International Association
for Cryptologic Research

Masking is an effective defense against side-channel attacks, yet it remains costly under hardware constraints. The Caliptra Root-of-Trust is a representative case, where its masked ML-DSA implementation incurs about 6× area overhead. We propose a novel first-order masking solution that optimizes Caliptra, achieving significant improvements in area–delay efficiency. Compared to Caliptra’s ML-DSA reduction, our design achieves a 12.1× speedup, reducing LUTs by 86.7% and FFs by 94.5%, while improving area–delay efficiency by 91×. TVLA, with over 1,000,000 traces, shows no first-order leakage, satisfies Caliptra’s security requirements, and significantly improves implementation efficiency.

Threshold signatures distribute trust across multiple parties, eliminating single points of failure and reducing insider and key-exfiltration risks—properties that are increasingly important for high-assurance deployments and recently emphasized by NIST’s Multi-Party Threshold Cryptography (MPTC) initiative. We present a practical t-out-of-n threshold variant and emulation of MAYO, a post-quantum signature candidate to NIST’s call for additional signatures. Our proposal builds upon the threshold MAYO design of Celi, Escudero and Niot (PQCrypto2025), which we significantly refine to achieve practical performance. To this end, we introduce two algorithmic modifications to MAYO tailored for the distributed setting: (1) Explicit-Salt MAYO, which allows for pre-determined salts to enable a single-round online phase; and (2) Depth-Reduced MAYO, which restructures the signing algorithm to minimize the depth of secret-dependent operations. We then propose a unified protocol framework that integrate these techniques, plus other MPC specific optimizations, with the goal of minimizing online latency. Finally, we provide a concrete instantiation and local emulation in the dishonest majority setting, secure against active adversaries. Our emulation shows that threshold signing is practical at typical threshold sizes and amenable to deployment. By releasing an open-source implementation and reporting end-to-end performance, this work offers a concrete reference for the thresholdization of post-quantum signatures. Clearly the aforementioned framework is not limited to MAYO, and can be applied to the UOV family of signatures more generally.

Retrieval-augmented generation (RAG) systems critically depend on a vector-retrieval stage that selects relevant documents from a large embedding database. In a RAG-as-a-Service setting, however, clients have no visibility into the server's proprietary embeddings and index structures, and thus cannot distinguish faithful execution from arbitrary deviations. This motivates service consistency for retrieval: the returned results must be consistent with executing an agreed approximate nearest neighbor search (ANNS) algorithm on a fixed, committed database together with a fixed, committed ANNS index, while revealing nothing beyond the outputs themselves.

We present the first polynomial interactive oracle proof (PIOP) tailored to the widely deployed HNSW ANNS algorithm. Building on this PIOP, we introduce zkRAG, a zero-knowledge, succinct, non-interactive argument for RAG retrieval that enables practical verification. Our design achieves asymptotically optimal online prover efficiency, with prover time linear in the HNSW search trace length, while keeping verification succinct. We introduce several new techniques that may be of independent interest, including a hybrid lookup argument, a highly efficient checker-based PIOP for checking priority-queue updates, and an efficient checker for membership selector vectors. For a benchmark with $10^6$ vectors of dimension $128$, single-thread zkRAG proves a typical HNSW query in $50$ seconds-over $1000\times$ faster than existing baselines--while keeping verification lightweight, demonstrating the feasibility of efficient zero-knowledge service-consistent RAG retrieval.

In this report, we describe how block circulant (BC) codes can serve as an alternative to one-dimensional (1D) and two-dimensional (2D) Reed–Solomon (RS) codes in the Ethereum PeerDAS protocol. We begin by reviewing the implementation of 1D RS codes in PeerDAS and then present efficient encoding and reconstruction algorithms for BC codes, developed within the same implementation framework as the respective 1D RS algorithms. The proposed encoding algorithm also permits a graceful integration of KZG commitment scheme. Finally, we evaluate and compare the performance of BC codes in terms of code rate, stopping rate, and the size of the local codes they contain, against both 1D and 2D RS codes.

