International Association
for Cryptologic Research

$\textit{Proxy re-encryption}$ (PRE) is an essential cryptographic primitive for managing secure access delegation in outsourced data environments, particularly public cloud systems. PRE is a public key encryption (PKE) with two additional algorithms - (i) re-encryption key generation by which a proxy server generates a re-encryption key; (ii) re-encryption algorithm by which the proxy server can transform the ciphertext under the delegator's public key to a ciphertext under the delegatee's public key enabling the delegatee to decrypt the message originally intended for the delegator. With the advent of quantum computing, a pressing need arises to design PRE schemes based on quantum-resistant assumptions. This paper addresses this requirement by presenting the first construction of a bidirectional PRE ($\mathsf{bPRE}$) from supersingular isogenies. Our $\mathsf{bPRE}$ is built upon the commutative supersingular isogeny-based PKE scheme $\mathsf{MSimS}$, a variant of the isogeny-based PKE scheme $\mathsf{SimS}$ and achieves security against $\textit{chosen-plaintext attack}$ (CPA) in the standard model under the hardness of the commutative supersingular isogeny decisional Diffie-Hellman (CSSIDDH) problem. The resultant $\mathsf{bPRE}$ supports efficient re-encryption of ciphertexts by the proxy server for the delegator as well as the delegatee and inherits the multi-hop property, enabling chainable delegation of access rights. Significantly, our isogeny-based $\mathsf{bPRE}$ is asymptotically efficient, offering an efficient reduction in bandwidth consumption compared to current lattice-based proposals in terms of key size and ciphertext size. This makes the scheme a highly compact and practical candidate for post-quantum cloud security. Furthermore, our PKE scheme $\mathsf{MSimS}$ is of independent interest which is proven to be CPA secure under the hardness of the CSSIDDH problem and secure against chosen ciphertext attack (CCA) under the hardness of the CSSIDDH problem and the commutative supersingular isogeny knowledge of exponent (CSSIKOE) problem.

Galteland and Gjøsteen observe that Dilithium-family signatures admit broadband subliminal channels in a secret-key-assisted setting where the receiver can reconstruct the signer’s hidden commitment from a public signature. This note gives a standards-specific instantiation for FIPS 204 ML-DSA. We do not claim a new subliminal-channel technique: our goal is to make the FIPS 204 patch point and byte-level embedding interface explicit and to list the resulting capacities for the approved parameter sets.

Two FIPS 204 facts drive the construction: for any accepted signature, the commitment vector \(y\) is recoverable from \((c, z)\) given \(s_1\), and the standardized \(\gamma_1\) values make the packing/unpacking mapping a bijection on its fixed-length byte input. We embed an \(L\)-byte payload by XOR-masking a pseudorandom packed container and decoding it with the standard unpacking routine: the resulting signatures verify under unmodified verifiers.

We implemented the patch in the mldsa-native C library and validated round-trip extraction, abort-rate statistics, and distribution sanity checks for all three parameter sets. Changes, scripts, and artifacts are available in the mldsa-native-sublime fork on GitHub. The per-signature covert capacity is \(32\ell w - 32\) bytes, where \(w = \log_2(2\gamma_1)\), namely 2,272 bytes for ML-DSA-44, 3,168 bytes for ML-DSA-65, and 4,448 bytes for ML-DSA-87. As in prior work, extraction requires \(s_1\), so the relevant setting is kleptographic/ASA-style secret sharing rather than public tagging.

Randomness that is unbiased, unpredictable and publicly verifiable is a crucial requirement for many blockchain-based Web3 ap- plications. Verifiable Random Functions (VRFs) inherently provide these properties. A practical VRF scheme requires fast key generation time as well as features like many evaluations also for different rounds in the blockchain. In this work, we propose a post-quantum secure key updat- able VRF construction namely XM-VRF that relies on symmetric cryp- tographic building blocks such as hash functions and PseudoRandom Generators (PRGs). At the heart of our construction lies a quantum safe Extended Merkle Signature Scheme(XMSS) organized across multi- ple layers. We reformulate the XMSS signature scheme in a structured manner to align with our XM-VRF construction. The principal benefit of proposed XM-VRF compared to existing solution is it’s enhanced key generation efficiency as well as the property of many evaluations from each secret-verification key pair. The proposed scheme is proven to sat- isfy forward security, while also being resilient against forgery attacks, as established through a rigorous security analysis. We emphasize that our XM-VRF autonomously updates its secret key during the evaluation process, performing this update concurrently with the VRF output gen- eration to maintain uninterrupted state progression. Finally, we design a protocol for random committee selection within the Algorand blockchain framework,leveraging XM-VRF to ensure unbiased, verifiable, and stake- proportional participant selection.

