International Association
for Cryptologic Research

Looking for two motivated PhD students to work on efficient post-quantum cryptography: quantum-resistant protocols that are provably secure, efficient, and relevant to blockchains, cloud services, secure computation, and privacy-preserving applications.

Possible directions:

Lattice-based cryptography, post-quantum threshold cryptography, blockchain protocols, secure multiparty computation, and post-quantum threshold cryptography. The work is theory-driven, with opportunities for prototypes and benchmarking.

The students will be supervised by Dr Sri AravindaKrishnan Thyagarajan and will be part of the Cybersecurity Research Cluster and SACT group in the School of Computer Science.

Funding:

The positions are funded for 3.5 years: AUD 42,754 per year, tuition fees, conference travel, and equipment support. The positions are in person. Start date is flexible in 2026 or 2027. Applications are rolling until filled. Optional paid teaching may be available.

Candidate profile:

Applicants should have, or expect to obtain, a Bachelor’s degree with first-class Honours or equivalent, or a Master’s degree. Prior crypto research experience is preferred. Strong TCS or maths candidates are encouraged.

Relevant background includes cryptography, algorithms, probability, complexity theory, number theory, lattices, and blockchains.

How to apply

Email with your CV, transcripts, a 200–300 word motivation and interests, and relevant thesis, publication, and referees.

Closing date for applications:

Contact: aravind[dot]thyagarajan[at]sydney[dot]edu[dot]au

The new positions in Computer Security and Privacy should conduct research in topics such as Computer Security and Privacy, including but not limited to cybersecurity, cryptography, privacy, data and integrity protection, computernetwork security, information technology security, software and application security, blockchain and smart contracts, computer forensics, intrusion detection and malware mitigation, security services and processes, security in hardware, human and societal aspects of security and privacy, among others. Requirements Applicants must have earned a Ph.D. degree in Computer Science, Cryptography, Cybersecurity, or a closely related field, with research experience in security and privacy, at the time of hiring. Applicants pursuing the Ph.D. in the mentioned areas will be considered. Due to the nature of our School the applicant will have the opportunity and should be willing to work collaboratively with other Departments in the School of Engineering. Previouspostdoctoral or international academic experience should be stated in the application. Candidates do not need to be fluent in Spanish at the time of application, but should be prepared to learn the language well enough to teach in Spanish in the short term (two years maximum). Fluency in English is a requirement. Applicants must demonstrate a strong commitment to all aspects of academic life and public good of the institution. They must be highly motivated to continuously improve their teaching skills, have a genuine interest in getting involved with our graduate programs (specially the doctoral program) and be able to develop and maintain an active research agenda leading to high quality publications, securing research grants, generating and participating in interdisciplinary projects, leading scientific and industry-liaison initiatives, strengthening and creating national and international academic networks, etc. Applicants should submit their application through the website: https://tinyurl.com/2s3s6e2d

Closing date for applications:

Contact: [email protected] Additional information can be obtained by emailing the Department Chair, Dr. Valeria Herskovic ([email protected])

More information: https://dcc.ing.uc.cl/departamento/vacantes-academicas/

Lattice-Based Zero-Knowledge Proofs Ref. 2026_013 About the position The cryptography group at IBM Research in Zurich is looking to hire a Ph.D. student to work on constructions and applications of lattice-based zero knowledge proofs. The group is one of the world-leaders in quantum-safe cryptography research and has significantly contributed to all three lattice-based NIST quantum-safe standards. Our current research emphasis is on practical zero-knowledge proofs based on the same foundations and their application to privacy-preserving cryptography. A motivated researcher should find this to be a very exciting environment to work in. A strong background in (applied) mathematics and some experience with cryptography is desirable. Additionally, the ideal candidate is someone who has a strong interest in high-performance implementations on modern CPU and/or GPU architectures. Zurich is consistently ranked as one of the top cities for living standards and the immediate proximity of lakes and mountains to the lab allows for the pursuit of numerous hobbies. Please apply via our career webpage: https://www.zurich.ibm.com/careers/2026_013.html

