International Association for Cryptologic Research

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19 September 2026

Zhen Yu Xiong, Mingsheng Wang, Zhedong Wang, Han Wang
ePrint Report ePrint Report
Bootstrapping is the bottleneck of BGV/BFV homomorphic encryption, and for large plaintext primes $p$ its cost is dominated by digit extraction. Recently, this stage has been accelerated along two separate routes. The first lowers the degree of the digit-extraction polynomial: the bounded-support construction of Ma et al. (Eurocrypt'24) confines its support, and the order-four filter of Xiong et al. (to appear in Asiacrypt'26) removes three quarters of its monomials. The second lowers the depth of its evaluation: the Galois norm map of Okada et al. (Asiacrypt'23) and Zhao et al. (Crypto'26) evaluates a degree-$d$ factor in logarithmic depth. However, how the two routes relate and whether they compose has remained open.

We propose a symmetry-graded framework that views the two evaluation routes as commuting group actions on the digit-extraction polynomial. Under this unified perspective, the existing evaluators correspond to different specializations of $\mathrm{cost}(D;r,d)$. For lower degree, we identify a novel rank-two lattice structure underlying digit extraction. The crystallographic restriction limits the filter order to $r\in\{1,2,3,4,6\}$. In particular, the methods of Ma et al. and Xiong et al. correspond to $r=2$ and $r=4$, respectively. Moreover, our framework derives a sparser order-six digit-extraction polynomial, enabling order-six symmetry for Mersenne primes. For lower evaluation cost, we construct a composed evaluator that first folds $P_A$ using the scalar filter and then evaluates the folded polynomial via the slot ring's Galois norm map. Since the rotation and Frobenius actions commute, the two optimizations can be combined within the same framework. Consequently, for any $(p,m)$ we select the optimal $(r,d)$ and evaluate digit extraction in $2\sqrt{D/(rd)}+O(\log D)$ non-scalar multiplications.

On 13 general cyclotomic rings at $\geq 80$-bit verified security, our single-threaded HElib implementation improves upon the state-of-the-art evaluator of Ma et al., accelerating digit extraction by $2.4$–$4.9\times$ and thin bootstrapping by $1.3$–$2.8\times$, while modifying only the digit-extraction stage. In particular, on Ma et al.'s set IV with the Mersenne prime $p=8191$ and set V with $p=65537$, digit extraction is accelerated by $3.6\times$ and $3.8\times$, respectively, reducing the total bootstrapping time from 180.4 s to 85.5 s and from 217.6 s to 103.1 s. The implementation is publicly available, and the core analysis is machine-checked in Lean 4.
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Yvonne Zhou, Mingyu Liang, Ivan Brugere, Danial Dervovic, Antigoni Polychroniadou, Min Wu, Dana Dachman-Soled
ePrint Report ePrint Report
The growing use of machine learning (ML) has raised concerns that an ML model may reveal private information about an individual who has contributed to the training dataset. To prevent leakage of sensitive data, we consider using differentially-private (DP), synthetic training data instead of real training data to train an ML model. A key desirable property of synthetic data is its ability to preserve the low-order marginals of the original distribution. Our main contribution comprises novel upper and lower bounds on the excess empirical risk of linear models trained on such synthetic data, for continuous and Lipschitz loss functions. We perform extensive experimentation alongside our theoretical results
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Ananya Appan, Pranav Shriram Arunachalaramanan, David Heath, Ling Ren
ePrint Report ePrint Report
Private aggregation schemes enable aggregation of sensitive data across clients without leaking any individual client's input. Their applications include privacy-preserving federated learning, private heavy hitters, and anonymous systems.

Many private aggregation schemes assume two non-colluding servers and aim to guarantee privacy even when one server is malicious, i.e., the malicious server learns an aggregation result that includes all honest client inputs. However, many private aggregation schemes in the literature fail to achieve privacy, which we believe is in large part due to a lack of formalism for the nuanced variations of privacy guarantees.

