We initiate the study of a new abstraction called incremental decentralized data archival (${\sf iDDA}$). Specifically, imagine that there is an ever-growing, massive database such as a blockchain, a comprehensive human knowledge base like Wikipedia, or the Internet archive. We want to build a decentralized archival of such datasets to ensure long-term robustness and sustainability. We identify several important properties that an ${\sf iDDA}$ scheme should satisfy. First, to promote heterogeneity and decentralization, we want to encourage even weak nodes with limited space (e.g., users' home computers) to contribute. The minimum space requirement to contribute should be approximately independent of the data size. Second, if a collection of nodes together receive rewards commensurate with contributing a total of $m$ blocks of space, then we want the following reassurances: 1) if $m$ is at least the database size, we should be able to reconstruct the entire dataset; and 2) these nodes should actually be commiting roughly $m$ space in aggregate --- even when $m$ is much larger than the data size, the nodes should be storing redundant copies of the database rather than storing just one copy, and yet impersonating arbitrarily many pseudonyms to get unbounded rewards. We propose new definitions that mathematically formalize the aforementioned requirements of an ${\sf iDDA}$ scheme. We also devise an efficient construction in the random oracle model which satisfies the desired security requirements. Our scheme incurs only $\widetilde{O}(1)$ audit cost, as well as $\widetilde{O}(1)$ update cost for both the publisher and each node, where $\widetilde{O}(\cdot)$ hides polylogarithmic factors. Further, the minimum space provisioning required to contribute is as small as polylogarithmic. Our construction exposes several interesting technical challenges. Specifically, we show that a straightforward application of the standard hierarchical data structure fails, since both our security definition and the underlying cryptographic primitives we employ lack the desired compositional guarantees. We devise novel techniques to overcome these compositional issues, resulting in a construction with provable security while still retaining efficiency. Finally, our new definitions also make a conceptual contribution, and lay the theoretical groundwork for the study of ${\sf iDDA}$. We raise several interesting open problems along this direction.

We study several asymmetric structured key agreement schemes based on noncommutative matrix operations, including the recent proposal of Lizama as well as the strongly asymmetric algorithms SAA-3 and SAA-5 of Accardi et al.\ We place them in a common algebraic framework for public key agreement and identify simple structural conditions under which an eavesdropper can reconstruct an effective key-derivation map and reduce key recovery to solving linear systems over finite fields. We then show that the three matrix-based schemes mentioned above all instantiate our algebraic framework and can therefore be broken in polynomial time from public information alone. In particular, their security reduce to the hardness of linear-algebraic problems and does not exceed that of the underlying discrete logarithm problem. Our results demonstrate that the weakness of these schemes is structural rather than parametric, and that minor algebraic modifications are insufficient to repair them.

We prove that SVP$_p$ is NP-hard to approximate within a factor of $2^{\log^{1 - \varepsilon} n}$, for all constants $\varepsilon > 0$ and $p > 2$, under standard deterministic Karp reductions. This result is also the first proof that \emph{exact} SVP$_p$ is NP-hard in a finite $\ell_p$ norm. Hardness for SVP$_p$ with $p$ finite was previously only known if NP $\not \subseteq$ RP, and under that assumption, hardness of approximation was only known for all constant factors. As a corollary to our main theorem, we show that under the Sliding Scale Conjecture, SVP$_p$ is NP-hard to approximate within a small polynomial factor, for all constants $p > 2$. Our proof techniques are surprisingly elementary; we reduce from a regularized PCP instance directly to the shortest vector problem by using simple gadgets related to Vandermonde matrices and Hadamard matrices.

We initiate the holistic study of Policy Compliant Secure Messaging (PCSM). A content policy is a predicate over messages deciding which messages are considered harmful and which not. A PCSM protocol is a type of end-to-end encrypted (E2EE) messaging system that guarantees E2EE privacy and authenticity for all policy compliant messages but detects and verifiably reports harmful content prior to its delivery. This stands in contrast to prior content moderation systems for E2EE messaging where detection relies on receivers reporting the harmful content themselves which makes them unsuited for most PCSM applications (e.g., for preventing the wilful distribution of harmful content). Our holistic PCSM notion explicitly captures several new roles such as policy creator, auditor and judge, to more accurately separate and model the different goals and security concerns of stakeholders when deploying PCSM. We present efficient PCSM constructions for arbitrary policy classes, as well as for hash-based ones, achieving various levels of security, while maintaining the core security properties of the underlying E2EE layer. For hash-based PCSM, we encapsulate Apple’s recent PSI protocol used in their content moderation system, and we properly adapt it to realize the desired PCSM functionality, and analyze the resulting protocol’s security. To our knowledge, our work is the first that rigorously study Apple’s PSI for server-side content moderation within the broader context of secure messaging, addressing the diverse goals and security considerations of stakeholders when deploying larger systems.

Authenticated Private Information Retrieval (APIR) enables a client to retrieve a record from a public database and verify that the record is “authentic” without revealing any information about which record was requested. In this work, we propose Tapir: the first two-server APIR scheme to achieve both sublinear communication and computation complexity for queries, while also supporting dates. Our scheme builds upon the unauthenticated two-server PIR scheme SinglePass (Lazzaretti and Papamanthou, USENIX’24). Due to its modular design, Tapir provides different trade-offs depending on the underlying vector commitment scheme used. Moreover, Tapir is the first APIR scheme with preprocessing to support appends and edits in time linear in the database partition size. This makes it an ideal candidate for transparency applications that require support for integrity, database appends, and private lookups. We provide a formal security analysis and a prototype implementation that demonstrates our scheme’s efficiency. Tapir incurs as little as 0.11 % online bandwidth overhead for databases of size $2^{22}$, compared to the unauthenticated SinglePass. For databases of size $\geq 2^{20}$, our scheme, when instantiated with Merkle trees, outperforms all prior multi-server APIR schemes with respect to online runtime.

The ongoing search for secure post-quantum cryptographic primitives has led to the development of numerous novel digital signature schemes. In this paper we introduce $\mathsf{SPECK}$, a new signature protocol based on the similarities between the Permuted Kernel Problem ($\mathsf{PKP}$) and the Permutation Code Equivalence Problem ($\mathsf{PEP}$). At its core, $\mathsf{SPECK}$ is built on the permutation version of LESS, but introduces a key modification to the commitment step. Indeed, instead of committing to an entire permuted code, the prover commits to a random relaxed $\mathsf{PKP}$ (that we call $\mathsf{PECK}$, Permutation Equivalence of Codes and Kernel) instance by randomly choosing a codeword from a random permutation of the initial code. In this sense, the secret key is used as a trapdoor to solve the committed $\mathsf{PECK}$ instance. The new approach allows for a faster verification that does not involve gaussian elimination, while maintains roughly the same signature size as LESS. We present the $\mathsf{Speck}$ protocol in detail and provide a deep analysis of the security of the new introduced assumptions.

This paper presents implementations that match and, where possible, exceed current quantum factorisation records using a VIC-20 8-bit home computer from 1981, an abacus, and a dog. We hope that this work will inspire future efforts to match any further quantum factorisation records, should they arise.

A recent study by Yamashita and Yasunaga (GameSec 2023) presented a constant-round deterministic broadcast protocol secure against \emph{detection-averse} adversaries --- those who prefer to attack without being detected. In this work, we revisit their protocol and observe that it remains secure even against a broader class of adversaries, not necessarily detection-averse. We formalize its detection mechanism as \emph{local detectability} and construct broadcast protocols with local detectability that address two weaknesses of the original protocol: (1) it only guarantees weak validity, and (2) it may cause false detections. Our first protocol achieves round complexity four against rational adversaries and $t+4$ against malicious adversaries, where the adversary corrupts at most $t$ parties. Our second protocol achieves the optimal round complexity of $t+1$ for malicious adversaries, while the round complexity is four against detection-averse adversaries.

This paper articulates short- and long-term research problems in AI agent security and privacy, using the lens of computer systems security. This approach examines end-to-end security properties of entire systems, rather than AI models in isolation. While we recognize that hardening a single model is useful, it is important to realize that it is often insufficient. By way of an analogy, creating a model that is always helpful and harmless is akin to creating software that is always helpful and harmless. The collective experience of decades of cybersecurity research and practice shows that this is insufficient. Rather, constructing an informed and realistic attacker model before building a system, applying hard-earned lessons from software security, and continuous improvement of security posture is a tried-and-tested approach to securing real computer systems. A key goal is to examine where research challenges arise when applying traditional security principles in the context of AI agents. A secondary goal of this report is to distill these ideas for AI and ML practitioners and researchers. We discuss the challenges of applying security principles to agentic computing, present 11 case studies of real attacks on agentic systems, and define a series of new research problems specific to the security of agentic systems.

Yao's garbled circuits have received huge attention in both theory and practice. While garbled circuits can be constructed using minimal assumption (i.e., the existence of pseudorandom functions or one-way functions), the state-of-the-art constructions (e.g., Rosulek-Roy, Crypto 2021) are based on stronger assumptions. In particular, the ``Free-XOR'' technique (Kolesnikov-Schneider, ICALP 2008) is essential in these state-of-the-art constructions, and their security can only be proven in the random oracle model, or rely on the ``circular-correlation robust hash'' assumption. In this paper, we aim to develop new techniques to construct efficient garbling schemes using minimal assumptions. Instead of generically replacing the Free-XOR technique, we focus on garbling schemes for specific functionalities. We successfully eliminated the need for Free-XOR in several state-of-the-art schemes, including the one-hot garbling (Heath and Kolesnikov, CCS 2021) and the garbled pseudorandom functions, and the garbled lookup tables (Heath, Kolesnikov and Ng, Eurocrypt 2024). Our schemes are based on minimal assumptions, i.e., standard pseudorandom functions (PRFs)---we resolved the need for circular security. The performance of our scheme is almost as efficient as the best results except for a small constant factor. Namely, for any lookup table $\{0,1\}^n \to \{0,1\}^m$, our scheme takes $n + (5n+9)m\lambda + 2^n \cdot m$ bits of communication, where $\lambda$ is the security parameter of PRF.

In this paper, we study practical constructions of asynchronous distributed key reconfiguration ($\mathsf{ADKR}$), which enables an asynchronous fault-tolerant system with an existing threshold cryptosystem to efficiently generate a new threshold cryptosystem for a reconfigured set of participants. While existing asynchronous distributed threshold key generation ($\mathsf{ADKG}$) protocols theoretically solve $\mathsf{ADKR}$, they fail to deliver satisfactory scalability due to cubic communication overhead, even with simplifications to the reconfiguration setting. We introduce an efficient \textit{share-dispersal-then-agree-and-recast} paradigm for constructing efficient $\mathsf{ADKR}$ while preserving adaptive security. Our method reduces the total overhead to $O(\kappa n^2)$ from $O(n^3)$, where $\kappa$ is a small constant (typically $\sim$30 or less). And our further optimizations in $\mathsf{PVSS}$ minimize redundant computations across different parties and reduce the dominating $\mathsf{PVSS}$ verification cost by about one-third. Our techniques developed for $\mathsf{ADKR}$ can also be leveraged to improve the asymptotic efficiency of various other asynchronous protocols: (i) it implies the first (coin-assisted) quadratic-communication $\mathsf{ADKG}$; and (ii) it can be extended to realize the first quadratic-communication asynchronous dynamic proactive secret sharing ($\mathsf{APSS}$) with adaptive security. Experimental evaluations on a global network of 256 AWS servers show up to 40\% lower latency compared to the state-of-the-art $\mathsf{ADKG}$ protocols that are simplified to the reconfiguration setting, highlighting the practicality of our $\mathsf{ADKR}$ in large-scale asynchronous systems.

Data availability sampling (DAS) is an important technique to horizontally scale consensus protocols without compromising on the number of adversarial nodes that can be tolerated. DAS is on the technical roadmap of major blockchains such as Ethereum. A major challenge for DAS schemes, that has not been formally studied in the literature, is how incomplete shares can be repaired. The need for repairing data shares motivates key aspects of Ethereum's DAS-based sharding vision called "Danksharding". In this work, we make two contributions. First, we provide a new definitional framework that formalizes the notion of local repair, along with the security guarantees that a DAS scheme must provide. Second, we propose a new DAS scheme designed with efficient local repair in mind, based on locally-correctable multiplicity codes. To facilitate using these codes, we introduce a new multivariate polynomial commitment scheme that (i) supports efficient openings of partial derivatives of a committed polynomial, (ii) supports fast batch opening proof generation at many points, and (iii) has an algorithm to recompute (repair) opening proofs at a point from only a few other proofs. The proposed scheme improves upon the state-of-the-art Ethereum PeerDAS scheme, deployed in December 2025, in storage overhead, local repair bandwidth and coordination, while only slightly increasing dispersal cost and sampling bandwidth. As an additional benefit, our construction also supports efficient partial reconstruction, i.e., retrieving parts of the stored data. All of our techniques readily carry over to data availability schemes based on verifiable information dispersal (VID) as well.

We present an optimized implementation of the GHASH and POLYVAL authentication algorithms used in AES-GCM and AES-GCM-SIV that eliminates the computational overhead of bit-reversal operations. Our approach computes these universal hash functions directly in bit-reversed representation, matching the native format used by carry-less multiplication instructions available on modern processors. The algorithm exploits 64-bit polynomial primitives and parallel execution on superscalar architectures. We achieve performance of 0.34 cycles/byte on POWER9 (35% faster than OpenSSL) and 0.33 cycles/byte on Intel Comet Lake (11% faster than OpenSSL), representing a 32-fold improvement over table-based software implementations. Combined with hardware accelerated AES, the complete AES-GCM mode achieves 1.12 cycles/byte throughput. For platforms with hardware carry-less multiplication (x86 PCLMULQDQ, ARM PMULL, PowerPC vpmsumd), the R/F algorithm achieves ∼1.7× speedup over Karatsuba. For portable software implementations without hardware acceleration, we demonstrate that Karatsuba remains 1.4-1.6× faster due to reduced multiplication count.

Ring signatures allow an individual to sign a message on behalf of a group in such a way that the verifier can only confirm that someone in the group signed it, but cannot identify the actual signer. This strong anonymity, while desirable, may also be exploited for repeated or harmful activities. Linkable ring signatures mitigate this issue by enabling the system to recognise whether two signatures originate from the same signer, while still keeping the signer anonymous. Such constructions are essential in domains like e-voting, e-cash, privacy-preserving blockchain systems, and whistleblowing, where detecting repeated actions—such as double-spending or double-voting—is necessary to maintain system reliability. In this paper, we present a lattice-based linkable ring signature scheme designed to withstand quantum-era adversaries. The framework relies on exact and efficient zero-knowledge proofs, and employs a weak pseudorandom function (wPRF) to enable linkability. To demonstrate both ring membership and the generation of a unique tag, we integrate a Merkle tree accumulator, which also streamlines the verification steps. The scheme is instantiated using concrete parameter choices, allowing us to precisely evaluate how the signature size scales with different ring sizes. An important feature of our design is that it eliminates the need for trapdoor techniques, yet still produces a signature of roughly 0.22 MB when the ring contains 2^10 users. We further outline practical application scenarios, such as anonymous but accountable whistleblowing, to highlight the usefulness of the proposed construction.

