International Association
for Cryptologic Research

This paper presents an efficient framework for private Transformer inference that combines Homomorphic Encryption (HE) and Secure Multi-party Computation (MPC) to protect data privacy. Existing methods often leverage HE for linear layers (e.g., matrix multiplications) and MPC for non-linear layers (e.g., Softmax activation functions), but the conversion between HE and MPC introduces significant communication costs. The proposed framework, dubbed BLB, overcomes this by breaking down layers into fine-grained operators and further fusing adjacent linear operators, reducing the need for HE/MPC conversions. To manage the increased ciphertext bit width from the fused linear operators, BLB proposes the first secure conversion protocol between CKKS and MPC and enables CKKS-based computation of the fused operators. Additionally, BLB proposes an efficient matrix multiplication protocol for fused computation in Transformers. Extensive evaluations on BERT-base, BERT-large, and GPT2-base show that BLB achieves a $21\times$ reduction in communication overhead compared to BOLT (S&P'24) and a $2\times$ reduction compared to Bumblebee (NDSS'25), along with latency reductions of $13\times$ and $1.8\times$, respectively, when leveraging GPU acceleration.

As an ISO/IEC standard, RIPEMD-160 has been extensively studied for (Semi-Free-Start) collision attacks. A significant breakthrough was achieved at FSE 2024 with the first 41-, 42-, and 43-step SFS collision attacks, which leveraged an automatic search model (EUROCRYPT 2023) and a message modification strategy (FSE 2020). However, these attacks are limited by reliance on heuristic objective functions and suboptimal message modification techniques. This paper enhances the existing framework from two perspectives. Firstly, we refine the automatic search model by incorporating a holistic objective function that considers all critical probability components, moving beyond simple Hamming weight. Secondly, we introduce two generic techniques to further improve (SFS) collision attacks: the first application of differential clustering and a dedicated message modification strategy. As a result, we present the first valid SFS collision attack on 44-step RIPEMD-160. Additionally, we significantly reduce the time complexities of existing attacks on 41-, 42-, and 43-step variants, making it feasible to find colliding message pairs for 41- and 42-step versions within practical time for the first time.

In this work, we propose a novel framework called PolySys for modeling and designing leakage attacks as constraint-solving algorithms over polynomial systems. PolySys formalizes the design of attacks using invertible encodings, structural and leakage equations, and efficient constraint-solving algorithms including SAT and constraint solvers. It is capable of modeling resolution, known-data, and inference attacks for common leakage patterns. To demonstrate the practicality of our framework, we implement a PolySys attack engine in Python and apply it to state-of-the-art query recovery, data resolution, and query inference attacks on point and range multi-maps. Our results show that PolySys outperforms all existing attacks under identical assumptions, achieving up to 60× higher recovery rates in some scenarios. While scalability remains a challenge for larger datasets, PolySys represents a promising step toward a general-purpose framework for designing leakage attacks. We believe future work can further enhance its efficiency to scale to larger and more complex workloads.

The CRO Trilemma formalizes the inherent incompatibility between confidentiality, reliability, and legal opposability in proof systems. This paper provides the complete Universal Composability (UC) security proof for the ZK-NR protocol, a layered architecture designed to approach this bound. We model each dialectical layer (Iron, Gold, Clay) as an ideal functionality with erasure semantics and prove indistinguishability between real and ideal executions under post-quantum assumptions. The results establish the composable security of ZK-NR and formally achieve a CRO index Γ_CRO < 0.4 + negl(λ) against adaptive contextual adversaries.

Many data types, such as video and audio, consist of sequential elements where both integrity and order are essential for authenticity. In practice, verifiers often access only partial sequences due to privacy or volume constraints, as in surveillance, journalism, and public records. Vector commitment (VC) schemes that support verifiable partial disclosures address this need, but constructing and maintaining such VCs is challenging for resource-constrained devices such as cameras. For example, in CCTV systems, a trusted module updating the VC for millions of frames must store and process hundreds of megabytes, which is often infeasible.