In this work, we present ideal functionalities for several variants of private aggregation. We also formalize a common paradigm underlying most prior private aggregation schemes. The formal treatment helps us identify security flaws or underspecifications in existing private aggregation schemes. We then present modular modifications or fill in critical details to help prior schemes in the share-aggregate paradigm securely realize the private aggregation functionalities we formally define, including in settings where clients may have unreliable networks.
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Yvonne Zhou, Mingyu Liang, Ivan Brugere, Danial Dervovic, Yue Guo, Antigoni Polychroniadou, Min Wu, Dana Dachman-Soled
ePrint Report ePrint Report
We present the first theoretical convergence analysis of machine learning training under fully homomorphic encryption (FHE), combined with a differentially private (DP) training algorithm tailored to encrypted computation. Our approach improves computational efficiency over standard differentially private gradient descent (DP-GD) while achieving comparable utility. In particular, we prove convergence of approximate gradient descent using polynomial approximations of activation and loss functions, which are required for FHE compatibility. To preserve privacy in downstream tasks, we integrate differential privacy without relying on costly per-sample gradient clipping, enabling scalable encrypted learning. We also provide data-independent hyperparameter selection and theoretically grounded strategies for polynomial approximation which can be of independent interest. Together, these contributions advance the feasibility of efficient, private, and secure machine learning on sensitive data.
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Aarushi Goel, Gabriel Kaptchuk, Yuange Li
ePrint Report ePrint Report
Freedom of information laws (informally known as Sunshine Laws), such as the US Federal Freedom of Information Act, provide legal pathways for members of the public to compel governments to produce internal documentation. These laws have become a powerful tool for government accountability, allowing journalists and activists to uncover malfeasance and advocate for change. However, because compliance with these laws requires government actors---the same entities who may be accused of malfeasance---to produce documentation, there is a risk that evidence of malfeasance may be suppressed rather than produced in response to a query.

