International Association
for Cryptologic Research

Applications are invited for a post-doctoral fellow position in one or more of these areas: applied cryptography, blockchain technology, and cryptographic engineering. The successful candidate will join Professor Anwar Hasan’s research group at the University of Waterloo. Applicants with a recent Ph.D. in Computer Engineering, Computer Science or a related discipline, and publications at premium venues are encouraged to send pdf copies of their CVs and cover letters via email to Professor Anwar Hasan (ahasan at uwaterloo.ca). Application deadline: February 20, 2026 for full consideration. After this deadline, applications will be processed as they arrive.

Closing date for applications:

Contact: Anwar Hasan (ahasan at uwaterloo.ca)

Although both blind signatures and adaptor signatures have individually attracted attention, there is little research on combining these primitives so far. To the best of our knowledge, although the only existing scheme is the scheme by Qin et al. (S\&P 2023), it does not consider practical security notions, namely full extractability, unlinkability, and pre-verify soundness, especially against adversaries with rich attack interfaces. In this paper, we propose the first blind adaptor signature scheme that satisfies the above security definitions. We first formalize the security of a blind adaptor signature scheme and prove a relationship between our security definitions and the existing security definitions, as well as showing several gaps in the existing schemes as a technical problem. Our main idea to overcome this problem is to leverage relations that support random self-reducibility instead of additional random numbers for blind signatures. Such a construction can embed relations into the signature components by re-randomizing them with the relations, and hence satisfies all the above security definitions. We then introduce new proof techniques to prove the full extractability by leveraging the unlinkability. We also discuss applications of the proposed scheme.

This paper presents Heli, a system that lets a pair of servers collect aggregate statistics about private client-held data without learning anything more about any individual client's data. Like prior systems, Heli protects client privacy against a malicious server, protects correctness against misbehaving clients, and supports common statistical functions: average, variance, and more. Heli's innovation is that only one of the servers (the "heavy server") needs to do per-run work proportional to the number of clients; the other server (the "light server") does work sublinear in the number of clients, after a one-time setup phase. As a result, a computationally limited party, such as a low-budget non-profit, could potentially serve as the second server for a Heli deployment with millions of clients.

Heli relies on a new cryptographic primitive, aggregation-only encryption, that allows computing certain restricted functions on many clients' encrypted data. In a deployment with ten million clients, in which the servers privately compute the sum of 32 client-held 1-bit integers, Heli's heavy server does 240,000 core-s of work and the light server does 7 core-ms of work. Compared with prior work, the heavy server does 38$\times$ more computation, but the light server does 120,000$\times$ less.

The paper is currently under embargo, and will be released mid-February 2026.

Introduced by Boneh and Naor (CRYPTO 2000), timed commitments are a versatile primitive that found numerous applications in e-voting, contract signing and auctions. In TCC 2020, Katz, Loss and Xu showed that non-interactive timed commitments (NITC) can be generically built from timed public key encryption (TPKE). Unfortunately, almost all constructions for either primitive rely on classical, i.e. non post-quantum, assumptions or require inefficient building blocks like indistinguishable obfuscation or fully homomorphic encryption.

In this work, we propose generic constructions for non-interactive timed commitments and timed encryption, assuming only efficient building blocks like verifiable random functions, trapdoor delay functions and NIZK proof systems. Both our NITC (called LEIBNITC) and our TPKE (called NYTPKE) can be instantiated from isogenies, making them post-quantum secure. The instantiation of LEIBNITC with isogenies is very efficient and yields commitments of size 2328 bits, representing one of the most efficient timed commitments in the literature.