We propose a proving system that enables trustless reconstruction of VCs from only the chained hash of the sequence. The data source computes and signs a cumulative hash. An untrusted prover then constructs the VC from the raw data and proves that the data used for construction is consistent with the signed hash chain. The constructed VC subsequently enables authentication of partial disclosures. The main challenge is that proving the full VC construction in zero-knowledge is computationally expensive. To address this, we design a folding-based zkSNARK tailored to this task.

We analyze the construction in a realistic setting with a constrained source device (Raspberry Pi Zero) and a consumer-grade prover (midrange laptop). Our results show that even for relatively short sequences (e.g., 30 minutes of video footage), handling the VC within the source device's trusted module is infeasible due to both storage and computational limitations. In contrast, the proposed trustless offloading imposes only a few minutes of local computation on the prover to generate a proof for full VC construction (around 2 minutes for the 30 minutes of footage). Our implementation is available as open source at: https://github.com/zero-savvy/proven-view.

While consistency and liveness are the defining properties of ledger consensus, fair ordering has emerged as an independent consideration whose importance is underscored by the observation of real world transaction inclusion strategies that manipulate fairness such as Miner Extractable Value. Receiver-order fairness is a fine-grain notion of fairness that determines the order of any two submitted transactions based on the two sequences of reception timestamps for the two transactions across all nodes in the network. Given this information, ledger serialization can be viewed as the social choice problem of producing the most agreeable transaction order based on the "preferences" of the miners or validators. In this work, our contribution is three-fold: (i) We put forward a formal Universally Composable definition for order fairness that encompasses receiver order fairness as well as input causality. (ii) We design a novel ledger protocol that preserves input causality and receiver order fairness. (iii) We capture in our composable definition and construction the role that transaction fees play when dealing with fairness.

Our protocol is based on a novel YOSO-style approach that allows encrypting transactions for a short period of time. Notably, the communication complexity required to decrypt the transactions is independent of the number of encrypted transactions. To the best our our knowledge, we are the first to provide a YOSO-style approach with such asymptotic complexity while relying on standard cryptographic assumptions.

We study a secondary construction of Boolean functions, which generalizes the direct sum and the indirect sum. We detail how these two classic secondary constructions are particular cases of this more general one, as well as two known generalizations of the indirect sum. This unifies the known secondary constructions of Boolean functions. We study very precisely the Walsh transform of the constructed functions. This leads us to an interesting observation on the Walsh transforms $W_g,W_{g'},W_{g''}$, and $W_{g\oplus g'\oplus g''}$ when $g,g',g''$ are Boolean functions such that $(g\oplus g')(g\oplus g'')$ equals the zero function.

Recent work showed that ML-based attacks on Learning with Errors (LWE), a hard problem used in post-quantum cryptography, outperform classical algebraic attacks in certain settings. Although promising, ML attacks struggle to scale to more complex LWE settings. Prior work connected this issue to the difficulty of training ML models to do modular arithmetic, a core feature of the LWE problem. To address this, we develop techniques that significantly boost the performance of ML models on modular arithmetic tasks—enabling the models to sum up to $N=128$ elements modulo $q \le 974269$. Our core innovation is the use of custom training data distributions and a carefully designed loss function that better represents the problem structure. We apply an initial proof of concept of our techniques to LWE specifically and find that they allow recovery of 2x harder secrets than prior work. Our techniques also help ML models learn other well-studied problems better, including copy, associative recall, and parity, motivating further study.