In this work, we introduce a cryptographic framework called Sunshine Systems, designed to constrain government actors' ability to circumvent freedom of information laws. At a high level, Sunshine Systems enable agencies to prove, in zero knowledge, that they have produced the complete and correct set of documents responsive to a given request. We instantiate a Sunshine System that supports keyword queries, building on recent advances in lookup arguments. We implement and evaluate our approach on low-cost hardware, demonstrating its practicality even for small government agencies.
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Maxime Lecomte, Julien Maillard, Antoine Moran, Guénaël Renault, Benjamin Smith
ePrint Report ePrint Report
We investigate the use of bit-level Soft Analytical Side-Channel Attacks (SASCA) to recover secret inputs of the SHA-256 hash function, and secret keys of HMAC-SHA-256, using Sentential Decision Diagrams to overcome the computational challenge posed to classical Belief Propagation by multiple-word modular addition. Our attack on HMAC requires no control nor knowledge of the input, and exploits its double manipulation of the key to improve key-recovery performance. We make comprehensive simulations to evaluate the attacker’s recovery capacity for both SHA-256 and HMAC-SHA-256. Finally, we study the profiling capabilities of load instructions in a multiposition EM probe setup on a STM32F303RET6 microcontroller, and use these results to evaluate the capability of our attack against software implementations of HMAC-SHA-256 in a realistic scenario.
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Zhao Song, Song Yue
ePrint Report ePrint Report
Marcus, Spielman, and Srivastava [MSS15] established the existence of Kadison--Singer partitions. We provide polynomial-time algorithms for the Kadison--Singer problem. For Hermitian matrices $A_1,\ldots,A_m\in\mathbb C^{n\times n}$ of rank at most one, we give two algorithms that find signs $\sigma\in\{\pm1\}^m$ satisfying $\|\sum_i \sigma_iA_i\|\le C\|\sum_i A_i^2\|^{1/2}$. The deterministic algorithm achieves $C=3.3443$ using $\widetilde O(mn^2+n^{56})$ arithmetic operations. The randomized algorithm achieves $C=4.8628$ using $\widetilde O(mn^2+n^{5.88})$ arithmetic operations in expectation. For vectors satisfying $\sum_i a_ia_i^*=I$ and $\|a_i\|^2\le\alpha$, the algorithms yield partitions $[m]=I_1\cup I_2$ satisfying $\|\sum_{i\in I_j}a_ia_i^*-I/2\|\le (C/2)\sqrt\alpha$ for $j=1,2$.
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Anirudh Jaiswal, Abhilash Kumar Das, Dhiman Saha
ePrint Report ePrint Report
The Fujisaki–Okamoto (FO) transform protects Kyber-KEM against chosen- ciphertext attacks and is based on a ciphertext comparison step. This comparison is usually treated as a single atomic check. However, in every mainstream implementation it is a short pipeline of independently faultable stages. It comprises a byte-wise mismatch accumulation, a two’s-complement Booleanisation, and a conditional move (cmov). In this work, we expose a previously unexamined stage of this pipeline, the Booleanisation, as a new attack surface. Our research reveals that a single sub-instruction clock glitch forces the mismatch flag fail to 0, so decapsulation accepts any ciphertext. Every prior fault attack on this comparison targets the equality test or the conditional move. So does the only countermeasure proposed for it: the default-fail cmov ordering of Xagawa et al. Our surface sits upstream of that move, so it escapes both. We instantiate this Default Correct fault on an ARM Cortex-M4 (ChipWhisperer-Lite) and demonstrate it across the pqm4, PQClean, and reference implementations of Kyber-512/768/1024 at all optimisation levels (-O0–O3). Crucially, every one of these implementations already carries Xagawa’s default-fail ordering, yet the fault succeeds on all of them: the surface is therefore not merely new but structurally beyond the reach of the state-of-the-art defence for this comparison. The Booleanisation is thus a single point of failure common to all three code bases. Leveraging the accept-everything behaviour, we use the standard plaintext-checking oracle and recover the full secret key of Kyber-512, Kyber-768, and Kyber-1024 in a single on-device run each. Finally, we analyse why defences that protect only the cmov or a single fail flag cannot address a fault that targets an upstream stage of the comparison, and we propose a producer-side countermeasure: an integrity-checked Booleanisation that computes the same flag while folding in an execution counter, so that any partial instruction skip is detected, at negligible overhead.
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Elette Boyle, Lalita Devadas
ePrint Report ePrint Report
Distributed certification is a method for monitoring the correctness of a distributed system. The model consists of a centralized prover in addition to multiple verifiers lying on the nodes of a communication network, where the goal is to assert that the network satisfies a desired property. In doing so, the prover generates certificates for each verifier; the verifiers can then communicate in a small number of rounds, and accordingly accept or reject. The prover’s assertion is accepted if all verifiers accept.

A significant body of work has gone toward developing and understanding limitations of distributed certification schemes, predominantly in the setting of information-theoretic soundness, and recently with computational soundness, achieving a form of distributed (locally verifiable) Succinct Non-interactive Arguments (SNARGs) (Aldema Tshuva et al, TCC 2023). As is standard in the model, soundness holds in existing constructions assuming that all verifiers in the network are honest.

