International Association
for Cryptologic Research

A garbling scheme encodes a function and an input into two independent artifacts from which the output can be recovered, but nothing else is revealed. This clean separation between function and input has made garbling one of the most versatile primitives in cryptography. Yet it hides an asymmetry that has gone largely unexamined: while the input is cryptographically protected, the function is fully exposed to whoever performs the garbling. As garbling is increasingly deployed in settings where garbling is delegated to untrusted infrastructure, published on public ledgers, or distributed among multiple parties, this asymmetry becomes a fundamental barrier. The function, which may encode proprietary models, confidential policies, or sensitive decision logic, is leaked unconditionally to the garbling server.

We introduce oblivious garbling, a new paradigm that closes this gap. In our framework, the garbler receives only a designated leakage of the circuit and remains oblivious to everything else. We present the first construction instantiating this notion where the leakage is the circuit topology alone, achieving linear complexity with no blow-up in the size of the garbled circuit. The construction extends to the malicious setting with no asymptotic overhead. Beyond its theoretical contribution, oblivious garbling has immediate practical consequences: it enables outsourced garbling without function exposure, garbling on untrusted hardware without leaking proprietary logic, and a multi-party garbling protocol in which no garbling party learns the function, all without resorting to universal circuits.

Side-channel attacks are a relevant threat to many modern cryptographic schemes and often have fatal consequences such as revealing partial information about secret keys. While leakage-resilient cryptography aims to solve this problem, existing works focus exclusively on showing security against classical leakage. Moreover, recent public key encryption (PKE) schemes utilizing quantum secret keys achieve security against unbounded classical leakage, but offer no guarantees on any amount of quantum leakage. Since security guarantees on classical side information do not necessarily translate to guarantees on quantum side information, showing PKE schemes that are secure in the presence of quantum leakage remains open.

In this work, we address this problem by extending the definition of leakage resilience for PKE in the bounded-leakage model to allow for quantum leakage. We provide the following two constructions: - PKE with Quantum Secret Keys: We construct a PKE scheme that tolerates unbounded classical leakage alongside bounded, constant-rate ($\lambda <0.057$) quantum leakage. Our construction assumes the existence of polynomially secure post-quantum indistinguishability obfuscation (iO) as well as one-way functions (OWFs). - PKE with Classical Secret Keys: We construct a classical PKE scheme that is secure against bounded quantum leakage. Our construction offers a tradeoff between the achievable leakage rate and the underlying cryptographic assumptions. Assuming the hardness of the learning with errors problem (LWE) we obtain an optimal leakage rate of $\lambda \leq 1-o(1)$. Alternatively, assuming only post-quantum PKE, we obtain a leakge rate of $\lambda\leq \frac{1}{poly(n)}$.

The idea of Hybrid Homomorphic Encryption (HHE) is to reduce the computational cost of Fully Homomorphic Encryption (FHE) by encrypting bulk data symmetrically while only encrypting the short symmetric key homomorphically. Its efficiency depends on the multiplicative depth of the symmetric cipher's decryption circuit, motivating FHE-friendly designs. The Learning Parity with Noise (LPN) problem is a natural candidate for such designs, as it gives rise to simple encryption and decryption circuits over binary fields. In this context, Fouque, Hadjibeyli, and Kirchner proposed LPN-based symmetric encryption schemes based on the LPN-C cryptosystem of Gilbert et al. LPN-C is attractive for HHE while allowing parameter choices that bound decryption failures. However, the concrete security of LPN-C and its HHE-oriented variants remains poorly understood. We quantify how enforcing bounded noise via rejection sampling reduces the observed noise rate, an effect not captured in prior analyses. This yields immediate speedups for all attacks based on LPN instance solving. We then extend the Arora-Ge-style algebraic attacks to the bounded-noise setting and derive new bounds on the dimension of the induced linear spaces, refining and partially correcting earlier analyses. We show that some parameter regimes are more robust than previously estimated, while new algebraic strategies yield the best known attacks in others. Overall, our results improve our understanding of the concrete security of LPN-based symmetric encryption schemes, informing parameter selection for FHE-friendly variants.

