Verifiable Databases (VDBs) allow clients to outsource data storage without trusting the provider: a client holding only a short digest can verify any query response using a compact server-provided proof. Given the ubiquity of both databases and outsourced storage, VDBs address a fundamental need. Our work advances the state of the art in VDB design. Our main contribution is $\mathsf{qedb}$, a simple and performant construction for SQL queries based on bilinear pairings. Like some prior VDB schemes, $\mathsf{qedb}$ leverages features specific to the database setting; however, it differs from such approaches in its technical blueprint, the breadth of supported queries, and performance. Notably, it is the first scheme of its kind with proof size independent of database size and without quadratic scaling for storage or preprocessing. Compared to VDB solutions based on general-purpose proofs, $\mathsf{qedb}$ offers stronger tradeoffs in at least one of the following: provable security, proof size and verification time, or system complexity and maintainability (over an order of magnitude fewer lines of code). As additional contributions, we provide both an implementation of $\mathsf{qedb}$ and new theoretical foundations for VDB design—a new framework modeling $\textit{idealized}$ protocols for verifiable databases, which future works can use in a plug-and-play manner. Through our modular approach we can get more provably secure instantiations of $\mathsf{qedb}$ $\textit{for free}$, including a post-quantum one from lattices.

Fully Homomorphic Encryption (FHE) and Post-Quantum Cryptography (PQC) involve polynomial multiplications, which are a common performance bottleneck. To resolve this bottleneck, polynomial multiplications are often accelerated in hardware using the Number-Theoretic Transformation (NTT) or the Fast Fourier Transformation (FFT). In particular, NTT operates over modular rings while FFT operates over complex numbers. NTT and FFT are widely deployed in applications with diverse parameter sets, leading to long design times for hardware accelerators. Existing hardware generation tools have limited functionality since they do not support generic on-the-fly twiddle factor generation or different memory-related optimizations. This paper improves the hardware design process and presents a generic and flexible tool to generate FFT and NTT architectures. In contrast to prior work, we combine on-the-fly twiddle factor generation and stall-free memory accesses. Moreover, we enhance hardware design flexibility through memory-optimized or routing-optimized design strategies. While our memory-optimized strategy minimizes twiddle factors in ROM, our routing-optimized strategy allows significantly higher clock frequencies on FPGAs. These optimization strategies allow effective customization of NTT/FFT architectures, spanning from low-end PQC to high-end FHE accelerators. Compared to existing works, we reach up to 15.9x lower latency and up to 7.4x improved ATP for FFT applications such as the Falcon signature scheme. Considering other NTT tools, we decrease latency by up to 1.8x and 2x for PQC and FHE parameter sets, respectively.

In this work, we study the communication complexity of MPC achieving perfect security with optimal resilience ($t<n/3$). We ask the question: ``Is it possible to build a perfectly secure MPC for arithmetic circuits of size $|C|$ with optimal resilience with communication of $o(|C|\cdot n)$ field elements?'' On the positive side, we construct a perfectly secure MPC protocol for general arithmetic circuits with communication complexity of $O(|C|)$ elements assuming preprocessing data of size $O(|C|)$, where the preprocessing data consists of packed Beaver triples over bivariate polynomials. Furthermore, we show that packed Beaver triples over bivariate polynomials can be prepared at an amortized cost of $O(1)$ elements plus $O(1)$ three-party Beaver triples per secret. On the negative side, we establish a communication lower bound proving that preparing packed Beaver triples over bivariate polynomials requires at least $\Omega(n)$ elements of communication per secret. This lower bound is derived by first proving a communication lower bound for verifying the correctness of packed Beaver triples with perfect security with abort, and then efficiently reducing the task of verifying packed Beaver triples to preparing packed Beaver triples over bivariate polynomials. To match this bound, we give a concrete construction for preparing packed Beaver triples over bivariate polynomials with $O(n)$ elements per secret, demonstrating the tightness of our lower bound. Our proof technique also extends to show that for the task of computing the inner-product of two length-$|C|$ vectors, any MPC protocol that achieves perfect security with abort requires either $\Omega(|C|\cdot n)$ elements of communication or $\Omega(|C|)$ elements of preprocessing data.

Common blockchain protocols are monolithic, i.e., their security relies on a single assumption, e.g., honest majority of hashing power (Bitcoin) or stake (Cardano, Algorand, Ethereum). In contrast, so-called optimistic approaches (Thunderella, Meshcash) rely on a combination of assumptions to achieve faster transaction liveness. We revisit, redesign, and augment the optimistic paradigm to a tiered approach. Our design assumes a primary (Tier 1) and a secondary (Tier 2, also referred to as fallback) blockchain, and achieves full security also in a tiered fashion: If the assumption underpinning the primary chain holds, then we guarantee safety, liveness and censorship resistance, irrespectively of the status of the fallback chain. And even if the primary assumption fails, all security properties are still satisfied (albeit with a temporary slow down) provided the fallback assumption holds. To our knowledge, no existing optimistic or tiered approach preserves both safety and liveness when any one of its underlying blockchain (assumptions) fails. The above is achieved by a new detection-and-recovery mechanism that links the two blockchains, so that any violation of safety, liveness, or censorship resistance on the (faster) primary blockchain is temporary—it is swiftly detected and recovered on the secondary chain—and thus cannot result in a persistent fork or halt of the blockchain ledger. We instantiate the above paradigm using a primary chain based on proof of reputation (PoR) and a fallback chain based on proof of stake (PoS). Our construction uses the PoR and PoS blockchains in a mostly black-box manner—where rather than assuming a concrete construction we distill abstract properties on the two blockchains that are sufficient for applying our tiered methodology. In fact, choosing reputation as the resource of the primary chain opens the door to an incentive mechanism—which we devise and analyze—that tokenizes reputation in order to deter cheating and boost participation (on both the primary/PoR and the fallback/PoS blockchain). As we demonstrate, such tokenization in combination with interpreting reputation as a built-in system-wide credit score, allows for embedding in our two-tiered methodology a novel mechanism which provides collateral-free, multi-use payment-channel-like functionality where payments can be instantly confirmed.

Message dissemination is a fundamental building block in distributed systems and guarantees that any message sent eventually reaches all parties. State of the art provably secure protocols for disseminating messages have a per-party communication complexity that is linear in the inverse of the fraction of parties that are guaranteed to be honest in the worst case. Unfortunately, this per-party communication complexity arises even in cases where the actual fraction of parties that behave honestly is close to 1. In this paper, we propose an optimistic message dissemination protocol that adopts to the actual conditions in which it is deployed, with optimal worst-case per-party communication complexity. Our protocol cuts the complexity of prior provably secure protocols for 49% worst-case corruption almost in half under optimistic conditions and allows practitioners to combine efficient heuristics with secure fallback mechanisms.

In fully homomorphic encryption, bootstrapping serves as a key component while also remaining the performance bottleneck of the scheme. Specifically, for CKKS bootstrapping, this bottleneck is reflected in significant computational overhead and modulus consumption. In this work, we improve the CKKS bootstrapping with lower time complexity and less modulus consumption. We first propose a novel rescaling operation, called level-conserving rescaling, that acts on CoeffsToSlots for saving moduli. Secondly, we reconstruct the rotation keys and merge the plaintext-ciphertext multiplication and rescaling operations into the key-switching procedure, which reduces the time complexity of matrix-vector multiplication for matrices with $\le$64 non-zero diagonals, albeit with increased space overhead. By combining the two methods in CoeffsToSlots in a non-trivial manner, we not only further accelerate the homomorphic linear transformations and save one level of moduli, but also reduce the total size of rotation keys. Experiments demonstrate the practicability of our techniques. Compared to the state of the art, our approaches save one level of moduli, achieving a $20\%\sim 35\%$ improvement in bootstrapping throughput and an 11.9\% $\sim$ 15.2\% reduction of rotation key size in CoeffsToSlots. Furthermore, with sufficient storage, our technology achieves up to 40\% higher bootstrapping throughput than before, at the cost of doubling the rotation key size in CoeffsToSlots. The bootstrapping precision and failure probability remain identical to the previous method.

The Syndrome Decoding Problem (SDP) underpins the security of most code-based cryptographic schemes, and Information Set Decoding (ISD) algorithms are the fastest known solvers for most parameter sets. While ISD is well developed in the binary setting, the landscape for non-binary ISD is less mature. Most $q$-ary methods are straightforward generalizations of their binary counterparts, with the recent projective Stern algorithm being the only exception. However, no existing algorithm is designed to leverage the specific algebraic properties of extension fields. This research gap -- highlighted by the first-round NIST PQC proposal SDitH -- motivates our central question: is decoding over an extension field fundamentally easier than over a prime field of similar size? This work explores whether the algebraic structure of extension fields can accelerate ISD. We analyze several techniques for translating the SDP to the base field, including the expansion map, subfield subcodes, and the trace map. We also develop new BJMM variants that restrict base list vectors to “small” field elements, aiming to counter the performance loss of advanced ISD when $q$ is large. Contrary to our initial intuition, our results provide no evidence of an asymptotic speedup, suggesting that decoding over extension fields is not easier than over prime fields. Additionally, we make two contributions of independent interest: we show that a three-level BJMM algorithm gives a slight improvement over the two-level version for small fields, and we extend Meurer’s proof to show that the complexity of advanced ISD algorithms converges to Prange’s, even when parameters grow simultaneously.

In this paper, we present a simple meet-in-the-middle attack that requires low data and memory resources. To evaluate the complexity of the attack, we also propose an automated tool that calculates the time, data, and memory complexities based on the suggested matching points. Our method operates at the bit level and employs a known-plaintext attack, with no constraints on the attacker's choice of data. We apply our tool on various lightweight block ciphers, including CRAFT, Midori, WARP, PRESENT, and ARADI. For CRAFT, our tool successfully identified an attack targeting 15 rounds using 3 known plaintexts. In the case of Midori64 and Midori128, the tool proposed attacks on 5 rounds with 16 known plaintexts and 7 rounds with 3 known plaintexts, respectively. For WARP, the tool discovered an attack on 18 rounds utilizing 7 known plaintexts. Additionally, for PRESENT80, the tool identified an attack on 6 rounds with 18 known plaintexts, and for ARADI, an attack on 5 rounds with 28 known plaintexts was determined.

The paper defines a novel type of consensus for a distributed smart contract system, named RGB, which is based on the concept of client-side validation, separating the contract state and operations from the blockchain. With this approach, contracts are sharded (each contract is a standalone shard), kept, and validated only by contract participants, providing native scalability and privacy mechanisms, exceeding all existing blockchain-based smart contract systems while not compromising on security or decentralization. The system is designed to operate on top of compatible layers 1, such as an UTXO-based blockchain (e.g., Bitcoin) without relying on it for transaction ordering or state replication. Instead, RGB keeps the state client-side, operating as partially replicated state machines (PRiSM). It employs a novel SONIC (State machine with Ownership Notation Involving Capabilities) architecture, which provides capability-based access control to the contract state, individually owned and operated by a well-defined contract parties via novel single-use seal mechanism. RGB does state validation using zk-AluVM virtual machine, designed to support zk-STARK provers. It has a single security assumption of the collision-resistance hash function and, thus, is quantum-secure. The proposed RGB consensus is distinct from traditional blockchain-based smart contract systems; it is scalable, provably-secure, and formally verifiable.

KEM-to-PAKE compilers have been recently proposed to leverage post-quantum KEM standardization efforts. These typically follow the Encrypted Key Exchange (EKE) paradigm, where the KEM public key is encrypted under a password. While KEM implementations generally aim to execute all secret-dependent computations in constant time, such guarantees do not always extend to computations that depend only on the public key, as public keys are generally assumed to be public. A notable example is ML-KEM, where public keys include a short seed from which a large matrix is expanded prior to algebraic computations. This expansion procedure relies on rejection sampling which is, typically, implemented as a variable-time algorithm. However, compilers that follow the EKE paradigm must treat the public key as secret, since knowledge of the public key hidden in a ciphertext enables an offline dictionary attack on the password; therefore, instantiating these compilers with off-the-shelf implementations of ML-KEM or encrypting the public key under a password using variable-time methods (e.g., cycle walking or rejection sampling, as proposed in related PAKE literature) can be problematic. In this paper we show two approaches which yield ML-KEM-based PAKEs resilient to timing attacks. First, we explore constant-time alternatives to ML-KEM rejection sampling, but as one might expect, such methods impose a performance penalty on ML-KEM. Our second approach introduces a new ML-KEM-to-PAKE compiler that mitigates this issue by design: our proposal transmits the seed in the clear, decoupling password-dependent computations from the seed expansion step. This means that off-the-shelf implementations of ML-KEM can be used. Our new protocol Tempo builds on an idea from CHIC (Asiacrypt'24), which considered splitting the KEM public key, and extends the NoIC protocol and proof (ePrint:2025/231) to show protocol simulation in the UC framework, assuming ML-KEM security under adversarially chosen seeds. We justify this assumption via a new hardness assumption, which we call Oracle-MLWE, and show that it is asymptotically equivalent to the MLWE problem in the Random Oracle Model.

The advent of quantum computing threatens the security assumptions underpinning classical public-key cryptographic algorithms such as RSA and ECC. As a response, the cryptographic community has focused on developing quantum-resistant alternatives, with hash-based signature schemes emerging as a compelling option due to their reliance on well-understood hash functions rather than number-theoretic hardness assumptions. This paper presents a comprehensive review of hash-based signature schemes, covering the foundational building blocks (Lamport signatures, Winternitz one-time signatures, Merkle trees, and FORS) as well as the three standardized constructions: XMSS (RFC 8391), LMS (RFC 8554), and the stateless SPHINCS+ (FIPS 205 / SLH-DSA). A systematic comparison highlights the trade-offs between statefulness, signature size, and implementation complexity. Furthermore, the paper analyzes several notable cryptanalytic attacks, examining for each the attack model, applicable constructions, complexity, and known countermeasures. By discussing both their strengths and vulnerabilities, this work provides a unified reference for understanding the design landscape of hash-based signatures as practical candidates for post-quantum digital signatures.