An improved low-memory hash function scheme called Alternating Sponge (ASP) is proposed to achieve the beyond-birthday-bound security with respect to the capacity $c$. The scheme redesigns the state layout and permutation mechanism of double sponge construction, effectively reducing the total state space from $2r+2c$ bits to $2r+c$ bits and increasing the number of bits squeezed per round from $r$ to $2r$. The scheme introduces a two-phase serial permutation sequence to update the shared state, achieving a complete state transition without increasing the input size of the permutation function. A security proof is provided within the indifferentiability framework, demonstrating that the scheme can achieve security comparable to the double sponge construction, while operating with a reduced state size and an increased number of squeezed bits. Overall, the design ensures the compactness and diffusion of each round of processing through layered absorption and alternating permutations, providing a solution for deploying high-security hash functions in memory-constrained environments.

The Permuted Kernel Problem (PKP), introduced by Shamir, is a computationally hard problem underlying recent post-quantum signature schemes such as PERK, SUSHSYFISH and PKP-DSS. Among these, PERK is a second-round candidate in NIST's Additional Digital Signature Schemes post-quantum standardization process, SUSHSYFISH appeared at EUROCRYPT~2020, and PKP-DSS was one of the finalists in the CACR competition. The best known attacks on PKP rely on combinatorial meet-in-the-middle techniques, notably the algorithms of Koussa, Macario-Rat, and Patarin (KMP) and Santini, Baldi, and Chiaraluce (SBC), whose complexities remain super-exponential, with memory requirements of the same order as their time complexities.

In this work, we obtain improved cryptanalytic results for PKP that strictly outperform all previously known attacks. In particular, although no parameter sets of PERK~v2.2.0 fall below the NIST security levels, we provide the first evidence that secret vector recovery for all PERK~v2.2.0 parameter sets can be achieved with complexity below their estimated bit-security levels. We additionally obtain improved bit-complexity estimates for the SUSHSYFISH and PKP-DSS parameter sets. We further introduce a Schroeppel--Shamir style time–memory trade-off in the PKP setting. Although PKP does not admit square-root memory as in the classical subset-sum problem, our adaptation achieves substantial memory reductions while keeping the time complexity close to the best known attacks. Overall, our results provide improved cryptanalytic insight into PKP and refine the current understanding of the concrete security of PKP-based signature schemes.

Restricted Syndrome Decoding (ResSD) is a variant of linear code decoding problem where each of the error's entries must belong to a fixed small set of values. This problem underlies the security of CROSS, a post-quantum signature scheme that is one of the Round~2 candidates of NIST's ongoing additional signatures call. We show that solutions to this problem can be deduced from vectors of a particular structure and a small norm in newly constructed codes, in both Hamming and Euclidean metrics. This allows us to reduce Restricted Syndrome Decoding to both code-based (Regular Syndrome Decoding) and lattice-based problems (Closest Vector Problem, List of Short/Close Vectors), increasing the attack surface and providing new insights into the security of ResSD. We evaluate our attacks on CROSS instances both theoretically and experimentally on reduced parameters.

We give efficient formulas to evaluate isogenies of ordinary elliptic curves over finite fields of characteristic $2$, extending the odd-characteristic techniques of Hisil--Costello and Renes to binary fields. For odd prime degree $\ell = 2s+1$, our affine product evaluation computes the image $x$-coordinate using $5s\mathbf{M}$ field multiplications, or $4s\mathbf{M}$ when the kernel points are normalized. We derive an inversion-free variant that evaluates the $x$-map in projective and twisted Kummer coordinates, allowing carried points to remain projective across successive isogeny steps. Over $\mathbb{F}_{2^{511}}$, microbenchmarks show that the inversion-free projective and twisted variants are faster than Vélu-style $x$-evaluation when outputs are kept in projective/twisted form, while the affine one-inversion variant is about $4.2\times$ faster.

