Token-weighted voting is widely used in DAO governance, but public voting weights together with weighted tallies can reveal identifiable voters' choices. Publishing only the final outcome reduces this disclosure, yet an output policy alone does not prevent a privileged participant from reconstructing the exact weighted tally during computation. We present a verifiable winner-only tally-hiding construction for weighted binary voting. Registered weights are bound to credentials in...

Modern public-key cryptography is threatened by advances in quantum computing. As a result, there has been a shift towards cryptographic algorithms that can resist attacks by a quantum computer. However, these algorithms use significantly longer keys, and produce larger ciphertexts and digital signatures than their classical counterparts. These bigger sizes pose problems for devices that are bandwidth- and/or power-limited, and wish to establish a secure, quantum resistant communication...

Anamorphic cryptography targets the scenario in which a dictator does not forbid the use of cryptography but requires all users to reveal their secret keys to them. Thus, the dictator can decrypt all honestly generated ciphertexts. The approach for bypassing this is to identify spots, such as random nonces, in existing cryptographic protocols in which secret messages can be hidden using an additional secret double key. So far, the literature mostly focused on identifying such spots in simple...

Anonymity infrastructures such as mix networks, anonymous storage, and privacy-preserving replication rely on public re-randomization: any party holding only public information can transform a ciphertext into a fresh-looking encryption of the same plaintext, hiding the linkage between the two. Classical ElGamal-based solutions are broken by quantum adversaries, while existing lattice-based alternatives carry very large ciphertexts with unanalyzed noise growth, rely on heavyweight...

Blockchains aim to provide open access and censorship resistance, but centralization of block production in blockchains like Ethereum undermines these goals. Inclusion List (IL) protocols mitigate this by requiring block proposers to include transactions selected by an IL committee to enforce the inclusion of transactions that appear to have been censored. However, protecting the confidentiality of individual committee members’ contributions is essential to prevent retaliation and ensure...

Bilinear groups, also known as pairing groups, are a versatile tool that enables many efficient cryptographic constructions. Among bilinear groups, those with a composite order (N = p · q for two large, secret primes p, q) offer an additional algebraic structure which is advantageous in many applications. They are however dramatically less efficient than their prime-order counterparts, so multiple translation frameworks for constructions from composite- to prime-order groups have been...

We formalize the notion of polynomial commitment schemes (PCSs) in the proof assistant Isabelle/HOL and formally verify the security proofs of two variants of the widely popular Kate, Zaverucha, and Goldberg (KZG) construction. Moreover, we formalize the Algebraic Group Model (AGM) by Fuchsbauer, Kiltz, and Loss using a novel constraint-programming-inspired approach. We formalize a reusable abstract definition of polynomial commitment schemes and define games for correctness, binding,...

We prove that under a plausible heuristic assumption (on the smoothness of certain random integers), the supersingular isogeny problem can be solved in time and memory $p^{1/3 + o(1)}$. This improves upon the previous best complexity of $p^{1/2} \cdot(\log p)^{O(1)}$. This problem is arguably the central hard problem underlying isogeny-based cryptography, and the cost of its resolution is a major (and often the only) factor in the choice of secure parameters. The impact on concrete...

Confidential sources are vital for investigative journalism and thus for holding those in power to account. However, sources often face great risks to their privacy and safety. SecureDrop is a system that enables sources to anonymously contact journalists, including at major news organisations around the world. Despite its widespread use, the current design requires physical servers hosted on premises. While cloud-based deployment would alleviate this burdensome requirement and improve...

In secret-key private information retrieval, a client with a short secret key retrieves a database item while hiding the requested index, and possibly also the database, from the server. The server answers using an encoded version of the database, generated via one-time preprocessing. Secret-key PIR provides an attractive "stateless" alternative to stateful PIR and oblivious RAM, and can be viewed as strengthening the standard notion of searchable symmetric encryption by not allowing any...

Fixed‑weight sampling is a core primitive in many post‑quantum schemes, including the HQC key encapsulation mechanism. An early implementation of fixed-weight vector sampling in HQC was shown by Guo et al. (CHES 2022) to suffer from a timing side-channel vulnerability, leading to complete key recovery. This timing side-channel was fixed in the current HQC version, however, power side-channel leakage is not addressed. In this work, we demonstrate that fixed-weight vector sampling in HQC...

Attribute-based inner-product functional encryption (AB-IPFE), introduced by Abdalla et al. (Asiacrypt'20), is a cryptosystem that combines the access-control capability of attribute-based encryption (ABE) with the linear-computation capability of inner-product functional encryption. By introducing a hierarchical structure between these two functionalities, we can decompose the key generation algorithm into two steps. While such a structure has been extensively studied in contexts such as...

Cross-chain atomic swaps enable decentralized asset exchange across independent ledgers, but their public transcripts may expose transaction flows, signer identities, and business relationships. Existing scriptless swap mechanisms based on adaptor signatures provide witness-coupled execution, yet the signer is public. Linkable ring adaptor signatures further hide the signer within a ring, but they do not support controlled opening when a completed swap becomes disputed. In this paper, we put...