In this work, we present a comprehensive analysis of QSF, the KEM combiner used by X-Wing (Communications in Cryptology 1(1), 2024). While the X-Wing paper focuses on the application of QSF to ML-KEM-768 and X25519, we discuss the combiner’s applicability to other post-quantum KEMs and ECDH instantiations. Particularly, we establish the compatibility of QSF to KEMs based on variants of the Fujisaki-Okamoto transform by proving ciphertext second-preimage resistance (C2PRI) for these variants. Building on these results, we show that QSF is compatible with, to the best of our knowledge, all post-quantum KEMs currently standardized or considered for standardization—including ML-KEM, (e)FrodoKEM, HQC, Classic McEliece, and various NTRU variants. Notably, this means these schemes can be used with QSF to construct PQ/T hybrid KEMs. In addition, we introduce QSI, a variant of QSF that combines two KEMs by hashing their shared keys, yielding a KEM that is IND-CCA-secure as long as one constituent KEM is IND-CCA-secure and the other is C2PRI-secure. We establish the same compatibility results for QSI as for QSF. Finally, we analyze both QSF and QSI regarding (their preservation of) the recently introduced family of binding properties for KEMs.

Let $N = pq$ be the product of two balanced prime numbers $p$ and $q$. In 2023, Cotan and Te\c seleanu introduced a family of RSA-like cryptosystems based on the key equation $ed - k(p^n - 1)(q^n - 1) = 1$, where $n \geq 1$. Note that when $n = 1$, we obtain the classical RSA system, while $n = 2$ yields the variant proposed by Elkamchouchi, Elshenawy, and Shaban. In this paper, we present a novel attack that combines continued fractions with lattice-based methods for the case $n = 6$. This represents a natural continuation of previous research, which successfully applied similar techniques for $n = 1, 2, 4$.

In smart grid (SG), key agreement protocols (KAPs) are used as one of the most prevalent means to establish secure data transmission channels between smart meters (SMs) and service providers (SPs). Quite recently, Wu et al. have indicated the vulnerability of Hu et al.'s KAP to key compromise impersonation (KCI) attack and proposed a security-enhanced one for secure communications of SMs and SPs in SG. Not to undermine the noteworthy contributions of their work, this comment demonstrates that their own KAP, i.e., Wu et al.'s scheme is still vulnerable to KCI attack. Accordingly, we suggest a simple modification to fix the KCI attack issue. Our attack procedure gives some delicate hints to scholars to protect their schemes against the KCI attack in future researches.

An important requirement in synchronous protocols is that, even when a party receives all its messages for a given round ahead of time, it must wait until the round officially concludes before sending its messages for the next round. In practice, however, implementations often overlook this waiting requirement. This leads to a mismatch between the security analysis and real-world deployments, giving adversaries a new, unaccounted-for capability: the ability to ``peek into the future.'' Specifically, an adversary can force certain honest parties to advance to round $r+1$, observe their round $r+1$ messages, and then use this information to determine its remaining round $r$ messages. We refer to adversaries with this capability as ``super-rushing" adversaries. We initiate a study of secure computation in the presence of super-rushing adversaries. We focus on understanding the conditions under which existing synchronous protocols remain secure in the presence of super-rushing adversaries. We show that not all protocols remain secure in this model, highlighting a critical gap between theoretical security guarantees and practical implementations. Even worse, we show that security against super-rushing adversaries is not necessarily maintained under sequential composition. Despite those limitations, we present a general positive result: secret-sharing based protocols in the perfect setting, such as BGW, or those that are based on multiplication triplets, remain secure against super-rushing adversaries. This general theorem effectively enhances the security of such protocols ``for free.'' It shows that these protocols do not require parties to wait for the end of a round, enabling potential optimizations and faster executions without compromising security. Moreover, it shows that there is no need to spend efforts to achieve perfect synchronization when establishing the communication networks for such protocols.

In this paper we introduce a rank $2$ lattice over a polynomial ring arising from the public key of the BIKE cryptosystem. The secret key is a sparse vector in this lattice. We study properties of this lattice and generalize the recovery of weak keys from "Weak keys for the quasi-cyclic MDPC public key encryption scheme". In particular, we show that they implicitly solved a shortest vector problem in the lattice we constructed. Rather than finding only a shortest vector, we obtain a reduced basis of the lattice which makes it possible to check for more weak keys.

This paper presents FLEX (Fraud proofs with Lightweight Escrows for eXits), a garbled circuit-based protocol designed to facilitate two-party disputes on Bitcoin without requiring permanent security bonds. FLEX enables conditional security deposits that are only activated in the event of a dispute, reducing the financial overhead for both parties. The main goal of FLEX is to improve the capital efficiency of BitVM-based bridges in a permissioned challenge setting but can also be used to improve the security of any other fraud proof-based protocol such as payment channels. The paper also introduces enhancements that allow faster reimbursements in scenarios where one party's node is unavailable, while preserving security and minimizing race conditions.

We introduce the \(Inverse\ Discrete\ Logarithm\ Problem\) (iDLP) framework, which inverts traditional discrete logarithm assumptions by making the exponent public but deliberately non-invertible modulo the group order, while hiding the base. This creates a many-to-one algebraic mapping that is computationally infeasible under both classical and quantum attack models. Within this framework, we define three post-quantum cryptographic primitives: Inverse Discrete Diffie–Hellman (IDDH), Inverse Discrete Key Encapsulation (IDKE), and Inverse Discrete Data Encapsulation (IDDE). Using a 512-bit modulus (prime or semiprime), a random generator \( g \), and a public exponent \( y \) with \(\gcd(y, \varphi(m)) = d\), the masking function \[ \mathsf{Mask}_{g,y}(x) := g^{x y} \bmod m \] induces a many-to-one mapping that renders discrete logarithm inversion infeasible. Our security analysis shows that known quantum algorithms yield only multiple candidates, requiring exhaustive search among equivalence classes, which remains intractable at 512-bit parameters. We demonstrate efficient prototype implementations with sub-millisecond key operations and AES-GCM-level data throughput. Full source code and parameters are publicly available at \url{https://github.com/AdamaSoftware/InverseDiscrete/}.

Zero-knowledge rollups represent a critical scaling solution for Ethereum, yet their practical deployment faces significant challenges in on-chain verification costs. This paper presents a comprehensive implementation of the Tokamak zkEVM verifier, specifically optimized for the BLS12-381 elliptic curve operations introduced by EIP-2537. We detail the complete verification architecture, from EVM compatible data formatting for pairing checks, multi-scalar multiplication (MSM), and elliptic curve addition, to the non-interactive protocol design between prover and verifier. Our key contribution lies in novel optimization techniques that substantially reduce on-chain verification costs. Through strategic polynomial aggregation and scalar factorization, we minimize G1 exponentiations from 40 to 31, achieving gas savings of 108,000 units per verification. Additionally, we introduce a dynamic barycentric interpolation method that replaces computationally intensive FFT operations, resulting in 92-95% gas reduction for sparse polynomial evaluations. We further present proof aggregation strategies that minimize precompile calls while maintaining the 128-bit security guarantees of BLS12-381. Our implementation demonstrates that careful protocol design and mathematical optimizations can make zk-rollup verification economically viable on Ethereum. The techniques presented are compatible with the upcoming Pectra upgrade and provide a blueprint for efficient on-chain verification of complex zero-knowledge proofs. Experimental results show total gas costs reduced from 857,200 to 748,450 units for complete proof verification, making our approach practical for high-throughput rollup deployments.

Human verification under adversarial information flow operates as a cost-bounded decision procedure constrained by working memory limits and cognitive biases. We introduce the Verification Cost Asymmetry (VCA) coefficient, formalizing it as the ratio of expected verification work between populations under identical claim distributions. Drawing on probabilistically checkable proofs (PCP) and parameterized complexity theory, we construct dissemination protocols that reduce verification for trusted audiences to constant human effort while imposing superlinear costs on adversarial populations lacking cryptographic infrastructure. We prove theoretical guarantees for this asymmetry, validate the framework through controlled user studies measuring verification effort with and without spot-checkable provenance, and demonstrate practical encoding of real-world information campaigns. The results establish complexity-theoretic foundations for engineering democratic advantage in cognitive warfare, with immediate applications to content authentication, platform governance, and information operations doctrine. We are concerned not with verifying ground truth, but with verifying provenance—the integrity of the chain of custody from source to receiver. Our protocols allow a user to efficiently check that a bundle of information is authentic and has not been tampered with, even though the underlying claims may still be right or wrong in substance.

Collaborative zkSNARKs, proposed by Ozdemir and Boneh in 2022, allow a prover to delegate the generation of zkSNARK proofs to multiple servers, without compromising the confidentiality of the secret witness. They enable the use of zkSNARK techniques on computational limited devices in critical applications such as blockchains. However, the running time of each server is at least as slow as computing the proof on a single server. Garg et al. attempted to improve the efficiency in their scheme named zkSaaS using packed secret sharing, but the scheme still requires a powerful central server with linear computation, communication and memory usage. In this paper, we propose a new collaborative zkSNARK scheme with $O(\frac{C}{n}\log\frac{C}{n})$ prover time and $O(1)$ proof size with $n$ servers for a circuit of size $C$. An adversary compromising less than $\frac{n}{4}$ servers cannot learn any information about the witness. The core of our technique lies in a new zkSNARK scheme for the Plonkish constraint system that is friendly to packed secret sharing. We utilize bivariate polynomials to avoid a large Fast Fourier Transform on the entire witness, which was the major bottleneck in prior work. We also construct permutation constraints based on logarithmic derivatives and univariate sumcheck to avoid the computation of prefix products. Finally, we build a bivariate polynomial commitment scheme that can be computed directly on packed secret shares. Experimental results show that for a circuit of size $2^{20}$, with 128 servers, our scheme can accelerate the proof generation by 36.2$\times$ compared to running the zkSNARK on a single server. The prover time of our system is 25.9$\times$ faster than the prior work of zkSaaS. The proof size of our scheme is only 960 Bytes.

The final exponentiation is a crucial step in pairing computations, ensuring cor- rectness and uniqueness of results in pairing-based cryptographic protocols. In this work, we propose an efficient method for computing the hard part of the final exponentiation on BW10-511, BW14-351 and BLS12 curves at 128 bits security level. Our approach reduces the computation cost by optimizing the exponenti- ation sequence and minimizing the number of required multiplications through an improved addition chain strategy. The computation cost of our method for the final exponentiation on these curves is about 25.6%, 33.2% and 10% faster than the previously fastest result on BW10-511, BW14-351 and BLS12 curves respectively. The correctness of our formulas has been verified by a Magma code.

Strong asymmetric password-authenticated key exchange (saPAKE) is the gold standard for password-based authentication. When authenticating using saPAKE, the client holds a cleartext password, and the server holds only a "digest" of the password. The two parties obtain a shared session key if and only if the client password matches the password encoded in the digest. In this work we initiate the study of strong asymmetric fuzzy PAKE (safPAKE), which allows the client and server to obtain a shared session key if the client's password is "close enough" to the password encoded in the digest, according to some policy. safPAKE can be used to tolerate incidental password typos in the PAKE setting, which is becoming a standard industry practice outside the PAKE setting. Our safPAKE functionality supports any "typo policy", and our protocol is practical when there are a small number of permissible mistypings of a password.

Protection of biometric templates is a critical and urgent area of focus. \textbf{IronMask} demonstrates superior recognition performance while protecting facial templates against existing known attacks. In high-level, IronMask can be conceptualized as a fuzzy commitment scheme building on the hypersphere directly. We devise an attack on IronMask targeting on the security notion of renewability. Our attack, termed as \textbf{Probabilistic Linear Regression Attack}, utilizes the linearity of underlying used error correcting code. This attack is the first algorithm to successfully recover the original template when getting multiple protected templates in acceptable time and requirement of storage. We implement experiments on \textbf{IronMask} applied to protect \textbf{ArcFace} that well verify the validity of our attacks. Furthermore, we carry out experiments in noisy environments and confirm that our attacks are still applicable. Finally, we discuss two strategies to mitigate this type of attacks.

Threshold encryption enables a sender to encrypt a message towards $n$ recipients, such that any $t+1$ parties can decrypt the message, whereas any subset of size $t$ cannot. Silent threshold encryption additionally requires that all recipients can generate their public keys independently of each other, without engaging in an interactive distributed key generation protocol. In this work, we consider a relaxed notion of silent threshold encryption with \emph{soft} thresholds. In this setting, we choose parameters $c \in (0,1)$ and $\epsilon >0$, and we only require that $(c - \epsilon)n$ parties cannot, while $(c + \epsilon)n$ parties can decrypt the message. We present a simple blueprint for constructing efficient silent threshold encryption schemes for soft thresholds. Our construction has ciphertexts and recipient public keys, whose sizes are independent of $n$. As an exemplary data point, tolerating $t < n/3$ corruptions and encrypting $1$ MB results in a ciphertext of size $1.072$ MB. When instantiating our construction for the same parameters in a plausibly post-quantum secure manner, we have a ciphertext size of $1.431$ MB. Our construction is proven secure in the presence of \emph{one-shot adaptive corruptions}, a novel notion introduced in this work that conceptually lays between static and fully adaptive corruptions. We believe that the notion itself and our associated proof techniques are of independent interest. In comparison to prior works for the exact threshold setting, we have smaller recipient public keys, we do not rely on strong assumptions, such as indistinguishability obfuscation, or the generic group model, we are plausibly post-quantum secure, and we prove security for a non-trivial notion of adaptive corruptions.