Closing date for applications:

Contact: https://www.zurich.ibm.com/careers/2026_013.html

More information: https://www.zurich.ibm.com/careers/2026_013.html

This paper studies privacy-preserving data analytics in settings where multiple parties hold sensitive datasets and want to compute global statistics without revealing their data. We focus on computing the total number of common elements (cardinality of intersections) across multiple pairs of datasets, while ensuring that only the final aggregated result is disclosed and no intermediate information (such as individual intersections) is leaked. To address this problem, we introduce a new cryptographic primitive called outsourced cardinality private set intersection with secret-shared outputs (CaOPSI-SS). Our solution is extremely simple and uses pseudorandom functions and two non-colluding servers to offload computation, making it suitable for environments with heterogeneous resources. Building on this primitive, we design a protocol for aggregated pairwise analytics that computes the sum of intersection cardinalities across many parties. We apply our framework to a real-world use case: privacy-preserving mail analytics in large organizations with multiple subsidiaries. The system allows useful fine-grained queries over email logs while protecting sensitive HR data. We also extend the solution with differential privacy mechanisms to further protect individual records. Finally, we implement and evaluate the protocol, showing its scalability and practicality for large datasets. Our solution enables parties to obliviously offload their datasets to two non-colluding servers using pseudorandom functions and further execute a circuit-PSI among these two servers to obtain secret shares of the output.

Secure backups are the Achilles' Heel of the E2EE ecosystem if they do not provide the same strong security properties as the E2EE messaging systems they support. They constitute a set of servers that, if compromised, would expose nearly all user messages. Unfortunately, state-of-the-art and deployed secure backup systems fail to consider forward secrecy and post-compromise security of these servers as first-order design constraints. Additionally, some proposals, in limited deployment, implicitly rely on the PKIs of trusted execution environments in order to provide security, creating a small number of keys whose compromise would be catastrophic.

We develop an elegant, efficient, and simple secure backup system that naturally addresses these issues by regularly rotating backup servers, each of which samples independent key material. To make this approach scalable, we design a silent backup procedure, reducing server load compared to state-of-the-art designs while providing improved security. Our design can be trivially extended to incorporate \emph{social key recovery}, enabling more flexible deployment configurations. We carefully prove the security of our construction and benchmark it to show that it is deployment-ready. Our approach works on commodity hardware making it deployable without the resources needed for WhatsApp or Apple's Encrypted Backups.

Distributed symmetric-key encryption (DiSE), introduced in CCS' 18 enables threshold versions of traditional (symmetric-key) authenticated encryption. In DiSE, the long-term master secret key is secret-shared among multiple parties following a threshold access structure, and both encryption and decryption are performed in a distributed manner. An adaptively secure DiSE, introduced in INDOCRYPT' 20 tolerates adaptive corruptions of the key-holding parties for arbitrary thresholds, while simultaneously retaining efficient encryption and decryption. Unfortunately, all existing instances of adaptively secure DiSE are either quantum-broken (due to their inherent-reliance on discrete log-hard groups), or incur exponential (in the number of parties) online overheads for encryption/decryption.

In this paper, we present EQuADiSE -- the first practically efficient, adaptively secure, and plausibly post-quantum construction of DiSE based on the Module Learning with Rounding (MLWR) assumption in the Quantum Random Oracle model (QROM). EQuADiSE is the first adaptively secure quantum-safe instance of DiSE that incurs linear (in the number of parties) encryption/decryption overheads. As a core technical tool of independent interest, we introduce an MLWR-based distributed pseudorandom function (DPRF) that enjoys adaptive security in the QROM and practically outperforms all existing adaptively secure DPRF constructions in terms of online evaluation time.

We present experimental evaluations demonstrating that EQuADiSE achieves higher online throughput than all prior realizations of DiSE, including quantum-broken realizations based on discrete log-hard groups.