Basically, public-key searchable encryption schemes require a linear search time with respect to the total number of ciphertexts. Xu, Wu, Wang, Susilo, Domingo-Ferrer, and Jin (IEEE Transactions on Information Forensics and Security, 2015) introduced Searchable Public-Key Ciphertexts with Hidden Structure (SPCHS). In SPCHS, ciphertexts associated with the same keyword are linked through a hidden structure that can be revealed using a trapdoor. This enables efficient extraction of matching ciphertexts and achieves optimal asymptotic search efficiency by traversing only the result set. However, a drawback of the SPCHS scheme and its subsequent works is that they are all pairing-based or rely on identity-based encryption (IBE) as a foundational component. To improve efficiency, this paper proposes a generic construction of SPCHS. Our core building block is Non-Interactive Key Exchange (NIKE), and the remaining components are symmetric-key primitives, namely secret-key encryption and a pseudorandom function (PRF). In particular, our search algorithm depends solely on these symmetric-key primitives and is independent of any public-key primitives. We implement the most efficient instantiation of the generic construction using Diffie-Hellman NIKE, an HMAC-based PRF, and AES. Our evaluation demonstrates that the search time of the DH-based instantiation is over 250 times faster than that of the asymmetric pairing-based scheme by Wang et al. (IEEE Transactions on Industrial Informatics, 2020). Moreover, we reduce the ciphertext size by a factor of approximately 20. In addition to this practical contribution of significantly improving efficiency, the proposed generic construction also makes a theoretical contribution by enabling the realization of the first set of post-quantum SPCHS schemes based on lattices, isogenies, and codes.

We review the traditional techniques of message authentication from the perspective of Constructive Cryptography, one of the major composable security frameworks. For each of the 'textbook' means of message authentication, known results are compiled, and various gaps are addressed. We also point out areas of remaining study, and obstacles to demonstrating composability in those cases. The results can be thought of as a toolkit showing how to realise composable authentication with various cryptographic primitives, with precise statements on the security guarantees and set-up requirements.

This paper studies efficient realizations of arithmetic over the binary field $\mathbb{F}_2$ in nonabelian groups using only intrinsic group operations, namely multiplication and inversion. The constructions rely on commutators to implement Boolean computation within the group structure. Two complementary approaches are presented: a realization of a universal Boolean gate (NAND) and direct realizations of the field operations XOR and AND. These approaches apply to finite nonabelian simple groups and can be implemented using a small number of group operations. Explicit realizations are provided in the alternating groups $A_5$ and $A_6$. For the smallest nonabelian simple group $A_5$, these constructions achieve state-of-the-art efficiency in the number of group operations.

GRAFHE is a recently proposed noise-free fully homomorphic encryption scheme based on rewriting systems in symmetric groups. We provide an efficiently computable distinguisher, breaking IND-CPA security.

Quantum computing threatens classical public key systems and has motivated NIST’s PQC standardization, and within this process HAWK has been submitted as a lattice-based signature scheme. While prior analyses focused on mathematical security, the consequences of side-channel leakage in practical HAWK implementations are less systematically understood. We address this gap by formalizing discrete Gaussian sampler leakage as HAWK with Hint and studying three leakage categories: (i) full coefficient recovery, (ii) sign-only recovery, and (iii) noisy sign recovery. For each category, including (i) which has been covered in prior work, we design algebraic key recovery algorithms that derive explicit linear relations between leaked information and the secret basis and solve the resulting structured linear systems in polynomial time.

For HAWK-1024, we obtain the following results under the stated threat models. With full coefficient leakage, a single signature suffices for secret key recovery by directly solving the induced linear system, improving prior work that required two signatures under the same conditions. With sign-only leakage, the secret key is recovered using 14 signatures in approximately 100 seconds. With noisy sign leakage, we achieve key recovery using 400 signatures within about 30 seconds at a 10% bit-error rate, and still succeed with roughly 7,000 signatures within about one minute even when the bit-error rate increases to 40%. We implement all attacks and empirically validate them, clarifying how measurement noise affects the required number of signatures.