ML-DSA (formerly CRYSTALS-Dilithium), NIST’s primary post-quantum signature standard, is increasingly deployed along with the post-quantum transitions. Yet when the implementations of ML-DSA are deployed in practice, their physical security remains underexplored. In this work, we reveal a new attack surface against ML-DSA by exploiting the leakages from both rejected signing trials and the final accepted signing trial. We present, to the best of our knowledge, the first side-channel attack that simultaneously leverages leakage from both trials without relying on clone devices. Unlike traditional Secret-based Template Attacks, which require profiling the leakage of the sensitive intermediates on a clone device, our PTA (Public-based Template Attack) builds leakage templates solely from publicly available data on the target device itself. With challenge $c$ known, we then perform CPA on the sensitive intermediates using traces from both rejected and accepted signing trials, quadrupling (on average) exploitable leakage per signing request for ML-DSA-44. The experimental results on power traces from an ARM Cortex-M4 board show that challenges $c$ are fully recovered with only {96 traces}, and then the key recovery succeeds in around 300 traces — a fact of 10x fewer than prior art. We highlight that our attack can be applied across all three ML-DSA variants with different security levels. Moreover, our attack works straightforwardly in the hedged (non-deterministic) mode of ML-DSA, demonstrating that the hedging offers no SCA protection in this scenario.

The revival of classical cryptography paradigms from the perspective of modern primitives offers promising avenues for the design of resilient stream ciphers. This work presents RotorCipher V2, an algorithm that reimagines the structural complexity of virtual rotor machines, integrating it with the proven security of the SHA-3 family of sponge functions. The system architecture begins with a robust key derivation process, employing the memory-hard Argon2id algorithm (with a memory cost of 64 MB) to convert user credentials into a 512-bit seed, mitigating brute-force attack vectors. The central innovation of the proposal lies in the deterministic “bootstrapping” of the internal components: using SHAKE256 as an Extendable Output Function (XOF), the system dynamically selects sizes for five virtual rotors from a permuted list of prime numbers (between 300 and 10,000). Unlike historical mechanical machines, the combined output of the rotors is not used directly; it undergoes non-linear mixing via modular multiplication 2^16 + 1 (a technique remaining from the IDEA cipher) to compose a temporary entropy table. This table feeds back into an independent instance of SHAKE256, which in turn generates 1024-byte keystream blocks, ensuring that the internal state of the rotors remains cryptographically isolated from the final output. From a software engineering perspective, the paper details a secure implementation in the Rust language, prioritizing memory security and mitigation of side-channel attacks. The code employs constant-time comparisons for integrity verification and automatic zeroing of critical secrets from memory. Simultaneously, performance is optimized through the explicit use of SIMD instructions (AVX2 and SSE2) for in-place XOR operations. The resulting protocol offers a complete solution for file encryption, guaranteeing authenticity and integrity through HMAC-SHA3-512 tags, establishing itself as a high-performance hybrid tool.

$\textit{Proxy re-encryption}$ (PRE) is an essential cryptographic primitive for managing secure access delegation in outsourced data environments, particularly public cloud systems. PRE is a public key encryption (PKE) with two additional algorithms - (i) re-encryption key generation by which a proxy server generates a re-encryption key; (ii) re-encryption algorithm by which the proxy server can transform the ciphertext under the delegator's public key to a ciphertext under the delegatee's public key enabling the delegatee to decrypt the message originally intended for the delegator. With the advent of quantum computing, a pressing need arises to design PRE schemes based on quantum-resistant assumptions. This paper addresses this requirement by presenting the first construction of a bidirectional PRE ($\mathsf{bPRE}$) from supersingular isogenies. Our $\mathsf{bPRE}$ is built upon the commutative supersingular isogeny-based PKE scheme $\mathsf{MSimS}$, a variant of the isogeny-based PKE scheme $\mathsf{SimS}$ and achieves security against $\textit{chosen-plaintext attack}$ (CPA) in the standard model under the hardness of the commutative supersingular isogeny decisional Diffie-Hellman (CSSIDDH) problem. The resultant $\mathsf{bPRE}$ supports efficient re-encryption of ciphertexts by the proxy server for the delegator as well as the delegatee and inherits the multi-hop property, enabling chainable delegation of access rights. Significantly, our isogeny-based $\mathsf{bPRE}$ is asymptotically efficient, offering an efficient reduction in bandwidth consumption compared to current lattice-based proposals in terms of key size and ciphertext size. This makes the scheme a highly compact and practical candidate for post-quantum cloud security. Furthermore, our PKE scheme $\mathsf{MSimS}$ is of independent interest which is proven to be CPA secure under the hardness of the CSSIDDH problem and secure against chosen ciphertext attack (CCA) under the hardness of the CSSIDDH problem and the commutative supersingular isogeny knowledge of exponent (CSSIKOE) problem.

