In a single secret leader election (SSLE) protocol, all parties collectively and obliviously elect one leader. Parties other than the selected leader should not be able to learn the identity of the leader unless it is revealed by the leader itself. The problem is first formalized by Boneh et al. (AFT 2020), and the first concretely feasible lattice-based SSLE with proof-of-concept implementations, $\mathsf{Qelect}$, was recently introduced by Wang and Zhang (USENIX 2025). In this work, we...

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...

Anonymous communication systems aim to hide which user sent which message. Existing designs span efficient mixnets that rely on at least one honest mix server and decentralized protocols such as Dining Cryptographers networks (DC-nets) or secure multi-party computation (MPC)-based shuffles, which typically require greater communication or interaction. We introduce \emph{verifiable self-mix} (VSM), an anonymity architecture for privately placing messages in a public bulletin-board...

Secure and anonymous messaging has many compelling use-cases and is becoming increasingly popular. In this paper, we consider it in the context of delay-and-disruption-prone networks, which are characterized by handicapped network access, disrupted operation, censorship, and intermittent network outages. With such settings in mind, we define and design a Private Identity-Based Bulletin Board (PIB^3) scheme, which allows users to anonymously post and retrieve messages to and from a...

Distributed monotone-policy encryption (DPE) lets each user sample and publish its own key, after which anyone can encrypt to a list of published keys under a monotone access policy that determines which coalitions can decrypt. Silent threshold encryption is the $t$-out-of-$N$ special case. What makes the primitive non-trivial is compactness, where the ciphertext stays sublinear in the policy description. Every post-quantum DPE scheme so far settles for selective security, fixing the...

Fully Homomorphic Encryption (FHE) has emerged as one of the key technologies for privacy-preserving computation, enabling arbitrary computation directly on encrypted data. Vectorized FHE schemes, such as Brakerski/Fan--Vercauteren (BFV), Brakerski--Gentry--Vaikuntanathan (BGV), and Cheon--Kim--Kim--Song (CKKS), are typically used in applications dealing with large datasets, for example, confidential database queries and private ML inference. These FHE schemes are based on the computational...

Field trace evaluation has emerged as a powerful tool in fully homomorphic encryption, with broad applications ranging from bootstrapping algorithms to privacy-preserving protocols. Recent advances have significantly reduced its noise growth by combining tower-based evaluation strategies with rescaling operations. However, existing analyses rely on uniform noise bounds that fail to capture the actual noise behavior across different coefficients, leading to substantial gaps between...

Designated Verifier Signatures (DVS) are an important variant of digital signatures that ensure only a specified verifier can validate a signature, while preserving non-transferability. With the advent of quantum computing, several quantum DVS schemes have been proposed to achieve quantum security. In this paper, we revisit the quantum DVS protocol of Xin et al. [Quantum Information Processing, 2022] and provide a structural cryptanalysis of its design. We show that the scheme admits an...

Neural differential distinguishers are usually compared at a fixed number of labeled samples. However, different input representations may require different numbers of ciphertexts per sample, making fixed-sample comparisons potentially misleading from a cryptanalytic data-complexity perspective. In this paper, we study neural differential distinguishers under a fixed ciphertext budget. We ask whether the available encryption queries should be spent on more independent plaintext bases, or on...

Witness encryption (WE) allows one party to encrypt a message under an arbitrary satisfiable circuit, so that anyone holding a satisfying input can decrypt. Efficient WE enables numerous modern applications, such as identity-based and attribute-based encryption. Recent candidates for efficient WE base their security on rank properties of structured ciphertext matrices, which encode the validity of a given witness. This shrinks ciphertext sizes considerably compared to previous...

This paper analyzes the bilinear embedding of matrix algebras into commutative cyclotomic rings. We apply the Cohn-Umans method. This establishes that single-multiplication bilinear monomial embeddings require a ring degree of $\widetilde{\Omega}(N^3)$. We circumvent this bound by routing Strassen tensor rank decompositions through orthogonal Chinese Remainder Theorem ideals. This reduces the asymptotic complexity to $\widetilde{\Omega}(N^{\log_2 7})$. We optimize the coprime tensor...