Deduplication for encrypted data reduces the storage costs of server while keeping the sensitive data secure. Fuzzy deduplication is developing for the multimedia data for its similarity not exact equality, hence it has better storage space saving capabilities than exact deduplication. However, the most of existing works face the security threat such as brute-force guessing attacks, key recovery attacks and so on. We conduct research on fuzzy deduplication from the fundamental layer for these security goals. In this work, the data similarity is novelty defined based on information entropy theory so that the similarity verification by cloud is without online clients assistance. Moreover, the parameter robustness verification is firstly proposed to be against the key recovery attacks and guessing attacks fundamentally. The simulation experiments show that our scheme can save approximately 87% of storage space while maintaining a tamper detection success rate of no less than 97%.

Ring signatures are cryptographic primitives that enable a user to sign a message on behalf of a group of users in an anonymous manner. The anonymity of the signer is the fundamental security property of ring signatures. However, unrestricted anonymity can be misused, as a malicious signer could use it to send spam or excessive messages. To address this issue, a controlled restriction on signer anonymity is required, which makes such schemes more practical. In this paper, we propose a k-times traceable ring signature scheme that allows the public key of the signer to be traced publicly if the signer exceeds a predetermined signing limit k. The novelty of our construction lies in its reliance on lattice-based assumptions, which ensure post-quantum security. Consequently, the proposed scheme is well-suited for practical deployment in the presence of emerging quantum threats. Our approach achieves competitive performance while providing stronger security guarantees, making it an appropriate candidate for modern cryptographic applications. We also present efficiency analysis and compare our scheme with existing constructions.

We study key-schedule design under boundary round-key leakage, namely leakage of the first round key, the last round key, or both end round keys. We propose the nonlinear key-schedule $\mathrm{RK}_i = K \oplus F\bigl(K \oplus T(i)\bigr)$, where $K$ is the master key, $T(i)$ is a public domain separation value, and $F$ is a public SPN-based permutation parameterized by its round count $N_F$.

Under the boundary-leakage model considered in this paper, leakage of one end round key yields an instance of the equation $Z=U\oplus F(U)$, whereas leakage of both end round keys yields a differential constraint of the form $F(U)\oplus F(U\oplus\Delta)=\Gamma$, where $\Delta$ is determined by the two end indices and $\Gamma$ is derived from the two leaked round-key values. These reductions clarify the nonlinear systems induced by boundary leakage and the absence of a linear elimination route to the master key.

We also evaluate reduced variants of the resulting systems through Gr\"obner basis experiments, and further examine them by SAT-based key-recovery experiments and right-censored runtime analysis via a Weibull AFT model. Within the tested range, we do not observe degree collapse or unusually strong linear bias. These results provide heuristic support for the view that, under the boundary-leakage model considered here, the tested instantiations of the proposed key-schedule family do not admit an obvious efficient inversion route.

Multi-scalar multiplication (MSM), $MSM(\vec{P},\vec{x})=\sum_{i=1}^n x_i P_i$, is a dominant computational kernel in discrete-logarithm–based cryptography and often becomes a bottleneck for verifiers and other resource-constrained clients. We present 2G2T, a simple protocol for verifiably outsourcing MSM to an untrusted server. 2G2T is efficient for both parties: the server performs only two MSM computations and returns only two group elements to the client, namely the claimed result $A=MSM(\vec{P},\vec{x})$ and an auxiliary group element $B$. Client-side verification consists of a single length-$n$ field inner product and only three group operations (two scalar multiplications and one group addition). In our Ristretto255 implementation, verification is up to $\sim 300\times$ faster than computing the MSM locally using a highly optimized MSM routine (for $n$ up to $2^{18}$). Moreover, 2G2T enables latency-hiding verification: nearly all verifier work can be performed while waiting for the server's response, so once $(A,B)$ arrives the verifier completes the check with only one scalar multiplication and one group addition (both independent of $n$). Finally, despite its simplicity and efficiency, we prove that 2G2T achieves statistical soundness: for any (even unbounded) adversarial server, the probability of accepting an incorrect result is at most $1/q$ per query, and at most $e/q$ over $e$ adaptive executions, in a prime-order group of size $q$.