Integrating Real-World Assets (RWA) into Decentralized Finance (DeFi) enables borrowers to leverage off-chain assets for on-chain transactions. However, this integration faces a critical security challenge: ensuring that private asset data, utilized within cryptographic proofs, is authenticated by and cryptographically bound to a trusted issuer. Existing solutions, such as decentralized identifiers (DIDs) and oracles, fail to simultaneously satisfy the requisite security standards and...

Post-quantum signatures built from Fiat--Shamir transforms of zero-knowledge identification protocols---including LESS, CROSS, and MEDS---use GGM-tree seed compression to shrink signatures, revealing only the seeds of public rounds while hiding the challenge-dependent ones. This mechanism introduces a fault-attack surface: faulting the seed-publication can expose hidden seeds alongside their zero-knowledge responses, enabling recovery of secret information. We introduce the...

Hybrid post-quantum migration is entering deployed handshake designs, but hybrid KEM security protects only one shared-secret input. It does not by itself say whether handshake, application, exporter, or resumption material remains pseudorandom after branch reveals, stage-key reveals, selective corruptions, or late corruptions. We characterize these staged claims through branch-formula freshness: each stage receives a monotone formula over branch exposure, authentication freshness,...

We present a post-quantum commitment scheme based on kernel-tagged punctured Richelot isogeny walks on superspecial genus-2 Jacobians. The puncturing rule skips every step landing in the product locus, detected by I10 = 0, so honest executions remain in the Jacobian locus and avoid the entry point of known product-locus attacks. Each opening is encoded as a deterministic non-backtracking walk together with a kernel tag recording its action on a small public auxiliary torsion basis....

Proximity testing is crucial to location-privacy applications, from discovering nearby friends to enabling UAV collision avoidance. In such settings, users must determine proximity without revealing their exact locations. This motivates privacy-preserving proximity testing (PPPT) protocols revealing only if the proximity condition holds, while hiding both parties’ inputs. However, most existing PPPT protocols rely on strong assumptions (e.g., non-colluding servers) or require simultaneous...

We show that private-key function-hiding inner-product functional encryption (FH-IPFE) is impossible in the generic group model (GGM). This impossibility extends to (non-compact) two-input quadratic functional encryption (QFE) under a weak security notion that allows only a single key corruption. Our results apply both to the variant where decryption outputs the result directly, and to the variant where the result is encoded in the exponent of a group element. Our results hold in both...

Fair and free elections are the foundation of democracies and democratic processes. They require voting protocols that guarantee the integrity and verifiability of the result, as well as the private choice of each voter. Currently deployed e-voting protocols rely on traditional hardness assumptions, like the discrete logarithm problem, to provide these security guarantees. They are not post-quantum secure (pq-secure). While first proposals for pq-secure protocols exist, they are limited...

Blockchain provides public verifiability for access control in Internet of Things (IoT) data sharing, but its transparency can expose requester attributes, access policies, and their satisfaction relations. Existing privacy-preserving approaches often protect only one side of the authorization decision or rely on pairing-based ABE/HVE, interactive homomorphic computation, or circuit-specific proof parameters. This paper proposes a blockchain-based access control scheme that verifies...

Topology-hiding computation (THC) enables a set of parties, communicating over an incomplete network, to execute a secure multiparty computation (MPC) protocol for securely computing a function, while also hiding the network topology from within a given class of graphs. Semi-honest THC can be achieved over arbitrary graph classes, facing an arbitrary number of corruptions, from various assumptions implying oblivious transfer (OT). These assumptions are justified by strong lower bounds,...

The increasing deployment of large language models (LLMs) in high-stakes domains demands infrastructure to ensure trust in artificial intelligence (AI)-generated outputs and actions. Users often struggle to validate results from LLMs because their reasoning is opaque and possibly beyond human comprehension. This paper introduces proof-carrying output (PCO), a framework in which an AI system returns an answer accompanied by a machine-checkable proof. We define φ-compliance formally (see the...

Threshold ring signatures (TRS) enable a quorum of $T$ users to jointly sign a message while hiding which $T$ of the $N$ ring members participated, supporting privacy-preserving endorsement in ad-hoc settings. That said, many deployments do not need anonymity over every $T$-subset of a ring: when the approval pattern is already public, a structured ring can be sufficient. In this work, we first formalize this setting as a structured threshold ring signature (sTRS) and introduce...

We present PQES-AKE, a novel two-party authenticated key exchange (AKE) protocol built upon the Post-Quantum Encryption and Signcryption Scheme (PQES) introduced by Kara et al. The protocol achieves mutual authentication, session key secrecy, and forward secrecy in a post-quantum adversarial model. The central design principle of PQES-AKE is the concealment of ephemeral Diffie-Hellman (DH) keys within affine masks derived from randomness generated internally by the PQES signcryption...

