International Association
for Cryptologic Research

The School of Computer Science and Electronic Engineering is seeking to recruit a full-time Lecturer in Cyber Security to expand our team of dynamic and highly skilled security researchers. It is part of a strategic investment in cyber security alongside a Senior Lecturer position in cyber security.

The Surrey Centre for Cyber Security (SCCS), within the School, has an international reputation in cyber security and resilience research excellence in applied and post-quantum cryptography, security verification and analysis, security and privacy, distributed systems, and networked systems. SCCS is recognised by the National Cyber Security Centre as an Academic Centre of Excellence for Cyber Security Research and Education. Its research was also a core contributor to Surrey’s 7th position in the UK for REF2021 outputs within Computer Science. Surrey was recognised as Cyber University of the Year 2023 at the National Cyber Awards.

Surrey has an international leading track record in security and communications research and runs the newly formed Doctoral Training centre in Future Open Secure and Resilient Communications in collaboration with Queens University Belfast with funding for 50 PhD students.

This post sits within SCCS and this role encourages applications in the areas of systems security, web security, cyber-physical systems, cyber resilience, ethical hacking, machine learning for security, with application in various domains with preference in communications, space, banking, and autonomous systems. Candidates with practical security experience and skills will complement our strengths in cryptography and formal verification.

This post will support the growing cohort of students across all undergraduate Computer Science programmes and support students in the highly successful MSc in Cyber Security.

Closing date for applications:

Contact: Professor Steve Schneider

More information: https://jobs.surrey.ac.uk/vacancy.aspx?ref=009425

Adva Network Security is a German-based company and was funded by leading security experts to help operators of critical infrastructure, government agencies and enterprises security-harden their networks. We are currently looking for a highly motivated Cryptography/Security Engineer (PhD track) (M/F/D) to join our Advanced Technology team in Munich. The position will allow to focus on research and innovation in cryptography with a high relevance for our cryptographic products. In cooperation with a University, we’ll support to pursue a PhD degree in the field.

Responsibilities
• Research and develop innovative and secure solutions for key-exchange, encryption and authentication in optical networks.
• Analyze the security of cryptographic algorithms and protocols.
• Collaborate with the research community in national and international projects.
• Demonstrate technical excellence at conferences or workshops.

Requirements
• Master’s degree in Electrical Engineering, Computer Science, Mathematics or a related field.
• Good knowledge of cryptographic concepts and information security principles.
• Solid programming skills in (C and Python preferred).
• Good presentation, communication, and scientific writing skills.
• Fluent in oral and written English, fluency in German is a plus.

Apply here: https://adtran.wd3.myworkdayjobs.com/en-US/ANS/job/Berlin-ANS-Germany/Engineer-Advanced-Technology--M-F-D----PhD_R003928

Closing date for applications:

Contact: Dr. Helmut Griesser [Helmut'Griesser(a)advasecurity'com]

More information: https://adtran.wd3.myworkdayjobs.com/en-US/ANS/job/Berlin-ANS-Germany/Engineer-Advanced-Technology--M-F-D----PhD_R003928

We establish the following theorem: Let $\mathsf{O}_0, \mathsf{O}_1, \mathsf{R}$ be random functions from $\{0,1\}^n$ to $\{0,1\}^n$, $n \in \mathbb{N}$. For all polynomial-query-bounded distinguishers $\mathsf{D}$ making at most $q=\mathsf{poly}(n)$ queries to each oracle, there exists a poly-time oracle simulator $\mathsf{Sim}^{(\cdot)}$ and a constant $c>0$ such that the probability is negligible, that is $$\left|\Pr\left[{\mathsf{D}^{(\mathsf{O}_0+\mathsf{O}_1),(\mathsf{O}_0,\mathsf{O}_1,\mathsf{O}_0^{-1},\mathsf{O}_1^{-1})}(1^n)=1}\right]-\Pr\left[{\mathsf{D}^{\mathsf{R},\mathsf{Sim}^\mathsf{R}}(1^n)=1}\right]\right| = negl(n).$$

The ChaCha20-Poly1305 AEAD scheme is widely used as an alternative for AES-GCM on platforms without AES hardware instructions. Although recent analysis by Degabriele et al. shows that ChaCha20-Poly1305 provides adequate security in the conventional multiuser model, the construction is totally broken when a single nonce is repeated – a real-word scenario that can occur due to faulty implementations or the desire to use random nonces.

