Setty '25]. Cyclo proposes a new framework for building lattice-based folding schemes that eliminates the need for norm checks \emph{on the accumulator} by adopting an amortized norm-refreshing design, ensuring that the witness norm grows additively per round within a (generously) bounded number of folds. This design simplifies the protocol and reduces prover overhead. In particular, Cyclo only performs range checks on the input \emph{non-accumulated} witness, and when applied to fold constraints over $\mathbb{F}_q$, it does not decompose any witnesses into low-norm chunks within the folding protocol itself. Cyclo, supporting a complete family of cyclotomic rings, combines two simple building blocks: an extension commitment that reduces the norm of the witness by decomposing it and recommitting, and an $\ell_\infty$ range test via a sum-check protocol. We demonstrate, by proving communication and runtime estimates, that the construction results in an efficient and proof-size-friendly folding scheme. We also establish an algebraic connection between $\mathcal{R}_q$ and $\mathbb{F}_q$ using the polynomial evaluation map, enabling efficient reduction from R1CS/CCS over $\mathbb{F}_q$ to a linear relation over $\mathcal{R}_q$, providing a new and simpler formulation of the techniques in [Nguyen and Setty '25]. In practical settings, Cyclo achieves succinct proof sizes on the order of $30$ KB, improving by an order of magnitude over LatticeFold+. Our efficiency benchmarks indicate that our protocol also outperforms LatticeFold+ in practice.

This paper presents a new method for approximating the correlations of differential-linear distinguishers. From the perspective of Beyne's geometric approach, the differential-linear correlation is a corresponding coordinate of the \textit{correlation vector} associated with the ciphertext multiset, which can be obtained by using the correlation matrix of the \textit{2-wise form} of the cipher. The composite nature of the correlation matrix leads to a round-based approach to approximate the correlation vector. This simple approximation is remarkably precise, yielding the most accurate estimation for differential-linear correlations in \ascon thus far and the first DL distinguishers for 6-round \ascon-128a initialization. For \present, we present 17-round DL distinguishers, 4 rounds longer than the current record. To apply the round-based approach to ciphers with the large Chi ($\chi$) function as nonlinear functions, we derive theorems to handle the correlation propagation for $\chi$ and its 2-wise form. Strong DL distinguishers for up to 6 rounds of \subterranean and \koala-$p$ are provided, 2 rounds longer than the previous differential and linear distinguishers. Furthermore, the round-based approximation idea is also extended to the higher-order differential-linear distinguishers. We give the first second-order DL distinguisher for 6-round \ascon-128 initialization and the first second-order DL distinguishers for up to 7 rounds of \subterranean and \koala-$p$.

Theoretical treatments of leakage-resilient cryptography typically work under the assumption that the leakage learned by the adversary (e.g., about an n-bit secret key) is arbitrary but bounded, in the sense that the leakage is an l-bit string for some threshold l significantly smaller than n. On the other hand, real-world side-channel attacks on physical implementations of cryptographic protocols produce leakage transcripts that are much longer than n. However, unlike the bounded leakage model, these transcripts are inherently noisy. We would like to generically claim that cryptographic schemes resilient to bounded leakage are also resilient to realistic noisy leakages. This boils down to showing that noisy leakages can be simulated using only one bounded leakage query. Prior work (EUROCRYPT 2021 and CRYPTO 2024) made important progress on this problem. Yet, barriers to applicability and interpretability remain, such as the need for large noise levels, the difficulty to estimate the necessary parameters of the leakage distributions, undesirable independence assumptions, and inefficient simulation in certain regimes. In this work, we resolve (or make progress towards resolving) these shortcomings:

1. We show that simple modifications to the simulation strategies in prior work simultaneously allow a cheaper computation of simulation parameters and better parameters than previous results.

2. Leveraging the first item, we obtain a reduction whose amount of extra bounded leakage to simulate correlated signals only increase very mildly. This captures the limited incentive for an adversary to oversample a side-channel signal leading to correlated signal, improving previous results treating these samples as independent.