Plaintext-awareness of AEAD schemes is one of the more obscure and easily misunderstood notions. Originally proposed by Andreeva et al., Mennink and Talnikar showed in 2025 that the original definitions are vague and leave too much room for interpretation. They presented new definitions and analyzed the three main AEAD compositions relative to the new definitions. In particular, they showed that MAC-then-Encrypt (MtE) is not plaintext-aware. However, they showed that an SIV-style variant is indeed plaintext-aware. In this work, we first show that their analysis contains a gap, voiding their proof. We show this by showing several attacks; against their choice of extractor, with trivial complexity, and against any extractor, with birthday-bound complexity. Next, we re-establish their results by designing a new extractor that captures their intended goal and prove a tight PA1 security bound. We also show that the result is not dependent on the encryption scheme used, by showing that an extractor can also be designed for sMtE[ΘCB3], a variant where the encryption step is done by an ΘCB3-like scheme. Afterwards, we strengthen their results, by revisiting other compositions. In particular, we show that Encrypt-then-MAC (EtM) is in fact PA2-secure. Furthermore, we show that SIV-style MtE cannot be PA2-secure. Additionally, we show that Encode-then-Encipher is also PA2-secure, but not beyond the first successful forgery. More importantly, we show that up to some necessary assumptions, PA2 and RAE are equivalent. This result, while positive, holds only up to the first successful forgery. This indicates that the PA2 formalization maybe too strong for practical schemes, since we believe RAE sufficient for intuitive security. Last but not least, we investigate the value of the notion of plaintext awareness. We look deeper into the relation between plaintext awareness and confidentiality. We show that the problem of confidentiality in the presence of release of unverified plaintext can be seen as a confidentiality-with-leakage problem in the simulatable leakage framework. In this regard, we start, by showing that PA1 security cannot imply confidentiality with leakage. Similarly, we compare our results to the AERUP notion of TOSC 2019. We show that a scheme can be AERUP secure but not secure against a somewhat straightforward left-or-right attack in the same model. This puts into question the meaning and relevance of the PA1 and AERUP security notions. Results based on these notions can be seen as providing security in a two-phase game, where the adversary does not observe any leakage after the first challenge query, as we argue in the paper. On the positive side, we show that if a scheme achieves IND-CPA, INT-RUP and PA2, then it achieves confidentiality with leakage for the appropriate leakage function. This closes a gap in the literature on the relation between confidentiality with leakage and RUP notions.

Ethereum has established itself as a world computer, enabling general-purpose, decentralized, and verifiable computation via smart contracts on a globally replicated state. However, because all computations and state are public by default, it is fundamentally unsuitable for confidential smart contracts that jointly process private data from multiple users. This motivates the notion of a private world computer: an ideal future form of Ethereum that preserves its integrity and availability guarantees while supporting such confidential smart contracts. Prior constructions based on implementable cryptographic primitives such as fully homomorphic encryption (FHE) inevitably rely on committees that hold secret shares and perform computations using those shares, a capability that is not provided by today's Ethereum validators. We cannot simply modify the Ethereum protocol so as to shift the committee’s role onto the Ethereum validators, because the computational and communication costs borne by the committee grow with the demand for confidential smart contracts, forcing higher hardware requirements for participation, undermining decentralization, and increasing the risk of malicious collusion. Hence, there remains a fundamental trade-off between committee decentralization and scalability for confidential smart contracts. In this position paper, we make two contributions toward a scalable private world computer. First, we show how indistinguishability/ideal obfuscation (iO), combined with FHE and succinct non-interactive arguments of knowledge (SNARK), yields a private world computer that, after a one-time obfuscation process, introduces no additional ongoing trust assumptions beyond Ethereum’s validators, incurring no additional overhead for validators to process confidential smart contracts compared to public smart contracts. In this design, a single application-agnostic obfuscated circuit, called root iO, suffices to realize arbitrary confidential smart contracts. The outputs of root iO can be verified on-chain at a cost comparable to signature verification, and the obfuscation process can be distributed among multiple parties while remaining secure as long as at least one party is honest. As the second contribution, we outline our roadmap toward a practical implementation of root iO. Assuming that the underlying assumptions of our lattice-based iO construction remain secure, the remaining missing pieces are technically concrete: namely, practical implementations of verifiable FHE and of homomorphic evaluation of a pseudorandom function (PRF) and SNARK verification over key-homomorphic encodings, which together would allow us to implement root iO without incurring prohibitive overhead.

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 $\textsf{THF}$.

We introduce a novel class of equations defined over Euclidean domains. These abstract equations establish a unified framework for deriving new, concrete computational problems useful for cryptography. We prove that solving a single such equation is NP-hard. For systems of these equations, we further prove NP-hardness, average-case hardness, random self-reducibility, search-to-decision reducibility, and trapdoorizability. Based on the hardness of solving these systems, we construct various cryptographic primitives. Our results are proved in an abstract, domain-agnostic manner and hold for a wide range of Euclidean domains. This generality allows the framework to accommodate rich mathematical structures, providing both theoretical depth and flexibility for diverse cryptographic applications.

A message authentication code (MAC) ensures authenticity and integrity in symmetric-key settings. The Carter–Wegman–Shoup (CWS) paradigm establishes that MACs for arbitrary-length messages can be built in a black-box way using a single call to a pseudorandom function (PRF) on a random input. More than a decade ago, Dodis, Kiltz, Pietrzak, and Wichs left open whether weak pseudorandom functions (wPRFs) would suffice in this construction. This work establishes tight upper and lower bounds that precisely characterize the minimal computational assumptions needed for the security of the CWS paradigm. On the negative side, we prove that weak PRFs are insufficient to instantiate the CWS paradigm. On the positive side, we introduce a new primitive, the 1-adaptive weak pseudorandom function (1-awPRF), which guarantees pseudorandomness for polynomially many non-adaptive queries followed by one adaptive query. We show that 1-awPRFs are sufficient to secure CWS in a black-box manner. Finally, we construct 1-adaptive weak pseudorandom functions in a black-box way from standard cryptographic assumptions, using a new randomized design paradigm that treats randomization as a fundamental structural element. Instantiating our generic construction under the Decisional Diffie Hellman and Learning with Errors assumptions yields concrete and efficient realizations. These lead to more efficient MAC schemes and illustrate how weak and abstract building blocks can be transformed into stronger and practically useful cryptographic constructions.

Inner product masking is a well-studied masking countermeasure against side-channel attacks. IPM-FD further extends the IPM scheme with fault detection capabilities. However, implementing IPM-FD in software especially on embedded devices results in high computational overhead. Therefore, in this work we perform a detailed analysis of all building blocks for IPM-FD scheme and propose a Masked Processing Unit to accelerate all operations, for example multiplication and IPM-FD specific Homogenization. We can then offload these computational extensive operations with dedicated hardware support. With only $4.05\%$ and $4.01\%$ increase in Look-Up Tables and Flip-Flops (Random Number Generator excluded), respectively, compared with baseline CV32E40p RISC-V core, we can achieve up to $16.55\times$ speed-up factor with optimal configuration. We then practically evaluate the side-channel security via uni- and bivariate Test Vector Leakage Assessment which exhibits no leakage. Finally, we use two different methods to simulate the injected fault and confirm the fault detection capability of up to $k-1$ faults, with $k$ being the replication factor.

A Rugged Pseudorandom Permutation (RPRP) is a variable-input-length tweakable cipher satisfying a security notion that is intermediate between tweakable PRP and tweakable SPRP. It was introduced at CRYPTO 2022 by Degabriele and Karadžić, who additionally showed how to generically convert such a primitive into nonce-based and nonce-hiding AEAD schemes satisfying either misuse-resistance or release-of-unverified-plaintext security as well as Nonce-Set AEAD which has applications in protocols like QUIC and DTLS. Their work shows that RPRPs are powerful and versatile cryptographic primitives. However, the RPRP security notion itself can seem rather contrived, and the motivation behind it is not immediately clear. Moreover, they only provided a single RPRP construction, called UIV, which puts into question the generality of their modular approach and whether other instantiations are even possible. In this work, we address this question positively by presenting new RPRP constructions, thereby validating their modular approach and providing further justification in support of the RPRP security definition. Furthermore, we present a more refined view of their results by showing that strictly weaker RPRP variants, which we introduce, suffice for many of their transformations. From a theoretical perspective, our results show that the well-known three-round Feistel structure achieves stronger security as a permutation than a mere pseudorandom permutation---as was established in the seminal result by Luby and Rackoff. We conclude on a more practical note by showing how to extend the left domain of one RPRP construction for applications that require larger values in order to meet the desired level of security.

We present a simple IND-CCA lattice-based threshold KEM. At a high level, our design is based on the BCHK transform (Canetti et al., EUROCRYPT 2004), which we adapt to the lattice setting by combining it with the FO transform (Fujisaki and Okamoto, PKC 1999) in order to achieve decryption consistency. As for the BCHK transform, our construction requires a threshold identity-based encryption (TIBE) scheme with suitable properties. We build such an IBE by combining the ABB IBE (Agrawal, Boneh, Boyen, EUROCRYPT 2010) with recent advances in lattice threshold cryptography, such as the threshold-friendly signature Plover (Esgin et al., EUROCRYPT 2024) and a variant of the Threshold Raccoon scheme (Katsumata et al., CRYPTO 2024). The security proof of our scheme relies on a new assumption which we call the Coset-Hint-MLWE assumption, and which is a natural generalisation of the Hint-MLWE assumption (Kim et al., CRYPTO 2023). We prove the hardness of Coset-Hint-MLWE under standard assumptions. We believe this new assumption may be of independent interest. Unlike prior works on IND-CCA lattice-based threshold KEMs, our construction only relies on simple algorithmic tools and does not use heavy machinery such as multi-party computation or threshold fully homomorphic encryption.

Let f be an arbitrary positive integer valued function. The goal of this note is to show that one can construct a finitely generated group in which the discrete log problem is polynomially equivalent to computing the function f. In particular, we provide infinite, but finitely generated groups, in which the discrete logarithm problem is arbitrarily hard. As another application, we construct a family of two-generated groups that have polynomial time word problem and NP-complete discrete log problem. Additionally, using our framework, we propose a generic scheme of cryptographic protocols, which might be of independent interest.

Robust (fuzzy) extractors are very useful for, e.g., authenticated exchange from shared weak secret and remote biometric authentication against active adversaries. They enable two parties to extract the same uniform randomness with the ``helper'' string. More importantly, they have an authentication mechanism built in that tampering of the ``helper'' string will be detected. Unfortunately, as shown by Dodis and Wichs, in the information-theoretic setting, a robust extractor for an $(n,k)$-source requires $k>n/2$, which is in sharp contrast with randomness extractors which only require $k=\omega(\log n)$. Existing work either relies on random oracles or introduces CRS and works only for CRS-independent sources (even in the computational setting). In this work, we give a systematic study of robust (fuzzy) extractors for general CRS-dependent sources. We show in the information-theoretic setting, the same entropy lower bound holds even in the CRS model; we then show we can have robust extractors in the computational setting for general CRS-dependent source that is only with minimal entropy. At the heart of our construction lies a new primitive called $\kappa$-MAC that is unforgeable with a weak key and hides all partial information about the key (both against auxiliary input), by which we can compile any conventional randomness extractor into a robust one. We further augment $\kappa$-MAC to defend against ``key manipulation" attacks, which yields a robust fuzzy extractor for CRS-dependent sources.

Hamming Quasi-Cyclic (HQC) has recently been selected by NIST, after the Round 4 submission, as a postquantum key encapsulation mechanism (KEM) standard and will soon be widely deployed. Therefore, it is important to ensure its implementation is constant-time, i.e., resistant to side-channel attacks. Existing timing attacks on HQC exploit non-constant-time source code and the decryption that is vulnerable to chosen-ciphertext attacks. These active attacks require constructing thousands of invalid ciphertexts, and thus, they can be easily detected. The latest HQC implementation has mitigated all these attacks by making its source code constant-time. In this work, we provide a new perspective on reviewing the implementation of HQC and exploiting timing leakages. For the first time, we show that an attacker can recover the secret key of HQC without targeting the CCA-insecure decryption and internal states of message decryption. Specifically, an attacker can exploit the timing leakages that occur when processing sparse vectors, which are ciphertext-independent, to recover the secret key by measuring the leakages only once. We find two such timing leakages in the latest stable HQC implementation, supposedly constant-time, and practically extract the leakages even when the process is protected by AMD Secure Encryption Virtualization. We also show that a power side-channel can extract similar leakages on embedded devices. Our findings apply to all code-based KEMs that are submitted to the NIST Round 4 PQC submission. We show that an attacker can also perform similar passive attacks to recover the session key of BIKE and Classic McEliece. To help write constant-time code, we propose and test a workflow that uses CT-grind when developing the code. We find that CT-grind can effectively find all timing leakages in various implementations of HQC. Therefore, we suggest that cryptographic developers constantly use constant-time analysis tools when developing code.

FrodoKEM provides conservative post-quantum security through unstructured lattices, yet its deployment on embedded systems is historically constrained by high memory requirements. While state-of-the-art implementations mitigate this by generating the public matrix on-the-fly, they remain bottlenecked by the sequential generation of secret matrices, which enforces a rigid trade-off between stack usage and recomputation overhead. To address this, we propose a blockwise secret generation mechanism that enables efficient random access to arbitrary matrix tiles. We formally prove that this modification is indistinguishable from the standard specification in the Random Oracle Model, thereby preserving IND-CCA2 security. By evaluating this approach on a 32-bit RISC-V core with custom cryptographic extensions, we demonstrate tiled encapsulation and key generation strategies that maintain constant transient stack usage ($\approx$2--3 kB) across all parameter sets. This design effectively decouples memory footprint from algorithmic complexity, enabling flexible buffering strategies that optimize performance according to the available heap memory of the target platform.