We present a new nonce-misuse resistant and key-committing authenticated encryption scheme, called ChaCha20-Poly1305-PSIV, that is based on carefully combining the ChaCha20-Poly1305 building blocks into the NSIV paradigm proposed by Peyrin and Seurin (CRYPTO 2016) without performance loss. We analyze the security of the underlying mode PSIV in the multi-user faulty-nonce model assuming that the underlying permutation is ideal, and prove its key-committing security in the cmt-1 model. Rust and C implementations are provided, and benchmarks confirm that performance is comparable to the ChaCha20-Poly1305 implementation in libsodium.

In terms of security and efficiency (without hardware support), our proposal compares favorably to AES-GCM-SIV. Since we reuse the ChaCha20-Poly1305 building blocks, we expect ChaCha20-Poly1305-PSIV to benefit from existing analysis and to be easy to deploy in practice.

We introduce a general, low-cost, low-power statistical test for transactions in transaction protocols with small anonymity set authentication (TPSASAs), such as Monero. The test classifies transactions as ad hoc (spontaneously constructed to spend a deterministically selected key) or self-churned (constructed from a probability distribution very close to that of the default wallet software, and with the same sender and receiver). The test is a uniformly most powerful (UMP) likelihood ratio tests (LRT) from the Neyman-Pearson Lemma, and makes no assumptions about user behavior. We extend these tests to expoit prior information about user behavior. We discuss test parameterization, as well as how anonymity set cardinality and user behavior impact test performance. We also describe a maximum-likelihood de-anonymization attack on Monero based on our test.

Quantum cryptography allows to achieve security goals which are unobtainable using classical cryptography alone: it offers the promise of everlasting privacy. Thatis, an adversary trying to attack a protocol must succeed during the run of the protocol. After the protocol has terminated, security holds unconditionally. In this work, we initiate the study of a new model which we call the quantum decoherence model (QDM). In a nutshell, this model captures adversaries that are computationally bounded during the run of a protocol (and some time after), but become computationally unbounded long after the protocol terminates. Importantly, once the adversary becomes computationally unbounded, he can only remember a bounded number of qubits from before the computational bound was lifted. We provide a variant of the Universal Composability framework which captures the new notion of quantum decoherence and augment it with quantum random oracles. As our main contribution, we construct a non-interactive commitment scheme achieving unconditional and statistical security against malicious senders and everlasting security against malicious receivers under our new security notion. Such commitments imply general secure multiparty computation with everlasting security. Finally, we show that our core technique can be applied to a broader spectrum of problems. We show that it gives rise to everlasting public key encryption and OT in the QDM. Finally, we also consider the weaker notion of incompressible encryption in the setting of quantum decoherence, and show that post-quantum IND-CPA secure public key encryption is sufficient to realize this notion without resorting to random oracles. At the technical core of our constructions is a new, conceptually simple yet powerful reverse entropic uncertainty relation.

In this paper, we demonstrate that Ethereum's current proof-of-stake (PoS) consensus mechanism poses a significant threat to decentralisation. Our research focuses on the manipulability of distributed randomness beacons (DRBs) in leader selection. Specifically, we show that RANDAO - Ethereum's DRB - is seriously vulnerable to manipulations in its current form. For example, if a lucrative slot is foreseen, there is a risk that staking entities may temporarily collude to control $33\%$ of the validators, enabling them to execute a series of RANDAO manipulation attacks that secure the target slot with a $99.5\%$ success rate. The effectiveness of our method stems from the fact that we work with a significantly richer model of the possible attacks compared to previous works. Our manipulative strategies work by missing blocks from the canonical chain - either by withholding blocks in the adversary's own slots or by forking out blocks proposed by others. We argue that while PoS can pave the path in the future for blockchains, Ethereum's current DRB implementation has to be replaced with a more secure mechanism.

The Log Structured Merge (LSM) Tree is a popular choice for key-value stores that focus on optimized write throughput while maintaining performant, production-ready read latencies. To optimize read performance, LSM stores rely on a probabilistic data structure called the Bloom Filter (BF). In this paper, we focus on adversarial workloads that lead to a sharp degradation in read performance by impacting the accuracy of BFs used within the LSM store. Our evaluation shows up to $800\%$ increase in the read latency of lookups for popular LSM stores. We define adversarial models and security definitions for LSM stores. We implement adversary resilience into two popular LSM stores, LevelDB and RocksDB. We use our implementations to demonstrate how performance degradation under adversarial workloads can be mitigated.

We present the first protocol for efficient Fuzzy Private Set Intersection (PSI) that achieves linear communication complexity, does not depend on restrictive assumptions on the distribution of party inputs, and abstains from inefficient fully homomorphic encryption. Specifically, our protocol enables two parties to compute all pairs of elements from their respective sets that are within a given Hamming distance, without constraints on how these sets are structured.