Galteland and Gjøsteen observe that Dilithium-family signatures admit broadband subliminal channels in a secret-key-assisted setting where the receiver can reconstruct the signer’s hidden commitment from a public signature. This note gives a standards-specific instantiation for FIPS 204 ML-DSA. We do not claim a new subliminal-channel technique: our goal is to make the FIPS 204 patch point and byte-level embedding interface explicit and to list the resulting capacities for the approved parameter sets.

Two FIPS 204 facts drive the construction: for any accepted signature, the commitment vector \(y\) is recoverable from \((c, z)\) given \(s_1\), and the standardized \(\gamma_1\) values make the packing/unpacking mapping a bijection on its fixed-length byte input. We embed an \(L\)-byte payload by XOR-masking a pseudorandom packed container and decoding it with the standard unpacking routine: the resulting signatures verify under unmodified verifiers.

We implemented the patch in the mldsa-native C library and validated round-trip extraction, abort-rate statistics, and distribution sanity checks for all three parameter sets. Changes, scripts, and artifacts are available in the mldsa-native-sublime fork on GitHub. The per-signature covert capacity is \(32\ell w - 32\) bytes, where \(w = \log_2(2\gamma_1)\), namely 2,272 bytes for ML-DSA-44, 3,168 bytes for ML-DSA-65, and 4,448 bytes for ML-DSA-87. As in prior work, extraction requires \(s_1\), so the relevant setting is kleptographic/ASA-style secret sharing rather than public tagging.

Randomness that is unbiased, unpredictable and publicly verifiable is a crucial requirement for many blockchain-based Web3 ap- plications. Verifiable Random Functions (VRFs) inherently provide these properties. A practical VRF scheme requires fast key generation time as well as features like many evaluations also for different rounds in the blockchain. In this work, we propose a post-quantum secure key updat- able VRF construction namely XM-VRF that relies on symmetric cryp- tographic building blocks such as hash functions and PseudoRandom Generators (PRGs). At the heart of our construction lies a quantum safe Extended Merkle Signature Scheme(XMSS) organized across multi- ple layers. We reformulate the XMSS signature scheme in a structured manner to align with our XM-VRF construction. The principal benefit of proposed XM-VRF compared to existing solution is it’s enhanced key generation efficiency as well as the property of many evaluations from each secret-verification key pair. The proposed scheme is proven to sat- isfy forward security, while also being resilient against forgery attacks, as established through a rigorous security analysis. We emphasize that our XM-VRF autonomously updates its secret key during the evaluation process, performing this update concurrently with the VRF output gen- eration to maintain uninterrupted state progression. Finally, we design a protocol for random committee selection within the Algorand blockchain framework,leveraging XM-VRF to ensure unbiased, verifiable, and stake- proportional participant selection.

We present an improved AKS condition $\binom {e \cdot |S|+ de - 1}{de - 1} \ge n^{\lceil \sqrt{d e/3} \rceil}$ for the random AKS algorithm, where $|S|$ is the number of congruences to be tested, $e$ the degree of the modulo polynomial $x^e-r$ and $d$ the multiplicative order of $n$ modulo $e$. It is based on Bernstein's result and better than his condition $\binom {e \cdot |S|+ e - 1}{e - 1} > n^{\lceil \sqrt{d^2 e/3} \rceil}$ when $d>1$; this improved condition enables us to choose a smaller $e$: theoretically by a factor $> d$ ($d \in (\log n)^{O(1)}$) and numerically $\ge d^2$ and $< d^3$ for most practical cases; and thus improves time and space complexities.