Communication locality of an $n$-party protocol measures the maximum degree of the communication graph induced by the protocol execution. While secure multi-party computation (MPC) with small, sublinear locality exists in the static-corruption setting, this goal seems nearly paradoxical in the adaptive-corruption setting: Even against fail-stop adversaries, small neighbour sets of honest parties lie vulnerable to identification and corruption. Surprisingly, Chandran et al. [ITCS '15]...

Convolutional neural network parameters are valuable intellectual property, yet many APIs expose only top-1 labels and assume hidden logits limit parameter recovery. Prior cryptanalytic extraction can recover functionally equivalent ReLU MLPs, but CNNs introduce weight sharing, parallel critical hyperplanes, coupled spatial perturbations, and channel-sign ambiguity. This paper presents an end-to-end hard-label extraction attack for known-architecture ReLU CNN classifiers with average...

The security of decentralized asset custody and blockchain consensus increasingly relies on threshold signatures to eliminate single points of failure. In these high-stakes environments, static security models are an insufficient theoretical abstraction. Real-world blockchain deployments demand adaptive security to ensure protocols remain secure against adversaries who reactively compromise participants based on observed network traffic and protocol state. While the NIST standardization...

We introduce new techniques for verifiable reporting of abusive messages in private messaging platforms. Our techniques are compatible with both metadata-hiding messaging systems, where the platform does not know who speaks to whom, and with third-party moderation, where the platform is not involved in the process of verifying or judging reported content. While prior work in this space considers the question of how a moderator would verify reports, prior works do not address the question...

Anonymous-credential (AC) schemes equip users with credentials on attested attributes such that users can later prove possession of a credential certifying (a subset of) those attributes without revealing anything else. In standard AC schemes, such proofs reveal the issuer of the credential, which may be more information than intended or necessary. Lately, there has been significant interest in designing stronger issuer-hiding anonymous-credential schemes that only reveal that the user has a...

We address the question of realizing privacy preserving analysis of user data. The abstract scenario considered is that an analyst aims to evaluate a function $f$ on some user data $X$. To achieve comprehensive privacy, it is necessary to protect the input $X$ directly. However, it is known that $f(X)$ may leak too much information about $X$ as well. A common approach to mitigate such risks is to make the computation differentially private. In practice, this is often accomplished by...

Verifiable Random Functions (VRFs) provide publicly verifiable pseudorandomness uniquely determined by a secret key and an input. While widely used in decentralized protocols, standard VRF verification reveals the signer's identity, exposing them to targeted adversarial disruption once their eligibility is known. We study Ring VRFs(RVRFs), which allow a member of a public key set (a ring) to publish a VRF value along with a proof of correct generation while hiding the signer's index...

Non-malleable codes allow a sender to transmit a message to a receiver, while providing a ``best-possible'' integrity guarantee to ensure that no attacker---who cannot already decode the message---can meaningfully tamper the message in transit. If tampered, the received message should either be invalid or unrelated to the original message. Non-malleable time-lock puzzles (TLPs) are a special case of non-malleable codes for bounded polynomial-depth tampering with very efficient...

We propose a new method to construct homomorphic authentication codes supporting the evaluation of *non-deterministic* computations, extending the celebrated homomorphic lattice encodings [Boneh et al., Eurocrypt 2014]. Our approach relies on the hardness of the decomposed learning with errors problem (LWE), a recently introduced modification of Regev's LWE assumption. We then use this new technical tool to make progress on several open problems in the literature. Specifically, we...

Multi-scalar multiplication (MSM), $MSM(\vec{P},\vec{x})=\sum_{i=1}^n x_i P_i$, is a dominant computational kernel in discrete-logarithm–based cryptography and often becomes a bottleneck for verifiers and other resource-constrained clients. We present 2G2T, a simple protocol for verifiably outsourcing MSM to an untrusted server. 2G2T is efficient for both parties: the server performs only two MSM computations and returns only two group elements to the client, namely the claimed result...

Adaptor signatures extend digital signatures with conditional disclosure capabilities, enabling atomic swaps, payment channels, and other advanced blockchain protocols. Although post-quantum adaptor signatures have been explored under lattice, isogeny, and coding-theoretic assumptions, no constructions have yet been realised from the multivariate quadratic (MQ) family of signatures. Classical algebraic adaptor techniques rely on embedding the witness into signing randomness, which is natural...

We introduce metric-aware code-based cryptography by moving beyond the Hamming metric to the Niederreiter-Rosenbloom-Tsfasman (NRT) and sum-rank metrics and by exploiting their linear isometry groups via Bruhat-Chevalley-Renner decompositions. On the structural side, we give isometry-invariant distance tests: a parity-check prefix-rank test for single-chain NRT, its multi-prefix extension for block-NRT, and a block rank-profile test for sum-rank. We also analyze orbit structure under the...