Cryptocurrencies, which have gained significant adoption in recent years, face ongoing challenges in scalability and privacy. Payment Channel Hubs (PCHs) constitute a solution to both issues by shifting transactions off the public ledger. Various PCH constructions have been proposed, offering different degrees of unlinkability, efficiency, and inter- operability. However, regulatory compliance remains a significant con- cern, particularly under emerging frameworks like the EU’s Markets in Crypto-Assets (MiCA) regulation and FATF Travel Rule requirements. This work addresses a gap in existing PCH constructions: the lack of regulatory-compliant auditability mechanisms. While concurrent work AuditPCH attempts to address this challenge, it suffers from fundamen- tal limitations, including reliance on channel closures for auditing, vul- nerability to unilateral de-anonymization by the hub, and lack of formal security guarantees for the auditing process. Our approach fundamen- tally differs by providing targeted, non-disruptive auditability that al- lows auditability for high-risk payments while preserving unlinkability for the rest. To achieve this, we present Verifiable Linkable Randomiz- able Puzzles (VLRP), a new cryptographic primitive that enables a party to commit to a secret using two distinct keys: a verifiability key (VK) and an auditability key (AK). This primitive provides (i) verifiability that the owner of the VK issued the commitment, (ii) the ability to ran- domize the commitment to ensure unlinkability, even for the owner of the VK, while still allowing traceability using the AK, and (iii) collaborative auditing that prevents unilateral de-anonymization. We then present Auditable Unlinkable Payment Channel Hubs, AUPCH, a PCH built on VLRP that offers auditability guarantees with stronger se- curity guarantees than existing approaches. AUPCH provides modular integration with existing PCH frameworks (A2L, BlindHub), operates without requiring channel closures, and ensures that auditing requires collaboration between hub and auditing agent, preventing abuse by ei- ther party alone. Crucially, our approach acts as a wrapper around exist- ing PCH implementations, requiring only replacing randomizable puzzle calls with VLRP calls, a minimal change that dramatically reduces de- ployment complexity compared to building new systems from scratch.

Information Set Decoding (ISD) refers to a class of algorithms designed to decode arbitrary linear codes over finite fields. It is among the state-of-the-art methods for solving the Syndrome Decoding Problem (SDP), which lies at the core of code-based cryptography. Since most cryptographic systems operate over the binary field, ISD algorithms are generally designed for this setting. However, emerging cryptographic systems, such as SDitH, that rely on the SDP over non-binary fields, make research into non-binary ISD increasingly relevant. While there have been numerous improvements to ISD algorithms for binary fields, generalizations of these improvements to non-binary fields have resulted in only modest runtime improvements. The only technique which applies specifically to non-binary fields was proposed only last year by Carrier, Hatey and Tillich and consists in solving the SDP over the projective space.

In this paper we continue along this line of research and introduce a novel technique to perform ISD in non-binary fields. Our key idea consists in speeding-up the enumeration of low weight vectors by enumerating only the supports and not the actual values, since these can be recovered by solving a (small) linear system. This idea is at the core of LA-ISD, the first algorithm we propose in the paper. We further enhance it by exploiting a meet-in-the-middle search leading to MitM-LA, the second algorithm we propose in this paper. We analyze our algorithms in both the finite and asymptotic regimes and show that they compare well with competitive solutions. In particular, LA-ISD results in the best memory-less algorithm, while MitM-LA is (slightly) faster than the state-of-the-art algorithm by Carrier, Hatey and Tillich for many parameter-sets as well as asymptotically.

Abstract. Linear algebraic relations, such as inner products ⟨a, b⟩, underlie a wide range of cryp- tographic constructions, including zero-knowledge proofs, SNARKs, polynomial commitment schemes, and more. In this work, we consider group-scalar relations, i.e., statements of the form ⟨A, b⟩, where A is a vector of group elements and b is a vector of field elements. In many crypto- graphic settings, it is necessary to prove relationships between group elements like public keys, or other cryptographic objects without access to the underlying discrete logarithms. Our results are as follows:

– At the protocol level, we introduce the first Inner Product Argument (IPA) that specifically fo- cuses on group-scalar relations in bilinear groups. It achieves constant-size proofs and constant- time verification, maintaining commitments and arguments entirely in the source group. Our techniques enable new applications and significantly improve efficiency compared to state-of- the-art IPAs such as Dory (TCC ’21) and GIPA (Asiacrypt ’21), which rely on recursive folding techniques and thus have logarithmic proofs and verification time. We prove security in the Algebraic Group Model under the q-DHE and q-DL assumptions.

– At the primitive level, we present a new class of functional commitments for linear functions over group-scalar elements. It enables even more applications such as polynomial commit- ments for values hidden inside group exponentiations.

– To showcase our contributions, we demonstrate new applications—most notably, we introduce the notion of dynamic threshold verifiable random functions, which we believe to be a valuable tool for distributed randomness generation. We further present dynamic threshold signatures without random oracles, polynomial commitments over group-encoded inputs, and their ap- plications to oblivious proofs.