In 2020 and 2024 respectively, NIST released a Special Publication (SP 800-208) and a Federal Information Processing Standard (FIPS 205) specifying hash-based signature schemes with natural quantum resistance thanks to their symmetric foundation. The former recommends the stateful hash-based signature schemes LMS and XMSS, whereas the latter standardizes their stateless counterpart SPHINCS+. While in principle all three constructions can be instantiated with any secure cryptographic hash function, the concrete instances recommended by NIST are currently limited to either the SHA-2 or the SHA-3 family. Building on the maturity of these standardized families is of course a sensible choice. Yet, we argue that neither is particularly well suited for this purpose, especially once physical security matters. As an alternative we suggest pSquare-hash, an arithmetization-oriented family of lightweight tweakable hash functions. We demonstrate that such dedicated tweakable constructions ideally suit the instantiation and security requirements of hash-based signature schemes, potentially leading to efficiency advantages over standard concatenation-based approaches through either a reduction of the permutation size or the number of calls. With respect to physical security, the presence of the tweak enables a clean separation between inputs that need to be protected against leakage/faults and those that are insensitive. The arithmetization-oriented nature and choice of prime enable the effective utilization of masking schemes with superior passive and active attack resistance (e.g., prime-field and/or inner-product masking) and keep the design suitable for zero-knowledge applications. We compare higher-order masked software (Cortex-M4) and hardware (NanGate 15 nm) implementations of pSquare-hash to equivalent SHA-2, SHA-3, SKINNY-Hash, Ascon-Hash and Poseidon2 instances and exhibit favorable characteristics whenever masking is applied.

Shor's algorithm represents the main threat of quantum computers to cryptography. In order to precisely understand its feasibility, many authors have worked towards reducing its costs, either at the logical level (assuming a fault-tolerant architecture), or at the physical level (taking into account the constraints of envisioned hardware). In particular, recent works by Chevignard et al. (CRYPTO 2024) and Gidney (arXiv 2025) used improved arithmetic to significantly reduce the qubit cost of factoring RSA public keys.

Even more recently, Babbush et al. (arXiv 2026) improved the cost of computing elliptic curve discrete logarithms, with a reduction of a factor 2 to 3 in gate count and qubit count compared to a previous work by Litinski (arXiv 2023). Their result relies on optimized point addition circuits on elliptic curves over prime fields. However they did not reveal their logical quantum circuits, relying instead on a zero-knowledge proof.

In this paper, we detail a quantum logical circuit architecture which gives similar results as Babbush et al., with a slightly higher number of qubits (around 1.5% increase) and a slightly smaller Toffoli gate count (between 6.5% and 10% reduction) for the curve secp256k1. We also give gate counts for a generic variant of the circuit, which is valid for any prime field.

We explicitly construct and benchmark the first lattice-based IVC scheme from folding. The scheme supports customizable constraint systems over rings which we exploit to obtain proofs of correct execution of an FHE bootstrapping, a critical component of verifiable FHE. Notably and of independent interest, we introduce a novel CCS relation capable of performing automorphism stability checks which yields better expressivity for CCS over rings. We use this new relation to arithmetize the folding scheme verifier as well as TFHE's bootstrapping operation, and measure the performance of our folding scheme implementation on this arithmetization. Benchmarks indicate smaller proofs compared to the state of the art at the cost of a sharp increase in prover and verifier time. Lastly, we consider the security of folding-based IVC schemes with a super-constant number of recursive rounds and give an argument for the knowledge soundness of our construction in the ROM. Our work also discusses and highlights key open questions for future work, such as the design of hash functions over rings that permit efficient arithmetizations.

Pseudo-random correlation generators based on the Quasi-Abelian syndrome decoding problem were first attacked in an article published at Asiacrypt~2025, using compressed sensing. In this paper, we revisit the security of the problem using a more traditional cryptanalytic tool, namely correlation attacks.