While quantum computing technologies are revolutionising key industries, distributed quantum hard- ware services are dominated by quantum providers such as IBM, Google, and AWS. It raises critical data security concerns across sectors such as banking, defence, and healthcare. To address this issue, Quantum Homomorphic Encryption (QHE) has emerged as a solution that enables computations on encrypted quantum data while preserving privacy. Despite its promise, deploying QHE remains challenging due to circuit complexity and the noise in today’s quantum systems. In this work, we confront these barriers directly by implementing QHE on Noisy Intermediate-scale Quantum (NISQ) devices using the Variation of Gate Teleportation (VGT) scheme. In particular, we focus on implementing the CCZ gate, a key non-Clifford gate that makes a quantum gate set universal when combined with Clifford gates. By leveraging the techniques from the Classical Quantum Circuit (CQC)- QHE framework proposed by Ortega et al. in 2025, our implementation reduces computational cost and improves resource efficiency. As a result, our approach can support 7 qubits and 14 T-gates in the circuit without large errors, improving on existing QHE implementations.

Trapdoor constructions are an active research area in Multivariate Cryptography. The presented work studies trapdoors based on factor decomposition in algebraic structures, with emphasis on polynomial rings over $F_p$. The main contribution is the formulation of a general property: if an algebraic structure admits a hidden factor decomposition then this property can be used as a trapdoor principle. Based on this approach, two constructions are given: one signature scheme and one encryption scheme.

Modern Byzantine fault-tolerant state machine replication (BFT SMR) systems adopt a decoupled BFT consensus process to separate data dissemination from transaction ordering as it enables efficient (asynchronous) dissemination even when ordering fails intermittently under partial synchrony. Nevertheless, they may still suffer from high transaction confirmation latency as the transaction-execution process waits for the ordering process to complete: when the ordering process stalls, the execution process does not proceed even when transactions are disseminated.

We propose Pufferfish, the first BFT SMR system that effectively masks intermittent ordering failures in practice. Pufferfish introduces a pre-commi execution scheme that enables replicas to speculatively execute transactions even during the ordering process stalls. These pre-commit execution results can be directly committed, if correct, when the ordering failures are resolved. To achieve this, Pufferfish builds an adaptive probabilistic speculation mechanism on top of a DAG-based BFT consensus protocol, enabling replicas to predict and speculatively execute transactions ahead of confirmed ordering. Additionally, Pufferfish adopts a commit-aware snapshot mechanism to minimize the overhead of transaction re-execution in cases of speculation failures. To demonstrate the effectiveness of Pufferfish, we implement and evaluate it on a geo-distributed AWS environment. The evaluation results show that Pufferfish achieves faster recovery and 1.36x speedup on the p99 transaction confirmation latency compared to the state-of-the-art BFT SMR in the presence of ordering failures. Even under normal execution, Pufferfish can achieve a 1.58x speedup on transaction confirmation latency under a transaction workload of 80k tps.

Cryptography based on error correction codes has gained significant interest due to its ability to provide security against both classical and quantum adversaries. In 2025, the U.S. National Institute of Standards and Technology selected the Hamming Quasi-Cyclic (HQC) key encapsulation mechanism for standardization. A key aspect of HQC is the possibility of decryption failures, which reveal information about the private key. To address this issue, the HQC authors developed a probabilistic model for the decoding failure rate (DFR) of the underlying error-correcting code, and adjusted the cryptosystem parameters to thwart attacks based on decryption failures. However, the DFR model relies on the assumption of independence between coordinates of the error vector, which does not hold in HQC. This approximation yields conservative DFR estimates in regimes where failure probabilities can be simulated, and it is hypothesized to remains conservative for cryptographic-grade parameter sets. In this work, we eliminate the independence assumptions and derive a new closed-form DFR model for HQC. We demonstrate that the previous approximation remains conservative in the cryptographic regime and that HQC's current decoding failure rates are lower than the required ones. We describe optimization techniques that enable our probabilistic model to serve as a parameter-tuning tool, and demonstrate how the size of HQC public keys and ciphertexts can be slightly reduced without compromising security.