Our results provide modular and efficient tools to build cryptographic protocols without typical SNARK frameworks, simplifying real-world deployments. To demonstrate the practicality of our contributions, we provide an implementation and related benchmarks.

Subversion-resilient cryptography has garnered increasing attention in recent years due to growing concerns about cryptographic subversions in real-world applications. Among the existing countermeasures, the notion of cryptographic reverse firewalls (RFs), initially proposed by Mironov and Stephens-Davidowitz (EUROCRYPT 2015) and later extended by Chakraborty et al. (EUROCRYPT 2022) to the universally composable (UC) model, has proven to be a powerful tool for building subversion-resilient cryptographic protocols. In this work, we focus on designing subversion-resilient authenticated key exchange (AKE) protocols, which are critical components of secure Internet communication. We present the f irst generic framework for subversion-resilient UC-secure AKE protocols leveraging RFs. In spired by the state-of-the-art advancements by Chakraborty et al. (ASIACRYPT 2024), we address subversions: where a party’s implementation is covertly altered to exfiltrate secrets or behave unpredictably when triggered by adversarial inputs. A key contribution of our work is the introduction of a new AKE functionality which, for the first time, incorporates security against key control, an essential aspect of achieving subversion resilience. We also provide a concrete instantiation of our framework, demonstrating its feasibility in practice. Notably, the RFs in our proposed AKE protocol are transparent, an important property of RF as defined originally, which allows deployment of RF without all parties explicitly knowing about it and allows robust security. Achieving transparency for RFs has been widely regarded as challenging, particularly when addressing broader subversion attacks (e.g., input-trigger attacks) in the UC model. Our approach, thus, not only advances the state of AKE protocol design, but also offers insights into building other subversion-resilient protocols in the UC model using transparent RFs.

This paper introduces DAWN, a compact and efficient NTRU encryption utilizing double encoding, which is provably secure under the NTRU assumption and the Ring-LWE assumption. We propose a novel technique for NTRU encryption called the zero divisor encoding. Unlike the polynomial encoding technique proposed by Hoffstein and Silverman (2001) and the vector encoding technique proposed by Zhang, Feng, and Yan in NEV (Asiacrypt 2023), our zero divisor encoding technique leverages the algebraic structure of the ring used in NTRU, enabling greater ciphertext compression while maintaining negligible decryption failure.

We further develop a paradigm for NTRU encryption called the double encoding paradigm to maximize the potential of the zero divisor encoding. This paradigm transforms optimizing an NTRU-based encryption into constructing a better encoding within the NTRU context, providing more concrete direction for scheme development. Several previous NTRU encryptions can be situated within this paradigm with different parameters, facilitating direct comparison. We instantiate this paradigm based on the provably IND-CPA secure NTRU variant by Stehlé and Steinfeld (Eurocrypt 2011) to achieve an IND-CPA secure PKE, and subsequently employ the Fujisaki-Okamoto transformation to achieve an IND-CCA secure KEM.

We present two parameter settings of DAWN: DAWN-$\alpha$ minimizes ciphertext size, achieving lengths of 436 bytes under NIST-I security and 973 bytes under NIST-V security; DAWN-$\beta$ minimizes the combined size of the public key and ciphertext, attaining combined sizes of 964 bytes under NIST-I security and 2054 bytes under NIST-V security. DAWN achieves superior compactness and performance among current lattice-based KEMs without introducing additional security assumptions. Compared to NEV (Asiacrypt 2023), the previously leading NTRU-based KEM in balancing compactness and performance, DAWN demonstrates 20\%--29\% greater compactness at approximate security levels and decryption failure probabilities, while executing 1.1X--2.0X faster in a complete ephemeral key exchange process.

A Password-Authenticated Key Exchange (PAKE) protocol allows two parties to jointly establish a cryptographically strong key, in the setting where the only information shared in advance is a low-entropy "password". The two standard security definitions for PAKE are the game-based one by Bellare, Pointcheval and Rogaway (BPR-security, EUROCRYPT 2000) and the Universally Composable (UC) one by Canetti et al. (EUROCRYPT 2005). It is well-known that UC-security implies BPR-security; however, there are a large number of variants of both definitions, and the relation between them is not entirely clear.