Oblivious Key-Value Stores (OKVS) (Garimella et al., CRYPTO 2021), once encoded, provide indistinguishability over keys and random values. This is an important property in many secure computation applications, such as private set intersection and multi-key searchable encryption. We introduce an Updatable Oblivious Key-Value Store with access control (UOKVS), a dynamic extension of OKVS that supports insertions over time. We provide meaningful security in the presence of updates by equipping...

Threshold public-key encryption (tPKE) has recently attracted renewed interest, largely due to NIST's call for Multi-Party Threshold Cryptography. While classical tPKE has approached a high state of maturity, its post-quantum counterpart has not. Indeed, thresholdizing the celebrated lattice-based Regev PKE, which forms the basis of ML-KEM, remains unsatisfactory. Interestingly, how to thresholdize Regev PKE has not fundamentally changed in over a decade --- the only thing that has...

At ITCS 2020, Bartusek, Ishai, Jain, Ma, Sahai, and Zhandry proposed a framework for witness encryption based on affine determinant programs and gave a concrete witness encryption candidate. Yao, Chen, and Yu later broke the separate ADP-based indistinguishability-obfuscation candidate, while noting that their attack did not apply to the witness-encryption construction. More recently, Soukhanov et al. proposed witness encryption from arithmetic affine determinant programs. Soukhanov...

Relying solely on encryption for privacy-preserving computations is prone to leakage-abuse/access-pattern attacks. TEEs, while cost-effective, are also vulnerable to side-channel attacks. Oblivious primitives, such as oblivious memory (ORAM) and data structures (ODS), are effective building blocks to mitigate these risks by concealing memory access patterns and side-channel information. Applications range from private contact discovery (Signal) to anonymous key transparency, encrypted email...

Since McEliece introduced the first code-based encryption scheme in 1978, most code-based cryptographic constructions have relied on hard problems related to decoding random linear codes (or variants thereof) or code equivalence. More recently, the use of the MPC-in-the-Head paradigm has enabled the construction of a new class of very competitive digital signature schemes relying on such assumptions, including the NIST submissions Mirath, PERK, RYDE, and SDitH, as well as a recent proposal...

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...

Modern zero-knowledge (ZK), fully homomorphic encryption (FHE) and Multi-party Computation (MPC) protocols have motivated research interest in Arithmetization-Oriented (AO) cryptographic primitives. The use of these protocols on embedded platforms requires consideration for protection against side-channel analysis (SCA), including timing and power attacks. Compared to traditional bit-oriented block ciphers, the design of side-channel countermeasures for AO-based ciphers poses unique...

Recent advances in lattice-based threshold cryptography, including threshold fully homomorphic encryption (ThFHE) and threshold public key encryption (ThPKE), commonly employ Shamir secret sharing over rings. While conceptually simple, these schemes suffer from rapidly growing denominator-clearing factors required for secret reconstruction as the number of parties $N$ increases, which in turn necessitates larger ciphertext moduli and complex reconstruction procedures. In this work, we...

Batched threshold encryption (BTE) is a novel public-key paradigm in which, once a batch of $B$ ciphertexts is designated, a decrypter evaluates them using decryption key shares generated by decryption committee nodes via threshold reconstruction. To mitigate Miner Extractable Value (MEV) attacks in fully decentralized environments like blockchains, it is essential to guarantee mempool privacy while supporting a silent setup that allows decentralized key generation among decryption nodes....

${\sharp}\textrm{Pencil}$ is a domain-extended pseudorandom function by Bhaumik et al, accepted at CRYPTO 2026, with a claim that it achieves close to $n$-bit security beyond the birthday bound. It is used as the key-derivation layer of the ${\sharp}\textrm{Pencil}$-CAU authenticated-encryption mode. We show that ${\sharp}\textrm{Pencil}$ has a birthday-bound collision attack: its front end $\textsf{Sharp}$ compresses the second half $N_2$ of the input through the $(n-8)$-bit...

Privacy-preserving machine learning under fully homomorphic encryption (FHE) faces a structural limitation: numerical precision is bound to cryptographic parameters and key material, forcing precision to be fixed at scheme initialization. Existing frameworks must regenerate keys or recompile circuits whenever bit-width changes, eliminating precision as a deployment-time performance knob and making mixed-precision strategies - widely used in plaintext machine learning - impractical under...