As a result, we get a new cryptanalysis which outperforms the attack from Asiacrypt 2025 in several directions. It allows recovery of secret error polynomials with larger Hamming weights, runs approximately $1\,000$ times faster and uses $1\,000$ times less memory over $\mathbb{F}_3$. Over $\mathbb{F}_4$, the speed-up and memory gain are even higher.

Due to this new attack, it becomes necessary to entirely revisit the parameters of several pseudo-random correlation generator proposals, including FOLEAGE.

Threshold cryptography distributes trust among multiple parties by enabling joint cryptographic operations without reconstructing secret keys. While post-quantum signature schemes based on the MPC-in-the-Head (MPCitH) paradigm are highly generic, recent impossibility results show that their thresholdization either incurs prohibitive distributed symmetric computations or leads to signature sizes growing with the number of signers. Achieving practical tradeoffs in this setting remains challenging. In this paper, we propose a generic framework for threshold MPCitH signatures based on Merkle-tree commitments. Our approach adapts the PIOP+PCS paradigm to the distributed setting by introducing and instantiating the notion of threshold polynomial commitment schemes (TPCS). We present a generic compiler combining a PIOP, a TPCS, and an arithmetic black box into a threshold signature scheme, and prove its unforgeability from the security of its components. We further provide a concrete Merkle-tree-based TPCS achieving moderate signature-size overhead, as low as 200 bytes per signer at the 128-bit security level. This is to be compared with an overhead of roughly 2 kB per signer for the previously suggested approach to thresholdize MPC-in-the-Head based on GGM trees. By compiling this TPCS with a standard PIOP, we obtain a generic threshold signature scheme from any hard problem or one-way function, which we showcase MQ-based and AES-based instantiations.

Functional adaptor signatures (FAS) are a novel cryptographic primitive introduced at CCS'24 that enable privacy-preserving, fine-grained data-payment exchanges between a seller and a buyer in a trustless and atomic manner. In this setup, the seller holds sensitive data \(x\) (e.g., patient records, climate data), and the buyer specifies a function \(f\) (e.g., aggregate, sum). FAS guarantees that the buyer learns \(f(x)\) (and nothing beyond) if and only if the seller receives payment in blockchain-based tokens. Unlike generic smart contracts, FAS-powered solutions excel in privacy, efficiency, and compatibility with diverse blockchain systems. However, prior FAS constructions were limited to linear functions (where $f$ was linear in $x$), restricting their applicability to more complex and prevalent applications including data analytics and ML model evaluations.

In this work, we extend the capabilities of FAS to support higher-degree functions \((\textit{deg} \geq 2)\), significantly broadening its range of applications. Our core contribution is a novel FAS design leveraging homomorphic encryption, which simultaneously achieves enhanced efficiency and compatibility for general functions. This approach diverges fundamentally from the restricted design in CCS'24 which relied on connections to functional encryption. We implement our homomorphic encryption-based FAS for functions arising in applications such as data analytics and machine learning inference. Remarkably, even for linear functions, our new design achieves an order-of-magnitude improvement in performance compared to CCS'24 constructions. Furthermore, our solutions seamlessly integrate with prominent blockchain systems, requiring only a basic signature verification script on standard transactions, thus ensuring practical deployability. As a conceptual contribution, we introduce the general paradigm of a blockchain-based functional fair exchange (FFE) protocol, rigorously define buyer and seller fairness, and show that FAS implies the general goal of FFE.

Cryptocurrency lending is growing rapidly, and smart-contract-based loans are expected to grow further. However, existing systems are fundamentally limited: they only operate on smart-contract-enabled blockchains, and assets from other blockchains can be used only via tokenized representations.

In this work, we propose an oracle-aided cryptographic protocol that implements the logic of collateralized loans without smart contracts, instead only requiring basic transactions from the underlying blockchain and hence, being compatible with limited-scripting blockchains, including Bitcoin.

For that, we introduce verifiable graph encryption for signatures (VGES), a new cryptographic primitive that, on input a graph modeling the correspondence between transactions for collateral distribution (vertices) and loan repayments (edges), permits to encrypt the signatures on collateral-distribution transactions ensuring: (1) a signature can only be decrypted after completing loan repayments corresponding to a valid path in the graph from the root (graph enforcement); and (2) anyone can verify that encrypted signatures are valid and can be decrypted after doing the required loan repayments according to the graph (verifiability).