In this work, we introduce and explore the notion of robust distributed SNARGs (rdSNARGs) which retain (computational) soundness guarantees even when the cheating prover can collude with some nodes in the network. Addressing cheating verifiers presents several challenges. We construct rdSNARGs for any distributed language in P with succinct certificate size and communication from extended versions of RAM SNARGs (Kalai et al, STOC 2023), where the level of succinctness scales with the threshold of corrupt nodes. Complementarily, we demonstrate a lower bound showing that an rdSNARG with significantly smaller certificates and communication implies a SNARG for NP.
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Katarina Cheng, Wilson Nguyen, Nirvan Tyagi
ePrint Report ePrint Report
Succinct polynomial commitment schemes are a key building block in succinct non-interactive arguments of knowledge (SNARKs). Existing succinct lattice-based polynomial commitment schemes take a "split-and-fold" strategy making use of homomorphism to compress proof size to $O(\text{polylog} N)$ for polynomials of size $N$. Prior works either (1) incur superlogarithmic verifier work (e.g., $O(\sqrt{N})$), (2) incur concretely large proof sizes and verifier work (e.g., hundreds of MB), or (3) rely on non-standard lattice assumptions. We proprose a new succinct polynomial commitment scheme Maltese that operates over a Merkle tree commitment of the lattice-based Ajtai hash function. We employ a folding strategy and propose new sum-check-based reductions for managing norm growth of the tree commitment over folding rounds. Maltese is secure under the standard Module-SIS assumption and produces opening proofs of $335$KB for multilinear polynomials of size $N=2^{30}$; proofs are around $300\times$ smaller than prior work with polylogarithmic verifier complexity but between $2$-$6\times$ larger than prior work with larger verifier complexity or stronger structured assumptions.
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JunHyeok Choi, DongHyun Shin, Seog Chung Seo
ePrint Report ePrint Report
The practicality of post-quantum cryptography (PQC) on IoT devices depends on both operation cycle counts and communication costs from public values (public keys, ciphertexts, and signatures). The DSA HAETAE and the KEM SMAUG-T, both selected in the KpqC competition, provide smaller public values than ML-DSA and ML-KEM; however, the lack of platform-specific optimization leaves their operation cycle counts high, which can offset this advantage. In this paper, we optimize HAETAE and SMAUG-T on the Cortex-M4, a representative 32-bit embedded MCU, and conduct a multi-faceted evaluation. We fix two bugs in the existing implementation of the HAETAE $\mathcal{N}(\mathbf{s})$ evaluation and propose Autocorrelation-based Spectral-Norm Evaluation (ASNE), which replaces the per-polynomial FFTs with a single autocorrelation FFT. Together with further optimizations, we achieve improvements of up to 309.1%, 4.8%, and 6.0% in KeyGen, Sign, and Verify, respectively, over the state-of-the-art implementation. For SMAUG-T, we analyze the coefficient ranges of the polynomial multiplication operands to select an auxiliary NTT-friendly modulus $q'$, and count the number of operations per layer to apply the optimal NTT. As a result, we achieve improvements of up to 266.7%, 348.9%, and 341.0% in KeyGen, Encaps, and Decaps, respectively, over the reference C implementation. Furthermore, we apply static analysis and dudect measurements to the optimized kernels and observe no evidence of timing leakage. Using models anchored to prior IoT protocol measurements, we estimate the transmission-unit count, end-to-end latency, and energy, showing that HAETAE and SMAUG-T can be competitive PQC alternatives in constrained wireless environments.
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James Bell-Clark, Albert Cheu, Adria Gascon, Jonathan Katz, Lukas Gerlach
ePrint Report ePrint Report
Systems for private group-by aggregation (e.g., computing histograms, min/max values, or averages) let a confidential virtual machine (CVM) generate statistics from streaming user data. A particular challenge in such systems is ensuring that the CVM's memory-access patterns do not reveal (too much) private information to the untrusted host. While it is possible to rely on oblivious RAM (ORAM), doing so imposes a significant performance penalty and requires allocating sufficient memory to handle a worst-case data stream.

We introduce ROGA, a scheme for Resizable Oblivious Group-by Aggregation. ROGA uses an extension of oblivious single-access machines and thus improves performance, both asymptotically and concretely, relative to using ORAM. It also incorporates a novel, differentially oblivious resizing mechanism that ensures the allocated memory is within a constant factor of the memory used by a non-oblivious solution. ROGA also parallelizes cleanly across multiple cores for improved performance.