SSLE-DAG Proof-of-Stake (PoS) blockchains with publicly visible leader schedules expose future proposers to targeted Denial-of-Service (DoS) attacks. Single Secret Leader Election (SSLE) techniques address this problem by hiding the leader's identity until block publication. However, existing SSLE techniques are difficult to integrate with high-throughput Directed Acyclic Graph (DAG)-based Proof-of-Stake consensus protocols. We introduce SSLE-DAG, a PoS consensus protocol that combines a...

In federated learning (FL), secure aggregation (SA) allows a server to compute aggregate model updates (gradients) without accessing individual client gradients. SA is intended to protect clients’ local dataset from being inferred through individual gradients. However, recent NDSS 2025 work shows that even state-of-the-art SA protocols can be vulnerable, as a malicious server may reconstruct clients’ datasets from aggregated gradients. This demonstrates that protecting dataset privacy...

Recent MPC-in-the-Head (MPCitH) signatures increasingly rely on aggressive GGM-tree optimizations to reduce signature size and cost, culminating in _secret-key-root correlated_ GGM tree as used in MQOM (NIST PQC Standardization for Additional Signature Round-2, 2024). While this technique yields substantial compression, it introduces a dependency loop in the proof. The transcript we would like to randomize for simulation is generated by expanding a GGM tree from a root that is part of the...

Design-hiding (DH) schemes, such as logic locking, aim to protect circuit-design intellectual property (IP) in the integrated-circuit (IC) supply chain. While many practical DH schemes have been proposed over the past 15 years, nearly all have been broken by efficient attacks. Security and efficiency claims for these schemes have been based primarily on evaluations using benchmark circuits from legacy test-suites such as ISCAS’85 and MCNC. Recent work suggests that some circuits are...

We present AHAB, a suite of protocols for threshold Schnorr signatures in the asynchronous communication setting with guaranteed output delivery (robustness). We build on the AVSS and GoAVSS protocols of Shoup–Smart and Groth–Shoup, which allow t < n/3 static corruptions. First, we provide protocol enhancements and a full security proof in the adaptive corruption model with erasures. Second, we introduce a signature production pipeline with a player elimination framework that bounds the...

Privacy-Enhancing Know Your Customer (KYC) integrates one-time-use anonymous tokens (OTATs) into self-sovereign identity frameworks, such as the EU Digital Identity (EUDI) Wallet, Apple’s Private Access Tokens, and W3C’s Privacy-Preserving Advertising proposals (e.g., Private State Tokens), to enable regulatory compliance while preserving user anonymity. To mitigate targeted denial-of-service (DoS) attacks and prevent token misuse (e.g., farming and replay), this paper designs a new OTAT,...

Zero-Knowledge Succinct Non-Interactive Arguments (zkSNARGs) are SNARGs in which the proof reveals nothing except the validity of the claim. zkSNARGs for NP can be constructed generically from SNARGs for NP using a Non-interactive Zero-knowledge (NIZK) proof, but this transformation uses either the NIZK or the SNARG in a non-black-box way. We design a new SNARGs-to-zkSNARGs transformation that is conceptually different from the NIZK+SNARG approach. Our transformation is inspired by the...

Attribute-based anonymous credential systems often fail to conceal the identity of the credential issuer. Recent attempts to address this limitation either suffer from efficiency issues or rely on security models that make unrealistic assumptions about the behavior of issuers. In this paper, we demonstrate that existing security models, which assume honest issuers, are inadequate for real-world deployments. Concretely, we present attack scenarios in which a malicious user collaborates...

Instant messaging services are an integral part of today's communication and their privacy has wide societal implications. Major messengers deploy end-to-end encryption, hiding message contents from the service provider. Group messaging, however, creates the challenge of also keeping the group membership list private. The Signal messenger currently implements private group management using techniques inspired by Chase, Perrin, and Zaverucha (CCS 2020). Transitioning this system to...

Traceable secret sharing complements traditional schemes by enabling the identification of parties who sell their shares. Recently, two independent works extended traceable secret sharing to general access structures. Goyal, Jain, and Partap [EC'26] introduced a model in which a reconstruction box is augmented with a label $I \subseteq [n]$ and is only required to distinguish between two secrets when queried with the shares of parties in $I$. Based on how this label relates to the...

We introduce CRISP (\underline{C}hannel-\underline{R}andomised Single-\underline{I}mage\\ \underline{S}teganography with \underline{P}ermutations), a homomorphic steganography scheme for outsourced computation. In the setting we consider, a client (Alice) hides Boolean inputs in the least-significant bits of cover images and asks an honest-but-curious cloud (Carol) to evaluate a logic circuit, gate by gate, directly on those images so that a receiver (Bob) can later extract the result. The...

Anonymous credentials (AC) equip users with credentials on attested attributes, which enable them to prove data-minimizing statements over their attributes. However, in standard ACs, each credential presentation reveals the credential issuer, which could be more information than intended and necessary, e.g., when merely proving age or personhood. Issuer-Hiding Anonymous Credentials (IHAC) address this limitation and hide the issuer in the presentation. That is, they only reveal that the user...