Masking is an essential countermeasure against side-channel attacks, yet implementing secure and low-latency hardware masking remains challenging. In particular, although OPINI provides strong composability guarantees for single-cycle iterative architectures, prior low-latency OPINI gadget, $\rm HPC4$, is limited to two-input multiplication. In this work, we present a low-latency, low-randomness, first-order OPINI gadget applicable to arbitrary Boolean functions, denoted as $\rm GOM$. Independent and concurrent work by Rahimi and Moradi proposes OTSM, which is also a generic, low-latency first-order OPINI gadget. Our construction involves two new techniques: (i)~extending the $\rm HPC4$ idea--originally masking each share of one secret input with two bits of randomness--to masking each shared monomial derived from the input shares accordingly, and (ii)~a randomness-reassignment technique that enables the two circuits generating the output shares to reuse the same set of randomness while preserving OPINI security. To validate OPINI security, we propose a formal verification technique based on three symbolic reduction rules, and use it to verify multiple low-latency OPINI gadgets (i.e., $\rm HPC4$, $\rm GOM$ and $\rm OTSM$). Leveraging the generality of our gadget, we instantiate several OPINI-secure S-boxes across different algebraic degrees. For the algebraic-degree-2 Ascon S-box, our gadget achieves a 21\% reduction in area and a 28\% reduction in randomness compared to the $\rm HPC4$-based implementation. We further construct higher-degree S-boxes from the PRESENT, PRINCE and AES ciphers and report their hardware performance as reference baselines. We also provide an apples-to-apples comparison with $\rm OTSM$. All masked S-boxes are successfully verified within 20~minutes using our formal verification method. Finally, FPGA-based experiments confirm the practical security of the masked implementations.

Off-chain cryptography enables more expressive smart contracts for Bitcoin. Recent work, including BitVM, use SNARKs to prove arbitrary computation, and garbled circuits to verifiably move proof verification off-chain. We define a new garbling primitive, Argo MAC, that enables over $1000\times$ more efficient garbled SNARK verifiers. Argo MAC efficiently translates from an encoding of the bit decomposition of a curve point to a homomorphic MAC of that point. These homomorphic MACs enable much more efficient garbling. In subsequent work, we will describe how to use Argo MAC to construct garbled SNARK verifiers for pairing-based SNARKs.

In response to the looming quantum threat, NIST has selected four algorithms for standardization (i.e., ML-KEM, ML-DSA, SLH-DSA, and FN-DSA), yet three of the four schemes are based on Euclidean lattices, which raises concerns about the mathematical diversity of post-quantum algorithms. NIST has therefore announced an additional call for post-quantum signatures with a preference for schemes constructed from assumptions other than lattices. Among such candidates, the Unbalanced Oil and Vinegar (UOV) signature over the multivariate quadratic (MQ) problem is attractive for its short signature and security against quantum cryptanalysis. However, the practical implementations of UOV remain vulnerable to power side-channel attacks. In this paper, we address this issue by presenting two improved techniques for masking linear equations system solving at arbitrary order, with a proof of security in the $t$-probing model. We show that in the masked setting, our inversion-based techniques outperform Gaussian elimination, unlike the unmasked setting where Gaussian elimination is typically more efficient. As an application, we develop a complete C implementation of the fully masked UOV signing using our improved techniques. Compared to masked Gaussian elimination, our techniques achieve at least $2.2$ times speedup at high-order. Against Kundu's latest implementation (CCS 2025), our masked UOV signing is faster by an average factor of $4.0$ at higher masking orders.

Deep neural networks (DNNs), a hot topic in this decade, are already solving many practical problems previously unchallenged. There are clear use cases of strong requirements for privacy protection in DNN models and input data. Fully Homomorphic Encryption (FHE) schemes provide privacy by enabling operations upon encrypted data with post-quantum security, at the expense of vast data size increase. Overwhelming execution times and memory sizes currently limit DNN inference with FHE to severely reduced models and datasets. In this article, we thoroughly review the state of the art and the state of the practice around this topic, and identify the current challenges remaining to enable efficient DNN inference with FHE in production-sized use cases, along with the most promising trends to address them. Advancing upon previous review articles in the literature, our focus is specifically on deep learning inference on top of high-performance hardware. From our analysis, we set what we consider to be an ideal private inference system for DNNs, capturing notions already present in the literature and generalizing them.