Our key insight is that securely computing the (threshold) Hamming distance between two inputs can be reduced to securely computing their inner product. Leveraging this reduction, we construct a Fuzzy PSI protocol using recent techniques for inner-product predicate encryption. To enable the use of predicate encryption in our setting, we establish that these predicate encryption schemes satisfy a weak notion of simulation security and demonstrate how their internal key derivation can be efficiently distributed without a trusted third party.

As a result, our Fuzzy PSI on top of predicate encryption features not only asymptotically optimal linear communication complexity but is also concretely practical.

Fully homomorphic encryption (FHE) enables the computation of arbitrary circuits over encrypted data. A widespread application of FHE is a simple two-party computation (2PC) protocol, where the server evaluates a circuit over the client's encrypted data and its private inputs. However, while the security of FHE guarantees that the client's data is protected from the server, there is no inherent support for the privacy of the server's input and the circuit.

One effective solution to this problem is an additional algorithm for FHE called sanitization, introduced by Ducas and Stehlé (Eurocrypt 2016). Roughly speaking, a sanitization algorithm removes any meaningful information contained in the ciphertext, including previous evaluations of circuits. Following their definition, several constructions for sanitization have been proposed, particularly for TFHE. However, all of these methods were impractical, requiring several bootstrappings or an excessive amount of randomized evaluations.

In this work, we construct a novel sanitization algorithm for TFHE that overcomes these issues. Our method only adds two lightweight randomization steps to the original TFHE bootstrapping, without any modifications to the core algorithms. As a result, our algorithm achieves sanitization with a single bootstrapping and minimal randomization, bringing sanitization closer to practicality.

To empirically evaluate the efficiency of our method, we provide concrete benchmark results based on our proof-of-concept implementation. Our algorithm sanitizes a single TFHE ciphertext in 35.88 ms, which is only 3.4% (1.18 ms) slower than the original TFHE bootstrapping with the same parameters. When directly compared to previous works, our method achieves a speedup by a factor of 4.82 to 209.03.

The cryptographic scheme and NIST candidate HAWK makes use of a particular module lattice and relies for its security on the assumption that finding module lattice isomorphisms (module LIP) is hard. To support this assumption, we compute the mass of the HAWK lattice, which gives a lower bound on the number of isometry classes of module lattices which cannot be distinguished from the HAWK lattice by an easily computed invariant called the genus. This number turns out to be so large that an attack based on the genus alone seems infeasible.

Rejection sampling is a crucial security mechanism in lattice-based signature schemes that follow the Fiat-Shamir with aborts paradigm, such as ML-DSA/CRYSTALS-Dilithium. This technique transforms secret-dependent signature samples into ones that are statistically close to a secret-independent distribution (in the random oracle model). While many side-channel attacks have directly targeted sensitive data such as nonces, secret keys, and decomposed commitments, fewer studies have explored the potential leakage associated with rejection sampling. Notably, Karabulut~et~al. showed that leakage from rejected challenges can undermine, but not entirely break, the security of the Dilithium scheme.

Motivated by the above, we convert the problem of key recovery (from the leakage of rejection sampling) to an integer linear programming problem (ILP), where rejected responses of unique Hamming weights set upper/lower constraints of the product between the challenge and the private key. We formally study the worst-case complexity of the problem as well as empirically confirm the practicality of the rejected challenge attack. For all three security levels of Dilithium-2/3/5, our attack recovers the private key in seconds or minutes with a 100% Success Rate (SR).

Our attack leverages knowledge of the rejected challenge and response, and thus we propose methods to extract this information by exploiting side-channel leakage from Number Theoretic Transform (NTT) operations. We demonstrate the practicality of this rejected challenge attack by using real side-channel leakage on a Dilithium-2 implementation running on an ARM Cortex-M4 microcontroller. To the best of our knowledge, it is the first efficient side-channel key recovery attack on ML-DSA/Dilithium that targets the rejection sampling procedure. Furthermore, we discuss some countermeasures to mitigate this security issue.

This paper introduces "Little OaldresPuzzle_Cryptic," a novel lightweight symmetric encryption algorithm.

At the core of this algorithm are two main cryptographic components: the NeoAlzette permutation S-box based on ARX (Addition-Rotation-XOR) primitives and the innovative pseudo-random number generator XorConstantRotation (XCR), used exclusively in the key expansion process. The NeoAlzette S-box, a non-linear function for 32-bit pairs, is meticulously designed for both encryption strength and operational efficiency, ensuring robust security in resource-constrained environments. During the encryption and decryption processes, a pseudo-randomly selected mixed linear diffusion function, distinct from XCR, is applied, enhancing the complexity and unpredictability of the encryption.