We present an improved AKS condition $\binom {e \cdot |S|+ de - 1}{de - 1} \ge n^{\lceil \sqrt{d e/3} \rceil}$ for the random AKS algorithm, where $|S|$ is the number of congruences to be tested, $e$ the degree of the modulo polynomial $x^e-r$ and $d$ the multiplicative order of $n$ modulo $e$. It is based on Bernstein's result and better than his condition $\binom {e \cdot |S|+ e - 1}{e - 1} > n^{\lceil \sqrt{d^2 e/3} \rceil}$ when $d>1$; this improved condition enables us to choose a smaller $e$: theoretically by a factor $> d$ ($d \in (\log n)^{O(1)}$) and numerically $\ge d^2$ and $< d^3$ for most practical cases; and thus improves time and space complexities.

Masking is an essential countermeasure against side-channel attacks, yet implementing secure and low-latency hardware masking remains challenging. In particular, although OPINI provides strong composability guarantees for single-cycle iterative architectures, prior low-latency OPINI gadget, $\rm HPC4$, is limited to two-input multiplication. In this work, we present a low-latency, low-randomness, first-order OPINI gadget applicable to arbitrary Boolean functions, denoted as $\rm GOM$. Independent and concurrent work by Rahimi and Moradi proposes OTSM, which is also a generic, low-latency first-order OPINI gadget. Our construction involves two new techniques: (i)~extending the $\rm HPC4$ idea--originally masking each share of one secret input with two bits of randomness--to masking each shared monomial derived from the input shares accordingly, and (ii)~a randomness-reassignment technique that enables the two circuits generating the output shares to reuse the same set of randomness while preserving OPINI security. To validate OPINI security, we propose a formal verification technique based on three symbolic reduction rules, and use it to verify multiple low-latency OPINI gadgets (i.e., $\rm HPC4$, $\rm GOM$ and $\rm OTSM$). Leveraging the generality of our gadget, we instantiate several OPINI-secure S-boxes across different algebraic degrees. For the algebraic-degree-2 Ascon S-box, our gadget achieves a 21\% reduction in area and a 28\% reduction in randomness compared to the $\rm HPC4$-based implementation. We further construct higher-degree S-boxes from the PRESENT, PRINCE and AES ciphers and report their hardware performance as reference baselines. We also provide an apples-to-apples comparison with $\rm OTSM$. All masked S-boxes are successfully verified within 20~minutes using our formal verification method. Finally, FPGA-based experiments confirm the practical security of the masked implementations.

Off-chain cryptography enables more expressive smart contracts for Bitcoin. Recent work, including BitVM, use SNARKs to prove arbitrary computation, and garbled circuits to verifiably move proof verification off-chain. We define a new garbling primitive, Argo MAC, that enables over $1000\times$ more efficient garbled SNARK verifiers. Argo MAC efficiently translates from an encoding of the bit decomposition of a curve point to a homomorphic MAC of that point. These homomorphic MACs enable much more efficient garbling. In subsequent work, we will describe how to use Argo MAC to construct garbled SNARK verifiers for pairing-based SNARKs.

In response to the looming quantum threat, NIST has selected four algorithms for standardization (i.e., ML-KEM, ML-DSA, SLH-DSA, and FN-DSA), yet three of the four schemes are based on Euclidean lattices, which raises concerns about the mathematical diversity of post-quantum algorithms. NIST has therefore announced an additional call for post-quantum signatures with a preference for schemes constructed from assumptions other than lattices. Among such candidates, the Unbalanced Oil and Vinegar (UOV) signature over the multivariate quadratic (MQ) problem is attractive for its short signature and security against quantum cryptanalysis. However, the practical implementations of UOV remain vulnerable to power side-channel attacks. In this paper, we address this issue by presenting two improved techniques for masking linear equations system solving at arbitrary order, with a proof of security in the $t$-probing model. We show that in the masked setting, our inversion-based techniques outperform Gaussian elimination, unlike the unmasked setting where Gaussian elimination is typically more efficient. As an application, we develop a complete C implementation of the fully masked UOV signing using our improved techniques. Compared to masked Gaussian elimination, our techniques achieve at least $2.2$ times speedup at high-order. Against Kundu's latest implementation (CCS 2025), our masked UOV signing is faster by an average factor of $4.0$ at higher masking orders.