Secure TransFormer Inference (STFI) frameworks have been proposed to address privacy concerns over user inputs and model parameters in Transformer-based LLMs. While most existing solutions rely on interactive protocols that incur substantial user-server communication overhead, non-interactive STFI variants have recently emerged to eliminate such dependencies. Nevertheless, state-of-the-art non-interactive STFI frameworks still suffer from critical limitations. (i) Large ciphertext sizes and multiple rotations alongside heavy user-side overhead in Homomorphic Matrix Multiplication (HMM). (ii) High approximation costs and depth consumptions in Homomorphic Nonlinear Evaluations (HNE).

To address these limitations, we present Euston, an efficient and user-friendly STFI with non-interactivity. By combining RNS-CKKS fully homomorphic encryption with optimized methods, Euston achieves unprecedented efficiency in offline online inference paradigm. The key innovations are twofold. (i) For linear operations, we adopt Singular Value Decomposition (SVD) with our novel batched HMMs to minimize ciphertext size and reduce rotation counts, simultaneously lowering user-side computational, communication and storage overhead. (ii) For nonlinear operations, we employ column(diagonal)-packed ciphertext matrix formats to eliminate costly rotations and depth regulation strategies to reduce depth consumption in non-interactive HNEs, which not only avoids user-server communications but also accelerates inference performance. In comparision with the state-of-the-art approach (NEXUS, NDSS 2025), Euston achieves up to 3100× lower preprocessing costs for the user and 8.8× higher system-wide inference performance, specifically delivering a 90× speedup for HMM and a 165.7× speedup for HNE. Our results demonstrate that Euston establishes new efficiency frontiers for user-friendly STFI deployment across cloud and edge environments.

The whitelist is a foundational and widely deployed access control mechanism. In its prevalent implementation, the verifying entity typically requires access to the plaintext authorization policy to perform enforcement. This creates a concentrated security risk: the verifier becomes a high-value target, and its compromise could lead to the full exposure of the sensitive whitelist—a single point of failure for policy confidentiality. This work formalizes and addresses this risk by introducing a new paradigm of Privacy-Enhanced Whitelists. Our framework cryptographically decouples policy enforcement from policy exposure. A trusted issuer encodes the whitelist, enabling the verifier to validate memberships using only cryptographically blinded commitments, without ever needing the plaintext list. We provide a formal security model that rigorously defines and achieves security even against an adversary who compromises the verifier’s state. The system is realized via an efficient construction based on polynomial commitments in elliptic curve groups and supports dynamic policy updates. By shifting the trust assumption from the verifier’s infrastructure to cryptographic verification, our work establishes a practical foundation for scenarios where the whitelist itself must remain a protected secret.

We present $\textsf{Jindo}$, a new lattice-based polynomial commitment scheme (PCS) readily available for compiling polynomial interactive oracle proofs (PIOP) into zero-knowledge arguments of knowledge (ZKAoK). $\textsf{Jindo}$ improves upon the previous lattice-based PCSs $\textsf{CELPC}$ (CRYPTO' 24) and $\textsf{Greyhound}$ (CRYPTO' 24) by seamlessly integrating their strengths. Specifically, we incorporate the coefficient encoding method of $\textsf{CELPC}$ with a new evaluation protocol inspired by $\textsf{Greyhound}$, inheriting only the advantages of both schemes. As a result, $\textsf{Jindo}$ enjoys native support for a large base field, a large challenge set, the evaluation hiding property, and efficient batched evaluation.