Homomorphic Signatures (HS) enable the authentication of data that has been processed by an untrusted party, allowing a verifier to check the correctness of a computation without access to the original signed inputs. Since their introduction, HS have evolved from algebraically restricted linear schemes to expressive non-linear and Fully Homomorphic Signature (FHS) constructions, spanning diverse cryptographic assumptions and security models. This paper presents a Systematization of...

This paper presents a formal framework for decentralized identity (DID), which achieves both minimal disclosure and session unlinkability under public verifiability. We instantiate this framework as PrivDID. In PrivDID, a user can prove a predicate about a committed attribute via a single ring signature, thereby hiding in an anonymity set dynamically selected from the public ledger. PrivDID builds on Pedersen commitments and binary-range encodings, and is proven secure in the random oracle...

Succinct zero-knowledge machine learning (zkML) uses zk succinct non-interactive arguments of knowledge (zkSNARKs) to prove neural-network (NN) computations with logarithmic-size proofs. However, general-purpose zkSNARKs do not scale in zkML because compiling matrix-heavy NNs into arithmetic circuits is memory-prohibitive. Existing zkML methods rely on rank-1 constraint systems (R1CS) to hide NN architectures while retaining succinctness. Removing circuit-based representations, it has...

We present $\textsf{Jindo}$, a new lattice-based polynomial commitment scheme (PCS) optimized for client-side proving, which requires fast prover performance while supporting evaluation hiding and flexible parameter regimes. To achieve this, we build $\textsf{Jindo}$ on the previous lattice-based PCSs $\textsf{CELPC}$ (CRYPTO'24) and $\textsf{Greyhound}$ (CRYPTO'24), which exhibit fast proving performance but have several limitations for client-side proving. We resolve these limitations by...

We study t-out-of-n threshold fully homomorphic encryption (ThFHE) in the synchronous setting, i.e., when the set of t decryptors is known at the outset of the decryption protocol. It has been observed in various works that the synchronous setting assumption enables to efficiently circumvent one of the major difficulties of ThFHE, namely hiding noise terms whose gigantic magnitude is incurred by the reconstruction coefficients of Shamir secret sharing. Yet, prior to this work, ThFHE in the...

Anamorphic signatures (Kutylowski {\it et al.}, Crypto'23) provide a way to covertly use encryption by hiding ciphertexts inside digital signatures without a dictator noticing. Recently (Asiacrypt'24), Jaeger and Stracovsky advocated stronger security notions for the primitive. Their notion of dictator unforgeability requires a dictator's inability to produce fresh signatures that decrypt to a meaningful covert message. The notion of recipient unforgeability requires that anamorphic...

Collecting statistics from users of software and online services is crucial to improve service quality, yet obtaining such insights while preserving individual privacy remains a challenge. Function secret sharing (FSS) is a promising tool for this problem. However, FSS-based solutions still face several challenges for streaming analytics, where messages are continuously sent, and secure computation tasks are repeatedly performed over incoming messages. We introduce a new cryptographic...

We introduce a simple yet novel framework for privacy-preserving machine learning inference that allows a client to query multiple models without a trusted third party aggregator by leveraging homomorphically encrypted model evaluation and multi-party computation. This setting allows for dispersed training of models such that a client can query each separately, and aggregate the results of this `ensemble inference'; this avoids the data leakage inherent to techniques that train collectively...

A zero-knowledge proof of machine learning (zkML) enables a party to prove that it has correctly executed a committed model using some public input, without revealing any information about the model itself. An ideal zkML scheme should conceal both the model architecture and the model parameters. However, existing zkML approaches for neural networks primarily focus on hiding model parameters. For convolutional neural network (CNN) models, these schemes reveal the entire architecture,...

Secure coin-tossing is typically modeled as an input-less functionality, where parties with no private inputs jointly generate a fair coin. In the dishonest majority setting, however, a strongly fair coin-tossing protocol is impossible. To circumvent this barrier, recent work has adopted the weaker notion of game-theoretic fairness, where adversaries are rational parties with preferences for specific outcomes, seeking to bias the coin in their favor. Yet these preferences may encode secret...

In a mercurial signature, a signer signs a representative $m$ of an equivalence class of messages on behalf of a representative $\mathsf{pk}$ of an equivalence class of public keys, receiving the signature $\sigma$. One can then transform $\sigma$ into a signature $\sigma'$ on an equivalent (to $m$) message $m'$ under an equivalent (to $\mathsf{pk}$) public key $\mathsf{pk}'$. Mercurial signatures are helpful in constructing delegatable anonymous credentials: their privacy properties enable...

Traditional commit-and-reveal mechanisms have been used to realize sealed-bid on-chain auctions. However, these leak timing information, impose inefficient participation costs -- the inclusion fee to be paid for adding the transaction on-chain -- and also require multiple slots to execute the auction. Recent research investigates single-slot auctions; however, it requires a high threshold of honest parties. We present a protocol that addresses these issues. Our design combines...