We implement ROGA in Rust and use Binsec/Rel to verify trace noninterference of its compiled fixed-capacity operations, resize estimator, and fixed-work noise sampler, showing that executions with equal public parameters have identical branch-target and memory-address traces for all secret inputs. The only data-dependent branch is the differentially private resize decision. Compared to state-of-the-art oblivious schemes for confidential analytics (which do not support private resizing), ROGA is up to 50.4$\times$ faster when sharded across 64 logical cores, and private resizing cuts memory by up to 14$\times$ compared to domain-provisioned instances. In a case study, ROGA using 16 cores processes the standard network statistics of a 277-million-packet backbone trace with $5.3\times$ end-to-end overhead over a non-oblivious pipeline while exactly matching the reference output.
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Esra Yeniaras
ePrint Report ePrint Report
Streamlined NTRU Prime (sntrup761) is a lattice-based key encapsulation mechanism that, although not a NIST standard, remains widely deployed in critical internet infrastructure. It is the post-quantum key-exchange default in OpenSSH, standardized in RFC 9941, and used well beyond SSH, in Red Hat Enterprise Linux, the liboqs library, PQConnect, and commercial VPNs. Its decapsulation performs a polynomial multiplication over the characteristic-three ring $\mathbb{Z}_3[x]/(x^{p}-x-1)$, so faster methods for this operation directly improve these protocols. We use the Yeniaras-Cenk 5-way multiplier (U1-hybrid), which has the lowest arithmetic complexity among characteristic-three multipliers and gives a 35.52% scalar-C software speedup over Bernstein's three-way method (B1). Yet every prior NTRU Prime hardware design, on FPGA or the single existing ASIC, uses only schoolbook or a single layer of two-way Karatsuba. Three-way splits have been implemented only in software; no 5-way split had been implemented at all before this work. We present the first ASIC evaluation of the Yeniaras-Cenk 5-way multiplier (U1-hybrid), synthesized to the Nangate 45 nm library and compared against the state-of-the-art parallel schoolbook multiplier of Peng et al. On the area-delay product (ADP), the Yeniaras-Cenk 5-way multiplier is 6.8x better than the Peng schoolbook at the multiplier level, and 1.27x better in the sntrup761 decapsulation core, which it completes in 2471 cycles against Peng's 3829, a 35.5% core reduction (12.4% once the fixed hash is included). We also compare against a 3-way Karatsuba baseline (Bernstein's B1), noting that no optimized hardware B1 exists and we do not build one; the comparison there is at the operation-count level only. Synthesizing U1 and B1 as combinational circuits isolates where the five-way advantage comes from. It is not gate count: each $\mathbb{F}_9$ product expands into four $\mathbb{F}_3$ products, so at the same architecture the two use nearly the same area. The gain is in depth, as those four $\mathbb{F}_3$ products run in parallel: 138.27 ps against 57.95 ps for one $\mathbb{F}_3$ multiplier, 2.4x rather than 4x. The advantage is thus a hardware effect: it grows with design parallelism and matches the scalar-C software figure across two parameter sets. All Verilog, testbenches, and synthesis scripts are openly available.
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Zhengzhong Jin
ePrint Report ePrint Report
We construct the first witness encryption for NP in the generic group model from succinct non-interactive arguments (SNARGs) for NP. Our construction applies to any SNARG with subexponential soundness and polylogarithmic online verification time after input preprocessing.

Central to our result is the first Karp-Levin reduction from satisfiability for circuits of size $\mathrm{polylog}(\lambda)$ to the minimum-distance problem for linear codes (GapMDP) over a prime field of size $\lambda^{\omega(1)}$, with an approximation factor of $\omega(\log \lambda)$, where $\lambda$ is the security parameter. We obtain this reduction by adapting Hair and Sahai's recent hardness result for GapSVP. Combining our reduction with the witness encryption framework due to Barta, Ishai, Ostrovsky, and Wu [CRYPTO 2020], we obtain the first unconditional extractable witness encryption for circuits of size $\mathrm{polylog}(\lambda)$ in the generic group model. These techniques may be of independent interest.
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Roberto La Scala, Marco Marchesin, Sharwan K. Tiwari
ePrint Report ePrint Report
We investigate an algebraic approach to the Syndrome Decoding Problem, based on a reformulation of the Hamming weight constraint and its integration with the Information Set Decoding paradigm. We begin with a systematic analysis of the Hamming variety, deriving its defining equations in terms of elementary symmetric functions. Since these equations may have high degree, we exploit convolution identities for elementary symmetric functions, together with factorizations based on Lucas' identity, to derive an equivalent formulation with auxiliary variables and equations of bounded degree.