Deep neural networks (DNNs), a hot topic in this decade, are already solving many practical problems previously unchallenged. There are clear use cases of strong requirements for privacy protection in DNN models and input data. Fully Homomorphic Encryption (FHE) schemes provide privacy by enabling operations upon encrypted data with post-quantum security, at the expense of vast data size increase. Overwhelming execution times and memory sizes currently limit DNN inference with FHE to severely reduced models and datasets. In this article, we thoroughly review the state of the art and the state of the practice around this topic, and identify the current challenges remaining to enable efficient DNN inference with FHE in production-sized use cases, along with the most promising trends to address them. Advancing upon previous review articles in the literature, our focus is specifically on deep learning inference on top of high-performance hardware. From our analysis, we set what we consider to be an ideal private inference system for DNNs, capturing notions already present in the literature and generalizing them.

Secure TransFormer Inference (STFI) frameworks have been proposed to address privacy concerns over user inputs and model parameters in Transformer-based LLMs. While most existing solutions rely on interactive protocols that incur substantial user-server communication overhead, non-interactive STFI variants have recently emerged to eliminate such dependencies. Nevertheless, state-of-the-art non-interactive STFI frameworks still suffer from critical limitations. (i) Large ciphertext sizes and multiple rotations alongside heavy user-side overhead in Homomorphic Matrix Multiplication (HMM). (ii) High approximation costs and depth consumptions in Homomorphic Nonlinear Evaluations (HNE).

To address these limitations, we present Euston, an efficient and user-friendly STFI with non-interactivity. By combining RNS-CKKS fully homomorphic encryption with optimized methods, Euston achieves unprecedented efficiency in offline online inference paradigm. The key innovations are twofold. (i) For linear operations, we adopt Singular Value Decomposition (SVD) with our novel batched HMMs to minimize ciphertext size and reduce rotation counts, simultaneously lowering user-side computational, communication and storage overhead. (ii) For nonlinear operations, we employ column(diagonal)-packed ciphertext matrix formats to eliminate costly rotations and depth regulation strategies to reduce depth consumption in non-interactive HNEs, which not only avoids user-server communications but also accelerates inference performance. In comparision with the state-of-the-art approach (NEXUS, NDSS 2025), Euston achieves up to 3100× lower preprocessing costs for the user and 8.8× higher system-wide inference performance, specifically delivering a 90× speedup for HMM and a 165.7× speedup for HNE. Our results demonstrate that Euston establishes new efficiency frontiers for user-friendly STFI deployment across cloud and edge environments.

The whitelist is a foundational and widely deployed access control mechanism. In its prevalent implementation, the verifying entity typically requires access to the plaintext authorization policy to perform enforcement. This creates a concentrated security risk: the verifier becomes a high-value target, and its compromise could lead to the full exposure of the sensitive whitelist—a single point of failure for policy confidentiality. This work formalizes and addresses this risk by introducing a new paradigm of Privacy-Enhanced Whitelists. Our framework cryptographically decouples policy enforcement from policy exposure. A trusted issuer encodes the whitelist, enabling the verifier to validate memberships using only cryptographically blinded commitments, without ever needing the plaintext list. We provide a formal security model that rigorously defines and achieves security even against an adversary who compromises the verifier’s state. The system is realized via an efficient construction based on polynomial commitments in elliptic curve groups and supports dynamic policy updates. By shifting the trust assumption from the verifier’s infrastructure to cryptographic verification, our work establishes a practical foundation for scenarios where the whitelist itself must remain a protected secret.