Leakage-resilient secret sharing is a fundamental building block for securing implementations against side-channel attacks. In general, such schemes correspond to a tradeoff between the complexity of the resulting masked implementations, their security guarantees and the physical assumptions they require to be effective. In this work, we revisit the Inner-Product (IP) framework, where a secret \(y\) is encoded by two vectors \((\vec{\omega},\vec{y})\), such that their inner product is equal to \(y\). So far, the state of the art is split in two. On the one hand, the most efficient IP masking schemes (in which \(\vec{\omega}\) is public but random) are provably secure with the same security notions (i.e., in the abstract probing model) as Boolean masking, yet at the cost of a slightly more expensive implementation. Hence, their theoretical interest and practical relevance remain unclear. On the other hand, the most secure IP masking schemes (in which \(\vec{\omega}\) is secret) lead to expensive implementations. We improve this state of the art by investigating the leakage resilience of IP masking with public \(\vec{\omega}\) coefficients in the bounded leakage model, which depicts well implementation contexts where the physical noise is negligible. Furthermore, we do that without assuming independent leakage from the shares, which may be challenging to enforce in practice. In this model, we show that if \(m\) bits are leaked from the \(d\) shares \(\vec{y}\) of the encoding over an \(n\)-bit field, then, with probability at least \(1 - 2^{-\lambda}\) over the choice of \(\vec{\omega}\), the scheme is \(\mathcal{O}{(\sqrt{2^{-(d-1)\cdot n + m + 2\lambda}}})\)-leakage resilient. We additionally show that in large Mersenne-prime fields, a wise choice of the public coefficients \(\vec{\omega}\) can yield leakage resilience up to \(\mathcal{O}({n \cdot 2^{-d \cdot n +n + d}})\), in the case where one physical bit from each share is revealed to the adversary. The exponential rate of the leakage resilience we put forward significantly improves upon previous bounds in additive masking, where the past literature exhibited a constant exponential rate only. We additionally discuss the applications of our results, and the new research challenges they raise.

Keyed-Verification anonymous credentials (KVAC) enable privacy-preserving authentication and can be seen as the symmetric primitive of conventional anonymous credentials: issuance and verification of credentials requires a shared secret key. The core advantage of KVACs is that they can be realized without pairings, which still appears to be a significant bottleneck when it comes to real-world adoption. KVACs provide all the benefits from anonymous credentials, in particular multi-show unlinkability, but only work in the setting where the issuer and verifier are the same entity, limiting the applications they can be used in. In this work we extend the idea of keyed-verification credential to a setting where again multiple verifiers are supported, each sharing an individual secret key with the issuer. We formally introduce this as multi-verifier keyed-verification anonymous credentials (mKVACs). While users must now get verifier-specific credentials, each credential still provides multi-show unlinkability. In terms of security, mKVAC naturally strengthens the single-verifier variant, as it guarantees that corruption of any verifier does not impact unforgeability guarantees for other verifiers. The main challenge therein is to not trade this added flexibility for privacy, and hide the verifier's identity in the credential issuance. We provide formal definitions of all desired security and privacy features and propose a provably secure and pairing-free construction. Along the way, we develop a new KVAC-like primitive that authenticates group elements and offers statistical privacy, solving the open problem of combining multi-verifier support and pairing-freeness. Finally, we demonstrate practicality of our protocol via implementation benchmarks.

Anamorphic encryption (AE), introduced by Persiano, Phan and Yung at Eurocrypt `22, allows to establish secure communication in scenarios where users might be forced to hand over their decryption keys to some hostile authority. Over the last few years, several works have improved our understanding of the primitive by proposing novel realizations, new security notions and studying inherent limitations. This work makes progress, mainly, on this last line of research. We show concrete realizations of public key encryption schemes that, provably, cannot be turned anamorphic. These were called Anamorphic Resistant Encryption (ARE, fort short) in a recent work of Dodis and Goldin. We also show that, under certain conditions, anamorphic encryption is equivalent to algorithm substitution attacks. This allows to positively reinterpret our AREs as PKE schemes provably resistant to subversion attacks. To the best of our knowledge, these seem to be the first IND-CPA secure schemes achieving subversion resistance without trust assumptions or non-black-box decomposition techniques. Our two AREs heavily rely, among other things, on a direct usage of extremely lossy functions: here the lossyness property is used in the constructions, rather than just in the proofs. The first construction is in the public parameters model and also requires iO. The second construction eliminates the need of both public parameters and iO, but is in the random oracle and relies on the novel concept of robust extremely lossy functions with group structure, a primitive that we define and (show how to) realize in this paper.

Symmetric cryptography is confronting threats posed by quantum computing, including Grover's search algorithm and Simon's algorithm. In the fault-tolerant quantum computation, the limited qubit count, connectivity constraints, and error rates of quantum hardware impose stringent requirements on the implementation of cryptographic quantum circuits. Constructing low-resource quantum circuit models forms the foundation for evaluating algorithmic resistance to quantum threats. At CRYPTO 2019, Jaques et al. justified the adoption of depth-times-width cost (DW-cost) as a metric for quantum circuits by incorporating advancements in quantum computation and error correction. In this work, we address the fundamental limitations in in-place implementations of AES quantum circuits by proposing a set of in-place synthesis methods centered on DW-cost optimization. First, we prove that within the composite field arithmetic framework, intermediate circuit states can be utilized to uncompute S-box input states, and introduce a novel design pathway and circuit structure for in-place S-box quantum circuits. Second, we establish the necessary conditions for maximizing parallelization of Toffoli gates under minimal-width constraints in binary field multiplication. Through co-design and optimization of multiple nonlinear components, we construct a compact in-place S-box with a DW-cost of merely 276. Finally, building on this, we achieve quantum circuit implementations for AES-128, AES-192, and AES-256 via co-optimization of key expansion and round functions, reducing their DW-cost values to 65,280, 87,552, and 112,896 respectively. These results indicate a reduction of at least 46%, 45%, and 45% compared to existing state-of-the-art solutions. This study establishes new technical benchmarks for low-resource fault-tolerant implementations of symmetric cryptography in the post-quantum era. (This is a revised version containing Clifford+T resource estimates for both AES-128 Grover oracle and encryption oracle. Key revisions are highlighted in red.)

One of the main issues to deal with for fully homomorphic encryption is the noise growth when operating on ciphertexts. To some extent, this can be controlled thanks to a so-called gadget decomposition. A gadget decomposition typically relies on radix- or CRT-based representations to split elements as vectors of smaller chunks whose inner products with the corresponding gadget vector rebuilds (an approximation of) the original elements. Radix-based gadget decompositions present the advantage of also supporting the approximate setting: for most homomorphic operations, this has a minor impact on the noise propagation but leads to substantial savings in bandwidth, memory requirements and computational costs. A typical use-case is the blind rotation as used for example in the bootstrapping of the TFHE scheme. On the other hand, CRT-based representations are convenient when machine words are too small for directly accommodating the arithmetic on large operands. This arises in two typical cases: (i) in the hardware case with multipliers of restricted size, e.g., 17 bits; (ii) in the software case for ciphertext moduli above, e.g., 128 bits. This paper presents new CRT-based gadget decompositions for the approximate setting, which combines the advantages of non-exact decompositions with those of CRT-based decompositions. Significantly, it enables certain hardware or software realizations otherwise hardly supported like the two aforementioned cases. In particular, we show that our new gadget decompositions provide implementations of the (programmable) bootstrapping in TFHE relying solely on native arithmetic and offering extra degrees of parallelism.

We construct a publicly-verifiable non-interactive zero-knowledge argument system for QMA with the following properties of interest. 1. Transparent setup. Our protocol only requires a uniformly random string (URS) setup. The only prior publicly-verifiable NIZK for QMA (Bartusek and Malavolta, ITCS 2022) requires an entire obfuscated program as the common reference string. 2. Extractability. Valid QMA witnesses can be extracted directly from our accepting proofs. That is, we obtain a publicly-verifiable non-interactive argument of quantum knowledge, previously only known in a privately-verifiable setting (Coladangelo, Vidick, and Zhang, CRYPTO 2020). Our construction introduces a novel ZX QMA verifier with "strong completeness" and builds upon the coset state authentication scheme from (Bartusek, Brakerski, and Vaikuntanathan, STOC 2024) within the context of QMA verification. Along the way, we establish new properties of the authentication scheme. The security of our construction rests on the heuristic use of a post-quantum indistinguishability obfuscator. Rather than rely on the full-fledged classical oracle model (i.e. ideal obfuscation), we isolate a particular game-based property of the obfuscator that suffices for our proof, which we dub the evasive composability heuristic. As an additional contribution, we study a general method for replacing heuristic use of obfuscation with heuristic use of hash functions in the post-quantum setting. In particular, we establish security of the ideal obfuscation scheme of Jain, Lin, Luo, and Wichs (CRYPTO 2023) in the quantum pseudorandom oracle model (QPrO), which can be heuristically instantiated with a hash function. This gives us NIZK arguments of quantum knowledge for QMA in the QPrO, and additionally allows us to translate several quantum-cryptographic results that were only known in the classical oracle model to results in the QPrO.

With the widespread development of cloud networks, performing searches on encrypted data (without decryption) has become a critical issue. Public key authenticated encryption with keyword search (PAEKS) allows for the retrieval of encrypted data while resisting insider keyword guessing attacks (IKGAs). Most PAEKS schemes do not support access control in multi-receiver models. To address this limitation, attribute-based encryption has been introduced. However, the access privileges for the ciphertext may change, and it is vulnerable to quantum computing attacks, which limit its applicability and compromise security in cloud networks. In this paper, we propose RABAEKS, the first revocable and authenticated attribute-based encrypted search scheme over lattice in cloud networks. Our design allows the cloud server to enforce access control for data receivers during the search process. For practical implementation, we introduce a revocation mechanism for receivers, enabling dynamic access control. We then formalize and analyze the security of our scheme rigorously. Through performance evaluations and comparisons, we demonstrate that the search time, ciphertext size, and trapdoor size of our RABAEKS scheme are independent of the number of keywords. Additionally, the computational overhead for ciphertext generation, trapdoor generation, and the search phase in RABAEKS is, at most, 0.91%, 39.21%, and 80.95% of that of previous approaches, respectively, indicating it is efficient and practical in cloud networks.

At Eurocrypt'19, Attrapadung presented several transformations that dynamically compose a set of attribute-based encryption (ABE) schemes for simpler predicates into a new ABE scheme for more expressive predicates. Due to the powerful unbounded and modular nature of his compositions, many new ABE schemes can be obtained in a systematic manner. However, his approach heavily relies on $q$-type assumptions, which are not standard. Devising such powerful compositions from standard assumptions was left as an important open problem. In this paper, we present a new framework for constructing ABE schemes that allow unbounded and dynamic predicate compositions among them, and show that the adaptive security of these composed ABE will be preserved by relying only on the standard matrix Diffie-Hellman (MDDH) assumption. This thus resolves the open problem posed by Attrapadung. As for applications, we obtain various ABEs that are the first such instantiations of their kinds from standard assumptions.These include the following adaptively secure large-universe ABEs for Boolean formulae under MDDH: - The first completely unbounded monotone key-policy (KP)/ciphertext-policy (CP) ABE. Such ABE was recently proposed, but only for the KP and small-universe flavor (Kowalczyk and Wee, Eurocrypt'19). - The first completely unbounded non-monotone KP/CP-ABE. Especially, our ABEs support a new type of non-monotonicity that subsumes previous two types of non-monotonicity, namely, by Ostrovsky et al. (CCS'07) and by Okamoto and Takashima (CRYPTO'10). - The first (non-monotone) KP and CP-ABE with constant-size ciphertexts and secret keys, respectively. - The first KP and CP-ABE with constant-size secret keys and ciphertexts, respectively. At the core of our framework lies a new partially symmetric design of the core 1-key 1-ciphertext oracle component called Key Encoding Indistinguishability, which exploits the symmetry so as to obtain compositions.

In 2002, Johnson et al. posed an open problem at the Cryptographers' Track of the RSA Conference: how to construct a secure homomorphic signature on a semigroup, rather than on a group. In this paper, we introduce, for the first time, a semigroup-homomorphic signature scheme. Under certain conditions, we prove that the security of this scheme is based on the hardness of the Short Integer Solution (SIS) problem and is tightly secure. Furthermore, we extend it to a linearly semigroup-homomorphic signature scheme over lattices, and this scheme can also ensure privacy.

In this paper we present two reductions between variants of the Code Equivalence problem. We give polynomial-time Karp reductions from Permutation Code Equivalence (PCE) to both Linear Code Equivalence (LCE) and Signed Permutation Code Equivalence (SPCE). Along with a Karp reduction from SPCE to the Lattice Isomorphism Problem (LIP) proved in a paper by Bennett and Win (2024), our second result implies a reduction from PCE to LIP.

Secure aggregation enables a central server to compute the sum of client inputs without learning any individual input, even in the presence of dropouts or partial participation. This primitive is fundamental to privacy-preserving applications such as federated learning, where clients collaboratively train models without revealing raw data. We present a new secure aggregation protocol, TACITA, in the single-server setting that satisfies four critical properties simultaneously: (1) one-shot communication from clients with no per-instance setup, (2) input-soundness, i.e. the server cannot manipulate the ciphertexts, (3) constant-size communication per client, independent of the number of participants per-instance, and (4) robustness to client dropouts Previous works on secure aggregation - Willow and OPA (CRYPTO'25) that achieve one-shot communication do not provide input soundness, and allow the server to manipulate the aggregation. They consequently do not achieve full privacy and only achieve Differential Privacy guarantees at best. We achieve full privacy at the cost of assuming a PKI. Specifically, TACITA relies on a novel cryptographic primitive we introduce and realize: succinct multi-key linearly homomorphic threshold signatures (MKLHTS), which enables verifiable aggregation of client-signed inputs with constant-size signatures. To encrypt client inputs, we adapt the Silent Threshold Encryption (STE) scheme of Garg et al. (CRYPTO 2024) to support ciphertext-specific decryption and additive homomorphism. We formally prove security in the Universal Composability framework and demonstrate practicality through an open-source proof-of-concept implementation, showing our protocol achieves scalability without sacrificing efficiency or requiring new trust assumptions.

Anonymous credential schemes allow users to prove claims about themselves in a privacy-preserving manner. Put simply, a user can prove that she has an attribute value (e.g., she is a citizen) without revealing any other information about herself. Traditional schemes (including those with multiple credential issuers) operate under the assumption that each recognized issuer produces credentials for all user attributes. This assumption, however, is not practical: in the real world, no such issuer exists; an identity provider today issues a user credentials for a subset of user attributes, not all. A promising approach to support this setting is aggregate anonymous credentials, which allow a user to receive credentials from several issuers such that she can aggregate them and prove various claims about her attribute values in one shot. In this paper, we first introduce what we call aggregate tag-based signatures and describe an efficient instantiation. We then leverage the latter together with structure-preserving signatures and signatures of knowledge to construct an efficient aggregate anonymous credential scheme. We finally, formally evaluate the security of the proposed schemes and run benchmarks to showcase the practicality of the resulting scheme and its relevance for decentralized identity applications.