3. We establish a new ``bounded leakage vs.\ simulation efficiency'' tradeoff, roughly trading $\mathcal{O}(\Delta)$ bits leaked by the bounded leakage query for a $\frac{2^{\Delta}}{\mathrm{poly}(\Delta)}$-factor reduction in simulation complexity. This widens the applicability of our results in the context of computational security, as former simulators were only efficient when simulating from $\mathcal{O}(\log \lambda)$ bits of bounded leakage, with $\lambda$ the security parameter.

Is it possible to publicly certify that a string was sampled from a high min-entropy distribution? Certified randomness protocols, such as Brakerski et al. (FOCS 2018) enable private certification—Alice can convince Bob—but it does not yield public certification. We construct a certified min-entropy scheme with the following properties: (1) public certification, so Alice can convince Bob, Charlie, and Dave; (2) all prover–verifier communication is classical; (3) transferability—if Bob has already been convinced, he can subsequently convince Eve and Frank; and (4) classical verification—Grace can be convinced even without a quantum computer, at the cost of losing transferability.

Assuming quantum one-shot signatures (and variants), we construct quantum fire with new properties and use it to obtain our publicly certifiable min-entropy scheme. Both primitives can be instantiated from sub-exponential iO and LWE, and our quantum fire scheme is the first standard-model construction of quantum fire.

The good-case latency of a consensus protocol measures the latency from block proposal by a consensus leader to decision, in the case in which the leader is correct. It is arguably the efficiency metric most pertinent for discussing the practical latency performance of consensus protocols. Well understood in the context of the authenticated setting, with PBFT [Castro 99], Tendermint [Buchman 16] & Simplex [Chan, Pass 23] achieving the optimal good-case latency of 3 rounds, significant gaps remain in the unauthenticated setting. We present Forget-IT, an unauthenticated consensus protocol with optimal good-case latency of 3 rounds. Furthermore, our protocol only requires constant persistent storage, and has $O(n^2)$ message complexity per view.

Amutha and Perumal recently proposed a two-party key exchange protocol based on \(\alpha\)-\(v\)-\(w\)-duo circulant matrices over the max-plus semiring, claiming resistance to known tropical attacks and suitability for IoT environments. This paper presents a complete cryptanalysis of this protocol. We uncover a fundamental structural weakness: the construction imposes an affine parameterization on the secret matrices, reducing each matrix to a single integer parameter. Consequently, the public messages become simple shifts of a publicly computable matrix, and the session key reduces to a constant shift of another public matrix. An eavesdropper can recover the shared secret in constant time after a one-time precomputation. The attack is deterministic, succeeds with probability 1, and requires only passive observation. We verify the attack on the authors' own example.

In this paper, we introduce a novel framework for meet-in-the-middle (MITM) attacks on ARX designs, termed \textit{dual-syncopation} MITM attack, which formalizes a compact, rule-based language for tracking deterministic and non-deterministic information for two independent propagations through ARX operations. The language provides an uniform abstraction for previous techniques, e.g., initial structure, partial matching, partial-fixing, and naturally supports automation. With the language, we additionally encode new technical insights that is not covered in literature and build an efficient automatic search tool for MITM attacks on ARX designs that can be fully optimized within hours.

As a result, we obtain the first preimage attacks on 46- and 47-step SHA-256, extending the previous record of 45 steps by two steps. For SHA-512, we present the first preimage attack on 51 steps, extending the prior record of 50 steps by one step. In addition, we provide a collection of improved preimage attacks on 43-, 44-, and 45-step SHA-256; 46-, 47-, 48-, 49-, and 50-step SHA-512; as well as full-step MD5. The proposed attacks can be converted to free-start collision attacks with the technique proposed by Li, Isobe, and Shibutani at FSE 2012. Our results mark the first improvements on theoretical attacks on SHA-2 in a decade and push the boundary of cryptanalysis of ARX designs.