Optical computing has garnered significant attention in recent years due to its high-speed parallel processing and low power consumption capabilities. It has the potential to replace traditional electronic components and systems for various computation tasks. Among these applications, leveraging optical techniques to address information security issues has emerged as a critical research topic. However, current attempts are predominantly focused on areas such as image encryption and...

As digital identity verification becomes increasingly pervasive, existing privacy-preserving approaches are still limited by complex circuit designs, large proof sizes, trusted setups, or high latency. We present Vega, a practical zero-knowledge proof system that proves statements about existing credentials without revealing anything else. Vega is simple, does not require a trusted setup, and is more efficient than the prior state-of-the-art: for a 1920-byte credential, Vega achieves 92 ms...

Anonymous-credential schemes allow users to obtain credentials on various attributes, and then use those credentials to give unlinkable proofs about the values of some attributes without leaking anything about others. They have recently received interest from companies including Google, Apple, and Cloudflare, and are being actively evaluated both at the IETF and in the EU. Anonymous credentials based on BBS signatures are a leading candidate for standardization. In some natural...

Anonymous credentials allow users to authenticate themselves in an anonymous and unlinkable fashion. By the end of 2026, EU member states will be required to issue digital identity wallets to their residents that enable authentication in this manner. In decentralized settings, we desire schemes with additional properties: schemes that allow multiple authorities to issue credentials, hide the identities of the issuers, and allow verifiers to dynamically choose their policies. We present...

We revisit multivariate commitments based on the hardness of solving systems of multivariate quadratic (MQ) equations over finite fields. We analyze a simple construction where a message µ is committed as c = (µ + F(r), G(r)), with F and G random quadratic maps. We prove that the scheme is computationally hiding assuming the intractability of the MQ problem. Its binding property reduces to solving random bilinear systems. We prove that this problem is NP-complete and study the performance of...

MEV (Maximal Extractable Value) remains one of the most corrosive forces in blockchain systems, enabling frontrunning, sandwiching, and other manipulations that directly exploit users. The core culprit is the transparent mempool: validators see transactions before they are ordered. Encrypted mempools are a promising solution by hiding transaction contents until after ordering. We present the first integration of encrypted mempools with a high-performance BFT protocol. Our system uses a...

Verifiable Secret Sharing (VSS) schemes are fundamental building blocks in distributed cryptography. While most existing works focus on threshold structures, many real-world applications require more general access structures, where participants have different levels of power and only certain subsets are authorized to reconstruct the secret. Existing computational VSS schemes for general access structures typically rely on Discrete Logarithm (DL)-based homomorphic commitments, which limits...

As three frequently used techniques for adaptive reprogramming in the QROM, the adaptive One-Way to Hiding (O2H) proposed by Unruh (CRYPTO 2014), the GHHM adaptive reprogramming proposed by Grilo et al. (ASIACRYPT 2021), and the Pan-Zeng adaptive reprogramming proposed by Pan and Zeng (PKC 2024), address different reprogramming scenarios, and do not appear to imply one another. A recent breakthrough by Jaeger (ASIACRYPT 2025) reveals a surprising connection: all three of these adaptive...

The growing need for secure computation has spurred interest in cryptographic techniques that operate on encrypted data without revealing its content. Fully Homomorphic Encryption (FHE), especially LWE-based schemes, enables such processing while preserving confidentiality. Decentralized computing offers scalable resources without requiring in-house servers, but it relies heavily on the confidentiality guarantees of underlying schemes. While many existing protocols successfully protect input...

In this paper, we present formally verified proofs of the popular KZG Polynomial Commitment Schemes (PCSs), including the security proofs for the properties of correctness, polynomial binding, evaluation binding and hiding. Polynomial commitment schemes have various applications in cryptography and computer science, including verifiable computation, blockchain and cryptocurrencies, secure multi-party computation as well as in the construction of ZK-SNARKs. To validate security, we utilise...

The European Commission's 2022 proposal for a regulation on child sexual abuse material, popularly labelled ChatControl, obliges online services to detect, report, and remove prohibited content, through client-side scanning. This paper examines the proposal as a case of undone science in computer security ethics: a domain where technical feasibility and rights-compatibility questions remain systematically underexplored. Combining legal analysis with philosophy of technology, the paper...

Leftover Hash Lemma (LHL) states that \(\mathbf{X} \cdot \mathbf{v}\) for a Gaussian \(\mathbf{v}\) is an essentially independent Gaussian sample. It has seen numerous applications in cryptography for hiding sensitive distributions of \(\mathbf{v}\). We generalise the Gaussian LHL initially stated over \(\mathbb{Z}\) by Agrawal, Gentry, Halevi, and Sahai (2013) to modules over number fields. Our results have a sub-linear dependency on the degree of the number field and require only...