In this work, we thoroughly study a variant of BPR-security by Katz, Ostrovsky and Yung (KOY-security, JACM 2009):

1. We show, via a counterexample, that UC-security does \emph{not} imply KOY-security;

2. We then prove that a variant of UC-security, called implicit-only UC-security (Dupont et al., EUROCRYPT 2018), implies KOY-security.

Interestingly, we make the observation that KOY- and implicit-only UC-security essentially strengthen their standard counterparts in the same manner. We also present detailed explanations of all four security notions.

The notion of indifferentiability was proposed by Maurer et al. to bound the distinguishing advantage of a construction built on a public primitive, from a public random function. In Indocrypt'10, Mandal et al. have shown that the sum of two independent permutations is indifferentiable from a public random function up to $2^{2n/3}$ queries. Later in ACNS'15, Mennink and Preneel identified an analytical flaw of Mandal et al's result and revised the security bound to $2^{2n/3}/n$. In Eurocrypt'18, Bhattacharya and Nandi have improved their indifferentiable bound to $2^n$ queries, which was again identified as incorrect in the analysis by Gunsing et al. In this paper, we study the indifferentiability of a few other PRF constructions, namely STH and EDM constructions. We will show that neither STH nor STH2 is indifferentiable, which led us to propose a generalized version called gSTH. We have shown that gSTH achieves a tight $l$-bit security bound, where $l$ denotes the size of the constants in terms of bits used in the construction. While we show that EDM achieves a tight $n/2$-bit indifferentiable bound with respect to our proposed simulator, single-keyed EDM is not indifferentiable from a public random function. We would like to mention that all the proofs and the attacks have been done in the sequential indifferentiability model.

Layer-2 protocols are pivotal in enhancing the scalability of blockchain systems, enabling faster off-chain transactions while maintaining security. These protocols can bridge consensus-based blockchain systems and advanced applications, such as Multiparty Computation (MPC) protocols, often defined within the Universal Composability (UC) Framework. However, despite the existence of some UC-defined protocols, there is currently no comprehensive UC definition for isomorphic multiparty state channels, in particular that are not dependent on the ledger model: account or UTxO based ledger. These protocols depend heavily on timelock mechanisms and the accurate representation of time, which are challenging to model within the UC Framework. Our work addresses this gap by proposing a UC-based definition, i.e., functionality, for isomorphic multi-party state channels that realistically model timely actions of honest users, a critical feature for the security of the channel protocol. Moreover our definition is agnostic with respect to the ledger model. Additionally, we introduce an extended timelock-aided global ledger functionality and demonstrate the security of existing protocols, namely Hydra proposed by Chakravarty et al. (FC'21), under the UC Framework and our proposed functionalities. This contribution provides a robust foundation for developing secure and scalable off-chain protocols in blockchain ecosystems. Finally, we concretely provide the construction of the extension of the Hydra Protocol, only outlined by the original work, and also prove it secure under our framework.

Asynchronous complete secret sharing (ACSS) and asynchronous dynamic proactive secret sharing (ADPSS) are fundamental primitives for secret sharing and resharing in threshold systems. They serve broad applications in distributed key management (DKM), multi-party computation, and blockchain. However, ACSS constructions that employ homomorphic commitments incur notable computational overhead, especially in batched executions. Conversely, lightweight variants require quadratic per-secret communication, which grows rapidly with the committee size. Building upon instances of ACSS, ADPSS constructions inevitably inherit these inefficiencies.