In this note we introduce the concept of proximity signatures, where verifiers who can only access a small part of some data would like a guarantee that (a) this data is “close” to a uniquely decodable message (so the message can be decoded from the data via error decoding) and (b) the uniquely decodable message is signed by an associated secret key. This is useful in situations where the message is very large but the verifiers are small devices who only need the guarantee that the message was signed by some specific secret key or set of keys. As a motivating example, we consider the data availability problem. There, users submit large signed pieces of data that together form a larger data matrix. The signatures and integrity of this data must then be checked by nodes who can only download a small proportion of this matrix. We present a construction inspired by linear subspace signatures.

Hamming Quasi-Cyclic (HQC) has been selected by NIST for standardization in the post-quantum landscape. As deployment approaches, implementation security becomes as critical as mathematical hardness. In this work, we demonstrate that source-level constant-time coding is not a standalone guarantee: the compiled binary must inherently preserve this behavior.

We identify a severe compiler-induced vulnerability within the official AVX2-optimized implementation of HQC, despite its claims of being constant-time. Although the C source code relies on secure, mask-based conditional selection, certain compiler optimizations rewrite this logic systematically. This transformation silently introduces secret-dependent control flow into the inner Reed-Muller decoding process, resulting in secret-dependent cache access patterns.

Exploiting this vulnerability, we mount, to the best of our knowledge, the first cache-timing Full-Decryption-style oracle attack against a post-quantum cryptosystem. Using Flush+Reload on shared libraries, an unprivileged co-located adversary can extract fine-grained predicates of the decoder's internal state. To achieve full key recovery, we develop a novel, reliability-aware Soft Information Set Decoding (Soft-ISD) post-processing framework. Leveraging a GPU-accelerated meet-in-the-middle strategy optimized for heterogeneous platforms (including Apple Silicon), we demonstrate end-to-end secret key recovery for hqc-1 with less than 10 seconds of online trace collection.

(Partially) blind signatures are foundational cryptographic primitives that enable privacy-preserving authentication in digital systems. Blind signatures allow a user to obtain a signature on a message without revealing its content, while partially blind signatures permit the controlled inclusion of agreed-upon public information into the signed message. These primitives are central to applications such as electronic voting, anonymous credentials, and digital cash.

The first isogeny-based construction of (partially) blind signatures, CSIOtter, were proposed by Katsumata et al. at CRYPTO'23. However, its concurrent security was later broken by Katsumata et al. (CRYPTO'24) and Do et al. (EUROCRYPT'24). These findings imply that CSI-Otter is secure only in sequential settings. Recently, Hanzlik et al. (ASIACRYPT'25) has proposed a novel framework for concurrently secure blind signatures which can be instantiated from isogenies with smaller signature size (but larger public key and secret key size). It is not known yet whether their construction can be extended to partially blind signatures.

In this paper, we present a new and efficient construction of partially blind signatures based on isogenies with substantially smaller signature and public key sizes than CSI-Otter. This makes our construction the most compact post-quantum partially blind signature scheme known to date. As similar to CSIOtter, our scheme uses small challenge space resulting in only achieving sequential concurrent security. Our design follows the Abe-Okamoto paradigm in the group action setting, building upon the framework introduced by Tessaro and Zhu (EUROCRYPT'22), whose security is based on the Discrete Logarithm Problem. We rigorously prove the security of our scheme in the Algebraic Group Action Model and the Random Oracle Model, under the hardness assumption of the Group Action Discrete Logarithm Problem.