We present new sample-runtime tradeoffs for the decisional sparse Learning With Errors (LWE) and sparse Learning Parity with Noise (LPN) problems over $\mathbb{Z}_q$, specifically in regimes where the secret vector is constrained by a small $l_{\infty}$ norm. While small-secret constraints are useful for the practical efficiency of lattice-based cryptography—such as homomorphic encryption and zero-knowledge proofs—the extent to which an adversary can exploit these bounds when the coefficient...

We study two central problems in threshold cryptography from lattices: (1)~threshold encryption with silent setup for general thresholds $t \geq 2$, where no post-quantum constructions were previously known, and (2)~threshold fully homomorphic encryption (TFHE) with sublinear parameters, an open problem since the work of Boneh~et~al.\ (CRYPTO~2018). We introduce \emph{$(\alpha,\beta)$-Scaled Linear Secret Sharing Schemes} (LSSS), a relaxation of standard LSSS in which each authorized...

Private Set Intersection (PSI) enables parties to compute the intersection of their input item sets while preserving privacy. In many real-world applications, however, each item is accompanied by a sensitive weight, and the ability to privately compute over such weights is crucial. Existing research in this direction is fragmented and driven by application-specific goals, with representative examples including PI-Sum (computing the sum of weights over the intersection), inner-product Private...

PRIVIDEMA project (Privacy-Preserving Identity Management for Digital Wallets and Secure Data Sharing and Processing for Cyber Threat Intelligence Data) advances the state of the art in cryptographic and Privacy-Enhancing Technologies (PETs) to enable secure, interoperable, and trustworthy data exchange across sectors, with a focus on the domains of Cyber Threat Intelligence and Digital Identity Management. This paper presents two representative real-world use-cases: (1)...

Torus Fully Homomorphic Encryption (TFHE) enables the homomorphic evaluation of arbitrary functions via Programmable Bootstrapping (PBS). However, the modulus switching step inherent to bootstrapping introduces a rounding error that forces the discretization of the input space, limiting the achievable precision on real-valued inputs. We propose a correction algorithm based on a first-order Taylor expansion, applied after bootstrapping, that directly mitigates this rounding error. Our...

Hybrid fully homomorphic encryption (FHE) inference improves the practicality of private inference by letting the server evaluate linear layers homomorphically while the client decrypts and applies nonlinearities. Recent schemes attempt to protect model confidentiality by returning noisy, output-permuted responses and appealing to shuffle-model differential privacy (DP). We show that this protection fails in the correctness regime required by hybrid FHE systems. For a $d$-input linear layer,...

A $t$-out-of-$n$ threshold decryption scheme distributes decryption key shares among $n$ parties so that any $t$ of them can jointly decrypt a ciphertext, while fewer than $t$ learn nothing about the plaintext. Traditional threshold schemes provide no accountability: a coalition of $t$ or more parties can combine their key shares and construct a pirate decoder that decrypts arbitrary well-formed ciphertexts, without any risk of being traced. To address this, Boneh, Partap, and Rotem [CRYPTO...

Maintaining a decentralized system requires a collective governance mechanism that allows participants to agree on changes to the system. In particular, the governance mechanism should offer a voting functionality for casting, collecting, and tallying votes in a confidential yet verifiable manner. Scaling this functionality for millions of participants in a cost-effective manner is a critical requirement for permissionless blockchains that remains unmet. We put forward a "layer-2"...

The Generalized Feistel Network (GFN) underpins widely standardized block ciphers, yet its resistance to full plaintext recovery remains largely unexplored. This paper extends the full-plaintext attack framework for standard Feistel ciphers to multi-branch scenarios, mainly makes the following $3$ research contributions: (1) Developed classic full plaintext recovery attacks on $d$-round Type-I GFN ($d\ge 3$) under CPA with $d+1$ encryption queries and $2d$-round Type-I GFN under CCA with...