Code-based cryptography has reached maturity for standard primitives such as encryption and digital signatures. However, when it comes to advanced encryption functionalities, particularly in multi-user settings involving collusions among users holding different secret keys, there is still no foundational framework for code-based schemes. In this work, we address this gap by introducing a multi-receiver encryption scheme with tracing capability based on coding assumptions. This primitive often serves as a foundation for more advanced constructions such as attribute-based or functional encryption. To achieve this goal, we propose a kernel sampling technique that enables the sampling of secret keys under a common public key, thereby realizing multi-receiver encryption. The resulting construction is as efficient as the underlying public-key encryption scheme, namely Alekhnovich's scheme from FOCS'03. We also introduce new hardness assumptions on problems with hints. These assumptions extend classical code-based problems to handle collusion among dishonest users in the multi-user setting. In particular, we define the $\ell$-Decoding Problem ($\ell$-DP), the code-based analogue of the $k$-LWE problem in lattices, and provide a reduction from the standard Decoding Problem (DP) to $\ell$-DP. We further introduce structural variants relying on Moderate Density Parity Check (MDPC) codes that we call $\ell$-MDPC-DP. Based on $\ell$-MDPC-DP, we design the first code-based traitor-tracing encryption scheme. Interestingly, the security of our scheme relies on $\ell$-MDPC-DP and a slight variation called $(\ell,\ell')$-OM-MDPC-DP, the latter of which we prove to be as hard as $\ell$-DP via a polynomial reduction, therefore reducing the security of our scheme to only $\ell$-MDPC-DP. Although no formal reduction from $\ell$-DP to $\ell$-MDPC-DP is given, the definition of $\ell$-MDPC-DP is a natural variant of $\ell$-DP adapted to the multi-user code-based setting. Furthermore, we also provide evidence of $\ell$-MDPC-DP hardness by presenting detailed cryptanalytic arguments.

We propose a new multivariate digital signature scheme whose central mapping arises from the product of two one-variate polynomials over a finite field $\mathbb{F}_q$. The resulting quadratic transformation is efficiently invertible through polynomial factorization, defining the trapdoor mechanism. The public key comprises $m$ bilinear forms in $2n$ variables, obtained by masking the central map with secret linear transformations. A reference implementation targeting NIST security level 1 achieves a 24-byte signature and a 12-kilobyte public key. This signature size is among the smallest ever proposed for level 1 security and the scheme achieves verification efficiency comparable to the fastest existing designs. Security relies on the hardness of solving certain bilinear systems, for which it seems no efficient classical or quantum algorithms are known.

Fully Homomorphic Encryption over the Torus (TFHE) is a fully homomorphic encryption scheme that efficiently supports Boolean logic gates by performing gate operations and refreshing ciphertext noise with single gate bootstrapping. However, its operation is limited to simple two-input gates such as AND, OR, XOR and NAND, requiring deep circuits and multiple bootstrapping steps to support more complex arithmetic. In this paper, we propose Primitive Gate Bootstrapping, a new algebraic framework that significantly expands the class of Boolean functions evaluable with a single bootstrapping. By formalizing bootstrappable functions as compositions of linear maps and negacyclic functions, called the Blind-Rotational Function Family (BRFF), we define a subclass, the Primitive Gate Family (PGF). This family includes multi-input hybrid gates such as l-input XOR, 3-input Majority, and AND-XOR, which can all be realized with a single bootstrapping. Building on PGF, we further design a general circuit framework called the Parallel Prefix Group Circuit (PPGC) for efficiently implementing arithmetic and logical operations. PPGC enable n-bit addition, subtraction, comparison, equality, select, minimum/maximum, absolute, and negation with logarithmic depth O(log n) and significantly reduced latency compared to TFHE. In particular, our optimized implementations of addition and subtraction achieve a 1.92× speedup over TFHE, while the size of the blind rotation key was reduced by approximately 40%. In addition to the two-input addition, we also introduce an efficient technique for multi-input addition, which is particularly useful in applications such as encrypted matrix multiplication. Therefore, it is clear that the PGF-based constructions offer a practically scalable and efficient foundation for depth-sensitive homomorphic computations

With the rapid advancement of cloud computing technology, outsourcing massive datasets to cloud servers has become a prominent trend, making secure and efficient data sharing mechanisms a critical requirement. Attribute-based proxy re-encryption (ABPRE) has emerged as an ideal solution due to its support for fine-grained, one-to-many access control and robust ciphertext transformation capabilities. However, existing ABPRE schemes still exhibit shortcomings in addressing forward security issues caused by long-term private key leakage, threats from quantum computer attacks, and vulnerabilities to honest re-encryption attacks (HRA). To simultaneously resolve these challenges, this paper introduces a novel cryptographic primitive termed puncturable attribute-based proxy re-encryption with switchable tags (PABPRE-ST), constructing a secure cloud data sharing scheme that supports fine-grained revocation. By integrating puncturable encryption (PE) mechanisms into the ABPRE framework, the scheme achieves fine-grained ciphertext revocation based on tags. In PABPRE-ST, data owners embed tags into ciphertexts, enabling data users to puncture specific tags and thereby revoke access to corresponding ciphertexts at a granular level. Furthermore, the scheme allows delegators to switch ciphertext tags, enhancing sharing flexibility. We formalize the security definitions for the proposed puncturable attribute-based proxy re-encryption scheme and prove its security under the learning with errors (LWE) assumption, which is widely believed to be resistant to quantum computer attacks. Security analysis demonstrates that the proposed scheme achieves HRA security in the standard model.

Verifiable registries allow clients to securely access a key-value mapping maintained by an untrusted server. Registries must be audited to ensure global invariants are preserved, which, in turn, allows for efficient monitoring of individual registry entries by their owners. To this end, existing proposals either assume trusted third-party auditors or rely on incrementally verifiable computation (IVC) via expensive recursive SNARKs to make registries client-auditable. In this work, we give new client-auditable verifiable registries with throughputs up to $100\times$ greater than baseline IVC solutions. Our approach relies on an authenticated dictionary based on RSA accumulators for which we develop a new constant-size invariant proof. We use this as a replacement for Merkle trees to optimize the baseline IVC approach, but also provide a novel construction which dispenses with SNARKs entirely. This latter solution adopts a new checkpointing method to ensure client view consistency.

In this paper, we provide details on the proofs of the quantum polynomial time algorithm of Biasse and Song (SODA 16) for computing the $S$-unit group of a number field. This algorithm directly implies polynomial time methods to calculate class groups, $S$-class groups, relative class group and unit group, ray class groups, solve the principal ideal problem, solve certain norm equations, and decompose ideal classes in the ideal class group. Additionally, combined with a result of Cramer, Ducas, Peikert and Regev (Eurocrypt 2016), the resolution of the principal ideal problem allows one to find short generators of a principal ideal. Likewise, methods due to Cramer, Ducas and Wesolowski (Eurocrypt 2017) use the resolution of the principal ideal problem and the decomposition of ideal classes to find so-called ``mildly short vectors'' in ideal lattices of cyclotomic fields.

Homomorphic encryption allows for computations on encrypted data without exposing the underlying plaintext, enabling secure and private data processing in various applications such as cloud computing and machine learning. This paper presents a comprehensive mathematical foundation for three prominent homomorphic encryption schemes: Brakerski-Gentry-Vaikuntanathan (BGV), Brakerski-Fan-Vercauteren (BFV), and Cheon-Kim-Kim-Song (CKKS), all based on the Ring Learning with Errors (RLWE) problem. We align our discussion with the functionalities proposed in the recent homomorphic encryption standard, providing detailed algorithms and correctness proofs for each scheme. Additionally, we propose improvements to the current schemes focusing on noise management and optimization of public key encryption and leveled homomorphic computation. Our modifications ensure that the noise bound remains within a fixed function for all levels of computation, guaranteeing correct decryption and maintaining efficiency comparable to existing methods. The proposed enhancements reduce ciphertext expansion and storage requirements, making these schemes more practical for real-world applications.

Linkable Ring Signatures (LRS) allow users to anonymously sign messages on behalf of ad-hoc rings, while ensuring that multiple signatures from the same user can be linked. This feature makes LRS widely used in privacy-preserving applications like e-voting and e-cash. To scale to systems with large user groups, efficient schemes with short signatures and fast verification are essential. Recent works, such as DualDory (ESORICS’22) and LLRing (ESORICS’24), improve verification efficiency through offline precomputations but rely on static rings, limiting their applicability in ad-hoc ring scenarios. Similarly, constant-size ring signature schemes based on accumulators face the same limitation. In this paper, we propose a framework for constructing constant-size LRS suitable for large ad-hoc rings. We introduce a novel pairing-based Set Membership Argument (SMA) with a proof size of only three group elements. By leveraging KZG polynomial commitments, we optimize the verification to require only constant group exponentiations and pairings, as well as linear field multiplications. Utilizing the SMA, our framework achieves constant-size signatures with verification dominated by linear field operations, outperforming existing schemes that require linear group exponentiations in ad-hoc ring settings. Moreover, it exhibits strong scalability: (i) compatibility with any PKI-based cryptosystem and (ii) scoped linkability, enabling flexible definitions of linking scope. We instantiate our framework using a discrete logarithm public key structure. On the $BN254$ curve, our signature size is fixed at 687 bytes, which to our best knowledge is the shortest LRS for ring sizes larger than 32. For a ring size of 1024, our verification cost is only 10.4 ms, achieving 48.6×, 2.6×–467×, 7.9×–13.2×, and 2.2×–102.5× improvements over Omniring (CCS’19), DualDory (with and without precomputation), LLRing-DL (with and without precomputation), and LLRing-P (with and without precomputation), respectively. Moreover, this performance gap continues to grow as the ring size increases.

Zero-knowledge protocols allow a prover to prove possession of a witness for an NP-statement without revealing any information about the witness itself. This kind of protocol has found extensive applications in various fields, including secure computation and blockchain. However, in certain scenarios (e.g. when the statements are complicated), existing zero-knowledge protocols may not be well-suited due to their limited applicability or high computational overhead. We address these limitations by incorporating the notion of publicly verifiable covert (PVC) security into zero-knowledge protocols. PVC security, recently emerging from secure computation, effectively balances security and efficiency in practical scenarios. With PVC security, while a malicious party may attempt to cheat, such cheating will be detected and become publicly verifiable with a significant probability (called deterrence factor, e.g. ${>}90\%$). This notion is well-suited for practical scenarios involving reputation-conscious parties (e.g. companies) and offers substantial efficiency improvements. In this paper, we present the first definition of zero-knowledge protocols with PVC security. We then propose a generic transformation to convert Sigma protocols with $1$-bit challenge, a kind of protocol widely used for zero-knowledge, into efficient zero-knowledge protocols with PVC security. By applying our transformation, we can substantially improve the efficiency of existing protocols for reputation-sensitive parties. For instance, applying the transformation to achieve a deterrence factor of $93.75\%$ incurs a cost of only around $20\%$ compared to the original protocol. Therefore, our results contribute to significant advancements in practical zero-knowledge protocols.

We present a derivative-free Richelot (2,2)-isogeny formulation using first subresultants and a canonical quadratic lift. Over odd characteristic, we prove its algebraic equivalence in Fp[x] to the classical Wronskian under natural normalization. Leveraging this, we introduce the Guarded Subresultant Route (GSR): a deterministic evaluator with constant-size algebraic guards, a lightweight post-check, and at most one affine retry. It returns a certified triple (U, V, W) or rejects non-admissible inputs, eliminating differentiation while enforcing admissibility and auditable control flow. Prototypes show the core is 1.46–1.70 times faster than the classical Wronskian across varied primes, with GSR adding about 5–10 microseconds of constant overhead. The backend-agnostic design suits batched and hierarchical genus-2 isogeny pipelines for reproducible computation.

This paper presents a security analysis of the ARX-based lightweight block cipher proposed by Mohanapriya and Nithish (Sci Rep 15, 36060 (2025)) for image encryption in IoT environments. The cipher employs a 64-bit key and a 64-bit block size, relying on Addition, Rotation, and XOR (ARX) operations. Our analysis demonstrates that the full-round version of this cipher is vulnerable to differential cryptanalysis. In fact, the cipher can be distinguished from a random permutation using $2^{41}$ chosen plaintexts. Consequently, the designers' security claims are not fully supported.

Linear Feedback Shift Registers (LFSRs) combined with non linear filtering functions have long been a fundamental design for stream ciphers, offering a well-understood structure that remains easy to analyze. However, the introduction of algebraic attacks in 2003 shifted the focus toward more complex designs, as filtered LFSRs required larger registers to maintain security. While this was seen as a drawback at the time, it is no longer a limiting factor, and emerging cryptographic applications benefit from specialized designs—challenges that filtered LFSRs can effectively address. In this work, we propose a new filtered LFSR design, called Nostalgia, tailored for Hybrid Homomorphic Encryption (HHE). We use a weightwise quadratic function as filtering function, leveraging its efficiency in the HHE setting while ensuring security against classical attacks. We also discuss the parameter selection of our design and demonstrate its efficiency in this setting by providing a proof-of-concept implementation. In terms of latency, our HHE solution outperforms current state-of-the-art for TFHE-based HHE (Baudrin et. al. Crypto 2025) by a factor of 6.1 times. By revisiting filtered LFSRs in light of modern security requirements, we aim to renew interest in their potential applications and stimulate further cryptanalysis efforts.

A rugged pseudorandom permutation (RPRP) is a security notion for variable-length tweakable ciphers that is strictly weaker than the traditional notion of a strong pseudorandom permutation. Being a weaker security notion it admits more efficient constructions. Yet the notion is strong enough so that any such construction can lend itself to a number of practical applications. It can be used to construct onion encryption, misuse-resistant AEAD, and AEAD secure under the release of unverified plaintext. Two recent works have introduced the notion, explored some of its applications, and studied a number of constructions that meet this notion. However, no constructions are known to achieve this notion with beyond-birthday-bound security. Current cloud applications are processing amounts of data that go well beyond the traditional $2^{32}$ barrier, and $2^{64}$ is becoming the new target. As such, the need for encryption with beyond-birthday-bound security has become a very practical concern. In this work, we present the first constructions for variable-length tweakable ciphers that satisfy RPRP security beyond the birthday bound. From these constructions, we readily obtain efficient AEAD schemes that are optimally secure against once misuse and the release of unverified plaintext.