Our implementation shows that $\textsf{Jindo}$ improves $\textsf{CELPC}$ with 1.3x faster proof generation, 3.7x faster verification, and 4.8x smaller proof size when evaluating polynomials of degree $2^{19}$ over a 255-bit prime field. Furthermore, $\textsf{Jindo}$ outperforms $\textsf{CELPC}$ with 3.5x faster proof generation, 9.7x faster verification, and 12.3x smaller proof size when compiling PIOP from $\textsf{Buckler}$ (CCS' 25) to prove the validity of an RLWE sample, demonstrating its practical efficacy in ZKAoK construction from PIOP.

A classical obfuscator for quantum circuits is a classical program that, given the classical description of a quantum circuit $Q$, outputs the classical description of a functionally equivalent quantum circuit $\widetilde{Q}$ that hides as much as possible about $Q$. Previously, the only known feasibility result for classical obfuscation of quantum circuits (Bartusek and Malavolta, ITCS 2022) was limited to "null" security, which is only meaningful for circuits that always reject. On the other hand, if the obfuscator is allowed to compile the quantum circuit $Q$ into a quantum state $\ket{\widetilde{Q}}$, there exist feasibility results for obfuscating much more expressive classes of circuits: All pseudo-deterministic quantum circuits (Bartusek, Kitagawa, Nishimaki and Yamakawa, STOC 2023, Bartusek, Brakerski and Vaikuntanathan, STOC 2024), and even all unitaries (Huang and Tang, FOCS 2025).

We show that (relative to a classical oracle) there exists a classical obfuscator for all pseudo-deterministic quantum circuits. As our main technical step, we give the first construction of a compact quantum fully-homomorphic encryption (QFHE) scheme that supports public verification of (pseudo-deterministic) quantum evaluation, relative to a classical oracle.

To construct our QFHE scheme, we improve on an approach introduced by Bartusek, Kitagawa, Nishimaki and Yamakawa (STOC 2023), which previously required ciphertexts that are both quantum and non-compact due to a heavy use of quantum coset states and their publicly-verifiable properties. As part of our core technical contribution, we introduce new techniques for analyzing coset states that can be generated "on the fly", by proving new cryptographic properties of the one-shot signature scheme of Shmueli and Zhandry (CRYPTO 2025). Our techniques allow us to produce QFHE ciphertexts that are purely classical, compact, and publicly-verifiable. This additionally yields the first classical verification of quantum computation protocol for BQP that simultaneously satisfies blindness and public-verifiability.

In EUROCRYPT 1999, Gennaro, Jarecki, Krawczyk, and Rabin (GJKR) showed that in the well-known Pedersen robust Distributed Key Generation (DKG) protocol for the Discrete Logarithm (DL), an adversary can bias the distribution of the resulting public key. To address this issue, they proposed a fully secure, statistically unbiased variant of the Pedersen DKG protocol. The GJKR protocol achieves robustness and guarantees that the final public key remains uniformly random, even in the presence of computationally unbounded corrupted parties, though at the cost of $O(n^2)$ computational complexity, where $n$ denotes the number of parties. In this paper, we revisit fully secure robust DKG protocols for the DL setting and propose three more efficient alternatives, each achieving $O(n)$ computational complexity while offering different trade-offs in security, efficiency, and round complexity. Our first protocol, like the GJKR scheme, guarantees that the distribution of the final public key remains uniformly random, even against computationally unbounded adversaries. The second protocol is concretely more efficient and ensures that the public key distribution is computationally indistinguishable from uniform. In our third construction, we focus on minimizing the number of rounds in the second protocol and present a 3-round variant of it. Our third scheme can be viewed as a fully secure and round-reduced variant of the biased construction by Atapoor et al. (ASIACRYPT 2023). In comparison with the most recent low-round fully secure DKG protocols by Katz (CRYPTO 2024), Cascudo-David (EUROCRYPT 2024), Kate et al. (CCS 2024), and Boneh et al. (EUROCRYPT 2025)--all of which achieve three rounds via two online rounds and one preprocessing round (or vice versa)--our three-round DKG protocol requires only $O(n)$ exponentiations, as opposed to at least $O(n^2)$.