Optimizing Boolean circuits presents a considerable challenge, especially when aiming to construct circuits amenable to Fully Homomorphic Encryption (FHE) schemes. FHE enables arbitrary computations on encrypted data but incorporates a computationally intensive operation called bootstrapping, necessary for reducing noise in ciphertexts to facilitate computations on circuits of arbitrary depth. This operation can consume a substantial amount of time, depending on the size of the circuits. To address this issue, we propose a technique for efficiently synthesizing circuits specific to FHE by utilizing multi-input homogeneous and composite Boolean gates. Following this we develop an automated framework for designing efficient circuits compatible with FHE schemes. In this work, we use Torus-FHE (TFHE) (JoC 2019), a widely used FHE scheme for Boolean circuits due to its fast bootstrapping operation per bit. Existing techniques typically employ either multi-input homogeneous gates or, multi-bit Look-Up tables during circuit synthesis, which often limits their ability to produce highly optimized circuits for FHE. Our approach addresses this limitation by proposing viable multi-input composite gates alongwith the homogeneous gates during circuit synthesis. Additionally, we propose an efficient and lightweight circuit synthesis approach based on graph optimization. Our approach identifies convex sub-graphs in a Directed Acyclic Graph (DAG) representing the input circuit and replaces them with a more compact structure. This results in a reduction of the number of nodes in the DAG and so as the number of Boolean gates in the input circuit. Our proposed framework provides the most efficient Boolean circuits for TFHE till date, achieving up to a 20% improvement in homomorphic evaluation time compared to the state-of-the-art general compiler optimization techniques for TFHE, and it also demonstrates a 4-6× improvement over prior work on FHEW-like schemes.

The Learning with Rounding (LWR) problem, introduced as a deterministic variant of Learning with Errors (LWE), has become a promising foundation for post-quantum cryptography. This Systematization of Knowledge (SoK) paper presents a comprehensive survey of the theoretical foundations, algorithmic developments, and practical implementations of LWR-based cryptographic schemes. We introduce LWR within the broader landscape of lattice-based cryptography and post-quantum security, highlighting its advantages such as reduced randomness, improved efficiency, and enhanced side-channel resistance. We explore the evolution of security reductions from LWR to LWE, including recent advances that support practical parameter regimes and address challenges in both bounded and unbounded sample settings. This paper systematically reviews existing LWR-based schemes --- including Saber, Lizard, Florete, Espada, Sable, and SMAUG --- analyzing their design choices, parameter sets, and performance trade-offs. Furthermore, we examine the impact of LWR on side-channel resistance, failure probabilities, and masking efficiency, demonstrating its suitability for secure and efficient implementations. By consolidating the research spanning theory and practice, this SoK aims to guide future cryptographic design and standardization efforts leveraging LWR.

The current Domain Name System (DNS) infrastructure faces critical vulnerabilities including poisoning attacks, censorship mechanisms, and centralized points of failure that compromise internet freedom and security. Recent incidents such as DNS poisoning attacks on ISP customers highlight the urgent need for resilient alternatives. This paper presents a novel blockchain-based Decentralized Domain Name System (DDNS). We designed a specialized Proof-of-Work blockchain to maximize support for DNS-related protocols and achieve node decentralization. The system integrates our blockchain with IPFS for distributed storage, implements cryptographic primitives for end-to-end trust signatures, and achieves Never Trust, Always Verify zero-trust verification. Our implementation achieves 15-second domain record propagation times, supports 20 standard DNS record types, and provides perpetual free .ddns domains. The system has been deployed across distributed infrastructure in San Jose, Los Angeles, and Orange County, demonstrating practical scalability and resistance to traditional DNS manipulation techniques. Performance evaluation shows the system can handle up to Max Theor. TPS 1,111.1 tx/s (minimal transactions) and Max Theor. TPS 266.7 tx/s (regular transactions) for domain operations while maintaining sub-second query resolution through intelligent caching mechanisms.

The fundamental incompatibility between confidentiality, reliability, and le gal opposability, formalized as the CRO trilemma, imposes an entropic bound Γ_CRO on cryptographic security in contextual adversarial settings. This pa per introduces Q2CSI (Quantum Composable Contextual Security Infras tructure), a layered framework resolving this trilemma through dialectical separation. Q2CSI decomposes security guarantees into three isolated yet composable layers: Iron (reliability: temporal/logging integrity), Gold (con f identiality: semantic entropy preservation), and Clay (opposability: insti tutional interpretability). By embedding entropic constraints into an ex tended Universal Composability (UC) model, Q2CSI achieves Γ_CRO < 0.4, surpassing monolithic designs, while maintaining post-quantum resilience. The architecture is abstractly instantiated with minimal primitives (IND CCA2 encryption, EUF-CMA signatures) and validated via a symbolic UC framework. Proofs demonstrate strict dialectical isolation, bounded contex tual leakage, and compatibility with quantum adversaries. Q2CSI establishes a foundation for legally verifiable post-quantum protocols, with applications in zero-knowledge attestations and regulatory-compliant signatures.

Deep learning-based side-channel analysis (DLSCA) has demonstrated remarkable performance over the past few years. Even with limited preprocessing and feature engineering, DLSCA is capable of breaking protected targets, sometimes requiring only a single attack trace. In the DLSCA context, the commonly investigated countermeasures are Boolean masking and desynchronization. While the exact mechanisms of how DLSCA breaks masking are less understood, the core idea behind handling desynchronization is simple. Convolutional neural networks (CNNs) are shift invariant, allowing them to overcome desynchronization. However, considering the importance and practicality of desynchronization countermeasures, we know remarkably little about the limits of CNNs or how to enhance their capabilities when dealing with desynchronization. In this work, we begin with the theoretical foundations of shift and temporal scale equivariance. Afterward, we build a neural network model allowing such equivariance and test it against several commonly considered targets. Our results demonstrate that equivariant CNNs are robust, easy to design, and achieve excellent attack performance. More precisely, we showcase how such a simple model can even outperform recent transformer-based neural networks. Finally, we demonstrate the practical relevance of scale equivariance by showing how an equivariant CNN can learn leakage from a device operating at one clock frequency and generalize to a device with a different clock frequency, a result not previously demonstrated in DLSCA.

We study additive positive accumulators, which maintain a short digest of a growing set such that each value in the set can prove membership via a generated witness. Due to the compactness of the digest, previously added values may require updated witnesses as the set grows. In this paper, we establish a trade-off between the bit-length of the accumulator value and the number of witness updates. Specifically, we show that if the accumulator value has bit-length \( \mathsf{poly}(\log n) \), where \( n \) is the number of accumulated values, then some values must incur \( \Omega(\log n / \log \log n) \) witness updates. This improves upon the recent \( \omega(1) \) lower bound of [BCCK25] and matches the upper bound in [MQ23]. Building on the framework of [MQR22], we introduce a new combinatorial structure that removes the fixed-update-time assumption. Our approach also applies to Registration-based Encryption [GHMR18], thereby resolving the open problem left in [MQR22]: it shows that the tight lower bound on decryption-update frequency continues to hold even without any fixed-update-time assumption.

Searchable symmetric encryption allows clients to outsource their databases to a semi-trusted cloud server while enabling private searches. The Oblivious Cross-Tag (OXT) protocol is a fundamental approach to conjunctive keyword search, ensuring that search performance scales with the least frequent keyword while introducing keyword pair result pattern (KPRP) and intersection result pattern (IP) leakages. However, recent studies show that the KPRP leakage in OXT can be exploited, allowing the cloud server to infer information about the client database. Several works have aimed to mitigate this issue, with Doris being the first non-interactive OXT-based scheme to hide KPRP and IP leakages. However, this comes at the cost of increased storage overhead. In this work, we propose a Doris-based conjunctive SSE scheme with improved storage efficiency. We replace the XOR filter in Doris with our XEBFF filter, which formalizes XOR filters and Binary Fuse Filters. Additionally, we introduce a frequency estimation approach using Count-Min Sketch to efficiently determine the least frequent keyword, which all previous OXT-based schemes overlook. Our scheme reduces storage overhead by 8% compared to Doris while maintaining search performance. With our s-term selection protocol, we ensure that search operations typically scale with the least frequent keyword.

The Lattice Isomorphism Problem (LIP) is a relatively recent cryptographic assumption whose precise hardness remains not fully understood. Certain weak instances have been identified through hull attacks on $p$-ary lattices constructed via Construction A using linear codes with trivial hulls. In this work, we generalize the notion of the hull by introducing ideal-based hulls for Hermitian lattices. We propose a new hull attack targeting lattices derived from Generalized Construction A over number fields, under specific structural conditions. Furthermore, we show that modular lattices offer intrinsic resistance to hull attacks: the hull introduces only a limited variation in the lattice gap, bounded by a factor depending on the root discriminant of the number field. In particular, for modular $\mathbb{Z}$-lattices, the hull gap coincides exactly with the original lattice gap. As a concrete example, we show that the family of Barnes-Wall lattices, which are alternatively unimodular and 2-modular over $\mathbb{Z}$, are resistant to hull attacks.

Ring Signatures allow a user to sign on behalf of an ad-hoc set of public keys, while hiding their identity inside that set. Linkable Ring Signatures (LRS) add the functionality of detecting signatures originating from the same signer. They have found many applications in anonymous transactions and e-voting. The LLRing family of linkable ring signature schemes by Hui and Chau (ESORICS 2024) is one of the more efficient LRS schemes. However, we show that it has an unlinkability vulnerability, meaning an adversary can create more unlinkable signatures than the number of secret keys they own. The vulnerability is caused by the introduction of unwanted structure to base elements used in proofs. We also find a similar attack against the Threshold Ring Referral (TRR) scheme of Ta, Hui, and Chau (Security and Privacy 2025), rendering it unsound. We show how to achieve strong linkability with logarithmic verification complexity in the pairing based setting by first reverting the unsafe construction of base elements, and by also adjusting the arguments of knowledge used in order to maintain efficiency. Concretely, by modifying the Dory argument to fit our scheme we are able to match the performance of LLRing-P. We separate the design and analysis of the scheme from the instantiation of the knowledge arguments, which helps prevent unwanted interactions between the two, and can provide easier upgrades to more efficient proof systems.

In this work, we explore the possibility of unconditionally secure universally composable (UC) commitments, a very relevant cryptographic primitive in the context of secure multi-party computation. To this end, we assume the existence of Physically Uncloneable Functions (PUFs), a hardware security assumption that has been proven useful for securely achieving diverse tasks. In prior work [ASIACRYPT 2013, LNCS, vol. 8270, pp. 100–119] it was shown that a protocol for unconditional UC-secure commitments can be constructed even when the PUFs are malicious. Here, we report an attack to this protocol, as well as a few more issues that we identified in its construction. To address them, first we revise some of the previous PUF properties, and introduce new properties and tools that allow us to rigorously develop and present the security proofs. Second, we propose two different ways for making the commitment scheme secure against the attack we found. The first involves considering a new model where the creator of a PUF is notified whenever the PUF is queried and the second involves restricting adversaries to only being able to create stateless malicious PUFs. Finally, we analyze the efficiency of our schemes and show that our constructions are advantageous in this respect compared to the original proposal.

The syndrome decoding problem is one of the NP-complete problems lying at the foundation of code-based cryptography. The variant thereof where the distance between vectors is measured with respect to the Lee metric, rather than the more commonly used Hamming metric, has been analyzed recently in several works due to its potential relevance for building more efficient code-based cryptosystems. The purpose of this article is to present a zero-knowledge proof of knowledge for this variant of the problem.

This paper introduces Gluon W, a novel stablecoin protocol inspired by nuclear physics and named after the particle responsible for the stability of matter in the universe. The key idea in Gluon W is to split (as in nuclear fission) an existing volatile asset into its stable and unstable components. These components can be merged back (as in nuclear fusion) into the original asset or transmuted into each other (as in nuclear beta decays). Various stability theorems are proven and their proofs are formally verified using the interactive proof assistant Rocq.

Credentials are used to verify a user’s identity and attributes and form the basis of securing user access to the system resources. Users obtain credentials and store them on their (mobile) devices, and present them when needed. Anonymous credentials protect the user’s identity, and ensure unlinkability of multiple showing of the credential. In this paper, we consider a setting where a user is issued multiple credentials in sequence (e.g., for completing courses), and credential subsequences must be presented in order of issuance. We focus on the anonymous credential system where information such as the time of issuing is hidden for anonymity, or settings where there is no global clock and issuing time information is not recorded. We propose a novel order-preserving Proof-of-Credential-Subsequence (PoCS) system called KROM that allows a user that is potentially untrusted, to present a subsequence of their locally stored credentials to a verifier, while the relative chronological order of issuance is preserved. We formalize the security and privacy of KROM and present two constructions: a basic one that is based on Merkle trees and one with batched verification that significantly improves the efficiency of the system. We use KROM to construct an anonymous order-preserving proof-of-location-subsequence system and prove its security. The system enables users to selectively present a subsequence of their visited locations to a verifier or an auditor. The main challenge that is addressed is to ensure that the location information that must be in plaintext, does not breach privacy when used in sequence.