Building on this modeling, we generalize the ISD paradigm through an ISD-like decoding strategy, implemented by the GBDecode algorithm, in which only a subset of an information set is fixed. This approach reduces the size of the combinatorial search space at the cost of solving the associated multivariate nonlinear systems. To handle this algebraic component, we employ the MultiSolve algorithm, which replaces a single Grobner basis computation with a collection of computations on simpler systems, obtained by exhaustively assigning a varying number of indeterminates over the finite field. This provides a tunable balance between combinatorial search and algebraic solving.

We evaluate the resulting approach experimentally on instances of the Syndrome Decoding Problem for random binary linear codes, using parameters corresponding to the NIST Security Category 1 parameter set of the Classic McEliece cryptosystem. The experiments assess the feasibility of this combinatorial-algebraic approach and provide insights into the practical behavior of Grobner basis techniques within an ISD-like decoding framework.
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Shi Tang, Zirui Chen, Yongjia Su, Zhengchao Gao, Lingyue Qin, Xiaoyang Dong
ePrint Report ePrint Report
At EUROCRYPT 2025, Carlini {\em et al.} proposed a breakthrough in the cryptanalytic extraction on hard‑label (S1) deep neural networks (DNNs), demonstrating polynomial-time signature and sign recovery. However, Carlini {\em et al.}'s sign‑recovery method ({which we call \em Future Toggle}) suffers only a marginal advantage over random guessing, producing high‑confidence wrong sign predictions in deeper layers. Such errors trigger expensive exponential‑time enumeration.

This work presents {\em Normal Alignment}, a novel statistical sign‑recovery approach for S1 DNNs. Drawing on the expected length difference between projected normals of adjacent decision facets at dual points, our method infers neuron signs via normal‑signature alignment. It delivers higher voting accuracy and pushes erroneous predictions to low‑confidence ranks, which further enables a more efficient combined method, {\em eSOE + Alignment}, by combining {\em Normal Alignment} with the hard‑label {SOE} extension. This combined strategy removes heavy enumeration overhead and realizes exact polynomial‑time full sign recovery.

Experiments demonstrate the effectiveness of our method, especially for deep layers. For example, with our method, the signs for CIFAR-10 (architecture 192-64$\times$8-10) and MNIST (architecture 64-96$\times$3-32-10) models can be fully recovered in polynomial time; in contrast, Carlini {\em et al.}'s sign‑recovery method would require exponential‑time enumerations involving $2^{52}$ or $2^{82}$ guesses of the signs, respectively.
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Rong Qian, Yu Cheng, Lingyu Gao, Yuchang Zhang, Zengli Guo
ePrint Report ePrint Report
EIP-7702, live on Ethereum since the Pectra upgrade, lets externally owned accounts delegate their execution to arbitrary contract code with a single signature. The consequences are measurable: 63% of observed delegations point to malicious contracts, with $2.36M in confirmed losses, and ecosystem guidance already warns about cross-chain replay and front-run initialization. What is missing is a formal account of the problem: the 7702 delegation lifecycle has no formal treatment, and none of the recommended mitigations has been machine-verified. We present DelegProof, to our knowledge the first symbolic formal analysis of EIP-7702 authorization semantics composed with the ERC-4337 EntryPoint pipeline. Our Tamarin models are calibrated by reproducing four documented attack classes, and yield ten machine-checked attack patterns—among them the silent failure of the advertised temporary-delegation bundle, storage confusion across re-delegation, and an ERC-1271 substitution attack that reaches into the signature checks of relying contracts—together with the security invariants that do hold. Formalizing the recommended mitigations shows that banning chainId-0 authorizations eliminates cross-chain replay, that an account-bound initialization gate restores init authorization while an unbound gate is provably still bypassable, and that namespaced storage slots make the storage-confusion class structurally inexpressible. All models and proofs are available at https://anonymous.4open.science/r/delegproof-artifact-F7FE/.
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18 September 2026

Fredrik Meisingseth
ePrint Report ePrint Report
There is a growing literature on differential privacy (DP) in multiparty protocols, enabling use in distributed settings and reduced trust assumptions. A largely overlooked aspect of such protocols is the extent to which an adversary can undermine the DP guarantees by making the protocol abort. Another is the DP properties of the honest parties' outputs. We initiate the study of both these issues.