We present $\textsf{Jindo}$, a new lattice-based polynomial commitment scheme (PCS) readily available for compiling polynomial interactive oracle proofs (PIOP) into zero-knowledge arguments of knowledge (ZKAoK). $\textsf{Jindo}$ improves upon the previous lattice-based PCSs $\textsf{CELPC}$ (CRYPTO' 24) and $\textsf{Greyhound}$ (CRYPTO' 24) by seamlessly integrating their strengths. Specifically, we incorporate the coefficient encoding method of $\textsf{CELPC}$ with a new evaluation protocol inspired by $\textsf{Greyhound}$, inheriting only the advantages of both schemes. As a result, $\textsf{Jindo}$ enjoys native support for a large base field, a large challenge set, the evaluation hiding property, and efficient batched evaluation.

Our implementation shows that $\textsf{Jindo}$ improves $\textsf{CELPC}$ with 1.3x faster proof generation, 3.7x faster verification, and 4.8x smaller proof size when evaluating polynomials of degree $2^{19}$ over a 255-bit prime field. Furthermore, $\textsf{Jindo}$ outperforms $\textsf{CELPC}$ with 3.5x faster proof generation, 9.7x faster verification, and 12.3x smaller proof size when compiling PIOP from $\textsf{Buckler}$ (CCS' 25) to prove the validity of an RLWE sample, demonstrating its practical efficacy in ZKAoK construction from PIOP.

A classical obfuscator for quantum circuits is a classical program that, given the classical description of a quantum circuit $Q$, outputs the classical description of a functionally equivalent quantum circuit $\widetilde{Q}$ that hides as much as possible about $Q$. Previously, the only known feasibility result for classical obfuscation of quantum circuits (Bartusek and Malavolta, ITCS 2022) was limited to "null" security, which is only meaningful for circuits that always reject. On the other hand, if the obfuscator is allowed to compile the quantum circuit $Q$ into a quantum state $\ket{\widetilde{Q}}$, there exist feasibility results for obfuscating much more expressive classes of circuits: All pseudo-deterministic quantum circuits (Bartusek, Kitagawa, Nishimaki and Yamakawa, STOC 2023, Bartusek, Brakerski and Vaikuntanathan, STOC 2024), and even all unitaries (Huang and Tang, FOCS 2025).

We show that (relative to a classical oracle) there exists a classical obfuscator for all pseudo-deterministic quantum circuits. As our main technical step, we give the first construction of a compact quantum fully-homomorphic encryption (QFHE) scheme that supports public verification of (pseudo-deterministic) quantum evaluation, relative to a classical oracle.

To construct our QFHE scheme, we improve on an approach introduced by Bartusek, Kitagawa, Nishimaki and Yamakawa (STOC 2023), which previously required ciphertexts that are both quantum and non-compact due to a heavy use of quantum coset states and their publicly-verifiable properties. As part of our core technical contribution, we introduce new techniques for analyzing coset states that can be generated "on the fly", by proving new cryptographic properties of the one-shot signature scheme of Shmueli and Zhandry (CRYPTO 2025). Our techniques allow us to produce QFHE ciphertexts that are purely classical, compact, and publicly-verifiable. This additionally yields the first classical verification of quantum computation protocol for BQP that simultaneously satisfies blindness and public-verifiability.

In EUROCRYPT 1999, Gennaro, Jarecki, Krawczyk, and Rabin (GJKR) showed that in the well-known Pedersen robust Distributed Key Generation (DKG) protocol for the Discrete Logarithm (DL), an adversary can bias the distribution of the resulting public key. To address this issue, they proposed a fully secure, statistically unbiased variant of the Pedersen DKG protocol. The GJKR protocol achieves robustness and guarantees that the final public key remains uniformly random, even in the presence of computationally unbounded corrupted parties, though at the cost of $O(n^2)$ computational complexity, where $n$ denotes the number of parties. In this paper, we revisit fully secure robust DKG protocols for the DL setting and propose three more efficient alternatives, each achieving $O(n)$ computational complexity while offering different trade-offs in security, efficiency, and round complexity. Our first protocol, like the GJKR scheme, guarantees that the distribution of the final public key remains uniformly random, even against computationally unbounded adversaries. The second protocol is concretely more efficient and ensures that the public key distribution is computationally indistinguishable from uniform. In our third construction, we focus on minimizing the number of rounds in the second protocol and present a 3-round variant of it. Our third scheme can be viewed as a fully secure and round-reduced variant of the biased construction by Atapoor et al. (ASIACRYPT 2023). In comparison with the most recent low-round fully secure DKG protocols by Katz (CRYPTO 2024), Cascudo-David (EUROCRYPT 2024), Kate et al. (CCS 2024), and Boneh et al. (EUROCRYPT 2025)--all of which achieve three rounds via two online rounds and one preprocessing round (or vice versa)--our three-round DKG protocol requires only $O(n)$ exponentiations, as opposed to at least $O(n^2)$.