We establish the randomized distributed function computation (RDFC) framework, in which a sender transmits just enough information for a receiver to generate a randomized function of the input data. Describing RDFC as a form of semantic communication, which can be essentially seen as a generalized remote‑source‑coding problem, we show that security and privacy constraints naturally fit this model, as they generally require a randomization step. Using strong coordination metrics, we ensure (local differential) privacy for every input sequence and prove that such guarantees can be met even when no common randomness is shared between the transmitter and receiver. This work provides lower bounds on Wyner's common information (WCI), which is the communication cost when common randomness is absent, and proposes numerical techniques to evaluate the other corner point of the RDFC rate region for continuous‑alphabet random variables with unlimited shared randomness. Experiments illustrate that a sufficient amount of common randomness can reduce the semantic communication rate by up to two orders of magnitude compared to the WCI point, while RDFC without any shared randomness still outperforms lossless transmission by a large margin. A finite blocklength analysis further confirms that the privacy parameter gap between the asymptotic and non-asymptotic RDFC methods closes exponentially fast with input length. Our results position RDFC as an energy-efficient semantic communication strategy for privacy‑aware distributed computation systems.

This paper presents an enhancement to cube-attack-like cryptanalysis by minimizing output-bit dependency on related key bits, thereby improving attack complexity. We construct two distinct initial states differing exclusively in predetermined bit positions. Through independent cube summation and state difference analysis, we observed reduced related key bits dependency for specific output bits. We validate our approach by targeting three Keccak keyed variants Ketje Minor, Keccak-MAC-512 and Keccak-MAC-384, developing a dedicated tool to recover all output-bit superpolies. Using our computational resources, we successfully attacked 4-round of Ketje Minor and 5-round of other variants, confirming both the method's validity and practical applicability. While the best known attacks on these structures reach 7-round, our results improve upon the 5-round. We construct our initial state configurations based on the automated method proposed by Bi et al.\ in \textit{Design, Codes and Cryptography} (2019), and compare our results with theirs. For the 4-round Ketje Minor, we reduce the time complexity from \(2^{20}\) to \(2^{16.8}\); for 5 round Keccak-MAC-512, from \(2^{34}\) to \(2^{31.2}\); and for 5 round Keccak-MAC-384, from \(2^{27.6}\) to \(2^{26.5}\).

Quantum computers pose a critical threat to blockchains that rely on ECDSA, such as Bitcoin and Ethereum, due to public key exposure and lack of post-quantum protections. Existing proposals for migrating to quantum-secure signatures, including hybrid constructions and zero knowledge key updates, often require address changes or fail to secure inactive accounts. In this work, we show that EdDSA-based blockchains like Sui, Solana, Near, and others offer a structural advantage: their keys are deterministically derived from a seed according to RFC 8032, allowing users to prove ownership through zero knowledge without revealing elliptic curve secrets or changing addresses. Our core contribution is a post-quantum secure protocol that uses the EdDSA seed as a witness in a zero knowledge proof to authorize new quantum-safe signatures. This construction supports seamless migration, even for users with publicly exposed keys, and preserves backward compatibility. We formalize a security model for post quantum ready signatures defined to support dual-mode security and backward compatibility and then we prove the security of our core construction via a game-based argument. Finally, we provide an implementation to validate the feasibility of our approach. Our proof of concept implementation shows a practical system and enables a seamless transition, with current benchmarks showing a proving time of $6.2$ seconds, a verification time of $2.3$ seconds, and a proof size of $5.4$ MB using the Ligetron zkVM.

Fully homomorphic encryption (FHE) enables computations over encrypted data without the need for decryption. Recently there has been an increased interest in developing FHE based algorithms to facilitate encrypted matrix multiplication (EMM) due to rising data security concerns surrounding cyber-physical systems, sensor processing, blockchain, and machine learning. Presently, FHE operations have a high computational overhead, resulting in an increased need for low operational complexity algorithms to compensate. We present a novel matrix encoding and EMM algorithm for power-of-2 cyclotomic based rings, utilizing three-dimensional rotations which offer improvements over the one-dimensional rotations used in previous work. We encode each $d \times d$ matrix as a single, batch-encoded, ciphertext, with minimum ciphertext size $d^3$. The proposed algorithm improves the number of plaintext-ciphertext multiplications from $O(d)$ to $O(1)$ and the number of rotations from $O(d)$ to $O(\log_2{d})$. In addition, our work supports rectangular matrix multiplication and matrix packing without incurring additional operations per execution. Benchmarks were obtained with a Microsoft SEAL implementation and compared against leading EMM algorithm, with our work performing $4$ times faster for $16 \times 16$ matrices on consumer hardware. Our algorithm is compatible with existing encrypted machine learning frameworks and can be a drop-in replacement for existing matrix multiplication algorithms for increased speed. The favorable time complexity is well suited for time sensitive encrypted algorithms such as computer vision, controls, and patient health monitoring.

Server authentication assures users that they are communicating with a server that genuinely represents a claimed domain. Today, server authentication relies on certification authorities (CAs), third parties who sign statements binding public keys to domains. CAs remain a weak spot in Internet security, as any faulty CA can issue a certificate for any domain. This paper describes the design, implementation, and experimental evaluation of NOPE, a new mechanism for server authentication that uses succinct proofs (for example, zero-knowledge proofs) to prove that a DNSSEC chain exists that links a public key to a specified domain. The use of DNSSEC dramatically reduces reliance on CAs, and the small size of the proofs enables compatibility with legacy infrastructure, including TLS servers, certificate formats, and certificate transparency. NOPE proofs add minimal performance overhead to clients, increasing the size of a typical certificate chain by about 10% and requiring just over 1 ms to verify. NOPE’s core technical contributions (which generalize beyond NOPE) include efficient techniques for representing parsing and cryptographic operations within succinct proofs, which reduce proof generation time and memory requirements by nearly an order of magnitude.

Privacy-preserving machine learning (PPML) based on cryptographic protocols has emerged as a promising paradigm to protect user data privacy in cloud-based machine learning services. While it achieves formal privacy protection, PPML often incurs significant efficiency and scalability costs due to orders of magnitude overhead compared to the plaintext counterpart. Therefore, there has been a considerable focus on mitigating the efficiency gap for PPML. In this survey, we provide a comprehensive and systematic review of recent PPML studies with a focus on cross-level optimizations. Specifically, we categorize existing papers into protocol level, model level, and system level, and review progress at each level. We also provide qualitative and quantitative comparisons of existing works with technical insights, based on which we discuss future research directions and highlight the necessity of integrating optimizations across protocol, model, and system levels. We hope this survey can provide an overarching understanding of existing approaches and potentially inspire future breakthroughs in the PPML field. As the field is evolving fast, we also provide a public GitHub repository to continuously track the developments, which is available at https://github.com/PKU-SEC-Lab/Awesome-PPML-Papers.

Witness Encryption (WE) is a powerful cryptographic primitive, enabling applications that would otherwise appear infeasible. While general-purpose WE requires strong cryptographic assumptions, and is highly inefficient, recent works have demonstrated that it is possible to design special-purpose WE schemes for targeted applications that can be built from weaker assumptions and can also be concretely efficient. Despite the plethora of constructions in the literature that (implicitly) use witness encryption schemes, there has been no systematic study of special purpose witness encryption schemes. In this work we make progress towards this goal by designing a modular and extensible framework, which allows us to better understand existing schemes and further enables us to construct new witness encryption schemes. The framework is designed around simple but powerful building blocks that we refer to as "gadgets". Gadgets can be thought of as witness encryption schemes for small targeted relations (induced by linearly verifiable arguments) but they can be composed with each other to build larger, more expressive relations that are useful in applications. To highlight the power of our framework we methodically recover past results, improve upon them and even provide new feasibility results. The first application of our framework is a Registered Attribute-Based Encryption Scheme [Hohenberger et al. (Eurocrypt 23)] with linear sized common reference string (CRS). Numerous Registered Attribute-Based Encryption (R-ABE) constructions have introduced though a black-box R-ABE construction with a linear--in the number of users--CRS has been a persistent open problem, with the state-of-the-art concretely being N^{1.58} (Garg et al. [GLWW, CRYPTO 24]). Empowered by our Witness Encryption framework we provide the first construction of black-box R-ABE with linear-sized CRS. Our construction is based on a novel realization of encryption for DNF formulas that leverages encryption for set membership. Our second application is a feasibility result for Registered Threshold Encryption (RTE) with succinct ciphertexts. RTE (Branco et al. [ASIACRYPT 2024] is an analogue of the recently introduced Silent Threshold Encryption (Garg et al. [GKPW, CRYPTO 24]) in the Registered Setting. We revisit Registered Threshold Encryption and provide an efficient construction, with constant-sized encryption key and ciphertexts, that makes use of our WE framework.

Adaptor signatures extend the functionality of digital signatures by enabling the computation of pre-signatures on messages relative to statements in NP relations. Pre-signatures are publicly verifiable objects that simultaneously hide and commit to a standard signature on the same message. Anyone possessing a valid witness for the statement can adapt the pre-signature into a full signature under the underlying signature scheme. Since adaptor signatures are commonly used as building blocks in larger systems, in particular blockchain protocols, it is natural to seek a security definition in the Universal Composability (UC) framework. Tairi et al. (CCS'23) recently took a first step in this direction by proposing a UC functionality for adaptor signatures. This paper investigates UC-secure adaptor signatures as a primitive, making both negative and positive contributions. On the negative side, we show that the functionality proposed by Tairi et al. suffers from critical limitations: - The functionality fails to guarantee extractability and adaptability, which are core security properties of adaptor signatures, to higher-level protocols. - No adaptor signature scheme can realize the functionality. On the positive side, we propose a new UC functionality that faithfully captures the latest security guarantees of adaptor signatures as formalized via game-based notions by Gerhart et al. (EUROCRYPT'24). - Our functionality guarantees extractability and pre-signature adaptability in a way that is composable and meaningful for higher-level protocols. - We show that it is realizable by an enhanced Schnorr-based adaptor signature scheme that we construct. Our construction maintains compatibility with existing infrastructure and is efficient enough for practical deployment, particularly in Bitcoin-like environments.

In the last few years, the old idea of internal perturbation for multivariate schemes has been resurrected. A form of this method was proposed with application to HFE and UOV and independently by another team for application to Rainbow. Most recently, a newer and more efficient version of internal perturbation was proposed as an enhanced measure for securing HFE for encryption. This efficient method, known as the LL' construction, is designed to add little complexity to HFE decryption while increasing the rank of the resulting map to resist the now very effective cryptanalyses powered by MinRank. The basic idea of the construction is to have two small lists of binary linear forms which when multiplied produce rank $1$ quadratic forms. Random linear combinations of these products are then added to each of the HFE equations, resulting in a masked HFE. The main trick to make the scheme usable is to encrypt an send many random messages so that statistically it is likely that the legitimate user can find a ciphertext that is not perturbed by the construction and which may be decrypted as a plain HFE ciphertext. We show that this approach is not secure. In particular, we present a method to recover the noise support, a collection of quadratic forms spanning the set of LL' quadratic forms. We then are able to filter out the effect of these maps to recover a compatible HFE map. Finally, we are able to complete the key recovery, achieving efficiently an equivalent private key.

We strengthen Kaneko's bound to prove that, away from the $j$-invariant $0$, edges of multiplicity at least three can occur in the supersingular $\ell$-isogeny graph $\mathcal{G}_\ell(p)$ only if the base field's characteristic satisfies $p < 4\ell^3$. Further we prove a diameter bound for $\mathcal{G}_\ell(p)$, while also showing that most vertex pairs have a substantially smaller distance, in the directed case; this bound is then used in conjunction with Kaneko's bound to deduce that the distance of $0$ and $1728$ in $\mathcal{G}_\ell(p)$ is at least one fourth of the graph's diameter if $p \equiv 11 \mathrel{\operatorname{mod}} 12$. We also study other phenomena in $\mathcal{G}_\ell(p)$ with Kaneko's bound and provide data to demonstrate that the resulting bounds are optimal; for one of these bounds we investigate the connection between loop multiplicities in isogeny graphs and the factorization of the `diagonal' classical modular polynomial $\Phi_\ell(X,X)$ in positive characteristic.

A private set operation (PSO) scheme [Rafiee, Comput. J. 2020] is a cryptographic primitive that enables a user to securely outsource their dataset to cloud storage, and then when needed, securely issue common set operation queries to the server and receive the results. In [Rafiee, Comput. J. 2020], the only security notion of the PSO schemes, named naSIM, is proposed. This security notion models a weak attacker who is far from the threats of practical environments, and providing stronger security notions has been raised as an open problem. In this paper, we propose a new security notion for the PSO schemes, called aIND, and show that this concept is stronger than naSIM. Furthermore, we propose a new PSO construction that satisfies the security notion aIND. We also show that our construction does not increase the computational and storage overheads compared to other existing constructions, despite covering a much higher level of security.

One of the main guidelines to prevent timing side-channel attacks against cryptographic implementations is to avoid array accesses indexed by secret data. However, alternatives and countermeasures often incur significant performance losses. We propose a novel methodology for secure, constant-time implementation of algorithms that read and write to small arrays with secret-dependent indices, with a constant-factor performance impact compared to timing-unprotected accesses. It is specifically suitable for simple in-order CPUs like those in embedded systems, e.g., the ARM Cortex-M4 core. Although our methodology is general, we illustrate it with secure implementation of permutation operations, such as composition, inversion, and sampling, the latter using the Fisher-Yates shuffle. We apply this methodology to the post-quantum cryptosystems PERK and NTRU, bridging most of the performance gap to unprotected implementations that employ secret-dependent array accesses.