We introduce a new software stack in Rust aimed at simplifying constructions and deployments of protocols based on modern anonymous credential systems.

The stack, called sigma-rs, through its layered design, abstracts cryptographic complexity while remaining flexible enough to support a range of credential schemes, proofs, and access policies. It emphasizes misuse resistance via type safety, domain separation, and prover-state discipline, and supports side-channel-aware constant-time strategies.

We evaluate practicality through re-implementations of Tor’s Lox bridge distribution protocols and of user authentication in the Open Observatory for Network Interference.

We present the first lattice-based, partially non-interactive threshold signature scheme that tolerates the adaptive corruption of up to $T-1$ signers, where $T$ is the signing threshold. Our construction relies on the MSIS and MLWE assumptions, and has two rounds, of which only the second is message-dependent. We substantially improve upon prior adaptively secure lattice-based schemes (CRYPTO '24 and EUROCRYPT '26), which require at least two message-dependent rounds. Compared to prior lattice-based partially non-interactive assumptions (CRYPTO '24, S\&P '25, CRYPTO '25), we achieve better communication complexity in addition to stronger security guarantees.

We present the first Distributed Broadcast Encryption (DBE) scheme from falsifiable lattice assumptions that achieves adaptive security with optimal parameters (short public/secret keys and ciphertexts). Our construction enjoys transparent setup and offers flexible instantiation: we achieve a succinct CRS in the Random Oracle Model, or a long CRS in the standard model. Previously, no lattice-based DBE simultaneously achieved adaptivity and optimal parameters in either setting.

To achieve this, we introduce a new methodology for proving adaptive security: $\textit{Equivocal Encryption Systems}$. This framework operates in two indistinguishable modes: a 'real' mode utilizing standard algorithms, and a 'fake' mode where keys and ciphertexts are jointly sampled with auxiliary trapdoors, enabling the dynamic equivocation of ciphertexts to arbitrary challenge values. While our approach is technically distinct from the celebrated Dual System Encryption (Waters, CRYPTO'09), we believe it could serve as a similarly powerful paradigm for realizing adaptive security across a broad class of lattice-based encryption systems.

Quantum Homomorphic Encryption (QHE) addresses Quantum Cloud Computing (QCC) security concerns by ensuring the privacy of a client’s data and algorithms when outsourced to untrusted third-party quantum servers. However, current QHE schemes face significant challenges: scaling computational resources introduces overhead and hardware noise, degrading accuracy and compromising security. This paper imple- ments and analyses a non-interactive AUX-QHE scheme that employs pre-generated auxiliary states for universal computation. We identify three critical computational bottlenecks: exponential growth in auxiliary state count, complex homomorphic evaluation, and extensive symbolic key updates. Through experimental evaluation on IBM Quantum hardware, we quantify the impact of NISQ noise on AUX-QHE performance and establish practical resource thresholds for deployment. Our results bridge the gap between theoretical QHE frameworks and their practical implementation on noisy quantum devices, providing concrete benchmarks for future noise mitigation efforts.