In recent years, unmanned aerial vehicles (UAVs) have shown great potential in logistics delivery due to their ability to bypass traffic congestion and adapt to complex terrains. Their high efficiency, low cost, and wide coverage make them a valuable supplement to last-mile logistics. However, third-party UAV systems operating in open environments are vulnerable to eavesdropping, tampering, and other cyber-attacks, which poses risks of sensitive information leakage. Meanwhile, warehouse nodes for sanitizing private information are widely deployed in logistics systems and need to be dynamically adjusted according to demand, which poses a challenges for the management of sanitization permissions. To address these issues, we propose a dynamic sanitizable signature with multiple sanitizers, enabling each sanitizer to independently sanitize sensitive information in signed messages, thus preserving logistics data privacy. Our scheme is applicable to UAV logistics scenarios and supports the addition and revocation of sanitizers without modifying existing keys, thereby enabling flexible and efficient permissions management. Security analysis shows that the proposed scheme ensures unforgeability, privacy preservation, and other security properties. A implementation on AmovLab Prometheus 600 UAVs demonstrates lower computational and communication overhead than existing privacy-preserving schemes, confirming its efficiency and practicality in UAV logistics systems.

It is well-known that evaluating a Boolean polynomial $f$ of any degree $d$ in $n$ variables over the full space $\mathbb F_2^n$ takes $n\cdot 2^n$ bit operations and $2^n$ bits of memory with standard Mobius transform. When $d$ is relatively small, Bouillaguet et al. proposed at CHES 2010 the fast exhaustive search (FES) algorithm. In this algorithm, by using Gray code to enumerate all elements in $\mathbb F_2^n$, evaluating $f$ on all inputs in $\mathbb F_2^n$ takes $\big(\sum_{i=0}^{d}\binom{n}{i}\big)^2+d\cdot 2^n=\binom{n}{\leq d}^2+d\cdot 2^n$ bit operations and $\binom{n}{\leq d}$ bits of memory. The term $\binom{n}{\leq d}^2$ represents the cost of the initialization phase. This problem has received new attention in recent years, which was studied by Dinur at EUROCRYPT 2021, by Furue and Takagi at PQCrypto 2023, and by Bouillaguet at TOMS 2024. All these algorithms work on the full space, and have a similar additional phase such as the initialization phase in the FES algorithm, which takes much more than $\binom{n}{\leq d}$ bit operations. In this work, we propose a simple yet efficient algorithm to evaluate $f$ over the structured space $P_{n_s}^{w_s}\times \cdots \times P_{n_1}^{w_1}\subseteq \mathbb F_2^n$ where $\sum_{i=1}^{s}n_i=n$ and $P_{n_i}^{w_i}$ denotes the set of $n_i$-bit binary strings with Hamming weight not larger than $w_i$. Our algorithm is inspired by the FES algorithm and Furue-Takagi's algorithm. However, our algorithm can work on a more general space, and is also distinguished by an efficient additional phase, which is simply reading all coefficients of $f$ and thus takes only $\binom{n}{\leq d}$ bit operations. For complexity, our algorithm takes $\binom{n}{\leq d}+d\cdot \Pi_{i=1}^{s}\binom{n_i}{\leq w_i}$ bit operations and consumes $(d+1)\cdot \binom{n}{\leq d}$ bits of memory. For applications, we prove that it is either infeasible or nontrivial to adapt the FES algorithm with monotone Gray code, which somehow answers a question raised by Dinur at EUROCRYPT 2021. Moreover, our algorithm provides a proven method to solve a critical step in Dinur's algorithm for the polynomial method, without affecting its time complexity. In particular, we also address the open problem proposed at TOMS 2024, and improve the polynomial evaluation algorithms even over the full space.