First, we propose an idealized model of aborts, where an aborter is leaked some information about a DP mechanism execution and then chooses whether or not to let an independent malicious analyst learn the mechanism output. We bound the effects of aborts according to what information (the database, randomness, output, or any combination of these) is leaked. These bounds are not only applicable to multiparty DP via general-purpose multiparty computation (MPC) but may also be used in the analysis of other methods to certify DP properties of a protocol. Second, we apply these bounds to analyze ideal protocol executions in MPC. We show, for the first time, that the ideal execution with fairness gives strictly stronger DP guarantees than that for security-with-abort, for the outputs to the honest parties. Further, solitary-output functionalities satisfy guarantees similar to those of the execution with fairness.

Finally, we analyze multiparty protocols with respect to the way in which they realize the respective ideal functionalities. We show that partially fair and fully fair protocols have very similar DP guarantees. Since partial fairness, as opposed to full fairness, can be achieved in dishonest-majority settings, and in particular the two-party setting, this opens up for enhanced DP guarantees in two-party computation.
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Dong Jin Park, Hyunseok Jeong, Minwook Jeong, Jaeky Oh, Yongwoo Lee, Young-Sik Kim
ePrint Report ePrint Report
Evaluation keys represent a primary memory and initialization bottleneck in matrix-native fully homomorphic encryption (FHE). In the Gentry–Lee (GL) framework, each Trace product yields a four component ciphertext whose BigSwitch procedure requires two extended-ring keys, dominated by a massive product-secret key (sXsY → sX). We present Trace-Factored BigSwitch (TFB), which structurally eliminates this product-secret evaluation key by exploiting the rank one tensor structure of the Trace-generated key, (1, sX, sY , sXsY ) = (1, sY ) ⊗ (1, sX). By routing the product secret through an sY → sX switch followed by standard base ring (s^2)X → sX relinearization, TFB achieves an exact evaluation-key memory saving of (n − 1)/(2n) (≈ 50%) without ever generating or storing evk_XY →X. To amortize TFB’s recurring base-ring relinearization cost in blocked matrix multiplication, we introduce FRee-L (Fused Relinearization with noise reduction). FRee-L accumulates K Trace products componentwise in the four-component domain and invokes BigSwitch only once per output tile, reducing post-processing noise injections from K to one and amortizing the latency overhead as O(1/K). In our OpenFHE-linked prototype (n = 256), TFB reduces the coefficient-domain BigSwitch key footprint from 768.0 to 385.5 MiB (49.80%), peak RSS by 15.31%, and cold key preparation by 51–63%. On real GPT-2 attention kernels (K = 4), FRee-L lowers TFB’s paired overhead to 5.90%, which further diminishes to 0.1933% (K = 160) and 0.0618% (K = 512) in deep accumulation workloads, confirming that substantial key savings are achieved with negligible workload-level compute penalty.
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RISE Research Institutes of Sweden, Stockholm, Sweden
Job Posting Job Posting

As AI agents start acting in groups, delegating, negotiating, and relying on each other's inputs and outputs, the security assumptions behind single-model systems stop holding. This project develops principled and scalable foundations for trustworthy collaboration between AI agents, sitting at the intersection of AI and cybersecurity. It is funded by the Swedish Foundation for Strategic Research (SSF) under a programme building research ties between Sweden and Taiwan, including opportunities for research visits among the participants.

We are looking for a dedicated PhD student to strengthen our research in trustworthy multi-agent AI systems. Example research topics include evaluating the robustness of multi-agent systems under adversarial manipulation, designing secure and privacy-preserving multi-agent collaborative mechanisms, and verifiable decision-making under uncertainty and adversarial influence. You will be based in the RISE office at Kista, Stockholm for 4 years, and you will be enrolled as a doctoral student at a Swedish University. PhD education also involves participation in relevant university courses.

Closing date for applications:

Contact: Dr. Apostolos Pyrgelis -- apostolos.pyrgelis(at)ri(dot)se

More information: https://www.ri.se/en/about-rise/work-with-us/open-job-positions/phd-student-in-security-and-privacy-of-multi-agent-ai

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