Recent years have witnessed significant progress in composable masked AES designs based on Hardware Private Circuits (HPCs) under the Probe-Isolating Non-Interference (PINI) framework. However, these designs still suffer from substantial randomness requirements and area overhead at higher protection orders. In this work, we revisit Domain-Oriented Masking (DOM), originally proposed by Gross et. al. in 2016, and leverage the DOM-$dep$ and DOM-$indep$ multipliers to construct efficient AES implementations based on the Strong Non-Interference (SNI) framework. Our contributions include: 1. a comprehensive security analysis of DOM-$dep$ and DOM-$indep$, including their compositional security under the SNI framework; 2. more efficient masked AES implementations for arbitrary protection orders, reducing randomness and area overhead while maintaining latency comparable to state-of-the-art HPC3-based designs. Specifically, our masked AES implementations maintain a latency of 41 clock cycles by using the Hadzic's decomposition for $F_2^8$ inverter. When $d <= 4$, they save at least 13% in area (RNG included) and reduce latency by 19.6% compared to the smallest $d$-PINI round-based masked AES implementations provided by Cassiers et.al. (The current version focuses on the core construction and its initial evaluation. Source code has been made publicly available to facilitate verification. Further performance optimizations and theoretical generalizations are underway and will appear in an upcoming revision.)

A quantum copy-protection scheme (Aaronson, CCC’09) encodes a functionality into a quantum state such that given this state, no efficient adversary can create two (possibly entangled) quantum states that are both capable of running the functionality. There has been a recent line of works on constructing provably-secure copy-protection schemes for general classes of schemes in the plain model, and most recently the recent work of Çakan and Goyal (IACR Eprint, 2025) showed how to copy-protect all cryptographically puncturable schemes with pseudorandom puncturing points. In this work, we show how to copy-protect even a larger class of schemes. We define a class of cryptographic schemes called malleable-puncturable schemes where the only requirement is that one can create a circuit that is capable of answering inputs at points that are unrelated to the challenge in the security game but does not help the adversary answer inputs related to the challenge. This is a flexible generalization of puncturable schemes, and can capture a wide range of primitives that was not known how to copy-protect prior to our work. Going further, we show that our scheme is secure against arbitrary high min-entropy challenge distributions whereas previous work has only considered schemes that are punctured at pseudorandom points.

Group signatures (GS, Chaum and van Heyst, EUROCRYPT 1991) are digital signatures that allow a signer to anonymously prove the membership and also allow the special authority called the opener can identify the signer. Group signatures with message-dependent opening (GS-MDO, Sakai et al., Pairing 2012) weakened the power of the opener by introducing another authority called the admitter who issues a message-dependent token. It would be a natural research topic to clarify whether cryptographic primitives that are required to construct GS-MDO are stronger than those of GS or not, according to the enhanced functionality of GS-MDO. In this paper, we propose a generic construction of timed-release encryption (TRE) from GS-MDO. Note that Sakai et al. have shown that GS-MDO implies identity-based encryption (IBE), and Nakai et al. (IWSEC 2009) and Matsuda et al. (Pairing 2010) demonstrated generic constructions of TRE from IBE. Thus, we do not show any new result from the viewpoint of feasibility. We show that (1) GS-MDO directly implies TRE without employing the generic constructions of TRE from IBE, and (2) the proposed TRE construction provides public verifiability, that is not usually supported by TRE, because a TRE ciphertext is a group signature in our construction. We also introduce a new security notion which we call token unforgeability where no adversary can forge a token even the adversary has the opener's secret key, and prove that token unforgeability is implied by opener anonymity which is a fundamental security notion of GS-MDO. Our result implies that GS-MDO is a very strong cryptographic primitive.

Quantum computational pseudorandomness has emerged as a fundamental notion that spans connections to complexity theory, cryptography, and fundamental physics. However, all known constructions of efficient quantum-secure pseudorandom objects rely on complexity-theoretic assumptions. In this work, we establish the first unconditionally secure efficient pseudorandom constructions against shallow-depth quantum circuit classes. We prove the following: (1) Any quantum state $2$-design yields unconditional pseudorandomness against both $\mathsf{QNC}^0$ circuits with arbitrarily many ancillae and $\mathsf{AC}^0 \circ \mathsf{QNC}^0$ circuits with nearly linear ancillae. (2) Random phased subspace states, where the phases are picked using a $4$-wise independent function, are unconditionally pseudoentangled against the above circuit classes. (3) Any unitary $2$-design yields unconditionally secure parallel-query pseudorandom unitaries against geometrically local $\mathsf{QNC}^0$ adversaries, even with limited $\mathsf{AC}^0$ postprocessing. Our indistinguishability results for $2$-designs stand in stark contrast to the standard setting of quantum pseudorandomness against $\mathsf{BQP}$ circuits, wherein they can be distinguishable from Haar random ensembles using more than two copies or queries. Our work demonstrates that quantum computational pseudorandomness can be achieved unconditionally for natural classes of restricted adversaries, opening new directions in quantum complexity theory.

Succinct non-interactive arguments of knowledge (SNARKs) rely on polynomial commitment schemes (PCSs) to verify polynomial evaluations succinctly. High-performance multilinear PCSs (MLPCSs) from linear codes reduce prover cost, and distributed MLPCSs reduce it further by parallelizing commitment and opening across provers. Employing a fast Reed--Solomon interactive oracle proof of proximity (FRI), we propose PIPFRI, an MLPCS that combines the linear-time proving of linear-time-encodable-code PCSs with the compact proofs and fast verification of Reed--Solomon (RS) PCSs. Reducing fast Fourier transform and hash overhead, PIPFRI is 10× faster to prove than the RS-based DeepFold (USENIX Security '25) while keeping competitive proof size and verifier time. Measured against Orion (CRYPTO '22) from linear-time-encodable codes, PIPFRI proves 3.5× faster and reduce proof size and verifier time by 15×. As a linearly scalable distributed variant, we propose DEPIPFRI, which adds accountability and distributes a single polynomial across provers, enabling the first code-based distributed SNARK for general circuits. Notably, compared with DeVirgo (CCS '22), which lacks accountability and supports only multiple independent polynomials, DEPIPFRI improves prover time by 25× and inter-prover communication by 7×. We identify shred-to-shine as the key insight: partitioning a polynomial into independently handled fragments while maintaining proof size and verifier time. Hitting the pairing regime, this insight yields a group-based MLPCS with a 16× shorter structured reference string (SRS) and a 10× faster opening time than a multilinear variant of Kate--Zaverucha--Goldberg (TCC '13).

In 2023, Barreto and Zanon proposed a three-round Schnorr-like blind signature scheme, leveraging zero-knowledge proofs to produce one-time signatures as an intermediate step of the protocol. The resulting scheme, called BZ, is proven secure in the discrete-logarithm setting under the one-more discrete logarithm assumption with (allegedly) resistance to the Random inhomogeneities in a Overdetermined Solvable system of linear equations modulo a prime number $p$ attack, commonly referred to as ROS attack. The authors argue that the scheme is resistant against a ROS-based attack by building an adversary whose success depends on extracting the discrete logarithm of the intermediate signing key. In this paper, however, we describe a distinct ROS attack on the BZ scheme, in which a probabilistic polynomial-time attacker can bypass the zero-knowledge proof step to break the one-more unforgeability of the scheme. We also built a BZ variant that, by using one secure hash function instead of two, can prevent this particular attack. Unfortunately, though, we show yet another ROS attack that leverages the BZ scheme's structure to break the one-more unforgeability principle again, thus revealing that this variant is also vulnerable. These results indicate that, like other Schnorr-based strategies, it is hard to build a secure blind signature scheme using BZ's underlying structure.

We present InsPIRe that is the first private information retrieval (PIR) construction simultaneously obtaining both high-throughput and low query communication while using silent preprocessing (meaning no offline communication). Prior PIR schemes with both high-throughput and low query communication required substantial offline communication of either downloading a database hint that is 10-100x larger than the communication cost of a single query (such as SimplePIR and DoublePIR [Henzinger et al., USENIX Security 2023]) or streaming the entire database (such as Piano [Zhou et al., S&P 2024]). In contrast, recent works such as YPIR [Menon and Wu, USENIX Security 2024] avoid offline communication at the cost of increasing the query size by 1.8-2x, up to 1-2 MB per query. Our new PIR protocol, InsPIRe, obtains the best of both worlds by obtaining high-throughput and low communication without requiring any offline communication. Compared to YPIR, InsPIRe requires 5x smaller cryptographic keys, requires up to 50% less online query communication while obtaining up to 25% higher throughput. We show that InsPIRe enables improvements across a wide range of applications and database shapes including the InterPlanetary File System and private device enrollment. At the core of InsPIRe, we develop a novel ring packing algorithm, InspiRING, for transforming LWE ciphertexts into RLWE ciphertexts. InspiRING is more amenable to the silent preprocessing setting that allows moving the majority of the necessary operations to offline preprocessing. InspiRING only requires two key-switching matrices whereas prior approaches needed logarithmic key-switching matrices. We also show that InspiRING has smaller noise growth and faster packing times than prior works in the setting when the total key-switching material sizes must be small. To further reduce communication costs in the PIR protocol, InsPIRe performs the second level of PIR using homomorphic polynomial evaluation, which only requires one additional ciphertext from the client.

The Generalized Birthday Problem ($\textsf{GBP}$), which seeks $k$ hash values from $k$ lists whose XOR is zero, is a fundamental problem across multiple cryptographic domains. While the $k$-list $\textsf{GBP}$ has been extensively studied, many schemes including $\textsf{Equihash}$ (NDSS'16) utilize a single-list variant (selecting hash values from a single list) without clear theoretical grounding. Our work reveals that the $k$-list $\textsf{GBP}$ implicitly exhibits a regularity property, a block-wise structure that has been thoroughly studied by Esser and Santini (Crypto'24) in the context of the Syndrome Decoding Problem. Such structured regularity can often be leveraged to design efficient protocols and enable new functionalities. In this work, we revisit these two long-conflated $\textsf{GBP}$s and initiate a systematic study of the regularity in the realm of $\textsf{GBP}$. $\textbf{Complexity.}$ In the worst-case setting, we develop a novel ISD-based framework for $\textsf{GBP}$. When $k/n > 0.188$ and $k/n > 0.11$ for the regular and non-regular cases, respectively, the proposed algorithms surpass the worst-case complexity of $2^{n/2}$. Through numerical optimization, we heuristically demonstrate that for any constant $k/n > 0$, the advanced ISD algorithms such as BJMM achieve an asymptotic complexity superior to the birthday bound when applied to density-one $\textsf{GBP}$ instances. Our results disprove the average-case-to-worst-case $k$-$\textsf{XOR}$ conjecture when $k$ is non-constant (e.g., linear in $n$). In the average-case regime, we fill in theoretical gaps in solving the single-list $\textsf{GBP}$ and show that the regular variant exhibits a $\sqrt{2}$-factor difference in the exponent, which extends naturally to the $k$-$\textsf{SUM}$ problem and offers new insights into its complexity. $\textbf{Implications for Cryptography.}$ We analyze the impact of regularity on incremental hash and propose a new collision attack against the ID-based incremental hash (Eurocrypt'97). Our attack achieves an asymptotic time complexity of $\mathcal{O}(\sqrt{n} \cdot 2^{\sqrt{2n}})$, significantly improving upon Wagner's previous bound of $\mathcal{O}(2^{\sqrt{4n}})$ (Crypto'02). Applying our attack to $\textsf{iSHAKE256}$, we reduce its security lower bound from $2^{256}$ to $2^{189}$. In the realm of $\textsf{Equihash}$, the index-pointer technique has significantly weakened its ASIC-resistance. To address this, we propose $\textsf{Requihash}$, a PoW with enhanced ASIC-resistance and a smaller solution size, rigorously aligned with the regular $k$-list $\textsf{GBP}$.

In this paper, we propose a new postquantum lattice-based digital signature named Rhyme. The scheme is based on the Fiat-Shamir structure and does not rely on flooding, rejection sampling, or Gaussian convolution as previous methods. Instead, its security is based on a variant of LWE combined with a new sampling method (3C sampling). We prove its security in ROM/QROM and provide concrete parameters as well as reference implementation to show that our scheme enjoys high efficiency and very compact signature size compared with former results.

Recent years have witnessed the surge of academic researches and industrial implementations of succinct non-interactive arguments of knowledge (SNARKs). However, proving time remains a bottleneck for applying SNARKs to large-scale circuits. To accelerate the proof generation process, a promising way is to distribute the workload to several machines running in parallel, the SNARKs with which feature are called \textit{distributed SNARKs}. Nevertheless, most existing works either require a trusted setup, or rely on quantum-insecure assumptions, or suffer from linear communication costs. In this paper, we introduce $\mathsf{HyperFond}$, the first distributed SNARK that enjoys a transparent setup, post-quantum security and polylogarithmic communication cost, as well as field-agnosticity (no reliance on specific choices of fields). To this end, we first propose a distributed proof system based on HyperPlonk (by Chen et al. in EUROCRYPT 2023). To instantiate the system, we then put forward a novel approach to distribute the multilinear polynomial commitment scheme in BaseFold (by Zeilberger et al. in CRYPTO 2024), and present a trade-off between communication cost and proof size. In $\mathsf{HyperFond}$, after committing to polynomial coefficients with quasilinear complexity, each sub-prover generates proofs with time linear in subcircuit size. We implement $\mathsf{HyperFond}$ using up to 16 machines. Experimental results demonstrate that the proving time of $\mathsf{HyperFond}$ is 15.6 $\times$ faster than HyperPlonk instantiated with BaseFold. We also compare to deVirgo (by Xie et al. in CCS 2022), so far the only post-quantum distributed SNARK, and achieve a 1.45 $\times$ speedup.