We develop a new method for the computation of $(3,3)$-isogenies between principally polarized abelian surfaces. The idea is to work with models in $\mathbb P^8$ induced by a symmetric level-$3$ theta structure. In this setting, the action of three-torsion points is linear, and the isogeny formulas can be described in a simple way as the composition of easy-to-evaluate maps. In the description of these formulas, the relation with the Burkhardt quartic threefold plays an important role. Furthermore, we discuss generalizations of the idea to higher dimensions as well as different isogeny degrees.

Secure multi-party computation (MPC) provides a promising approach for privacy-preserving machine learning (ML). Existing solutions generally fall into two categories but face scalability and efficiency limitations. Protocols based on Shamir secret sharing (SS) incur high communication costs, while those relying on packed Shamir secret sharing (PS) remain largely theoretical and often require costly secret routing, especially for complex ML tasks.

In this work, we propose a mixed secret sharing strategy that leverages PS sharing for non-linear layers with repeated and independent operations, and SS sharing for linear layers such as matrix multiplications. To efficiently support alternating linear and non-linear computations, we design generic conversions between SS and PS sharings and further integrate them into the corresponding ML protocols, thereby eliminating additional communication and computation overhead. Moreover, we develop efficient PS sharing-based protocols for primitive non-linear building blocks, which enable multiple non-linear operations to be executed with essentially the same communication cost as a single operation.

We implement our framework for secure multi-party ML inference and conduct extensive experiments. Compared to the SOTA work LXY24 (USENIX Security '24), our approach reduces communication by $3.6$-$6.1 \times$, while achieving $1.5$-$4.3 \times$ runtime improvement in the WAN setting and comparable or up to $2.3 \times$ better performance in the LAN setting.

Boolean functions having only one Walsh zero (or equivalently up to a translation, balanced functions whose sums with non-constant affine Boolean functions are all unbalanced) have been constructed for every n ≥ 10, by Mesnager and the first author, twenty years ago. This same paper had checked (partly mathematically and partly thanks to computer investigations) that no such function exists for n ≤ 6 but left open the question of constructing them for 7 ≤ n ≤ 9. Since then, functions in 7, 8 and 9 variables having one Walsh zero have been found by Lou and Wang, thanks to ad hoc methods combined with computer searches, but not as elements in infinite classes of functions having this property. In the present paper, we provide such infinite classes for n ≥ 8. For n = 7, we provide one more function (found by a computer investigation thanks to an algorithm) but we leave open the possibility of finding an infinite class valid for n ≥ 7. We also provide a secondary construction of functions with one Walsh zero in n + 2 variables from such functions in n variables, which does not need particular conditions on the latter for being successful (and which provides then a systematic way to obtain functions in n + 2 variables from functions in n variables). We investigate mathematical proofs of non-existence of such functions in n ≤ 6 variables.

With the advent of quantum computing, which threatens the very foundations of classical cryptography, several authenticated key exchange (AKE) protocols have been proposed, combining classical and post-quantum cryptographic algorithms, and a quantum key distribution (QKD) sub-protocol. The goal being to associate the claimed information theoretic security of QKD, and the security based upon computational assumptions of classical and post-quantum cryptography. To our knowledge, in existing security proofs of such hybrid AKE protocols, the QKD phase is treated as a black box and the impact of establishing the output quantum key appears similar as setting a symmetric key beforehand at the two communicating parties. In this paper, we describe an hybrid AKE protocol and a security model that captures multiple security properties. Our security analysis integrates the security loss induced by the QKD phase as well as that of implied by the classical and post-quantum cryptographic algorithms involved in the protocol.

This paper presents the first construction of adaptively secure non-interactive key exchange (NIKE) for an unbounded number of parties in the standard model. While prior unbounded protocols were restricted to static security or required random oracles, this work achieves adaptive security in the standard model. The proposed scheme supports an unbounded number of honest and malicious users, as well as unbounded party sizes, while tolerating a bounded number of dynamic user corruptions. The construction is based on sub-exponential indistinguishability obfuscation and sub-exponential fully-homomorphic encryption. A key technical contribution is a new application of what we call a function-extractable hash function. This is a variant of a function binding hash function that enables resilient extraction of properties from maliciously hashed digests.