One-way puzzles (OWPuzzs) introduced by Khurana and Tomer [STOC 2024] are a natural quantum analogue of one-way functions (OWFs), and one of the most fundamental primitives in ''Microcrypt'' where OWFs do not exist but quantum cryptography is possible. OWPuzzs are implied by almost all quantum cryptographic primitives, and imply several important applications such as non-interactive commitments and multi-party computations. A significant goal in the field of quantum cryptography is to base...

Traditional single-proposer blockchains suffer from miner extractable value (MEV), where validators exploit their serial monopoly on transaction inclusion and ordering to extract rents from users. While there have been many developments at the application layer to reduce the impact of MEV, these approaches largely require auctions as a subcomponent. Running auctions efficiently on chain requires two key properties of the underlying consensus protocol: selective-censorship resistance and...

Private information retrieval (PIR) enables a client to fetch a record from databases held by untrusted servers while hiding the access pattern (index or keyword) from the servers. In practical settings, however, data objects (e.g., articles, videos) are commonly tagged with multiple identifiers, which can be structured as {index, value, keywords}. Current PIR schemes are constrained to retrieving records based on a single index or a single keyword, and cannot efficiently handle conjunctive...

This paper introduces efficient, practical methods for encrypting IPv4/IPv6 addresses while preserving utility in logs, telemetry, and third-party data exchange. We focus on three practical goals: (i) format-compatible encryption that keeps outputs in the IPv6 address space and handles IPv4 inputs canonically; (ii) prefix-preserving encryption that retains network structure for analytics while hiding host identity; and (iii) non-deterministic encryption that resists correlation while...

Modern messengers use advanced end-to-end encryption protocols to protect message content even if user secrets are ever temporarily exposed. Yet, encryption alone does not prevent user tracking, as protocols often attach metadata, such as sequence numbers, public keys, or even plain user identifiers. This metadata reveals the social network as well as communication patterns between users. Existing protocols that hide metadata in Signal (i.e., Sealed Sender), for MLS-like constructions...

Oblivious RAM (ORAM) is a central cryptographic primitive that enables secure memory access while hiding access patterns. Among existing ORAM paradigms, hierarchical ORAMs were long considered impractical despite their asymptotic optimality. However, recent advancements (FutORAMa, CCS'23) demonstrate that hierarchical ORAM-based schemes can be made efficient given sufficient client-side memory. In this work, we present a new hierarchical ORAM construction that achieves practical performance...

Standard symmetric encryption schemes, such as AES, other block ciphers and their modes, and stream ciphers, are highly effective and efficient for many standard scenarios. All of them have been derived from Shannon's 1948 seminal work on the communication theory of secrecy systems. Here we look at other settings where the situation is somewhat different from the standard one: \textit{e}.\textit{g}., while the encryption process may fail to update the ciphertext a limited number of times, or...

At EUROCRYPT2012, Banerjee, Peikert, and Rosen introduced Ring Learning With Rounding (RLWR) problem and constructed lattice-based pseudorandom functions for the first time. Subsequently, Banerjee, Brenner, Leurent, Peikert, and Rosen named this family of lattice-based pseudorandom functions as SPRING, reanalyzed the security, and gave two practical instances. Building upon the SPRING family, Bouillaguet, Delaplace, Fouque, and Kirchner further extended it to a pseudorandom number generator...

Achieving (at least) a worst-case correctness error is essential for an underlying public-key encryption (PKE) scheme to which the Fujisaki-Okamoto (FO) transformation is applied. There are three average-case to worst-case (ACWC) transformations—denoted as $\mathsf{ACWC}_{0}$, $\mathsf{ACWC}_{1}$ (PKC 2023), and $\mathsf{ACWC}_{2}$ (TIFS 2023)-which generically convert a PKE scheme with an average-case correctness error into one with a worst-case correctness error. However, in these ACWC...

Rekeying is an effective technique for protecting symmetric ciphers against side-channel and key-search attacks. Since its introduction, numerous rekeying schemes have been developed. We introduce Post-Quantum Stateless Auditable Rekeying (PQ-STAR), a novel post-quantum secure stateless rekeying scheme with audit support. PQ-STAR is presented in three variants of increasing security guarantees: (i) Plain PQ-STAR lets an authorized auditor decrypt and verify selected ciphertexts; (ii)...

The World Wide Web Consortium (W3C) has established standards for decentralized identities (DIDs) and verifiable credentials (VCs). A DID serves as a unique identifier for an entity, while a VC validates specific attributes associated with the DID holder. To prove ownership of credentials, users generate verifiable presentations (VPs). To enhance privacy, the W3C standards advocate for randomizable signatures in VC creation and zero-knowledge proofs for VP generation. However, these...

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),...

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...

As of November 2021, Bitcoin supports “Taproot” spending policies whose on-chain format is a single elliptic curve point. A transaction spending the funds associated with a Taproot policy can be authorized by interpreting the curve point either (a) as a public key of the Schnorr signature scheme and providing a suitable signature, or (b) as a commitment to alternative spending conditions and satisfying those. Since a sufficiently powerful quantum adversary would be able to forge Schnorr...