We present the Synergeia (Συνεργία) protocol, a novel, permissionless blockchain protocol that synergistically integrates Proof-of-Work (PoW) and a dynamically regulated Proof-of-Stake (PoS) mechanism. Traditional Nakamoto protocols exhibit consistency violations decaying as $\epsilon \approx exp(-\Omega(k))$ leading to long finality times. Our primary contribution is leveraging a Local Dynamic Difficulty (LDD) scheme to reshape the block inter-arrival time distribution towards a Rayleigh distribution. We prove this yields a full consistency bound of $\epsilon(k) \le exp(-C_{1}k^{2}) + exp(-C_{2}k)$. While this provides a quadratic asymptotic advantage, we demonstrate that for practical security parameters, the bound is dominated by the linear term. Our LDD mechanism achieves a superior constant factor ($C_{2}$) in this linear exponent, requiring only $k=26$ blocks against a 40% adversary for enterprise-grade security ($\epsilon \le 10^{-9}$). Furthermore, we introduce the Decentralized Consensus Service ($\mathcal{F}_{DCS}$) providing BFT-robust consensus on network time, stake, delay, and load via on-chain beacons. This enables a fully autonomous LDD system that dynamically adapts its Slot Gap ($\psi$) and target block time ($\mu_{target}$) to measured network conditions, ensuring the security assumption $\psi > \Delta$ holds robustly. The protocol utilizes an Accumulated Synergistic Work (ASW) metric incorporating Proof-of-Burn for PoS block commitment. As a result of this constant-factor improvement, Synergeia achieves probabilistic finality in approximately 6.5 minutes under typical Bitcoin-like network conditions ($\mathbb{E}[\Delta] \approx 8s$). Additionally, we introduce Burst Finality, an optional mechanism triggered by high transaction fees (secured by Proof-of-Burn) that provides execution-driven confirmation for instant finality. Synergeia establishes a new paradigm for adaptive consensus, offering a significant constant-factor improvement for probabilistic finality alongside optional near-instant settlement.

On the road to eliminating censorship from modern blockchain protocols, recent work in consensus has explored protocol design choices that delegate the duty of block assembly away from a single consensus leader and instead to multiple parties, referred to as includers. As opposed to the traditional leader-based approach, which guarantees transaction inclusion in a block produced by the next correct leader, the multiple includer approach allows blockchain protocols to provide a strong censorship-resistance property for users: A timely submitted transaction is guaranteed to be included in the next confirmed block, regardless of the leader's behavior. Such a guarantee, however, comes at the cost of 2 additional rounds of latency to block confirmation, compared to the leader-based approach. Is this cost necessary? We introduce the Censorship Resistant Byzantine Broadcast (CRBB) problem, a one-shot variant that distills the core functionality underlying the multiple-includer design paradigm. We then provide a full characterization, both in synchrony and partial synchrony, of the achievable latency of CRBB in executions with a correct leader, which is the most relevant case to practice. Our main result is an inherent latency cost of two additional rounds compared to the classic Byzantine Broadcast (BB) problem. For example, synchronous protocols for CRBB require 4 rounds whenever BB requires 2 rounds. Similarly, up to a small constant in the resilience, partial synchrony protocols for CRBB require 5 rounds whenever BB requires 3 rounds.

The study of cryptographic criteria for Boolean functions with restricted domains has been an important topic over the last 20 years. A revived interest has sparked after the work of Carlet, Méaux and Rotella in 2017, where the authors studied cryptographic properties of restricted-domain functions and introduced the concept of weightwise perfectly balanced functions as part of the analysis of the FLIP stream cipher. Weightwise (almost) perfectly balanced functions are defined as Boolean functions that are (almost) balanced on each of the sets of vectors of the same Hamming weight. Several approaches have been considered to build new families of such functions. In this article, we present some new constructions of weightwise (almost) perfectly balanced functions via two approaches, the first class is constructed using the $t$-concatenation of Boolean functions, whereas the second one draws certain functions from the so-called general Maiorana-McFarland class. A generic analysis of these two classes is given, as well as explicit examples in both classes. Namely, we provide instances of functions in both classes attaining high overall nonlinearities, as well as slice nonlinearities. Notably, we present examples in 16 variables that attain some of the best overall nonlinearities, and more importantly, the highest slice nonlinearities among all of the constructions presented in the literature.

We analyse the binding properties of explicitly-rejecting key-encapsulation mechanisms (KEMs) obtained by the Fujisaki-Okamoto (FO) transform. The framework for binding notions, introduced by [CDM24], generalises robustness and collision-freeness, and was motivated by the discovery of new types of attacks against KEMs. Implicitly-rejecting FO-KEMs have already been analysed with regards to the binding notions, with [KSW25b] providing the full picture. Binding notions for explicitly-rejecting FO-KEMs have been examined only partially, leaving several gaps. Moreover, the analysis of the explicit-rejection setting must account for additional binding notions that implicitly-rejecting KEMs cannot satisfy. We give mostly positive results for the explicitly-rejecting FO transform—though many notions require further robustness assumptions on the underlying PKE. We then show that the explicit FO transform with plaintext confirmation hash (HFO) achieves all notions and requires weaker robustness assumptions. Finally, we introduce a slightly modified version of the HFO transform that achieves all binding notions without requiring any robustness of the underlying PKE.

ARX-based ciphers such as Salsa20 and ChaCha achieve high performance using only modular addition, rotation, and XOR. While ARX constructions are widely deployed in practice, linear and differential-linear cryptanalysis often reveal non-negligible biases in their reduced-round variants. Previous work has shown that a 7-round distinguisher on ChaCha is feasible, requiring about \(2^{214}\) operations and relying on a linear approximation with a theoretical bias of \(2^{-53}\). However, such theoretical approximations significantly deviate from experimental observations. In this work, we resolve these discrepancies by introducing new fundamental linear approximations for two consecutive additions over three independent variables. We rigorously derive the exact probabilities of these approximations, demonstrating that the conventional independence assumption leads to systematic errors in bias estimation. Applying our theorem to ChaCha, we refine the probabilities of key approximations used in previous attacks. Our refined estimates closely match experimentally observed biases, reducing the gap between theory and practice. These results provide a more accurate foundation for future differential-linear cryptanalysis of ChaCha and other ARX-based designs.

Akavia, Gentry, Halevi, and Vald (TCC’22, JoC'25) introduced the security notion of function-chosen-plaintext-attack ($\mathsf{FuncCPA}$ security) for public-key encryption schemes. $\mathsf{FuncCPA}$ is defined by adding a functional re-encryption oracle to the $\mathsf{IND}$-$\mathsf{CPA}$ game. This notion is crucial for secure computation applications where the server is allowed to delegate a part of the computation to the client. Dodis, Halevi, and Wichs (TCC’23) introduced a stronger variant called $\mathsf{FuncCPA^+}$, and conjectured that $\mathsf{FuncCPA^+}$ is strictly stronger than $\mathsf{FuncCPA}$, while they showed $\mathsf{FuncCPA^+}$ implies $\mathsf{FuncCPA}$. Seeking insights into this conjecture, they showed that $\mathsf{ReEncCPA^+}$ is strictly stronger than $\mathsf{ReEncCPA}$, where $\mathsf{ReEncCPA}$ and $\mathsf{ReEncCPA^+}$ are restricted versions of $\mathsf{FuncCPA}$ and $\mathsf{FuncCPA^+}$ respectively. In this paper, contrary to their conjecture, we show that $\mathsf{FuncCPA^+}$ is equivalent to $\mathsf{FuncCPA}$. We also introduce new variants of $\mathsf{FuncCPA}$; $\mathsf{WeakFuncCPA}$, $\mathsf{OW}$-$\mathsf{FuncCPA}$, and $\mathsf{OW}$-$\mathsf{WeakFuncCPA}$. $\mathsf{WeakFuncCPA}$ is a restricted variant of $\mathsf{FuncCPA}$ in that an oracle query is prohibited after the challenge query (like $\mathsf{IND}$-$\mathsf{CCA1}$). $\mathsf{OW}$-$\mathsf{FuncCPA}$ and $\mathsf{OW}$-$\mathsf{WeakFuncCPA}$ are the one-way ($\mathsf{OW}$) versions of $\mathsf{FuncCPA}$ and $\mathsf{WeakFuncCPA}$, respectively. This paper shows that $\mathsf{WeakFuncCPA}$ and $\mathsf{OW}$-$\mathsf{FuncCPA}$ are equivalent to $\mathsf{FuncCPA}$, that is, all of $\mathsf{FuncCPA}$, $\mathsf{FuncCPA^+}$, $\mathsf{WeakFuncCPA}$, and $\mathsf{OW}$-$\mathsf{FuncCPA}$ are equivalent. Considering the separation of $\mathsf{IND}$-$\mathsf{CCA1}$ and $\mathsf{IND}$-$\mathsf{CCA2}$, and that of $\mathsf{OW}$-$\mathsf{CPA}$ and $\mathsf{IND}$-$\mathsf{CPA}$, these results are surprising. To show the equivalence, we develop novel techniques to utilize functional re-encryption oracles. We then provide the separation results that $\mathsf{OW}$-$\mathsf{WeakFuncCPA}$ does not imply $\mathsf{FuncCPA}$ and $\mathsf{ReEncCPA^+}$ does not imply $\mathsf{FuncCPA}$.

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 timestamp-based certificates with censorship resistance through inclusion lists. The resulting protocol satisfies four properties, the first being a strong hiding property which consists of Value Indistinguishability, Existential Obfuscation and User Obfuscation. This not only ensures that the adversary cannot differentiate between two value of bids (as the previously defined Hiding property does in Pranav et al. [MCP]), but also that the very existence of a bid and the identity of the bidder remain obfuscated. The second property is Short-Term Censorship Resistance, ensuring that, if the underlying blockchain outputs a block, then the auction would contain bids from all honest users. The third is a new property we introduce, Auction Participation Efficiency (APE), that measures how closely on-chain outcomes resemble classical auctions in terms of costs for participating users. And the fourth property is No Free Bid Withdrawal, which disallows committed bids from being withdrawn in case the bidder changes its mind. Together, these properties yield a fair, private, and economically robust auction primitive that can be integrated into any blockchain to support secure and efficient auction execution.

MPC-in-the-Head (MPCitH) has recently gained traction as a foundation for post-quantum signature schemes, offering robust security without trapdoors. Despite its strong security profile, MPCitH-based schemes suffer from high computational overhead and large signature sizes, limiting their practical application. This work addresses these inefficiencies by relaxing vector commitments within MPCitH-based schemes. We introduce the concept of vector semi-commitment, which relaxes the binding property of traditional vector commitment. Vector semi-commitment schemes may allow an adversary to find more than one preimage of a commitment. We instantiate vector semi-commitment schemes in both the random oracle model and the ideal cipher model, leveraging recent optimizations on GGM tree such as correlated GGM tree. We apply the ideal-cipher-based vector semi-commitment scheme to the BN++ signature scheme and prove it almost fully secure in the ideal cipher model. Implementing these improvements in the AIMer v2.0 signature scheme, we achieve up to 8.7% shorter signatures and up to 112% faster signing and verification speeds, setting new benchmarks for MPCitH-based schemes.

In the isogeny-based track of post-quantum cryptography, optimal instances of the signature scheme SQISign rely on primes $p$ such that $p\pm1$ is smooth. In 2021 a new approach to find those numbers was discovered using solutions to the Prouhet-Tarry-Escott (PTE) problem. With these solutions we can sieve for smooth integers $A$ and $B$ with a difference of $|A-B|=C$ fixed by the solution. Then some $2A/C$ and $2B/C$ are smooth integers hopefully enclosing a prime. They took many different PTE solutions and combined them into a tree to process them more efficiently. But for larger numbers there are fewer promising PTE solutions so their advantage over the naive approach (checking a single solution at a time) fades. For a single PTE solution the search can be optimised for the corresponding $C$ and allows to check smoothness only for those integers that are divisible by $C$. In this work we investigate such optimisations and show a significant speed-up compared to the naive approach - both heuristically and empirically. Along the way we compute the number of roots of a given polynomial modulo prime powers and give an upper bound for the number of roots modulo a composite number.

Approximate Homomorphic Encryption (AHE), introduced by Cheon et al. [CKKS17] offers a powerful solution for encrypting real-valued data by relaxing the correctness requirement and allowing small decryption errors. Existing constructions from (Ring) Learning with Errors achieve standard IND-CPA security, but this does not fully capture scenarios where an adversary observes decrypted outputs. Li and Micciancio [LiMic21] showed that when decryptions are passively leaked, these schemes become vulnerable to practical key recovery attacks even against honest-but-curious attackers. They formalise security when decryptions are shared with new notions of IND-CPA-D and KR-D security. We propose new techniques to achieve provable IND-CPA-D and KR-D security for AHE, while adding substantially less additional decryption noise than the prior provable results. Our approach hinges on refined "game-hopping" tools in the bit-security framework, which allow bounding security loss with a lower noise overhead. We also give a noise-adding strategy independent of the number of oracle queries, removing a costly dependence inherent in the previous solution. Beyond generic noise-flooding, we show that leveraging the recently introduced HintLWE problem [KLSS23] can yield particularly large security gains for AHE ciphertexts that are the result of "rescaling", a common operation in CKKS. Our analysis uses the fact that rescale-induced noise amounts to a linear ``hint" on the secret to enable a tighter reduction to LWE (via HintLWE). In many practical parameter regimes where the rescaling noise dominates, our results imply an additional precision loss of as little as two bits is sufficient to restore a high level of security against passive key-recovery attacks for standard parameters. Overall, our results enable a provably secure and efficient real-world deployment of Approximate Homomorphic Encryption in scenarios with realistic security requirements.

Ideal functionalities are used to study increasingly complex protocols within the Universal Composability framework. However, such functionalities are often complex themselves, making it difficult to assess whether they truly fulfill their promises. In this paper, we present four attacks on functionalities from various applications (e-voting, SMPC, anonymous lotteries, and smart metering), demonstrating that they do not capture the intuitively expected properties. We argue that ideal functionalities should not merely be justified secure at a high level but rigorously proven to be so. To this end, we propose a methodology that combines game-based proofs and computer-aided verification: ideal functionalities can in fact be treated as protocols, and one can use traditional game-based proofs to study them, where any game-based security property proven on the functionality does transfer to any protocol that realizes it. We also propose fixed versions of the ideal functionalities we studied, and formally define the security properties they should satisfy through a game. Finally, using Squirrel, a proof assistant for protocol security, we formally prove that the fixed functionalities verify the specified game-based security properties.

In the last decade, the introduction of advanced cryptographic protocols operating on large finite fields $\mathbb{F}_q$ has raised the need for efficient cryptographic primitives in this setting, commonly referred to as Arithmetization-Oriented (AO). The cryptanalysis of AO hash functions is essentially done through the study of the CICO problem on the underlying permutation. Two recent works at Crypto 2024 and Asiacrypt 2024 managed to solve the CICO problem much more efficiently than traditional Gröbner basis methods, using respectively advanced Gröbner basis techniques and resultants. In this paper, we propose an attack framework based on resultants that applies to a wide range of AO permutations and improves significantly upon these two recent works. Our improvements mainly come from an efficient reduction procedure that we propose and rigorously analyze, taking advantage of fast multivariate multiplication. We present the most efficient attacks on Griffin, Arion, Anemoi, and Rescue. We show that most variants of Griffin, Arion and Anemoi fail to reach the claimed security level. For the first time, we successfully break a parameter set of Rescue, namely its $512$-bit security variant. The presented theory and complexity estimates are backed up with experimental attacks. Notably, we practically find CICO solutions for $8$ out of $10$ rounds of Griffin, $11$ out of $20$ rounds of Anemoi, $6$ out of $18$ rounds of Rescue, improving by respectively $1$, $3$ and $1$ rounds on the previous best practical attacks.