GRAFHEN is a group-based homomorphic-encryption proposal whose public key is a rewriting system and whose secret key is a permutation representation. We present Maverick, an equivalent-key recovery attack. Maverick breaks every released GRAFHEN challenge, including the recommended two-copy $S_{11}$ instance: it reconstructs an equivalent key from public rules and correctly decrypts all $20{,}000$ supplied labelled ciphertexts. On $12$ independently generated recommended-parameter...

Almost fifty years after its introduction, the McEliece cryptosystem occupies an unusual place in the post-quantum landscape. Its public keys are far larger than those of most competing schemes, its original parameters no longer provide adequate security, and several compact variants proposed to reduce key size have subsequently been broken. Nevertheless, the binary Goppa-code foundation retained in Classic McEliece continues to resist known practical attacks for the selected Classic...

We give an unconditional construction of information-theoretically secure one-time private-key unclonable encryption scheme for one-bit messages, with efficient encryption and decryption and exponentially small unclonable-indistinguishability advantage.

We give, to our knowledge, the first plain-model, one-time information-theoretically secure, efficient unclonable encryption scheme for one classical bit. Previous work by Bhattacharyya and Culf (Nature Physics, 2026) and Bhattacharyya, Broadbent, and Culf (arXiv:2603.08916) either only showed $1/\mathsf{poly}(\lambda)$ security loss or required inefficient encryption/decryption operations. We avoid both of these caveats; in doing so, we obtain (to our knowledge) the first plain-model...

Public blockchains expose all state and computation by default, which is incompatible with financial applications that require confidentiality. Solana achieves high throughput and sub-second confirmation, making it an attractive settlement layer, yet it offers no general mechanism for computing over encrypted state: fully homomorphic encryption (FHE) remains orders of magnitude too slow for interactive use, secure multi-party computation (MPC) incurs heavy communication, and Solana’s native...

Recent advances in fully homomorphic encryption (FHE) have enabled privacy-preserving machine learning directly over encrypted data. As a representative recurrent architecture, the long short-term memory (LSTM) network is widely used for modeling sequential dependencies, yet existing FHE-based LSTM inference schemes still suffer from high latency and limited scalability. In this paper, we present an efficient privacy-preserving LSTM inference protocol on encrypted sequential data based on...

Outsourcing computations to cloud providers raises significant data privacy concerns, making Privacy-Preserving Computation via Fully Homomorphic Encryption (FHE) increasingly vital. However, adapting data sorting routines to the FHE domain introduces severe performance bottlenecks. This survey systematizes the state-of-the-art in FHE-based sorting algorithms. A novel complexity metric, FHE-Effort, is introduced to accurately evaluate homomorphic circuit efficiency. Eighteen algorithms are...

As the usage of Artificial Intelligence (AI) for sensitive purposes increases, there is a growing need for privacy-aware explainable AI (XAI) tools. In this paper, we present a privacy-preserving counterfactual explanation algorithm. Our starting point is a decision-support model that is able to operate on vertically partitioned datasets, meaning that each party holds a different subset of datapoint attributes. The goal of a counterfactual algorithm is to find, given an observation, a...

Hybrid homomorphic encryption (HHE) lets a constrained client send compact symmetric ciphertexts while a server transciphers them into homomorphic ciphertexts, making HE-friendly ciphers such as PASTA a practical choice. Efficient and side-channel-secure execution of PASTA on embedded devices, however, remains challenging, since existing hardware relies on dedicated cipher cores and provides no side-channel protection. We present a hardware/software co-design of PASTA on RISQrypt, an...

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...

Searchable Symmetric Encryption (SSE) enables data owners to securely store encrypted data on untrusted cloud servers while retaining the ability to perform secure searches and retrieve relevant documents. However, standard SSE schemes expose search patterns (whether two queries are identical), and result patterns (which documents are returned), making them susceptible to leakage-abuse attacks that can infer sensitive information such as the queried keywords and/or document contents. While...

Distributed cryptography is a new cryptographic paradigm that enables fine-grained decryption capabilities in a trustless setting. In a distributed monotone-policy encryption scheme, users generate their own public and private keys. Thereafter, one can encrypt a message with respect to an arbitrary set of public keys together with an access policy. Any group of users that satisfies the access policy can recover the message; conversely, the message is computationally hidden from any group of...