To address these limitations, we introduce GoSSamer, a concretely and asymptotically efficient protocol suite, where both GoSSamer-ACSS and GoSSamer-ADPSS achieve (1) lightweight computation with only finite-field arithmetic and hash functions, (2) asymptotically optimal, linear per-secret communication, (3) optimal resilience in asynchronous networks, a nd (4) post-quantum security.Leveraging our proposed share propagation and verification mechanisms, GoSSamer-ACSS reduces the runtime by 97% against the linear-communication scheme hbACSS (NDSS'22), and lowers the bandwidth usage by 75% compared to the lightweight solution SS24 (JoC'24) in a 64-node committee. By decoupling the ADPSS framework from the commitment-based ACSS through a new consistency verification technique, GoSSamer-ADPSS boosts key resharing throughput by 16-22$\times$ compared to LongLive (Usenix Security'23), and reduces its bandwidth by 47.6% in 16-node committees. GoSSamer directly accelerates real-world applications like distributed key management. Specifically, the runtime in GoSSamer-ACSS-based distributed key generation outperforms DXK+23 (Usenix Security'23) by 7-11$\times$, while GoSSamer-ADPSS-based key resharing outperforms LongLive by 9-13$\times$.

In recent years, federated learning has gained significant momentum as a collaborative machine learning approach, particularly in the field of medicine. While the decentralized nature of federated learning boasts greater security guarantees compared to traditional machine learning methods, it is still susceptible to myriad attacks. Moreover, as federated learning becomes increasingly ubiquitous in medicine, its use for classification tasks is expected to increase; however, maintaining patient data confidentiality remains a significant challenge, especially for genetic data. In this work, we introduce a novel framework for secure federated inference on nucleotide-based genotype data and provide a gateway to private inference through fully homomorphic encryption. A federated model with five local clients was created and trained before being encrypted with the TFHE cryptosystem and placed for inference. This framework successfully identified promoter sequences encoded within given DNA sequences, showing its potential applications in secure genomic data analysis in a federated context. Our work represents a crucial step in privacy-preserving federated inference on nucleotide-based data.

We present the first algorithm for computing class groups and unit groups of arbitrary number fields that provably runs in probabilistic subexponential time, assuming the Extended Riemann Hypothesis (ERH). Previous subexponential algorithms were either restricted to imaginary quadratic fields, or relied on several heuristic assumptions that have long resisted rigorous analysis.

The heart of our method is a new general strategy to provably solve a recurring computational problem in number theory (assuming ERH): given an ideal class $[\mathfrak a]$ of a number field $K$, sample an ideal $\mathfrak b \in [\mathfrak a]$ belonging to a particular family of ideals (e.g., the family of smooth ideals, or near-prime ideals). More precisely, let $\mathcal{S}$ be an arbitrary family of ideals, and $\mathcal{S}_B$ the family of $B$-smooth ideals. We describe an efficient algorithm that samples ideals $\mathfrak b \in [\mathfrak a]$ such that $\mathfrak b \in \mathcal{S}\cdot\mathcal{S}_B$ with probability proportional to the density of $\mathcal{S}$ within the set of all ideals.

The case where $\mathcal{S}$ is the set of prime ideals yields the family $\mathcal{S}\cdot\mathcal{S}_B$ of near-prime ideals, of particular interest in that it constitutes a dense family of efficiently factorable ideals. The case of smooth ideals $\mathcal{S} = \mathcal{S}_B$ regularly comes up in index-calculus algorithms (notably to compute class groups and unit groups), where it has long constituted a theoretical obstacle overcome only by heuristic arguments.

In this paper we present a Schnorr-like linkable ring signature scheme we call d/v-CLSAG that is an extension of the d-CLSAG scheme proposed in 2019 by Brandon Goodell, Sarang Noether, and Arthur Blue. The proposed extension allows the use of different group generators for different layers of ring members: $\mathbf{pk} := \mathbf{sk} \circ \mathbf{G},\ \mathbf{G} = (G_{k_0},\dots,G_{k_{d-1}}) \in \texttt{G}^d$, while the original scheme assumes the use of the same generator $G$ across all layers: $\mathbf{pk} := \mathbf{sk} \circ \mathbf{G},\ \mathbf{G} = (G,\dots,G) \in \texttt{G}^d$. To improve the signature size, we use key aggregation techniques in the same way, but for distinct group generators $\{G_k\}$ individually. Note that we don't require the absence of efficiently-computable discrete logarithm relations between $\{G_k\}$. However, it might be possible, that adding such a limitation would allow us to reduce the signature size. This is the subject of future studies. We provide the security statements for the proposed updated scheme.