This is a systematization of knowledge (SoK) on BitVM with succinct on-chain cost. 1. from different cryptographic primitives: - Minicrypt privacy-free garbled circuits (PFGC) - homomorphic message authentication codes (HMAC), which implies succinct PFGC - attribute-based laconic function evaluation (AB-LFE), which implies reusable PFGC 2. using different malicious security compilers: - cut-and-choose (C&C) - non-interactive zero-knowledge proofs (NIZK) - fraud proofs on Bitcoin 3. with different proof systems: - publicly verifiable SNARK - designated-verifiable SNARK (DV-SNARK) 4. in different protocol directions: - standard BitVM (operator = garbler, challengers = evaluators) - reverse BitVM (operator = evaluator, challengers = garblers) 5. given different operator liveness setup: - existential honesty - honest majority

Lookup arguments have recently attracted a lot of developments due to their applications in the constructions of succinct non-interactive arguments of knowledge (SNARKs). A closely related topic is subsequence arguments in which one can prove that string $\mathbf{s}$ is a subsequence of another string $\mathbf{t}$, i.e., deleting some characters in $\mathbf{t}$ can achieve $\mathbf{s}$. A dual notion, namely, non-subsequence arguments, is to prove that $\mathbf{s}$ is not a subsequence of $\mathbf{t}$. These problems have a lot of important applications in DNA sequence analysis, internet of things, blockchains, natural language processing, speech recognition, etc. However, despite their applications, they are not well-studied in cryptography, especially succinct arguments for non-subsequences with efficient proving time and sublinear verification time. In this work, we propose the first succinct non-subsequence argument. Our solution applies the sumcheck protocol and is instantiable by any multivariate polynomial commitment schemes (PCSs). We achieve an efficient prover whose running time is linear in the size of sequences $\mathbf{s}$, $\mathbf{t}$ and their respective alphabet $\Sigma$. Our proof is succinct and the verifier time is sublinear assuming the employed PCS has succinct commitments and sublinear verification time. When instantiating with Sona PCS (EUROCRYPT'24), we achieve proof size $\mathcal{O}(\log_2|\mathbf{s}| + \log_2|\mathbf{t}|+\log_2|\Sigma|)$, prover time $\mathcal{O}(|\mathbf{s}|+|\mathbf{t}|+|\Sigma|)$ and verifier time $\mathcal{O}(\sqrt{|\mathbf{s}|}+\sqrt{|\mathbf{t}|}+\sqrt{|\Sigma|})$. Extending our technique, we can achieve a batch subsequence argument for proving in batch $k$ interleaving subsequence and non-subsequence arguments without proof size suffering a linear blow-up in $k$.

Anamorphic signature schemes (KPPYZ, Crypto 2023) allow users to hide encrypted messages in signatures to allow covert communication in a hypothesized scenario where encryption is outlawed by a "dictator" but authentication is permitted. We enhance the security of anamorphic signatures by proposing two parallel notions of unforgeability which close gaps in existing security definitions. The first notion considers a dictator who wishes to forge anamorphic signatures. This notion patches a divide between the definition and a stated security goal of robustness (BGHMR, Eurocrypt 2024). We port two related BGHMR constructions to the signature scheme setting and demonstrate that, as presented, both of these and a construction from KPPYZ are insecure under an active dictator. However, two of the three can easily be modified to satisfy our definition. The second notion we propose considers a recipient who wishes to forge signatures. To motivate this notion, we identify a gap in an existing security definition from KPPYZ and present attacks that allow parties to be impersonated when using schemes erroneously deemed secure. We then formalize our new unforgeability definition to close this gap. Interestingly, while the new definition is only modestly different from the old one, the change introduces subtle technical challenges that arise when proving security. We overcome these challenges in our reanalysis of existing anamorphic signature schemes by showing they achieve our new notion when built from chosen-randomness secure signatures or with encryption that satisfies a novel ideal-model simulatability property.

The Fuchsbauer, Kiltz, and Loss (CRYPTO 2018) claim that (some) hardness results in the algebraic group model imply the same hardness results in the generic group model was recently called into question by Katz, Zhang, and Zhou (ASIACRYPT 2022). The latter gave an interpretation of the claim under which it is incorrect. We give an alternate interpretation under which it is correct, using natural frameworks for capturing generic and algebraic models for arbitrary algebraic structures. Most algebraic analyses in the literature can be captured by our frameworks, making the claim correct for them.

There is a gap between the security of constrained PRFs required in some applications and the security provided by existing definitions. This gap is typically patched by only considering nonadaptive security or manually mixing the CPRF with a random oracle (implicitly constructing a new CPRF) to achieve adaptive security. We fill this gap with a new definition for constrained PRFs with strong adaptive security properties and proofs that it is achieved by practical constructions based on the cascade PRF (which generalizes the GGM construction) and AMAC. We apply the definition for analyzing searchable symmetric encryption and puncturable key wrapping.

An important proof technique in the random oracle model involves reprogramming it on hard to predict inputs and arguing that an attacker cannot detect that this occurred. In the quantum setting, a particularly challenging version of this considers adaptive reprogramming wherein the points to be reprogrammed (or the output values they should be programmed to) are dependent on choices made by the adversary. Some quantum frameworks for analyzing adaptive reprogramming were given by Unruh (CRYPTO 2014, EUROCRYPT 2015), Grilo-Hövelmanns-Hülsing-Majenz (ASIACRYPT 2021), and Pan-Zeng (PKC 2024). We show, counterintuitively, that these adaptive results follow from the nonadaptive one-way to hiding theorem of Ambainis-Hamburg-Unruh (CRYPTO 2019). These implications contradict beliefs (whether stated explicitly or implicitly) that some properties of the adaptive frameworks cannot be provided by the Ambainis-Hamburg-Unruh result. We show, counterintuitively, that these adaptive results follow directly from the non-adaptive one-way to hiding theorem of Ambainis-Hamburg-Unruh (CRYPTO 2019). These implications contradict beliefs (whether stated explicitly or implicitly) that some properties of the adaptive frameworks cannot be provided by the Ambainis-Hamburg-Unruh result.

The search for optimal differential trails for ARX ciphers is known to be difficult and scale poorly as the word size (and the branching through the carries of modular additions) increases.To overcome this problem, one may approximate the modular addition with the XOR operation, a process called linearization. The immediate drawback of this approach is that many valid and good trails are discarded. In this work, we explore different partial linearization trade-offs to model the modular addition through the \emph{window heuristic}, which restricts carry propagation to windows of $w_s$ consecutive positions. This strategy enables the exploration of full linearization ($w_s = 0$), normal modelling ($w_s = n$), and all the different trade-offs between completeness and speed in between. We give the corresponding SAT and MILP model and their parallel versions, and apply them to \chachacore, \speckfamily, \leafamily, and \hightfamily. Our method greatly outperforms all previous modeling of modular addition. In particular, we find the first differential path for 4 rounds of \chachacore with a probability greater than $2^{-256}$, and a corresponding 6 rounds boomerang distinguisher. This indicates that purely differential-based attacks have the potential to become competitive with differential-linear attacks, currently, the best-known attacks against \chachacore and other ARX ciphers. Finally, we exhibit an improved key recovery attack on reduced \leafamily.

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 (Hashimoto et al., CCS 2022), or in mesh networks (Bienstock et al., CCS 2023) are relatively inefficient or specially tailored for only particular settings. Moreover, all existing practical solutions reveal crucial metadata upon exposures of user secrets. In this work, we introduce a formal definition of Anonymity Wrappers (AW) that generically hide metadata of underlying two-party and group messaging protocols. Our definition captures forward and post-compromise anonymity as well as authenticity in the presence of temporary state exposures. Inspired by prior wrapper designs, the idea of our provably secure AW construction is to use shared keys of the underlying wrapped (group) messaging protocols to derive and continuously update symmetric keys for hiding metadata. Beyond hiding metadata on the wire, we also avoid and hide structural metadata in users' local states for stronger anonymity upon their exposure. We implement our construction, evaluate its performance, and provide a detailed comparison with Signal's current approach based on Sealed Sender: Our construction reduces the wire size of small 1:1 messages from 441 bytes to 114 bytes. For a group of 100 members, it reduces the wire size of outgoing group messages from 7240 bytes to 155 bytes. We see similar improvements in computation time for encryption and decryption, but these improvements come with substantial storage costs for receivers. For this reason, we develop extensions with a Bloom filter for compressing the receiver storage. Based on this, Signal considers deploying our solution.

Format-preserving encryption (FPE) enables encryption while maintaining syntactic properties such as character sets. The current NIST standard FF1 uses multi-round Feistel networks that sacrifice performance for flexibility, while FF3-1 was withdrawn in 2025 following successful cryptanalytic attacks. FAST, proposed as a faster alternative, has not been widely implemented due to its complexity, leaving limited practical alternatives. We present HCTR2-FP and HCTR3-FP, format-preserving adaptations of the HCTR2 and HCTR3 wide-block tweakable ciphers. These variants preserve the single-pass Hash-Encrypt-Hash structure while operating on arbitrary radix domains through base-radix encoding and modular arithmetic. The constructions are simple to implement and analyze, and benchmarks demonstrate significant speedup over FF1.

In this paper, we aim to explore the design of low-latency authenticated encryption schemes particularly for memory encryption, with a focus on the temporal uniqueness property. To achieve this, we present the low-latency Pseudo-Random Function (PRF) called $\mathtt{Twinkle}$ with an output up to 1152 bits. Leveraging only one block of $\texttt{Twinkle}$, we developed $\texttt{Twinkle-AE}$, a specialized authenticated encryption scheme with six variants covering different cache line sizes and security requirements. We also propose $\texttt{Twinkle-PA}$, a pointer authentication algorithm, which takes a 64-bit pointer and 64-bit context as input and outputs a tag of 1 to 32 bits. We conducted thorough security evaluations of both the PRFs and these schemes, examining their robustness against various common attacks. The results of our cryptanalysis indicate that these designs successfully achieve their targeted security objectives. Hardware implementations using the FreePDK45nm library show that $\texttt{Twinkle-AE}$ achieves an encryption and authentication latency of 3.83 $ns$ for a cache line. In comparison, $\texttt{AES}$-CTR with WC-MAC scheme and Ascon-128a achieve latencies of 9.78 $ns$ and 27.30 $ns$, respectively. For the pointer authentication scheme $\texttt{Twinkle-PA}$, the latency is 2.04 $ns$, while $\texttt{QARMA-64-}\sigma_0$ has a latency of 5.57 $ns$.

Single Sign-On (SSO) is a popular authentication mechanism enabling a user to access different online services (called Relying Parties, or RPs) with a single login credential obtained from the Identity Provider (IdP). Despite its convenience, SSO schemes represented by the OIDC standard faces significant privacy concerns---the IdP can track users across different RPs; colluding RPs may share data to find linkage of user access. Recent anonymous credential-based SSO solutions provide a promising direction to enhancing user privacy and mitigating IdP single-point failure; however, they fail to support RP authentication, an important security property of the incumbent SSO workflow, and require RPs to perform non-trivial cryptographic verification. This paper introduces VeriSSO, a novel privacy-preserving SSO protocol based on verifiable credentials (VC) that supports RP authentication and is fully compatible with the incumbent SSO workflow. The key intuition is to employ a committee of independent authentication servers (i) to bind RP authentication to VC-based user verification and (ii) to issue identity tokens in a threshold manner, which crucially ensures RP authentication and user unlinkability without IdP involvement or reliance on a trusted central party. Our scheme allows RPs to continue using their existing signature-based identity token verification routine and supports lawful de-anonymization, providing user accountability for misbehavior. Our experiment shows the feasibility and efficiency and VeriSSO, with one SSO workflow completed within 30 milliseconds.

Given a small number of base oblivious transfers (OTs), how does one generate a large number of extended OTs as efficiently as possible? The answer has long been the seminal work of IKNP (Ishai et al., Crypto 2003) and the family of protocols it inspired, which only use Minicrypt assumptions. Recently, Boyle et al. (Crypto 2019) proposed the Silent-OT technique that improves on IKNP, but at the cost of a much stronger, non-Minicrypt assumption: the learning parity with noise (LPN) assumption. We present SoftSpokenOT, the first OT extension to improve on IKNP's communication cost in the Minicrypt model. While IKNP requires security parameter $\lambda$ bits of communication for each OT, SoftSpokenOT only needs $\lambda / k$ bits, for any $k$, at the expense of requiring $2^{k-1} / k$ times the computation. For small values of $k$, this tradeoff is favorable since IKNP-style protocols are network-bound. We implemented SoftSpokenOT and found that our protocol gives almost a $5 \times$ speedup over IKNP in the LAN setting. Our technique is based on a novel silent protocol for vector oblivious linear evaluation (VOLE) over polynomial-sized fields. We created a framework to build maliciously secure 1-of-N OT extension from this VOLE, revisiting and improving the existing work for each step. Along the way, we found several flaws in the existing work, including a practical attack against the consistency check of Patra et al. (NDSS 2017).

Group signatures allow a user to sign anonymously on behalf of a group of users while allowing a tracing authority to trace the signer's identity in case of misuse. In Chaum and van Heyst's original model (EUROCRYPT'91), the group needs to stay fixed. Throughout various attempts, including partially dynamic group signatures and revocations, Bootle et al. (ACNS'16, J. Cryptol.) formalized the notion of fully dynamic group signatures (FDGS), enabling both enrolling and revoking users of the group. However, in their scheme, the verification process needs to take into account the latest system information, and a previously generated signature will be invalidated as soon as, for example, there is a change in the group. We therefore raise a research question: Is it possible to construct an FDGS under which the validity of a signature can survive future changes in the system information? In this paper, we propose Everlasting Fully Dynamic Group Signatures (EFDGS) that allow signers to generate signatures that do not require verification with any specific epoch. Specifically, once the signatures are created, they are valid forever. It also guarantees that the signer can only output such a signature when she is a valid user of the system. We realize the above new model by constructing a plausibly post-quantum standard-lattice-based EFDGS.

Post-Quantum key encapsulation mechanisms based on the re-encryption framework of Fujisaki and Okamoto have proved very sensitive to Plaintext Checking Oracle (PCO) attacks. The first theoretic works on PCO attacks were rapidly followed by practical attacks on real implementations, notably on NIST standardized ML-KEM. The actual realization of a PCO relies on side-channel leakages that are inherently noisy ; even more so if the implementation embeds side-channel countermeasures. In this paper we tackle the often overlooked complications caused by highly noisy PCOs. We demonstrate that the impact of wrong oracle answers can be very efficiently reduced with the use of the so-called Sequential Probability Ratio Test (SPRT). This test can be seen as an elegant and natural early abort strategy on top of the commonly used approaches based on majority-voting or the likelyhood ratio test. As far as we know, this is the first use of SPRT in the context of side-channel attacks. We show that it allows to divide by a factor up to 3 the attack complexity compared to the traditional approaches. By establishing new comparisons with recently published noisy PCO attacks we emphasize that SPRT should be considered as the novel baseline for all future works in this line of research.