We present two provably secure constructions of VGES and the evaluation of our implementation shows that they offer a tradeoff between the number of required on-chain transactions and off-chain computation, while both remain efficient on commodity hardware.

The concrete security of multivariate post-quantum signature schemes is coming under increasing scrutiny as the NIST standardisation process for additional signatures approaches its final stages. Among the leading candidates, the security of MAYO and QR-UOV relies on the hardness of the underdetermined multivariate quadratic (MQ) problem. This work revisits Hashimoto's algorithm for solving underdetermined systems of MQ equations, reinterpreting it as a computation of a pseudo-oil subspace. In light of this geometric point of view, we design a new algorithm that, by computing richer pseudo-oil structures, distributes algebraic work across more than two Gröbner Basis steps, subdividing the initial MQ problem into multiple subproblems that can be solved separately, while linearising multiple equations. Optimising a set of discrete parameters, we select the best trade-off between algebraic solving and combinatorial search. Concretely, our approach lowers the cost of the direct attack against Security Level I parameter sets of MAYO and QR-UOV by 8 and 10 bits, respectively.

A robust combiner for a cryptographic primitive $P$ takes multiple candidate constructions of $P$ and produces a secure construction of $P$ provided that sufficiently many of the candidates are secure. A closely related notion is that of a security amplifier, where given a weakly secure construction of $P$, we aim to obtain a (strongly) secure one. Intuitively, one may expect that any robust combiner should act as an amplifier by thinking of "good randomness" as inducing secure instances, and of "bad randomness" as inducing insecure instances. Formalizing this intuition, however, has turned out to be challenging. Despite significant progress, general results remain limited and confined either to specific primitives or only to the statistical setting.

We establish a new framework of robust indistinguishability combiners, which greatly extends the class of combiners covered by prior work, and prove that they inherently act as security amplifiers. Our results extend to the computational setting, provided that the combiner makes a single query to each candidate. The new framework allows us to rederive previously known amplification results in a simplified manner, as well as prove new amplification results that have so far been out of reach.

As our main application, we present the first security amplifier for functional encryption, resolving an open question that first arose in constructions of indistinguishability obfuscation, and for which a gap was discovered in previous proofs. Our amplifier transforms a weak scheme with any constant indistinguishability error into one with full negligible security.

The SHA-2 family is a U.S. federal standard and mainly includes SHA-256 and SHA-512. In particular, SHA-256 plays a central role in real-world applications and is widely regarded as one of the most important hash functions in use today. At CRYPTO 2026, Li et al. proposed collision attacks up to 37-step SHA-2, but they could not reach 38 steps due to the low-probability uncontrolled part in the corresponding differential characteristics. In this paper, we propose an improved search procedure to find high-quality differential characteristics for 38-step SHA-256 and SHA-512, respectively. Exploiting the special shape of the 38-step differential characteristics, the meet-in-the-middle method to fulfill the corresponding differential conditions is extremely memory-efficient. Consequently, we successfully achieve the first 38-step collision attack on both SHA-256 and SHA-512, whose time complexity is $2^{104.3}$ and $2^{125.4}$, respectively. The memory complexity of the 38-step collision attack is negligible. The methods are also applied to the 36-step and 37-step collision attacks on SHA-2 published at CRYPTO 2026, leading to a significant improvement in both time and memory complexity. In particular, the time complexity of the collision attack on 36-step SHA-256 is only $2^{58.1}$ and the memory complexity is negligible, implying that a practical collision can be found. More remarkably, we apply the new method to 39 steps of SHA-2 and obtain the first effective collision attack on 39-step SHA-512, with a time complexity of $2^{178}$ and negligible memory complexity. However, the method does not yield an effective collision attack on 39-step SHA-256 due to the same issue arising from the low-probability uncontrolled part. Overall, this work further pushed the limit of memory-efficient collision attacks on round-reduced SHA-2 and significantly advances the state of the art.