This work establishes the CRO Trilemma: no post-quantum proof system can simultaneously satisfy the following three properties beyond negligible failure probability: (i) Confidentiality, quantified by Priv > 1 - negl(lambda); (ii) Reliability, with Rel > 1 - negl(lambda); and (iii) Legal Opposability, measured by contextual entropy H_Opp ≈ log |V_J|, where V_J denotes the validation space of a polynomial-time institutional verifier J. The result formalizes the Invisible Authenticity Paradox through contextual entropy H(C) and quantum interpretability loss eta_q(C). Under standard quantum assumptions, we prove the following impossibility bound against QPT adversaries: H_Opp <= (Priv * Rel) / (epsilon_eff * 2^H(C)) + eta_q(C) + negl(lambda) A composable framework is introduced, including a composable model with verifier J (Algorithm 1), and an optimal entropy decomposition theorem (Theorem 2.3). Theoretical predictions are supported by empirical evidence indicating consistent violation of the bound (Gamma_CRO > 0.8) across NIST PQC finalists (e.g., Dilithium) and structured ZKPs (e.g., STARKs, Groth16).

Tracing techniques have been used to identify users who have leaked their decryption keys in a secure multi-receiver encryption system. Very recently, in the field of distributed cryptography, where trust is distributed, Boneh et al. extended traitor tracing to the framework of threshold decryption, where a single user doesn't hold the whole secret to decrypt but needs to collaborate with others. However, the tracing capacity in their collusion-secure codes-based schemes is still centralized: only the authority holding the secret tracing key can perform tracing. We continue in the direction of not relying on a single entity and propose decentralizing tracing in this context so that the tracing procedure does not need to rely on any secret key and can be done by anyone. Technically, as binary collusion-secure codes only support secret tracing, we switch to robust $q$-ary IPP codes supporting public tracing. This requires us to generalize the bipartite threshold KEM for two users in Boneh et al.'s paper to $q$-partite KEM for q users. In terms of security, their static one-sided security in the binary case is not appropriate, which requires us to define an adaptive one-sided security notion for $q$-partite KEM to be compatible with $q$-ary IPP codes. Finally, we generalize the Boneh et al. construction to achieve this security notion and achieve public traceability for threshold decryption without degrading efficiency.

FRAST is a TFHE-friendly stream cipher that was published at FSE 2025. The cipher is defined over $\mathbb{Z}_{16}$, and makes extensive use of negacyclic S-boxes over $\mathbb Z_{16}$ as they are less costly in TFHE. Like many FHE-friendly ciphers, FRAST randomizes some of its components to increase its security against statistical attacks. In the case of FRAST, some S-boxes are randomized using an XOF that takes a nonce as input. In this work, we point out a strong structural property of the full FRAST permutation, which leads to a much simpler alternative representation of the primitive. We study the consequences of this representation and find a weak key space of non-negligible size (i.e., much larger than $2^{128}$) on which every ciphertext leaks one bit of plaintext. This corresponds to a distinguishing attack on the full FRAST in the weak-key setting. In particular, we emphasize that, apart from the structural property, the usage of negacyclic S-boxes further leads to a much larger weak-key space for our attack. Finally, we provide a general framework to mount a linear attack on FRAST in the average key setting. We briefly describe our approach in the end of the paper, and observe that standard assumptions expected to work in the context of linear cryptanalysis do not hold in the case of FRAST: our experiment indicate that a linear attack in the average key setting does not work as expected.

Eagen introduced a framework for proof-of-computation over elliptic curves, replacing costly group operations with efficient computations over a function field. This work lacks clear protocol descriptions, formal security proofs, and a thorough efficiency analysis; we improve upon the literature, present a detailed protocol description, then analyze completeness, soundness, and complexity. We apply our construction to the Schnorr and Bulletproofs protocols, highlighting how this reduces verifier costs significantly compared to the original proposals. This tradeoff most clearly benefits privacy-centered constructions like blockchain cryptocurrencies and Tor routing - where proofs must be verified repeatedly - but more generally may be used to improve verification time in generic curve-based zero-knowledge proof systems.

Hamming Quasi-Cyclic (HQC) has recently been officially selected for standardization by NIST as a post-quantum KEM alternative to ML-KEM. This milestone raises new requirements, in particular the need to design and deploy secure implementations of the scheme. This paper presents two major contributions to secure HQC against Side-Channel Attacks (SCAs). First, we present a detailed sensitivity analysis of HQC, highlighting the critical variables and critical internal functions that need to be protected. Second and main contribution, we propose the first fully masked HQC implementation at any order. It is also the first PQC masked implementation that is formally proved to be secure in the MIMO-SNI security model. This security, introduced by Cassiers and Standaert in 2020, ensures the security of gadgets composition against propagating probes. In this paper, we provide benchmarks of our implementation, showing that our masked implementation is competitive in the state-of-the-art masked PQC implementations.

Symmetric encryption allows us to establish a secure channel based on a shared, strong key. However, users cannot remember or cannot store such keys securely. Password-Authenticated Key Exchange (PAKE) protocols address this by using low-entropy, human-memorizable passwords to establish secure channels. PAKEs are widely used and are foundational in practical cryptographic protocols, but while cryptographic tools like Key Encapsulation Mechanism (KEM) and Signatures have been implemented to resist attacks from quantum computers, PAKEs have gained quantum security only recently. To hedge against any potential vulnerabilities in recent quantum-secure PAKEs and in their implementations, we primarily focus on hybrid PAKE constructions that compose CPace, a classically-secure PAKE, with a variant of a recently proposed quantum-secure PAKE, which we call OQUAKE. Specifically we introduce and analyze two new hybrid PAKEs designed to be efficient, easy to implement, and utilize a minimized set of standard building blocks. The first, called CPaceOQUAKE, is a hybrid symmetric PAKE that remains secure as long as either a classical or post-quantum assumption holds. The second, called CPaceOQUAKE+, is a hybrid asymmetric PAKE (aPAKE) where the server party holds a verifier that obscures the password, instead of holding the password itself. In our analysis we present the necessary security proofs in the Universal Composability framework. In particular, we prove that OQUAKE, the underlying KEM-based PAKE in our hybrid constructions, realizes a relaxed UC PAKE variant that exposes password equality to passive observers, an observation available anyway in typical applications of PAKEs where the network interactions which follow the PAKE depend on authentication success. Moreover, we prove that our variant of the PAKE(+KEM)-to-aPAKE compiler is a similarly relaxed UC aPAKE.

Discrete Gaussian Sampling (DGS) over the integers—also known as integer Gaussian sampling— is used to generate integer values that statistically follow the discrete Gaussian distribution and plays a central role in lattice-based cryptography. Among existing approaches for integer DGS, the cumulative distribution table (CDT) method is widely adopted. However, CDT sampling typically incurs substantial storage costs due to the need to store high-precision fixed-point probability tables, where a precision of $k$ bits is required to achieve a statistical distance of $2^{-k}$ from the ideal distribution. In this work, we propose a more compact representation of CDT based on Simultaneous Diophantine Approximation (SDA). Instead of storing fixed-point values, our method expresses the probabilities in the CDT as a sequence of rational numbers with a common denominator. With parameter selection guided by SDA, this compact fractional representation enables reducing data width while maintaining the same level of statistical accuracy. Our SDA-CDT construction offers clear advantages in both computation speed and storage compared to classical CDT implementations. For example, in Frodo-1344, our sampler achieves a 19.97% increase in speed (from 12.10 million to 14.51 million samples per second) and a 3.85% reduction in memory usage (from 104 bits to 100 bits). Similarly, in Frodo-976, we observe a 10.88% speedup and a 21.60% decrease in memory cost. In addition, our design eliminates floating-point arithmetic and supports a fully constant-time online sampling procedure, which ensures resistance to timing side-channel attacks without compromising performance.

HPPC is a multivariate signature scheme submitted to the NIST PQC standardization process in response to the recent call for additional signature schemes. We show that, despite some non-standard notational choices in the submission document, HPPC can be viewed as a special case of the well-studied, but broken for all practical parameters, HFE signature scheme. We further show that the HPPC construction introduces additional structure that further weakens the scheme. For instance, the central map has $Q$-rank $2$ independently from the degree $D$ of the central polynomial that is used. Using these observations, we show that HPPC is weaker against the direct attack than claimed in the submission document and more crucially that all parameter sets can be practically broken using MinRank techniques. For instance, with a very naive implementation, we have been able to recover an equivalent key in approximately 8 minutes for security level 2, an hour and a half for security level 4, and slightly more than 7 hours for security level 5.

Private Information Retreival (PIR) schemes without preprocessing are known to incur linear server computation per client query. Several recent works have shown that by relying on a one-time preprocessing phase, we can get around this barrier, and achieve sublinear computation per query without relying on any cryptographic assumptions. Beimel et al. (CRYPTO'00) first showed a family of schemes whose bandwidth and computation per query scale as fast as $n^{O(1/S)}$ where $S$ denotes the number of servers and $n$ denotes the database size. Unfortunately, their schemes are not practical partly because the servers must each store an encoded version of the database, and the encoding length grows sharply as we increase $S$. The recent work of Singh et al. (TCC'24) showed how to achieve similar bandwidth scaling but without the server space blowup. To get this, they rely on a different type of preprocessing called client-specific preprocessing, where the stateful client stores some hints and the servers store only the original database. Unfortunately, Singh et al.'s result is completely impractical due to the reliance on Dvir and Gopi's PIR as a building block. We propose Zelda (short for ZEro-Leakage Data Access), the first concretely efficient, information-theoretic multi-server PIR scheme with sublinear computation. Our work makes both theoretical and practical contributions. On the theoretical front, we devise a unified framework for constructing multi-server PIR with client-specific preprocessing. This gives us a parametrizable family of schemes that asymptotically outperform all prior constructions in the same setting, including Singh et al. (TCC'24) and Ishai et al. (CRYPTO'24). On the practical front, Zelda is conceptually simple, self-contained, and does not rely on any underlying PIR as a building block. We implemented Zelda and open sourced our code. We compared the concrete performance of Zelda with a state-of-the-art PIR scheme called QuarterPIR (Eurocrypt'24), which relies on pseudorandom functions for security. Experimental results show that Zelda outperforms QuarterPIR in terms of online response time and client space (assuming typical fiber optical links), at the price of increased costs for offline maintenance operations.

This paper studies the Twinkle family of low-latency symmetric key schemes designed by Wang et al. (CiC 2024). In particular, it presents cryptanalysis of both the mode and the underlying primitive. Twinkle is a PRF-based design, and an authenticated encryption scheme Twinkle-AE is specified based on a dedicated PRF called Twinkle-PRF. To achieve low latency, Twinkle-PRF uses a large key and state to produce sufficient randomness in a single step. Twinkle-AE uses a 1024- or 512-bit key for authentication and generates a $t$-bit tag, where $t \in \{64, 128\}$. It claims to provide $t$ bits of integrity. Several Twinkle-AE parameter sets claim higher confidentiality than integrity. In this setup, for any ciphertext, an adversary can obtain the message after $O(2^t)$ decryption attempts by guessing the tag, allowing attacks in the chosen-ciphertext setting. We show that a 1024- or 512-bit authentication key can be recovered using only $O(2^t)$ queries. The recovered authentication key enables the generation of valid ciphertexts for arbitrary plaintexts, thus achieving universal forgery. In the second part of the paper, we perform cryptanalysis on reduced-round variants of the 1280-bit public permutation Twinkle-P, which serves as a core component of Twinkle-PRF. We investigate impossible differential, zero-correlation linear, integral, and differential-linear distinguishers by developing automated analytic tools. We provide practical distinguishers for up to 5 rounds, and the longest distinguisher reaches 6 rounds with a complexity of $2^{74.32}$. This surpasses the round bounds evaluated by the designers. We stress that our attacks on mode exploits the gap between the claimed confidentiality and integrity levels, thus have no impact on the parameter sets having the same security level. Our attacks on the permutation do not have any significant impact on the whole specifications. Moreover, we note that Twinkle-AE-512b/Twinkle-AE-1024b and Twinkle-PA remain secure, and the versions we attacked would also be secure if the claimed confidentiality level matched the integrity level.

Constrained PRFs are PRFs that allow the generation of constrained keys, which can be used to evaluate the PRF on a subset of the inputs. The PRF is still pseudorandom for an adversary who obtains multiple of these constrained keys on all inputs where none of the constrained keys allow it to evaluate the PRF. Constrained PRFs are known for some simple constraint classes (such as puncturing or intervals) from one-way functions, but for more powerful constraint classes, such as bitfixing, the only known constructions need heavy machinery, like indistinguishability obfuscation or multilinear maps. In this work we show that constrained PRFs (for any constraint class) do not imply key agreement in a black-box way with an oracle separation. The result also applies to delegatable constrained PRFs, where constrained keys can be used to generate other, more restrictive constrained keys. We show that this result has interesting implications for identity-based cryptography, where users obtain secret keys from a trusted, central authority. Namely, it shows that primitives that allow key agreement in this setting, like identity-based non-interactive key exchange and a weaker variant of identity-based encryption that we introduce in this work, do not imply key agreement and thus can exist even in a world where traditional key agreement and public-key encryption is impossible.