We comprehensively explore the various technical aspects of the Little OaldresPuzzle_Cryptic algorithm.

Its design aims to balance speed and security in the encryption process, particularly for high-speed data transmission scenarios. Recognizing that resource efficiency and execution speed are crucial for lightweight encryption algorithms, without compromising security, we conducted a series of statistical tests to validate the cryptographic security of our algorithm. These tests included assessments of resistance to linear and differential cryptanalysis, among other measures.

By combining the NeoAlzette S-box with sophisticated key expansion using XCR, and integrating the pseudo-randomly selected mixed linear diffusion function in its encryption and decryption processes, our algorithm significantly enhances its capability to withstand advanced cryptographic analysis techniques while maintaining lightweight and efficient operation. Our test results demonstrate that the Little OaldresPuzzle_Cryptic algorithm effectively supports the encryption and decryption needs of high-speed data, ensuring robust security and making it an ideal choice for various modern cryptographic application scenarios.

Keywords: Symmetric Encryption Algorithm, Lightweight Cryptography, ARX Primitives, PRNG, NeoAlzette S-boxes, XorConstantRotation, Diffusion and Confusion Layers, Cryptographic Security, Statistical Tests, Resource-Constrained Environments.

We are looking for a PhD student to join our Team at UNSW Canberra with Dr Shabnam Kasra as main supervisor. The positions are fully funded for up to 3/5 years for successful applicants. Topics including, but not limited to: - Design and cryptanalysis of cryptographic primitives - Post-quantum cryptography - Tools for cryptanalysis - Side-channel attacks - Cryptography for autonomous vehicles Applicant skills/background: -Strong research track record - A strong background in cryptography, Computer Science, Mathematics, or a related discipline . - Excellent communication and interpersonal skills, with the ability to thrive in a collaborative research environment. - Critical thinking and analytical skills, with fluency in technical English. - Proficiency in programming.

Closing date for applications:

Contact: Dr Shabnam Kasra

More information: https://www.unsw.edu.au/research/hdr/application

With the rapid development of quantum computers, optimizing the quantum implementations of symmetric-key ciphers, which constitute the primary components of the quantum oracles used in quantum attacks based on Grover and Simon's algorithms, has become an active topic in the cryptography community. In this field, a challenge is to construct quantum circuits that require the least amount of quantum resources. In this work, we aim to address the problem of constructing quantum circuits with the minimal T-depth or width (number of qubits) for nonlinear components, thereby enabling implementations of symmetric-key ciphers with the minimal T-depth or width. Specifically, we propose several general methods for obtaining quantum implementation of generic vectorial Boolean functions and multiplicative inversions in GF(2^n), achieving the minimal T-depth and low costs across other metrics. As an application, we present a highly compact T-depth-3 Clifford+T circuit for the AES S-box. Compared to the T-depth-3 circuits presented in previous works (ASIACRYPT 2022, IEEE TC 2024), our circuit has significant reductions in T-count, full depth and Clifford gate count. Compared to the state-of-the-art T-depth-4 circuits, our circuit not only achieves the minimal T-depth but also exhibits reduced full depth and closely comparable width. This leads to lower costs for the DW-cost and T-DW-cost. Additionally, we propose two methods for constructing minimal-width implementations of vectorial Boolean functions. As applications, for the first time, we present a 9-qubit Clifford+T circuit for the AES S-box, a 16-qubit Clifford+T circuit for a pair of AES S-boxes, and a 5-qubit Clifford+T circuit for the chi function of SHA3. These circuits can be used to derive quantum circuits that implement AES or SHA3 without ancilla qubits.

Differential privacy (DP) is a fundamental technique used in machine learning (ML) training for protecting the privacy of sensitive individual user data. In the past few years, a new approach for combining prior-based Local Differential Privacy (LDP) mechanisms with a relaxed DP criterion, known as Label DP, has shown great promise in increasing the utility of the final trained model without compromising on the DP privacy budget. In this work, we identify a crucial privacy gap in the current implementations of these prior-based LDP mechanisms, namely the leakage of sensitive priors. We address the challenge of implementing such LDP mechanisms without leaking any information about the priors while preserving the efficiency and accuracy of the current insecure implementations. To that end, we design simple and efficient secure two-party computation (2PC) protocols for addressing this challenge, implement them, and perform end-to-end testing on standard datasets such as MNIST, CIFAR-10. Our empirical results indicate that the added security benefit essentially comes almost for free in the sense that the gap between the current insecure implementations and our proposed secure version, in terms of run-time overhead and accuracy degradation, is minimal. E.g., for CIFAR-10, with strong DP privacy parameter, the additional runtime due to 2PC is $\approx 3.9\%$ over WAN with $0.4\%$ decrease in accuracy over an insecure (non-2PC) approach.