Pre-constructed Publicly Verifiable Secret Sharing (PPVSS) extends conventional Publicly Verifiable Secret Sharing (PVSS) by requiring the dealer to publish a commitment or encryption of the shared secret, enabling more efficient and versatile constructions for a variety of cryptographic protocols. In this paper, we further enhance this paradigm by introducing Packed Pre-constructed PVSS (3PVSS), which allows a dealer to encode multiple secrets within a single polynomial while maintaining the pre-constructability property. We present two constructions of 3PVSS schemes. In the first construction, the dealer publishes a single commitment to all shared secrets, providing a compact representation that is particularly suitable for applications requiring efficient communication. In the second construction, the dealer publishes individual commitments to each secret, enabling greater flexibility in applications that require independent verification of multiple shared values. Both schemes preserve the key advantages of PPVSS, including the optimistic reconstruction approach enabled by pre-constructability. We demonstrate that these two variants naturally support different applications. Using the first 3PVSS construction, we revisit the ALBATROSS randomness generation protocol proposed by Cascudo and David (ASIACRYPT 2020) and present a more efficient variant with reduced computation and communication costs. As an application of the second construction, we extend the universally verifiable e-voting protocol recently proposed by Baghery, Knapen, Nicolas, and Rahimi (ACNS 2025) to support multi-candidate elections, while preserving universal verifiability. Our results show that the resulting protocols outperform their original counterparts in terms of efficiency.

This paper introduces AuditPay, a novel mechanism for blockchain mixers that enables controlled oversight through an ``auditing budget.’’ Auditors may monitor up to a budgeted number of addresses per epoch (e.g., an hour or a day), without revealing to users which addresses are monitored. Unlike traditional approaches that require users to voluntarily disclose viewing keys to trusted gatekeepers, AuditPay cryptographically enforces auditing compliance while preserving privacy for non-monitored user addresses and without introducing additional trust assumptions.

At the core of AuditPay’s design is a selective encryption mechanism coupled with an efficient audit-key encoding scheme, enforced by a lightweight zero-knowledge proof. Users encrypt audit-relevant information under an audit key, which permits decryption only if the payment is to (or, alternatively, from) an address selected by the auditor for monitoring.

We implement AuditPay as an Ethereum-based payment mixer and show through experiments on our prototype that its performance and gas-cost overheads are modest, providing a practical solution for balancing payment oversight with user privacy.

ML-KEM (FIPS 203) draws a fresh 32-byte coin at each encapsulation. The shared secret is a deterministic function of the public key and this coin, so a known coin is a recovered key. This is elementary. We ask instead how well the coin's secrecy is protected in practice, and we answer by experiment. On six unmodified libraries (OpenSSL 3.5, wolfSSL 5.9, AWS-LC, Go 1.26, Bouncy Castle 1.83, and CIRCL), and a from-scratch reference, the coin-recovery is reachable in every one; what differs is the guard, from a test-walled package in Go to an ordinary production call in wolfSSL. A second path needs no injection function at all: substituting the generator at build time makes the ordinary encapsulation predictable, while the public re-seed interface correctly refuses to. Outside the validated FIPS-140-3 configuration that most deployments do not yet use, the coin's secrecy rests on convention, not construction. The predictability this permits is externally invisible and parameter-controlled, of the class shown once before in Dual_EC_DRBG. We claim no backdoor; we claim only that the door is reachable, and say so while it is still being closed.

One of the main hallmarks of proof-of-work (PoW) consensus protocols is their ability to adjust the difficulty of the PoW, so that it accurately reflects the level of participation and hence maintains security in a setting where protocol participation is unknown and may over time change dramatically. Importantly, this enables the protocol to retain its fundamental characteristics (such as the regularity of dispensing new tokens) irrespectively of the number of parties running the protocol (also known as ``miners'') at any given time.