Migration to quantum-safe cryptography represents a significant technological shift, addressing the vulnerabilities of traditional cryptographic primitives, such as KEMs and digital signatures. Yet, a number of challenges remain, especially in the development of secure solutions for sophisticated cryptographic applications. One of them is Smart-ID, European server-supported (threshold) signing service. To address this issue, we present $\textsf{Electrum}$, a fail-stop server-supported signature scheme designed to enhance security of existing Smart-ID service. $\textsf{Electrum}$ combines multiprime RSA-based signatures with fail-stop features: providing not only unforgeability against classical adversaries but also allowing to prove that a given signature is a forgery made by classical and/or quantum adversaries. Proposed protocol can be seen as a temporary remedy against the quantum threat until standardised threshold signature schemes become a common practice. To prove security of $\textsf{Electrum}$, we introduce a new ideal functionality $\mathcal{F}^{\textsf{SplFS}}$ for a fail-stop server-supported signing in the Universal Composability model. We show that $\textsf{Electrum}$ protocol securely realizes the proposed functionality $\mathcal{F}^{\textsf{SplFS}}$.

This paper presents a family of representations of elementary vectors, which covers existing representations as special cases. We make use of the family of representations to reduce signature size of existing signature schemes based on the VOLE-in-the-head framework. In particular, we use new representations to build modelings for the regular syndrome decoding problem in $\mathbb{F}_2$, which is used in the post-quantum signature scheme SDith, and for the permuted kernel problem in characteristic-2 fields, which is used in a post-quantum signature scheme recently proposed by Bettaieb, Bidoux, Gaborit, and Kulkarni. For the “short” parameter sets of SDith, which are designed for minimiz- ing signature size, we achieve a size reduction of 3.6% to 4.2%. For parameter sets of the Bettaieb-Bidoux-Gaborit-Kulkarni signature scheme, we achieve a size reduction of 9% to 12%.

Strong designated verifier signatures are a variant of digital signatures in which only one party—the designated verifier—is able to verify the authenticity of a signature. We propose a new strong designated verifier signature scheme based on (abelian) cryptographic group actions.

In 2009, Galindo and Garcia proposed the usage of concatenated Schnorr signatures for the hierarchical delegation of public keys, creating a quite efficient identity-based signature scheme (IBS). Essentially, the scheme builds upon the Schnorr signature scheme to generate a primary signature, part of which is then used as a secret key to produce signatures on subsequent messages. The resulting IBS is proven secure against existential forgery on adaptive chosen-message and adaptive identity attacks using variants of the Forking Lemma. In this paper, our goal is to answer the following question: would it be feasible to build upon the widely used elliptic curve digital signature algorithm (ECDSA) scheme to obtain a similarly secure and efficient IBS? We answer this affirmatively, opening interesting possibilities not only for identity-based signatures with ECDSA but also for applications such as secure credential delegation. This latter application is of particular interest considering the wide support for ECDSA in web- and cloud-oriented authentication systems (e.g., based on JSON Web Tokens). The resulting scheme is proven secure, combining the Bijective Random Oracle model and the existential unforgeability game in an identity-based setup. Our results show that even considering ECDSA's non-linear characteristic and more convoluted verification process when compared to Schnorr signatures, it is possible to obtain shorter signatures than Galindo-Garcia's scheme.

A redactable set signature scheme is a signature scheme that allows a redactor, without possessing the signing key, to convert a signature on set $S$ to a signature on set $S'$ if $S' \subset S$. This paper introduces a new form of redactable set signature scheme called a policy-based redactable set signature scheme. These redactable set signatures allow for a signer to provide a redaction policy at signing time that limits the possible redactions that can be made by a redactor. In particular, a signature on set $S$ can only be redacted to a signature on $S'$ if $S' \subset S$ and $P\left(S'\right) = 1$.

In this note, we present a new instantiation of the hash-based multi-signature framework introduced by Drake, Khovratovich, Kudinov, and Wagner (CiC Vol 2 Issue 1, eprint 2025/055) for Ethereum’s consensus layer. Inspired by a recent work of Khovratovich, Kudinov, and Wagner (Crypto 2025, eprint 2025/889), we instantiate the framework with a novel incomparable encoding that improves the tradeoff between signature size and verification hashing. The purpose of this document is to make explicit how to use the ideas of the latter work within the framework of Drake, Khovratovich, Kudinov, and Wagner.

The efficient implementation of Boolean masking with minimal overhead in terms of latency has become a critical topic due to the increasing demand for physically secure yet high-performance cryptographic primitives. However, achieving low latency in masked circuits while ensuring that glitches and transitions do not compromise their security remains a significant challenge. State-of-the-art multiplication gadgets, such as the recently introduced HPC4 (CHES 2024), offer composable security against glitches and transitions, as proven under the robust d-probing model. However, these gadgets require at least one clock cycle per computation, resulting in a latency overhead that increases with the algebraic degree. In contrast, LMDPL gadgets (CHES 2014 & CHES 2020) can achieve fixed latency independent of the algebraic degree, effectively addressing this issue. However, they are limited to two shares, and extending them to guarantee composable security at order d with d+1 shares is considered an open challenge. In this work, we introduce CCHPC, a novel hardware masking scheme built on the concept of LMDPL. Specifically, CCHPC achieves a fixed latency of d clock cycles by masking a Boolean function of arbitrary algebraic degree with d+1 shares. CCHPC gadgets are secure and trivially composable, as formally proven under the RR d-probing model (CHES 2024). Using CCHPC gadgets, we design a masked AES encryption core which can be instantiated for an arbitrary number of d+1 shares with a total latency of 11 + d clock cycles.

The cube attack is one of the most powerful attacks on stream ciphers, with recovering the superpoly as its key step. The core monomial prediction is the state-of-the-art technique for superpoly recovery, which can reach 851 rounds for Trivium thus far (EUROCRYPT 2024). The core monomial prediction heavily relies on the trail enumeration which is the bottleneck for its efficiency. This paper further explores the potential of the core monomial prediction for Trivium by constructing a composite representation for the superpoly. This representation allows us to detect the algebraic structure of the superpoly under specific conditions on the intermediate variables, without the computational burden of trail enumerations. Leveraging these discovered conditions, we successfully recovered weak-key superpolies for 852-round Trivium, establishing the first cryptanalytic result against 852-round Trivium in the literature to date.

We consider the multivariate scheme $\texttt{Pesto}$, which was introduced by Calderini, Caminata, and Villa. In this scheme, the public polynomials are obtained by applying a CCZ transformation to a set of quadratic secret polynomials. As a consequence, the public key consists of polynomials of degree $4$. In this work, we show that the public degree $4$ polynomial system can be efficiently reduced to a system of quadratic polynomials. This seems to suggest that the CCZ transformation may not offer a significant increase in security, contrary to what was initially believed.

We present a collection of protocols to perform privacy-preserving set operations in the third-party private set intersection (PSI) setting. This includes several protocols for multi-party third party PSI. In this model, there are multiple input parties (or clients) each holding a private set of elements and the receiver is an external party (termed as third-party) with no inputs. Multi-party third party PSI enables the receiver to learn only the intersection result of all input clients' private sets while revealing nothing else to the clients and the receiver. Our solutions include constructions that are provably secure against an arbitrary number of colluding parties in the semi-honest model. Additionally, we present protocols for third-party private set difference and private symmetric difference, whereby the learned output by the inputless third-party is the set difference and symmetric difference respectively of two other input parties, while preserving the same privacy guarantees. The motivation in the design of these protocols stems from their utilities in numerous real-world applications. We implemented our protocols and conducted experiments across various input and output set sizes.

Granular Synchrony (Giridharan et al. DISC 2024) is a new network model that unifies the classic timing models of synchrony and asynchrony. The network is viewed as a graph consisting of a mixture of synchronous, eventually synchronous, and asynchronous communication links. It has been shown that Granular Synchrony allows deterministic Byzantine agreement protocols to achieve a corruption threshold in between complete synchrony and complete asynchrony if and only if the network graph satisfies the right condition, namely, that no two groups of honest parties of size $n-2t$ can be partitioned from each other. In this work, we show that the same network condition is also tight for Agreement on a Common Subset (ACS), Verifiable Secret Sharing (VSS), and secure Multi-Party Computation (MPC) with guaranteed output delivery, when the corruption threshold is between one-third and one-half. Our protocols are randomized and assume that all links are either synchronous or asynchronous. %(no partially synchronous links are needed). Our ACS protocol incurs an amortized communication cost of $O(n^3\lambda)$ bits per input, and our VSS and MPC protocols incur amortized communication costs of $O(n^3)$ and $O(n^4)$ field elements per secret and per multiplication gate, respectively. To design our protocols, we also construct protocols for Reliable Broadcast and Externally Valid Byzantine Agreement (EVBA), which are of independent interest.

We propose new techniques for estimating the probability that an input difference leads to an output difference in a block cipher (i.e., the probability of a differential) under the assumption of independent round-keys. We apply our techniques to AES, and show that the probability of every non-trivial differential in 8-round AES is within an additive factor of $2^{-128} \cdot \frac{1}{50}$ from the expected value of $\frac{1}{2^{128} - 1}$. We further apply our techniques to prove that 40-round AES is at most $2^{-135}$-close to a pairwise independent permutation. This improves upon the work of Liu, Tessaro and Vaikuntanathan [CRYPTO 2021], who proved a similar bound for 9000-round AES. To obtain our results, we develop and adapt a variety of techniques for analyzing differentials using functional analysis. We expect these techniques to be useful for analyzing differentials in additional block ciphers besides the AES.

Inner Product Arguments (IPA) [BCC+16,BBB+17] are a family of proof systems with $O(\log n)$ sized proofs, $O(n)$ time verifiers, and transparent setup. Bootle, Chiesa and Sotiraki [BCS21] observed that an IPA can be viewed as a sumcheck protocol [LFKN92] where the summed polynomial is allowed to have coefficients in a group rather than a field. We leverage this viewpoint to improve the performance of multi-linear polynomial commitments based on IPA. Specifically, - We introduce a simplified variant of Halo-style accumulation that works for multilinear evaluation claims, rather than only univariate ones as in [BGH19,BCMS20]. - We show that the size $n$ MSM the IPA verifier performs can be replaced by a ``group variant'' of $\mathsf{basefold}$[ZCF23]. This reduces the verifier complexity from $O(n)$ to $O_{\lambda}(\log^2 n)$ time at the expense of an additional $4n$ scalar multiplications for the IPA prover.

One of the main layers in the Advanced Encryption Standard (AES) is the substitution layer, where an $8 \times 8$ S-Box is used $16$ times. The substitution layer provides confusion and makes the algorithm resistant to cryptanalysis techniques. Therefore, the security of the algorithm is also highly dependent on this layer. However, the cost of implementing $8 \times 8$ S-Box on FPGA platforms is considerably higher than other layers of the algorithm. Since S-Boxes are repeatedly used in the algorithm, the cost of the algorithm highly comes from the substitution layer. In 2005, Canright used different extension fields to represent AES S-Box to get FPGA-friendly compact designs. The best optimization proposed by Canright reduced the gate-area of the AES S-Box implementation by $20\%$. In this study, we use the same optimization methods that Canright used to optimize AES S-Box on hardware platforms. Our purpose is not to optimize AES S-Box; we aim to create another $8 \times 8$ S-Box which is strong and compact enough for FPGA platforms. We create an $8 \times 8$ S-Box using the inverse field operation as in the case of AES S-Box. We use another irreducible polynomial to represent the finite field and get an FPGA-friendly compact and efficient $8 \times 8$ S-Box. The finite field we propose provides the same level of security against cryptanalysis techniques with a $3.125\%$ less gate-area on Virtex-7 and Artix-7 FPGAs compared to Canright’s results. Moreover, our proposed S-Box requires $11.76\%$ less gate on Virtex-4 FPGAs. These gate-area improvements are beneficial for resource-constraint IoT devices and allow more copies of the S-Box for algorithm parallelism. Therefore, we claim that our proposed S-Box is more compact and efficient than AES S-Box. Cryptographers who need an $8 \times 8$ S-Box can use our proposed S-Box in their designs instead of AES S-Box with the same level of security but better efficiency.

Non-interactive batch arguments (BARGs) for NP allow a prover to prove $\ell$ NP statements with a proof whose size scales sublinearly with $\ell$. In this work, we construct a pairing-based BARG where the size of the common reference string (CRS) scales linearly with the number of instances and the prover's computational overhead is quasi-linear in the number of instances. Our construction is fully black box in the use of the group. Security relies on a $q$-type assumption in composite-order pairing groups. The best black-box pairing-based BARG prior to this work has a nearly-linear size CRS (i.e., a CRS of size $\ell^{1 + o(1)}$) and the prover overhead is quadratic in the number of instances. All previous pairing-based BARGs with a sublinear-size CRS relied on some type of recursive composition and correspondingly, non-black-box use of the group. The main technical insight underlying our construction is to substitute the vector commitment in previous pairing-based BARGs with a polynomial commitment. This yields a scheme that does not rely on cross terms in the common reference string. In previous black-box pairing-based schemes, the super-linear-size CRS and quadratic prover complexity was due to the need for cross terms.

Finite field arithmetic is central to several cryptographic algorithms on embedded devices like the ARM Cortex-M4, particularly for elliptic curve and isogeny-based cryptography. However, rapid algorithm evolution, driven by initiatives such as NIST’s post-quantum standardization, might frequently render hand-optimized implementations obsolete. We address this challenge with m4-modarith, a library generating C code with inline assembly for the Cortex-M4 that rivals custom-tuned assembly, enabling agile development in this ever-changing landscape. Our generated modular multiplications obtains fast performances, competitive with hand-optimized assembly implementations published in the literature, even outperforming some of them for Curve25519. Two contributions are pivotal to this success. First, we introduce a novel multiplication strategy that matches the memory access complexity of the operand caching method while being applicable to a larger cache size for Cortex-M4 implementations. Second, we generalize an efficient pseudo-Mersenne reduction strategy, and formally prove its correctness and applicability for most primes of cryptographic interest. Our generator allowed agile optimization of SQIsign’s NIST PQC Round 2 submission, improving level 1 verification from 123 Mcycles to only 54 Mcycles, a $2.3\times$ speedup. As an additional case study, we use our generator to improve performance of portable implementations of RFC~7748 by up to $2.2\times$.