This paper introduces practical schemes for keyword Private Information Retrieval (keyword PIR), enabling private queries on public databases using keywords. Unlike standard index-based PIR, keyword PIR presents greater challenges, since the query's position within the database is unknown and the domain of keywords is vast. Our key insight is to construct an efficient and compact key-to-index mapping, thereby reducing the keyword PIR problem to standard PIR. To achieve this, we propose three constructions incorporating several new techniques. The high-level approach involves (1) encoding the server's key-value database into an indexable database with a key-to-index mapping and (2) invoking standard PIR on the encoded database to retrieve specific positions based on the mapping. We conduct comprehensive experiments, with results showing substantial improvements over the state-of-the-art keyword PIR, ChalametPIR (CCS'24), i.e., a $15\sim178 \times$ reduction in communication and $1.1 \sim 2.4 \times$ runtime improvement, depending on database size and entry length. Our constructions are practical, executing keyword PIR in just 47 ms for a database containing 1 million 32-byte entries.

NovaTEE is a novel private multilateral settlement network designed to address critical inefficiencies in both traditional financial markets and cryptocurrency trading. The current clearing landscape suffers from fragmented capital allocation, restrictive prime brokerage relationships, and prolonged settlement timeframes in traditional finance, while cryptocurrency markets face challenges with over-collateralization, siloed lending pools, and security risks from centralized exchanges.

We introduce a settlement system that leverages Trusted Execution Environments (TEEs) and threshold cryptography to enable secure, private, and efficient settlement of obligations between multiple parties. The system utilizes a distributed key generation model and novel clearing mechanisms to optimize capital efficiency through multilateral netting, while maintaining strong privacy guarantees and regulatory compliance capabilities. By combining TEE-based security with advanced cryptographic protocols, including zero-knowledge proofs and sparse Merkle trees for data verification, our solution enables efficient cross-venue and cross-chain settlement while protecting sensitive trading information. This approach significantly reduces capital requirements for market participants, optimizes transaction costs, and provides institutional-grade clearing infrastructure without compromising on security or privacy. The system's architecture ensures that no single party has complete access to transaction details while maintaining auditability through a distributed backup network, offering a practical solution for institutional adoption of on-chain settlement.

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

We present new techniques for garbling mixed arithmetic and boolean circuits, utilizing the homomorphic secret sharing scheme introduced by Roy \& Singh (Crypto 2021), along with the half-tree protocol developed by Guo et al (Eurocrypt 2023). Compared to some two-party interactive protocols, our mixed garbling only requires several times $(<10)$ more communication cost.

We construct the bit decomposition/composition gadgets with communication cost $O((\lambda+\lambda_{\text{DCR}}/k)b)$ for integers in the range $(-2^{b-1}, 2^{b-1})$, requiring $O(2^k)$ computations for the GGM-tree. Our approach is compatible with constant-rate multiplication protocols, and the cost decreases as $k$ increases. Even for a small $k=8$, the concrete efficiency ranges from $6\lambda b$ ($b \geq 1000$ bits) to $9\lambda b$ ($b \sim 100$ bits) per decomposition/composition. In addition, we develop the efficient gadgets for mod $q$ and unsigned truncation based on bit decomposition and composition.

We construct efficient arithmetic gadgets over various domains. For bound integers, we improve the multiplication rate in the work of Meyer et al. (TCC 2024) from $\textstyle\frac{\zeta-2}{\zeta+1}$ to $\frac{\zeta-2}{\zeta}$. We propose new garbling schemes over other domains through bounded integers with our modular and truncation gadgets, which is more efficient than previous constructions. For $\mathbb{Z}_{2^b}$, additions and multiplication can be garbled with a communication cost comparable to our bit decomposition. For general finite field $\mathbb{F}_{p^n}$, particularly for large values of $p$ and $n$, we garble the addition and multiplication at the cost of $O((\lambda+\lambda_{\text{DCR}}/k)b)$, where $b = n\lceil \log p \rceil$. For applications to real numbers, we introduce an ``error-based'' truncation that makes the cost of multiplication dependent solely on the desired precision.