The speed with which difficulty can be adjusted is a fundamental feature of a blockchain protocol: The faster the rate with which the difficulty is adjusted, the more agile the protocol is in the face of fluctuating participation. In this work, we put forward, for the first time, a blockchain protocol that performs difficulty adjustment in constant time; prior provably secure designs only offered protocols with, at best, poly-logarithmic overhead for difficulty adjustment. Our construction is based on the parallel-chain approach and a new target recalculation function that adjusts mining difficulty making use of information from all chains in the past epoch via a novel application of approximate-agreement techniques that may be of independent interest.

Tweakable block ciphers are important cryptographic primitives for secure memory encryption and partial mitigation of bit flip attacks. Rapid advancements in data-intensive applications such as artificial intelligence and machine learning have motivated the development of new memory technologies with very large data bus widths requiring wide-block memory encryption and its efficient implementation. Recently, the MATTER family of wide-block tweakable ciphers has been proposed for memory encryption in emerging applications. MATTER is a 512-bit balanced Feistel construction which uses the light-weight ASCON permutation as its round function. In this work, we present a comprehensive design space exploration of hardware architectures for accelerating different configurations of MATTER. We provide a detailed comparative analysis of power, performance, area and energy of round-based, unrolled and pipelined hardware implementations of MATTER based on digital synthesis using a 7nm FinFET ASIC standard cell library. We also discuss the suitability of these architectures for different application-specific memory encryption hardware requirements in emerging edge computing systems.

We give several examples of families of polynomials $p_1, ... , p_t \in \mathbb R[x_1, ... , x_n]/\langle x_i^d - 1\rangle_i$ on which the Low-Norm Nullstellensatz Hypothesis of [Devadas-Hopkins-Kalai-Kothari-Lombardi-Mathialagan, STOC 2026] fails to hold. That is, we prove the existence of polynomials $f \in \langle p_1, ... , p_t\rangle$ with coefficient $L^1$ norm $||f||_1 = 1$ but such that every decomposition $f = \sum_i p_i \cdot q_i$ has cost $\sum_i ||q_i||_1 = 2^{\Omega(n)}$. Our examples include one with $d=2$, the regime originally studied by [Devadas et al.], as well as generalizations that would also have sufficed for their purposes.

Our counterexamples highlight an important class of polynomials for (potentially) falsifying the LNNH: for prime $d$, functions $f(x) = f_C(x)=\frac 1 {|C|}\sum_{c\in C} x^c$ that are indicator functions for the input $x \in \mu_d^n\simeq \mathbb Z_d^n$ belonging to a linear subspace $C^\bot \subset \mathbb Z_d^n$, or more generally a coset $C^\bot + \sigma$.

Proxy re-encryption (PRE) enables a semi-trusted proxy to transform a ciphertext under one key into a ciphertext decryptable under another key without learning the underlying plaintext. Existing lattice-based PRE schemes that achieve security against honest re-encryption attacks (HRAs) typically rely on noise flooding during re-encryption to statistically hide dependencies on the original ciphertext and the re-encryption key. However, noise flooding substantially increases ciphertext noise and often causes significant parameter growth.

In this work, we present a single-hop owner-encrypted proxy re-encryption (oePRE) scheme that achieves HRA security without statistical noise flooding. In the owner-encrypted setting, ciphertexts are generated directly by the data owner using her secret key, resulting in a simpler noise structure that facilitates efficient re-encryption. Instead of statistically hiding the inherited ciphertext noise, our construction introduces a small deterministic padding error and relies on computational leakage masking.

To formalise this approach, we introduce the noisy error-leakage LWE (NEL-LWE) assumption, which models the hardness of distinguishing LWE samples given a noisy version of the error term. We show that NEL-LWE follows from the recent Leaky-LWE framework of Lai, Swarnakar, and Woo (CiC'25). We further define computational re-encryption simulatability for owner-encrypted PRE and prove that our BGV-style construction achieves HRA security under standard LWE and PRF assumptions.

Compared with flooding-based HRA-secure lattice PRE schemes, our approach requires only a small additional padding noise and therefore remains much closer to the parameter regime of the underlying IND-CPA-secure construction. Our work demonstrates that computational leakage masking provides a viable alternative to statistical noise flooding for practical single-hop lattice-based proxy re-encryption.