Ongoing advances in quantum computing represent a growing risk to modern cryptography (potentially threatening both asymmetric and symmetric encryption protocols), thereby challenging the foundations of digital security. In response, global cybersecurity communities, led by standardization bodies such as NIST and ETSI, launched initiatives to establish migration pathways toward post-quantum cryptography (PQC). However, the migration of legacy systems to quantum-safe cryptography presents many challenges that have not yet been addressed due to their limited cryptographic agility, outdated infrastructure, and regulatory constraints. These legacy environments, even though they rely on aging technologies and constrained hardware, are still vital to major sectors (such as finance, energy, healthcare, and government). This paper explores some obstacles to the implementation of PQC in these environments, such as hard-coded cryptographic functions, outdated programming languages, hardware limitations, vendor lock-in, interoperability constraints, and certification issues. This shows that, in contrast to contemporary systems, legacy systems cannot be readily modified or easily re-engineered. A critical review of existing standards and academic publications revealed key limitations: their focus on algorithms specifications, the abstract guidance provided without operational depth, the lack of empirical validations, and the insufficient risk modeling and attention to legacy constraints. These gaps prevent effective planning and secure execution of the PQC migration in legacy systems. Consequently, this position paper argues that existing deliverables remain insufficient to address the specific challenges of PQC migration in legacy systems. It proposes the elaboration of a field-informed risk-based framework for PQC Migration in Legacy Systems to guide this transition. This proposed framework combines three interdepedent layers: a diagnostic characterization of legacy system constraints, a qualitative risk assessment grounded in those constraints, and a quantitative evaluation of migration options through an ROI-based analysis to support decision-making. Unlike existing approaches that treat legacy as generic labels, this framework begins by exploring what makes each system legacy in its specific context before applying the risk model. Its development is informed by an empirical survey conducted among large organizations across critical sectors, ensuring relevance beyond theoretical assumptions. Future work will focus on elaborating the framework through applied research, tool development, and real-world case studies in collaboration with financial institutions and critical infrastructure operators. In addition, continued engagement with cyber authorities and standardization bodies will help us ensure alignment with emerging regulations.

Many blockchain-based applications can be seen as instances of fair exchange of two signatures. Adaptor signatures (AS) and, more concretely, their extractability property, are commonly combined with blockchain-based economic incentives to achieve fairness in the exchange of two signatures in the blockchain. Certain blockchain applications require unique signatures (e.g., BLS), but it is formally impossible to build AS from unique signatures. Other applications need blind signatures, however, we found a tension between extractability and blindness. To address these limitations, we observe that fair exchange protocols based on AS only require extractability for one of the two exchanged signatures. This observation allows the other AS to be replaced with a primitive that provides similar security guarantees without inheriting the limitations of AS with respect to unique and blind signatures. A natural candidate is verifiably encrypted signatures (VES), introduced by Boneh et al. (Eurocrypt'03). However, this primitive predates blockchain systems and relies on a trusted party, the adjudicator.

Our first contribution is to eliminate the need for an adjudicator by shifting trust to the blockchain and redefining the VES security model accordingly. We introduce two new security notions and prove that our notions imply existing guarantees. We revisit classical VES constructions by Boneh et al. (Eurocrypt'03) for unique signatures and by Hanser et al. (ESORICS'15) for probabilistic signatures, and show that they satisfy our new definitions. Furthermore, we compare our new notions with AS, and conclude that our revised VES is equivalent in terms of security to AS without extractability. Our second contribution extends VES to support blind and non-interactive blind signatures, introducing a new primitive: Verifiably Encrypted Blind Signatures (VEBS). We present a novel construction for non-interactive blind signatures and prove its security. We implement our construction and demonstrate its practical efficiency: encryption requires 3 ms, verification 6 ms, and decryption 13 ms, with a communication cost of 912 bytes. Finally, we discuss how VES/VEBS apply to diverse use cases, including anonymous credentials, contingent payments, atomic swaps, intermediated payments, coin mixing, and applications involving blind signatures.

In this work, we introduce the concept of Obliviously Checkable Secret-Carrying Puzzles (OxSP) and build proof-friendly Garbled Circuits (GCs) to enable their practical implementation. OxSPs allow one to publicly pose puzzles and verify purported solutions received in response, keeping the desired parts of the puzzles and the responses hidden.

We show how OxSPs can be based on Garbled Circuits (GCs). However, this requires ZK-SNARK proofs of correctness of garbling. We note that combining existing GC and ZK-SNARK constructions results in very large computational costs for the OxSP solvers. Our main technical contribution is to design a new proof-friendly GC construction which cuts down the cost of generating a proof of correct garbling to almost a third, without resorting to non-standard cryptographic assumptions.