EME is a parallelizable encrypt-mix-encrypt wide-block construction proved secure for m-block messages only in the range m <= n, where n is the block length of the underlying block cipher. Halevi and Rogaway justified this restriction by giving a splicing distinguisher for m >= n + 2, but left open the first excluded length, m = n + 1. We resolve that boundary for the direct, unrefreshed EME-core extension beyond its specified m <= n domain: the original formulas are applied to m = n + 1...

We give a structural cryptanalysis of GRAFHEN, a proposed group-based fully homomorphic encryption scheme whose public rewriting rules hide a group representation used for decryption. Under the designers' isomorphism hypothesis, the compatible representations in a finite target $T$ form one free $\mathrm{Aut}(T)$-orbit. Thus every representative induces the same zero predicate. For a fixed publication, the published key-class expression is the expected trial count of uniform verified...

We provide the first construction of identity-based encryption from isogeny-based assumptions. Security of our construction relies on a novel assumption called the "CDH with Mismatched Torsion” (CD-HwMT) assumption, which we introduce. At a high level, the assumption posits the hardness of solving a CDH-like problem even when the adversary is given some additional “safe” leakage. We justify our assumption by showing that, in the Algebraic Isogeny Model, our assumption reduces to well-known...

Batched identity-based encryption (batched IBE), introduced by Agarwal, Fernando, and Pinkas (CRYPTO 2025), enables a key authority to issue a single succinct key that decrypts an entire batch of ciphertexts. However, existing batched encryption protocols support only identity-based access control and do not accommodate expressive attribute-based policies. We are the first to introduce Batched Attribute-Based Encryption (B-ABE), a generalization of batched encryption to the attribute-based...

We study Batched IBE through the lens of Multi-Message Signatures -- a natural extension of standard digital signatures in which a single signing operation signs an entire vector of messages at once. A public open algorithm then derives an opening for each message, allowing anyone to verify that an individual message was signed. First we show that Multi-Message Signatures are essential by constructing a Multi-Message Signature scheme from every Batched IBE scheme with a sufficiently large...

Identity-based key encapsulation remains attractive for managed systems, but practical post-quantum instantiations must balance compact ciphertexts, low decryption-failure rate (DFR), high-throughput and protection-friendly private-key extraction, and meaningful concrete security reductions. Existing NTRU-based IBE schemes satisfy these requirements only partially: compact DLP-style constructions lack a satisfactory reduction and have high failure rates, while LATTE's higher-rank structure...

NTRU-based bootstrapping offers a high-performance variant of FHEW-like bootstrapping schemes and is simpler than its RLWE-based counterparts. Nevertheless, it remains costly in terms of both memory and time. A key computational bottleneck arises from the constraint $q\mid 2N$ which links the LWE ciphertext modulus $q$ to the NTRU dimension $N$. In this work, we apply extended techniques to remove the limitation $q \mid 2N$. With a large modulus $q$, we are able to complete the bootstrapping...

The server-aided Secure Multi-Party Computation (MPC) model with dynamic participation, where servers may join or leave during the computation is particularly well-suited for practical, long-running applications. Unfortunately, existing protocols supporting dynamic participation either incur communication costs that scale linearly with the circuit size or rely on the heavy hammer of Fully Homomorphic Encryption (FHE). This contrasts with “classic” MPC protocols, where sublinear communication...

The recent work of Hsieh, Lin and Luo [HLL23] (HLL23) provided the first construction of ABE for unbounded depth circuits from the circular evasive LWE assumption, which they introduced. Unfortunately, this assumption has been recently broken [AMYY25]. Finding a new construction for unbounded depth ABE from a safe assumption, without relying on compact functional encryption or obfuscation, is therefore an important open problem. In this work, we provide a new candidate for ABE for...

Vote privacy and verifiability are two fundamental properties which must be maintained for elections. Studies in e-voting technology have demonstrated how elections may be secured through cryptographic techniques including mix-nets, homomorphic encryption, and Zero Knowledge Proofs (ZKPs). The implications and trade-offs that must be considered when designing an e-voting system using multiple cryptographic techniques for simple majority or plurality voting are well understood in the...