In this work, we initiate the formal study of oblivious batch updates over outsourced encrypted Bloom filters, focusing on scenarios where a storage-limited sender must insert or delete batches of elements in a Bloom filter maintained on an untrusted server. Our survey identifies only two prior approaches (CCS 2008 and CCS 2012) that can be adapted to this problem. However, they either fail to provide adequate security in dynamic scenarios or incur prohibitive update costs that scale with the filter’s maximum capacity rather than the actual batch size. To address these limitations, we introduce a new cryptographic primitive, $\textit{Oblivious Bloom Filter Insertion}$ ($\textsf{OBFI}$), and propose novel constructions. At the core of our design is a novel building block, $\textit{Oblivious Bucket Distribution}$ ($\textsf{OBD}$), which enables a storage-limited sender to distribute a large array of elements, uniformly sampled from a finite domain, into small, fixed-size buckets in a data-oblivious manner determined by element order. The design of $\textsf{OBD}$ is further supported by identifying and proving a new structural property of such arrays, which establishes tight and explicit probabilistic bounds on the number of elements falling within predefined subranges of the domain. Our $\textsf{OBFI}$ constructions achieve adaptive data-obliviousness and ensure that batch update costs scale primarily with the batch size. Depending on the variant, the sender’s storage requirement ranges from $O(\lambda)$, where $\lambda$ is the security parameter, down to $O(1)$. Finally, we demonstrate the practicality of $\textsf{OBFI}$ by integrating it into representative Bloom-filter-based cryptographic protocols for Searchable Symmetric Encryption, Public-key Encryption with Keyword Search, and Outsourced Private Set Intersection, thereby obtaining batch-updatable counterparts with state-of-the-art security and performance.

A Batched Threshold Encryption (BTE) scheme enables a committee of servers to perform a lightweight (in terms of communication and computation) threshold decryption of an arbitrary batch of ciphertexts from a larger pool, while ensuring the privacy of ciphertexts that are outside the batch. Such a primitive has a direct application in designing encrypted mempools for MEV protection in modern blockchains. Bormet et al. (USENIX 2025) recently proposed a BTE scheme called “BEAT-MEV” which is concretely efficient for small to moderate batch sizes. In this work, we improve and extend the BEAT-MEV scheme in multiple ways. First, we improve the computational cost from quadratic to quasilinear in the batch size, thus making it practical for large batch sizes. This improvement is achieved by substituting the key-homomorphic punctured PRF used in BEAT-MEV with an FFT-friendly alternative. Second, we extend the ideas in their scheme to the weighted setting, where each server in the committee has an associated 'weight' value (e.g., stake weight of validators in PoS blockchains), while crucially ensuring that the communication cost remains independent of the weights. In contrast, BEAT-MEV with naive virtualization would incur communication cost linear in the total weight. Third, for handling the small failure rate inherent in BEAT-MEV scheme due to index collisions across different clients at the time of encryption, we propose a generalization of their suggested approach which offers an option to trade off between ciphertext size and server communication for a given failure rate. We implement and evaluate our scheme and compare it with BEAT-MEV to demonstrate our concrete improvement. In the unweighted setting, we improve the computational cost (without increasing the communication cost) by ≈ 6× for a batch size of 512 ciphertexts. In the weighted setting, we improve the communication cost (without compromising computation time), over BEAT-MEV with naive virtualization, by ≈ 50× for 100 validators with total stake weight 5000 distributed as per the latest Solana stake distribution.

Given a circuit $G: \{0, 1\}^n \to \{0, 1\}^m$ with $m > n$, the *range avoidance* problem ($\text{Avoid}$) asks to output a string $y\in \{0, 1\}^m$ that is not in the range of $G$. Besides its profound connection to circuit complexity and explicit construction problems, this problem is also related to the existence of *proof complexity generators* --- circuits $G: \{0, 1\}^n \to \{0, 1\}^m$ where $m > n$ but for every $y\in \{0, 1\}^m$, it is infeasible to prove the statement "$y\not\in\mathrm{Range}(G)$" in a given propositional proof system. This paper connects these two problems with the existence of *demi-bits generators*, a fundamental cryptographic primitive against nondeterministic adversaries introduced by Rudich (RANDOM '97). $\bullet$ We show that the existence of demi-bits generators implies $\text{Avoid}$ is hard for nondeterministic algorithms. This resolves an open problem raised by Chen and Li (STOC '24). Furthermore, assuming the demi-hardness of certain LPN-style generators or Goldreich's PRG, we prove the hardness of $\text{Avoid}$ even when the instances are constant-degree polynomials over $\mathbb{F}_2$. $\bullet$ We show that the dual weak pigeonhole principle is unprovable in Cook's theory $\mathsf{PV}_1$ under the existence of demi-bits generators secure against $\mathbf{AM}/_{O(1)}$, thereby separating Jeřábek's theory $\mathsf{APC}_1$ from $\mathsf{PV}_1$. Previously, Ilango, Li, and Williams (STOC '23) obtained the same separation under different (and arguably stronger) cryptographic assumptions. $\bullet$ We transform demi-bits generators to proof complexity generators that are *pseudo-surjective* in certain parameter regime. Pseudo-surjectivity is the strongest form of hardness considered in the literature for proof complexity generators. Our constructions are inspired by the recent breakthroughs on the hardness of $\text{Avoid}$ by Ilango, Li, and Williams (STOC '23) and Chen and Li (STOC '24). We use *randomness extractors* to significantly simplify the construction and the proof.

Multi-user (mu) security considers large-scale attackers (e.g., state actors) that given access to a number of sessions, attempt to compromise {\em at least} one of them. Mu security of authenticated encryption (AE) was explicitly considered in the development of TLS 1.3. This paper revisits the mu security of GCM, which remains to date the most widely used dedicated AE mode. We provide new concrete security bounds which improve upon previous work by adopting a refined parameterization of adversarial resources that highlights the impact on security of (1) nonce re-use across users and of (2) re-keying. As one of the main applications, we give tight security bounds for the nonce-randomization mechanism adopted in the record protocol of TLS 1.3 as a mitigation of large-scale multi-user attacks. We provide tight security bounds that yield the first validation of this method. In particular, we solve the main open question of Bellare and Tackmann (CRYPTO '16), who only considered restricted attackers which do not attempt to violate integrity, and only gave non-tight bounds.

We introduce a general template for building garbled circuits with low communication, assuming decisional composite residuosity (DCR) and a circular security assumption. For the case of layered Boolean circuits, we can garble a circuit of size $s$ with communication proportional to $O(s/\log\log s)$ bits, plus an additive factor that is polynomial in the security parameter. For layered arithmetic circuits with $B$-bounded integer computation, we obtain a similar result: the garbled arithmetic circuit has size $O(s/\log\log s) \cdot (\lambda + \log B)$ bits, where $\lambda$ is the security parameter. In both cases, we can remove the circular security assumption by adding a term proportional to the circuit depth. These are the first constructions of general-purpose, garbled circuits with sublinear size, without relying on heavy tools like indistinguishability obfuscation or attribute-based and fully homomorphic encryption. To achieve these results, our main technical tool is a new construction of a form of homomorphic secret sharing (HSS) where some of the inputs are semi-private, that is, known to one of the evaluating parties. Through a new relinearisation technique that allows performing arbitrary additions and multiplications on semi-private shares, we build such an HSS scheme that supports evaluating any function of the form $C(x) \cdot C'(y)$, where $C$ is any polynomially-sized circuit applied to the semi-private input $x$, and $C'$ is a restricted-multiplication (or, NC1) circuit applied to the private input $y$. This significantly broadens the expressiveness of known HSS constructions.

Fully Homomorphic Encryption (FHE) schemes typically experience significant data expansion during encryption, leading to increased computational costs and memory demands during homomorphic evaluations compared to their plaintext counterparts. This work builds upon prior methods aimed at reducing ciphertext expansion by leveraging matrix secrets under the Matrix-LWE assumption. In particular, we consider a ciphertext format referred to in this work as common mask (CM) ciphertexts, which comprises a shared mask and multiple message bodies. Each body encrypts a distinct message while reusing the common random mask. We demonstrate that all known FHEW/TFHE style ciphertext variants and operations can be naturally extended to this CM format. Our benchmarks highlight the potential for amortizing operations using the CM structure, significantly reducing overhead. For instance, in the boolean setting, we have up to a 51% improvement when packing 8 messages. Beyond ciphertext compression and amortized evaluations, the CM format also enables the generalization of several core-TFHE operations. Specifically, we support applying distinct lookup tables on different encrypted messages within a single CM ciphertext and private linear operations on messages encrypted within the same CM ciphertext.

Designing cryptographic protocols and proving these rigorously secure is an arduous and challenging task. Among the methods commonly used to prove security of cryptographic protocols, formalizing it in Canneti's Universal Composability (UC) Framework offers several benefits: (1) Modular design, (2) demonstrating that security remains under arbitrary composition and concurrent execution, (3) the security against any computationally polynomially bound adversary. However, working within the UC Framework can be cumbersome, requires a long time commitment by the prover, and it is prone to errors. While utilization of proof assistants in Cryptography and IT Security is a prominent research area, proof assistants for UC are still in their infancy. Here we show our ongoing work to utilize model checking for verification of proofs in the UC Framework, which to the best of our knowledge is the first attempt to do so. In this work we (1) formally create a Markov Decision Process (MDP) encoding a given proof in the UC Framework, (2) define and proof notions of soundness and completeness for the constructed MDP, (3) implement a proof of concept and (4) demonstrate practical feasibility through experimental evaluation. In summary, in this work we lay out the formal foundations for model checking UC proofs and create a tool that can not only be used for proof verification but also as an assistant for developing proofs in the UC Framework.

We outline how to generalize the Guruswami-Sudan list decoder anal- ysis from Ben–Sasson, Carmon, Ishai, Kopparty and Saraf [BCI+20] in order to obtain a “global” proximity gap, called mutual correlated agree- ment in Arnon, Chiesa, Fenzi and Yogev [WHIR 2024], or strong correlated agreement in Zeilberger [Khatam 24].

Threshold cryptography is typically based on the idea of secret-sharing a private-key $s\in F$ ``in the exponent'' of some cryptographic group $G$, or more generally, encoding $s$ in some linearly homomorphic domain. In each invocation of the threshold system (e.g., for signing or decrypting) an ``encoding'' of the secret is being recovered and so the complexity, measured as the number of group multiplications over $G$, is equal to the number of $F$-additions that are needed to reconstruct the secret. Motivated by this scenario, we initiate the study of $n$-party secret-sharing schemes whose reconstruction algorithm makes a minimal number of \emph{additions}. The complexity of existing schemes either scales linearly with $n\log |F|$ (e.g., Shamir, CACM'79) or, at least, quadratically with $n$ independently of the size of the domain $F$ (e.g., Cramer-Xing, EUROCRYPT '20). This leaves open the existence of a secret sharing whose recovery algorithm can be computed by performing only $O(n)$ additions. We resolve the question in the affirmative and present such a near-threshold secret sharing scheme that provides privacy against unauthorized sets of density at most $\tau_p$, and correctness for authorized sets of density at least $\tau_c$, for any given arbitrarily close constants $\tau_p<\tau_c$. Reconstruction can be computed by making at most $O(n)$ additions and, in addition, (1) the share size is constant, (2) the sharing procedure also makes only $O(n)$ additions, and (3) the scheme is a blackbox secret-sharing scheme, i.e., the sharing and reconstruction algorithms work universally for all finite abelian groups $F$. Prior to our work, no such scheme was known even without features (1)--(3) and even for the ramp setting where $\tau_p$ and $\tau_c$ are far apart. As a by-product, we derive the first blackbox near-threshold secret-sharing scheme with linear-time sharing. We also present several concrete instantiations of our approach that seem practically efficient (e.g., for threshold discrete-log-based signatures). Our constructions are combinatorial in nature. We combine graph-based erasure codes that support ``peeling-based'' decoding with a new randomness extraction method that is based on inner-product with a small-integer vector. We also introduce a general concatenation-like transform for secret-sharing schemes that allows us to arbitrarily shrink the privacy-correctness gap with only a minor overhead. Our techniques enrich the secret-sharing toolbox and, in the context of blackbox secret sharing, offer a new randomized combinatorial alternative to existing deterministic number-theoretic approaches.

The development of cloud computing facilitates data sharing and storage, but it has also raised several security concerns. Public key authenticated encryption with keyword search (PAEKS) enables the encrypted search over cloud data while resisting the insider keyword guessing attacks (IKGAs). However, existing PAEKS schemes are limited to a single receiver, restricting application prospects in the cloud. In addition, quantum computing attacks and key leakage issues further threaten data security. Therefore, designing an encrypted search scheme to resist the above-mentioned attacks is still far-reaching. In this paper, we first propose BroSearch, a secure and efficient broadcast encrypted search scheme in cloud computing. It utilizes lattice sampling algorithms to authenticate the keyword and offers searchability over broadcasting ciphertext while enjoying IKGAs-resistance in a quantum setting. To get around key leakage issues, we then incorporate the minimal cover set technique and lattice basis extension algorithm to construct FS-BroSearch as an enhanced version. Furthermore, we give a rigorous security analysis and a comprehensive performance evaluation of BroSearch and FS-BroSearch. Specifically, BroSearch consumes only 61.11\%, 81.82\%, and 83.33\% of the execution time compared to prior art in terms of ciphertext calculation, trapdoor generation, and search procedures, which is efficient in cloud computing.

The first contribution of the paper is to put forward an abstract definition of the Grain family of stream ciphers which formalises the different components that are required to specify a particular member of the family. Our second contribution is to provide new and strengthened definitions of the components. These include definining new classes of nonlinear Boolean functions, improved definition of the state update function during initialisation, choice of the tap positions, and the possibility of the linear feedback shift register being smaller than the nonlinear feedback shift register. The third contribution of the paper is to put forward seven concrete proposals of stream ciphers by suitably instantiating the abstract family, one at the 80-bit security level, and two each at the 128-bit, 192-bit, and the 256-bit security levels. At the 80-bit security level, compared to the well known Grain~v1, the new proposal uses Boolean functions with improved cryptographic properties \textit{and} an overall lower gate count. At the 128-bit level, compared to ISO/IEC standard Grain-128a, the new proposals use Boolean functions with improved cryptographic properties; one of the proposals require a few extra gates, while the other has an overall lower gate count. At the 192-bit, and the 256-bit security levels, there are no proposals in the literature with smaller gate counts.