Beyond its use in OxSP, we expect our proof-friendly GCs to be of significant independent interest, as a tool for auditable secure 2-party computation.

BBS+ signatures are widely adopted in privacy-preserving systems such as anonymous credentials and Direct Anonymous Attestation (DAA). To strengthen key security and eliminate single points of failure, threshold variants of BBS+ signatures have become increasingly important. However, existing constructions suffer from notable inefficiencies: some entail excessive communication overhead (e.g., DKL+23, S&P 2023), while others impose substantial computational costs and require additional interaction rounds (e.g., WMC24, NDSS 2024).

In this work, we present a novel and efficient three-round threshold BBS+ signature scheme from the Castagnos–Laguillaumie (CL) cryptosystem. Our construction achieves best communication–computation trade-offs than previous works. Specifically, compared to the four-round WMC24 scheme, our protocol reduces communication by $77.4\%$ and demonstrates faster computation, with benchmarks indicating speedups of $10.6$--$16.6\times$ in single-threading and $3.3$--$5.4\times$ in multi-threading. Against the three-round protocol DKL+23, our scheme exhibits an asymptotic slowdown factor of $4\times$, but enhances communication by two orders of magnitude.

We further extend our techniques to threshold BBS signatures, Dodis-Yampolskiy verifiable random functions (DY VRFs), and multiplication protocols (DNP25 and LLZ+25, CCS'25). This yields: (1) a three-round threshold protocol for the original BBS scheme; (2) two-round threshold protocols for both DY VRFs (focusing on its oblivious variant) and the AGM-secure BBS variant; and (3) one fewer group element in broadcasts for the multiplication protocol with reduced ZKP costs via simplified relations.

The integral-resistance property provides strong arguments against integral distinguishers. Recently, Zeng and Tian proposed a new method to show this property for AES. In this paper, we provide a generalized framework and tool called intres to extend and apply this method to other ciphers with complex linear layers. We derive properties that a cipher must fulfill in order for the method to be applicable. Furthermore, we introduce a degree propagation model which helps us determine the valid key masks for the integral-resistance matrix. The degree model can also be used to upper-bound the algebraic degree of cipher constructions. This allows us to provide tighter upper bounds for the degree of Rijndael-256. We propose algorithmic improvements to substantially decrease the runtime of the offline phase with the intres framework. As a result, we are able to show the integral-resistance property for 7 rounds of PRINCE and 6 rounds of Beanie. Finally, we develop a heuristic MILP-based approach to search for lower-latency alternatives to the MixColumns matrices of PRINCE while maintaining integral resistance. After showing that using this new matrix we still achieve 7-round integral resistance, we validate our method with SAT-based trail counting. While using a MixColumns matrix only optimized for integral resistance might affect security against other types of attacks, we believe these lower-latency matrices have their place in constructions similar to ZIP-ciphers, where integral resistance is particularly critical.

MPC-in-the-Head protocols enable post-quantum digital signatures based solely on symmetric primitives, with PICNIC being a prominent example built on the LowMC block cipher. While existing analyses assume exact Boolean circuit semantics, recent advances in neural representations suggest that piecewise-linear implementations may introduce activation boundary leakage. In this work, we investigate whether such leakage can be exploited in the context of LowMC and MPC-in-the-Head transcripts. We propose a perturbation-based probing methodology that models neural leakage and reduces round-key recovery to independent binary hypothesis tests via majority voting. Exploiting the linear structure of the LowMC key schedule, we demonstrate that recovery of the first-round key enables efficient reconstruction of the master key with linear complexity. Experimental results confirm successful recovery of 128-, 192-, and 256-bit keys under the proposed model, highlighting a new dimension in symmetric cryptanalysis and the need to consider learning-based leakage in future designs.