Proving the validity of ballots is a central element of verifiable elections. Such proofs can however create challenges when one desires to make a protocol receipt-free. We explore the challenges raised by validity proofs in the context of protocols where threshold receipt-freeness is obtained by secret sharing an encryption of a vote between multiple authorities. In such contexts, previous solutions verified the validity of votes by decrypting them after passing them through a mix-net. This approach however creates subtle privacy risks, especially when invalid votes leak structural patterns that threaten receipt-freeness. We propose a different approach of threshold receipt-free voting in which authorities re-randomize ballot shares then jointly compute a ZK proof of ballot validity before letting the ballots enter a (possibly homomorphic) tallying phase. Our approach keeps the voter computational costs limited while offering verifiability and improving the ballot privacy of previous solutions. We present two protocols that enable a group of servers to verify and publicly prove that encrypted votes satisfy some validity properties: Minimix, which preserves prior voter-side behavior with minimal overhead, and Homorand, which requires voters to submit auxiliary data to facilitate validation over large vote domains. We show how to use our two protocols within a threshold receipt-free voting framework. We provide formal security proofs and efficiency analyses to illustrate trade-offs in our designs.

Physical attacks pose a major challenge to the secure implementation of cryptographic algorithms. Although significant progress has been made in countering passive attacks such as side-channel analysis (SCA), protection against fault attacks is still less developed. One reason for this is the broader and more complex nature of fault attacks, which makes it difficult to create standardized fault evaluation methodologies for countermeasures like those used for SCA. This makes it easier to overlook potential vulnerabilities that attackers could exploit. RS-Mask, published at HOST 2020, is such a countermeasure that has been affected by the absence of a systematic analysis method. The fundamental concept behind the countermeasure is to maintain a uniform distribution of variables, regardless of whether they are faulty or correct. This property is particularly effective against Statistical Ineffective Fault Attacks (SIFA), which exploit the dependency between fault propagation and the secret data. In this work, we present several fault scenarios involving single fault injections on the AES implementation protected with RS-Mask, where the fault propagation depends on the secret data. This happens because the random space mapping used in RS-Mask countermeasure retains a dependency on the secret data, as it is derived based on the S-box input. To address this, we propose a new countermeasure based on the core concept of RS-Mask, implementing a single mapping for all S-box inputs, involving an intrinsic duplication. Next, we evaluate the effectiveness of the new countermeasure against fault attacks by comparing the fault detection rate across all possible fault locations and values for every input. Additionally, we examine the output differences between faulty and correct outputs for each input. Our results show that the detection rate is uniform for each input, which ensures security against statistical attacks utilizing both effective and ineffective faults. Moreover, the output differences being uniform for each input ensures security against differential fault attacks.

Homomorphic encryption (HE) offers strong privacy guarantees by enabling computation over encrypted data. However, the performance of tensor operations in HE is highly sensitive to how the plaintext data is packed into ciphertexts. Large tensor programs introduce numerous possible layout assignments, making it both challenging and tedious for users to manually write efficient HE programs. In this paper, we present Rotom, a compilation framework that autovectorizes tensor programs into optimized HE programs. Rotom systematically explores a wide range of layout assignments, applies state-of-the-art optimizations, and automatically generates an equivalent, efficient HE program. At its core, Rotom utilizes a novel, lightweight ApplyRoll layout conversion operator to easily modify the underlying data layouts and unlock new avenues for performance gains. Our evaluation demonstrates Rotom scalably compiles all tensor workloads in under 5 minutes, reduces rotations in hand-tuned protocols by up to 3×, and achieves up to 80× performance improvement over prior autovectorization systems.

The synchrony model allows Byzantine Agreement (BA) protocols to be deterministic, tolerate minority faults, and achieve the asymptotically optimal $O(n)$ rounds, and $O(n^2)$ bits of communication where $n$ is the number of parties. We study the deterministic BA problem in a model in which every communication link is either synchronous or partially synchronous. Our main result for this model is that feasibility implies optimality: For every $\frac{n}{3}\leq f<\frac{n}{2}$, the minimal network conditions required for BA to be solvable against $f$ byzantine faults, are also sufficient for it to be solvable optimally, i.e., with $O(f)$ rounds and $O(f^2)$ communication. In particular, BA against minority byzantine faults can be solved when the synchronous links in the network form a mere path ($f$ synchronous links) as efficiently (up to constant factors) as when all communication links are synchronous ($\Omega(f^2)$ synchronous links).

High-throughput technologies (e.g., the microarray) have fostered the rapid growth of gene expression data collection. These biomedical datasets, increasingly distributed among research institutes and hospitals, fuel various machine learning applications such as anomaly detection, prediction or clustering. In particular, unsupervised classification techniques based on biclustering like the Cheng and Church Algorithm (CCA) have proven to adapt particularly well to gene expression data. However, biomedical data is highly sensitive, hence its sharing across multiple entities introduces privacy and security concerns, with an ever-present threat of accidental disclosure or leakage of private patient information. To address such threat, this work introduces a novel, highly efficient privacy-preserving protocol based on secure multiparty computation (MPC) between two servers to compute CCA. Our protocol performs operations relying on an additive secret sharing and function secret sharing, leading us to reformulate the steps of the CCA into MPC-friendly equivalents. Leveraging lightweight cryptographic primitives, our new technique named FunBic-CCA is first to exploit the efficiency of function secret sharing to achieve fast evaluation of the CCA biclustering algorithm.

Evaluating the security of a device against side-channel attacks is a difficult task. One prominent strategy for this purpose is to characterize the distribution of the rank of the correct key among the different key hypotheses produced by a maximum likelihood attack, depending on the number of measured traces. In practice, evaluators can estimate some statistics of the rank that are used as security indicators---e.g., the arithmetic and geometric mean rank, the median rank, the $\alpha$-marginal guesswork, or the success rate of level $L$. Yet, a direct estimation becomes time-consuming as security levels increase. In this work, we provide new bounds on these figures of merit in terms of the mutual information between the secret and its side-channel leakages. These bounds provide theoretical insights on the evolution of the figures of merit in terms of noise level, computational complexity (how many keys are evaluated) and data complexity (how many side-channel traces are used for the attack). To the best of our knowledge, these bounds are the first to formally characterize security guarantees that depend on the computational power of the adversary, based on a measure of their informational leakages. It follows that our results enable fast shortcut formulas for the certification laboratories, potentially enabling them to speed up the security evaluation process. We demonstrate the tightness of our bounds on both synthetic traces (in a controlled environment) and real-world traces from two popular datasets (Aisylab/AES\_HD and SMAesH).

The widespread use of machine learning on sensitive data makes Privacy-Preserving Machine Learning (PPML) essential for data confidentiality. Current state-of-the-art PPML systems employ hybrid protocol designs to evaluate various operators to achieve better performance; yet, existing hybrid approaches adopt fixed protocol assignments without considering the deployment setting, resulting in inefficiencies across diverse network environments, such as LANs and WANs. To address this, we introduce NetAdapt, a cost-model-driven framework that automatically assigns FHE and MPC protocols to optimize inference efficiency under varying network conditions, by designing a predictive cost model based on the dialect of the Multi-Level Intermediate Representation (MLIR)’s Tensor Operator Set Architecture (TOSA), and an ILP-based solver for managing the cross-protocol conversion while dynamically updating FHE costs based on homomorphic multiplication depth. Experimental results demonstrate that NetAdapt delivers $6.68\times$ to $12.92\times$ improvements in inference running time compared to state-of-the-art solutions, allowing network-agnostic PPML.

We introduce the $\textsf{Three-Hash Framework}$ ($\textsf{THF}$), a new instantiation of the $\textsf{LRW+}$ paradigm that employs three hash functions to process tweak inputs. We prove that $\textsf{THF}$ achieves beyond-birthday-bound security under standard assumptions. By extending the general practical cryptanalysis framework to the multiple-tweak setting, we further demonstrate that $\textsf{THF}$ offers balanced resistance to both single- and multiple-tweak attacks, thereby enabling the potential for lower latency compared to existing constructions. Building on this framework, we design $\texttt{Blink}$, a family of tweakable block ciphers optimized for ultra-low latency. $\texttt{Blink}$ features logarithmic-depth Toeplitz-based hashing, which ensures efficient diffusion and scalability with varying tweak lengths. Our cryptanalysis shows that $\texttt{Blink}$ achieves strong security with fewer rounds, while hardware evaluations confirm its superior latency performance. Notably, $\texttt{Blink}$ maintains comparable latency even when the tweak length is doubled, underscoring the scalability advantage of $\textsf{THF}$.

The field of private information retrieval (PIR) has made significant strides with a recent focus on protocols that offer sublinear online time, ensuring efficient access to public databases without compromising the privacy of the queries. The pioneering two-server PIR protocols developed by Corrigan-Gibbs and Kogan (EUROCRYPT 2020) enjoy the dual benefits of sublinear online time and statistical security. This allows their protocols to provide high efficiency and resist computationally unbounded adversaries. In this work, we extend this seminal work to the symmetric PIR (SPIR) context, where the protocol must ensure that the client is privy only to the requested database entries, with no knowledge of the remaining data. This enhancement aligns with scenarios where the confidentiality of non-requested information is as critical as the query itself. Our main result is the introduction of the first two-server SPIR protocols that achieve both sublinear online time and statistical security, together with an enhancement for achieving sublinear amortized time. Our protocols require a pragmatic level of shared randomness between the servers, which however is necessary for implementing statistical security in two-server SPIR, as showed by Gertner et al. (STOC 1998).

FrodoKEM is a post-quantum key encapsulation mechanism based on plain Learning With Errors (LWE). In contrast to module-lattice-based schemes, it relies on an unstructured variant of the LWE problem, providing more conservative and better-understood security guarantees. As a result, FrodoKEM has been recommended by European cybersecurity agencies such as BSI and ANSSI, and has also been proposed in international standardization efforts, including ISO and the IETF Internet-Draft process. In this paper, we explore hardware-level parallelization techniques for FrodoKEM. To date, the only notable attempt to parallelize FrodoKEM in hardware was made by Howe et al. in 2021. In their work, the SHAKE function was identified as a performance bottleneck and replaced by the Trivium stream cipher. However, this replacement renders the implementation incompatible with standardized recommendations. In contrast, our work adheres strictly to the original FrodoKEM specification, including its use of SHAKE as the PRNG, and introduces a scalable architecture enabling high-throughput parallel execution. For FrodoKEM-640, we present parallel architectures for key generation, encapsulation, and decapsulation. Our implementation achieves between 976 and 1077 operations per second, making it the fastest FrodoKEM hardware implementation reported to date. Furthermore, we propose a general architecture that offers a scalable area-throughput trade-off: by increasing the number of DSPs and proportionally scaling BRAM usage, our design can be scaled to achieve significantly higher performance beyond the reported implementation. This demonstrates that SHAKE is not inherently a barrier to parallel matrix multiplication, and that efficient, standard-compliant FrodoKEM implementations are achievable for high-speed cryptographic applications.

A major challenge in elliptic curve cryptosystems consists in efficiently mitigating the small-subgroup attack. This paper explores batch subgroup membership testing (SMT) on pairing-friendly curves, particularly for the Barreto–Lynn–Scott family of embedding degree 12 (BLS12) due to its critical role in modern pairing-based cryptography. Our research introduces a novel two-step procedure for batch SMT to rapidly verify multiple points at once, cleverly combining the already existing tests based on the Tate pairing and a non-trivial curve endo- morphism. We clarify why the invented technique is significantly faster (despite a negligible error probability) than testing each point individu- ally. Moreover, it is applicable to prominent curves like BLS12-381 and BLS12-377 being frequently employed in zero-knowledge applications. Nonetheless, to further enhance the speed (or reduce the error proba- bility) of the proposed batch point validation, we have generated two new BLS12 curves that are specifically optimized for this purpose. We also provide an open-source high-speed software implementation in Go, showcasing significant performance improvements achieved by our work.

Decision trees are extensively employed in artificial intelligence and machine learning due to their interpretability, efficiency, and robustness-qualities that are particularly valued in sensitive domains such as healthcare, finance, and cybersecurity. In response to evolving data privacy regulations, there is an increasing demand for models that ensure data confidentiality during both training and inference. Homomorphic encryption emerges as a promising solution by enabling computations directly on encrypted data without exposing plaintext inputs. This survey provides a comprehensive review of privacy-preserving decision tree protocols leveraging homomorphic encryption. After introducing fundamental concepts and the adopted methodology, a dual-layer taxonomy is presented, encompassing system and data characteristics as well as employed processing techniques. This taxonomy facilitates the classification and comparison of existing protocols, evaluating their effectiveness in addressing key challenges related to privacy, efficiency, usability, and deploy- ment. Finally, current limitations, emerging trends, and future research directions are discussed to enhance the security and practicality of homomorphic encryption frameworks for decision trees in privacy-sensitive applications.

Deep learning-based side-channel analysis (DLSCA) represents a powerful paradigm for running side-channel attacks. DLSCA, in a state-of-the-art setting, can break multiple targets with a single attack trace, requiring minimal feature engineering. As such, DLSCA is an extremely active research area for both industry and academia. At the same time, due to domain activity, it becomes more difficult to understand the current trends and challenges. In this systematization of knowledge, we provide a critical overview of developments in DLSCA over the past years, enabling us to offer concrete suggestions and taxonomies. Moreover, we examine the reproducibility perspective and show that achieving it in full is difficult and requires a careful experimental setup.