We present RECPIR, a hintless single-server Private Information Retrieval (PIR) protocol that achieves low client-side latency while preserving practical end-to-end performance at scale. Motivated by the increasing asymmetry between resource-constrained clients and compute-intensive servers, RECPIR introduces a Rotation-based Extension Code (REC) that shifts computation toward the server, enabling extremely lightweight client-side query generation. Built on a coding-theoretic foundation, RECPIR requires no offline preprocessing, naturally supporting dynamic and frequently updated databases. Compared with the best prior fully online protocol (PIRANA), RECPIR reduces the client's query overhead by a factor of $\mathcal{O}(\sqrt{N})$, where $N$ denotes the polynomial ring degree. To offset the increased server overhead, RECPIR further incorporates a Rotation-optimized Query Expansion mechanism that refines homomorphic operations and enables highly parallel execution. Empirical results show that RECPIR achieves up to $\mathbf{37\times}$ and $\mathbf{38\times}$ lower end-to-end latency than PIRANA (the best fully online baseline) and YPIR (the most efficient preprocessing-based baseline), respectively. Its minimal client overhead makes RECPIR particularly suitable for mobile environments: in real-world mobile-to-server experiments, RECPIR improves client-side query generation by $\mathbf{87\times}-\mathbf{10^4\times}$ over state-of-the-art protocols on standard benchmarks.

Password-based Authenticated Key Exchange (${\sf PAKE}$) is a widely acknowledged, promising security mechanism for establishing secure communication between devices. It enables two parties to mutually authenticate each other over insecure networks and generate a session key using a low-entropy password. However, the existing $\mathsf{PAKE}$ protocols encounter significant challenges concerning both security and efficiency in the context of the \textit{Internet of Things} (IoT). In response to these challenges, we contribute to the advancement of post-quantum secure $\mathsf{PAKE}$ protocols tailored for IoT applications, enriching the existing landscape. In this study, we introduce two novel protocols, $\mathsf{PAKE}$-\textup{I} and $\mathsf{PAKE}$-\textup{II}, designed to address these concerns and enhance the security standards of $\mathsf{PAKE}$ protocol. While $\mathsf{PAKE}$-\textup{I} is secure under lattice-based hardness assumptions, $\mathsf{PAKE}$-\textup{II} derives its security from isogeny-based hard problems. Our lattice-based protocol $\mathsf{PAKE}$-\textup{I} is secure based on the \textit{Pairing with Errors} ($\mathsf{PWE}$) assumption and the \textit{Decision Ring Learning with Errors} ($\mathsf{DRLWE}$) assumption and our isogeny-based protocol $\mathsf{PAKE}$-\textup{II} is secure based on the hardness of the \textit{Group Action Inverse Problem} ($\mathsf{GAIP}$) and the \textit{Commutative SuperSingular Diffie-Hellman} ($\mathsf{CSSDH}$) problem in the Random Oracle Model $(\mathsf{ROM})$. We present a comprehensive security proof in a conventional game-based indistinguishability security model that addresses offline dictionary attacks, replay attacks, compromise attacks for both parties (client and server) and perfect forward secrecy. Additionally, our proposed $\mathsf{PAKE}$ protocols are the first post-quantum secure $\mathsf{PAKE}$s that achieve identity privacy and resistance to pre-computation attacks. Through rigorous performance evaluations, the paper demonstrates that the proposed $\mathsf{PAKE}$ schemes are ultralight and exhibit notable advantages in terms of total computation cost and enhanced security properties when compared to the existing protocols. More positively, both the proposed $\mathsf{PAKE}$ are optimal in the sense that they achieve mutual authentication explicitly in only three rounds which is the least number of rounds required for acquiring mutual authentication between two parties.

Distributed Key Generation (DKG) is essential for secure, decentralized cryptographic systems, enabling collaborative key pair generation without a trusted authority. This capability underpins critical applications such as threshold signatures and blockchain-based protocols. To achieve post-quantum security, existing robust lattice-based DKG protocols, tailored for synchronous networks, rely on complaint-based Verifiable Secret Sharing (VSS). However, these protocols lack public verifiability and compatibility with asynchronous environments, constraining their use in Byzantine fault-tolerant settings. This paper presents LADKG, the first Lattice-Based Asynchronous Distributed Key Generation protocol designed for post-quantum secure and scalable distributed systems. LADKG integrates Asynchronous Verifiable Short Secret Sharing (AV3S) with an Approximate Asynchronous Common Subset (AACS) protocol to achieve efficient key generation. By deferring verification and leveraging deterministic approximate agreement, LADKG reduces computational and communication overhead while maintaining security and robustness. Evaluations on geo-distributed AWS EC2 clusters demonstrate that LADKG is comparable or better than classical Asynchronous Distributed Key Generation (ADKG) schemes in scalability and efficiency. Under optimistic conditions with $n=121$ nodes, completion is achieved in 45 seconds, ensuring robust key generation for post-quantum secure applications.

One-more problems like One-More Discrete Logarithm (OMDL) and One-More Diffie--Hellman (OMDH) have found wide use in cryptography, due to their ability to naturally model security definitions for interactive primitives like blind signatures and oblivious PRF. Furthermore, a generalization of OMDH called Threshold OMDH (TOMDH) has proven useful for building threshold versions of interactive protocols. However, due to their complexity it is often unclear how hard such problems actually are, leading cryptographers to analyze them in idealized models like the Generic Group Model (GGM) and Algebraic Group Model (AGM). In this work we give a complete characterization of known group-based one-more problems in the AGM, using the $Q$-DL hierarchy of assumptions defined in the work of Bauer, Fuchsbauer and Loss (CRYPTO '20). 1. Regarding (T)OMDH, we show (T)OMDH is part of the $Q$-DL hierarchy in the AGM; in particular, $Q$-OMDH is equivalent to $Q$-DL. Along the way we find and repair a flaw in the original GGM hardness proof of TOMDH, thereby giving the first correct proof that TOMDH is hard in the GGM. 2. Regarding OMDL, we show the $Q$-OMDL problems constitute an infinite hierarchy of problems in the AGM incomparable to the $Q$-DL hierarchy; that is, $Q$-OMDL is separate from $Q'$-OMDL if $Q' \neq Q$, and also separate from $Q'$-DL unless $Q = Q' = 0$. We give two practical applications of the above results. 1. We give formal evidence for a folklore conjecture that the best known attack on the widely used OPAQUE asymmetric PAKE protocol is due to Cheon (EUROCRYPT '06). 2. We show that threshold schemes reliant on TOMDH have the same level of concrete security as non-threshold versions, thus achieving threshold security "for free".

The Unbalanced Oil and Vinegar (UOV) construction is the foundation of several post-quantum digital signature algorithms currently under consideration in NIST's standardization process for additional post-quantum digital signature schemes. This paper introduces new single fault injection attacks against the signing procedure of deterministic variants of signature schemes based on the UOV construction. We show how these attacks can be applied to attack MAYO and PROV, two signature schemes submitted to the NIST call for additional post-quantum signature schemes. The attacks are demonstrated with reference implementations that run on an ARM Cortex-M4 processor. Our attacks do not require precise triggering or precise fault injection capabilities. Any type of fault in large portions of the code has the potential to result in successful key recovery. We demonstrate our attacks with very cheap equipment and simple clock glitching techniques, enabling the recovery of the secret key with either two faulty signatures or one correct signature and one faulty signature in the case of MAYO and one correct signature and two faulty signatures in case of PROV. The fact that our attacks do not require precise fault injection capabilities and can be successful with only a few signatures makes them particularly powerful, hence harmful for the implementation security of post-quantum digital signature schemes.

The existing lattice-based signature and IBE schemes suffer from the non-compactness of public keys or larger reduction loss in the security analysis. Thus we solve and improve those deficiencies as follows: – First, we construct a lattice-based short signature scheme with a compact verification key in the standard model based on the ring short integer solution (RSIS) assumption. Under the same com- pactness, the ring modulus of our signature scheme is significantly smaller than the compact sig- nature scheme of Alperin-Sheriff (PKC 2015). More importantly, our signature scheme achieves better reduction loss than all the previous confined guessing-based signatures. In other words, our signature scheme achieves better security and efficiency simultaneously. – Secondly, we further design a short signature scheme with a nearly compact public key size and an even smaller reduction loss. Our second signature scheme achieves even better reduction loss than our first signature scheme yet at the cost of increasing the public key to a super-constant number of ring vectors. – Last but not least, we construct an adaptively secure compact IBE scheme from the lattice as- sumptions and the truncation collision-resistant hash functions (TCRHF) introduced by Jager and Kurek (ASIACRYPT 2018). Note that the previous TCRHF-based IBE schemes are not even close to compactness. The above improvements mainly benefited from our compact design of the tag functions and their more compact homomorphic evaluations. We also believe that our newly designed tag function may find new applications in designing other cryptographic schemes, like ABE and others.

Accumulation schemes are a simple yet powerful primitive that enable highly efficient constructions of incrementally verifiable computation (IVC). Unfortunately, all prior accumulation schemes rely on homomorphic vector commitments whose security is based on public-key assumptions. It is an interesting open question to construct efficient accumulation schemes that avoid the need for such assumptions. In this paper, we answer this question affirmatively by constructing an accumulation scheme from *non-homomorphic* vector commitments which can be realized from solely symmetric-key assumptions (e.g. Merkle trees). We overcome the need for homomorphisms by instead performing spot-checks over error-correcting encodings of the committed vectors. Unlike prior accumulation schemes, our scheme only supports a bounded number of accumulation steps. We show that such *bounded-depth* accumulation still suffices to construct proof-carrying data (a generalization of IVC). We also demonstrate several optimizations to our PCD construction which greatly improve concrete efficiency.

Truncation of cryptographic outputs is a technique that was recently introduced in Baldimtsi et al. [BCCK22]. The general idea is to try out many inputs to some cryptographic algorithm until the output (e.g. a public-key or some hash value) falls into some sparse set and thus can be compressed: by trying out an expected $2^k$ different inputs one will find an output that starts with $k$ zeros. Using such truncation one can for example save substantial gas fees on Blockchains where storing values is very expensive. While [BCCK22] show that truncation preserves the security of the underlying primitive, they only consider a setting without preprocessing. In this work we show that lower bounds on the time-space tradeoff for inverting random functions and permutations also hold with truncation, except for parameters ranges where the bound fails to hold for ''trivial'' reasons. Concretely, it's known that any algorithm that inverts a random function or permutation with range $N$ making $T$ queries and using $S$ bits of auxiliary input must satisfy $S\cdot T\ge N\log N$. This lower bound no longer holds in the truncated setting where one must only invert a challenge from a range of size $N/2^k$, as now one can simply save the replies to all $N/2^k$ challenges, which requires $S=\log N\cdot N /2^k$ bits and allows to invert with $T=1$ query. We show that with truncation, whenever $S$ is somewhat smaller than the $\log N\cdot N /2^k$ bits required to store the entire truncated function table, the known $S\cdot T\ge N\log N$ lower bound applies.

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 information hiding, with limited exploration of other modern information security concepts, including zero-knowledge proof (ZKP). In this paper, we propose an optical ZKP method based on single-pixel imaging (SPI). By utilizing the flexibility of SPI, our proposed approach can directly acquire randomly permuted results of the source problem's solution in the form of encoded images, thereby encrypting and verifying the original solution. ZKP for the source problem can be realized with optical computing based on a proving protocol without disclosing additional information. Simulated and experimental results show that our proposed method can be effectively applied to two typical ZKP problems: Sudoku and Hamiltonian cycle problem.

The interest in hash-based signatures (HBS) has increased since the need for post-quantum cryptography (PQC) emerged that could withstand attacks by quantum computers. Since their standardization, stateful HBS algorithms have been deployed in several products ranging from embedded devices up to servers. In practice, they are most applicable to verify the integrity and authenticity of data that rarely changes, such as the firmware of embedded devices. The verification procedure then takes place during a secure boot or firmware update process. In past works, the research community has investigated hardware and software optimizations for this use case and vendors brought forward products. In this study, we practically evaluate a fault attack on the Winternitz One-Time Signature (WOTS) scheme. The attack can be mounted on different HBS schemes, such as LMS, XMSS, and SPHINCS+. Both, the verification as well as the signing operation can be targeted. The study describes the preparation and implementation of the attack on a standard microcontroller as well as the difficulties the attacker has to overcome. Additionally it presents a countermeasure, which is easy to implement and can increase the effort for an attacker significantly.

Existing payment systems make fixed trade-offs between performance and security assumptions. Traditional centralized systems like Visa assume synchronous networks and crash faults to achieve high throughput, while blockchain-based systems (e.g., Algorand, Aptos) adopt Byzantine fault tolerance and partial synchrony for stronger security at the cost of performance. This rigid approach forces all users to accept the same security-performance trade-off regardless of their individual trust and threat models. We present a flexible payment system where clients independently choose assumptions about (i) network timing (bounded or partial synchrony), (ii) corruption (static or adaptive), and (iii) faults (crash or Byzantine), supporting eight assumption combinations simultaneously. Unlike traditional systems requiring consensus, our approach uses a novel flexible variant of consistent broadcast where clients external to the protocol verify delivery through cryptographic proofs, eliminating the need for global ordering. We implemented our system in Rust and demonstrated that clients choosing partially synchronous network and crash assumptions achieve $+242.1\%$ higher throughput and $+70.4\%$ better latency compared to clients with synchronous network and Byzantine assumptions, confirming that our system enables users to optimize their individual security-performance trade-offs.

Quasi-Abelian Syndrome Decoding (QA-SD) is a recently introduced generalization of Ring-LPN that uses multivariate polynomials rings. As opposed to Ring-LPN, it enables the use of small finite field such as GF(3) and GF(4). It was introduced by Bombar et al (Crypto 2023) in order to obtain pseudorandom correlation generators for Beaver triples over small fields. This theoretical work was turned into a concrete and efficient protocol called F4OLEage by Bombar et al. (Asiacrypt 2024) that allows several parties to generate Beaver triples over GF(2). We propose efficient algorithms to solve the decoding problem underlying the QA-SD assumption. We observe that it reduce to a sparse multivariate polynomial interpolation problem over a small finite field where the adversary only has access to random evaluation points, a blind spot in the otherwise rich landscape of sparse multivariate interpolation. We develop new algorithms for this problem: using simple techniques we interpolate polynomials with up to two monomials. By sending the problem to the field of complex numbers and using convex optimization techniques inspired by the field of “compressed sensing”, we can interpolate polynomials with more terms. This enables us to break in practice parameters proposed by Bombar et al. at Crypto’23 and Asiacrypt’24 as well as Li et al. at Eurocrypt’25 (IACR flagship conferences Grand Slam). In the case of the F4OLEage protocol, our implementation distinguishes the output of the pseudorandom correlation generator from random with advantage 60% in a few hours. This not only invalidates the security proofs, but it yields real-life privacy attacks against multiparty protocols using the Beaver triples generated by the broken pseudorandom correlation generators.