During NIST's post-quantum cryptography standardization process, two generic transforms, Fujisaki-Okamoto (FO) and OAEP, are widely used to achieve the IND-CCA security. For instance, the final winner Kyber has utilized FO, and a variant of the 3rd-round finalist NTRU has utilized OAEP. The FO and OAEP are both constructed in the random oracle model (ROM), so to evaluate their post-quantum security, a security proof in the quantum random oracle model (QROM) is required. So far, the QROM...

In electronic voting systems, guaranteeing voter anonymity is essential. One primary method to ensure this is the use of a mix-net, in which a set of mix-servers sequentially shuffle a set of encrypted votes, and generate proofs that a correct permutation has been applied. Whilst mix-nets offer advantages over alternative approaches, their traditional use during the tallying phase introduces a significant robustness bottleneck: the process is inherently sequential and critically depends on...

We introduce a trapdoorless tracker construction for electronic voting that fundamentally reimagines verifiability through information flow control. Unlike existing E2E verifiable systems where receipt-freeness compromises individual verifiability, our approach achieves both simultaneously by requiring only temporary isolation of the voting calculator between ballot casting and verification—when voters enter unique challenges to compute trackers for locating their votes on the public tally...

Program verification ensures software correctness through formal methods but often incurs substantial computational overhead. In SAT-based verification, the verification task is reduced to satisfiability checking, where satisfiable instances yield concrete counterexamples and unsatisfiable instances are certified by resolution proofs. While satisfying assignments and resolution proofs are useful for establishing correctness, they may expose defect-relevant details, including concrete inputs...

Group Signatures are fundamental cryptographic primitives that allow users to sign a message on behalf of a predefined set of users, curated by the group manager. The security properties ensure that members of the group can sign anonymously and without fear of being framed. In dynamic group signatures, the group manager has finer-grained control over group updates while ensuring membership privacy (i.e., hiding when users join and leave). The only known scheme that achieves standard security...

While popular messaging apps already offer end-to-end confidentially, end-to-end metadata privacy is still far from being practical. Although several meta-data hiding systems have been developed and some like Tor have been popular, the proposed solutions lack in one or more aspects: the Tor network is prone to easy low-resourced attacks, and most others solely focus on anonymity for senders or receivers but do not both. Some recent solutions do consider end-to-end anonymity, however, they...

Equivalence class signatures (EQS), introduced by Hanser and Slamanig (AC’14, J.Crypto’19), sign vectors of elements from a bi- linear group. Their main feature is “adaptivity”: given a signature on a vector, anyone can transform it to a (uniformly random) signature on any multiple of the vector. A signature thus authenticates equivalence classes and unforgeability is defined accordingly. EQS have been used to improve the efficiency of many cryptographic applications, notably...

Public-coin protocols are cryptographic protocols in which all messages sent by a specific party (typically the receiver or verifier) consist solely of random bits. These protocols have been extensively studied $\textit{in the classical setting}$ due to their advantageous properties in several scenarios, such as the parallel repetition of interactive arguments, and the design of secure multi-party computation with low round complexity, among others. Curiously, $\textit{post-quantum}$...

Web3 applications, such as on-chain gaming, require unbiased and publicly verifiable randomness that can be obtained quickly and cost-effectively whenever needed. Existing services, such as those based on Verifiable Random Functions (VRF), incur network delays and high fees due to their highly interactive nature. FlexiRand [CCS 2023] addressed these problems by hiding the output of the VRF and using that as a seed to derive many randomnesses locally. These randomnesses are instantly...

Implementations of modern FHE schemes are available in various highly-optimized libraries. Many of these libraries are designed to allow developers who may not have deep expertise in FHE to build fast and secure privacy-preserving applications. To support such users, the API of these libraries often hides the internals of the schemes in question from the user. However, this design choice makes it hard for users of these libraries to modify existing schemes, or implement new ones; work that...

We introduce posterior security of digital signatures, the additional security features after the original signature is generated. It is motivated by the scenario that some people store their secret keys in secure hardware and can only obtain a standard signature through a standardized interface. In this paper, we consider two different posterior security features: anonymity and message hiding. We first introduce incognito signature, a new mechanism to anonymize a standard signature....

Sampling from non-uniform randomness according to an algorithm which keeps the internal randomness used by the sampler hidden is increasingly important for cryptographic applications, such as timing-attack-resistant lattice-based cryptography or certified differential privacy. In this paper we present a provably efficient sampler that maintains random sample privacy, or random sample hiding, and is applicable to arbitrary discrete random variables. Namely, we present a constant-time version...

Multi-client Attribute-Based Encryption (ABE) is a generalization of key-policy ABE where attributes can be independently encrypted across several ciphertexts w.r.t. labels, and a joint decryption of these ciphertexts is possible if and only if (1) all ciphertexts share the same label, and (2) the combination of attributes satisfies the policy of the decryption key. All encryptors have their own secret key and security is preserved even if some of them are known to the adversary. Very...