International Association
for Cryptologic Research

Bulletproofs, introduced by Bünz, Bootle, Boneh, Poelstra, Wuille and Maxwell (IEEE S&P, 2018), is a highly efficient non-interactive argument system that does not require a trusted setup. Recently, Bünz (PhD Thesis, 2023) extended Bulletproofs to support arguments for rank-1 constraint satisfaction (R1CS) systems, a widely-used representation for arithmetic satisfiability problems. Although the argument system constructed by Bünz preserves the attractive properties of Bulletproofs, it presents a gap between its completeness and soundness guarantees: The system is complete for a restricted set of instances, but sound only for a significantly broader set. Although argument systems for such gap relations nevertheless provide clear and concrete guarantees, the gaps they introduce may lead to various inconsistencies or undesirable gaps within proofs of security, especially when used as building blocks within larger systems.

In this work we show that the argument system presented by Bünz can be extended to bridge the gap between its completeness and soundness, and to additionally provide honest-verifier zero-knowledge. For the extended argument system, we introduce a refined R1CS relation that captures the precise set of instances for which both completeness and soundness hold without resorting to a gap formulation. The extended argument system preserves the performance guarantees of the argument system presented by Bünz, and yields a non-interactive argument system using the Fiat-Shamir transform.

A Garbling Scheme is a fundamental cryptographic primitive, with numerous theoretical and practical applications. Since its inception by Yao (FOCS'82, '86), optimizing the communication and computation complexities of securely garbling circuits has been an area of active research. One such optimization, and perhaps the most fundamental, is the `Free-XOR' technique (Kolesnikov and Schneider, ICALP'08) which allows XOR gates in a function garbling to not require representation, and therefore communication.

Since then, several works have designed and analysed the security of schemes that adopt the Free-XOR optimisation. In particular: (1) Applebaum (JoC'16) proved that this can be securely instantiated assuming symmetric-key encryption satisfying a notion called RK-KDM security; and (2) Zahur, Rosulek and Evans (Eurocrypt'15) proposed the so-called `Half Gates' scheme, and proved that it can be instantiated assuming hash functions satisfying a notion called CCR security. Although both schemes have been proven selectively secure, prior work leaves it open to analyze whether they satisfy a stronger security notion -- adaptive security -- in the plain model.

In this work, we formally show that the selective security of these two schemes cannot be lifted to adaptive security under the same assumptions. To establish these barriers, we adopt techniques from the work of Kamath et al (Crypto'21), who proved similar negative results for Yao's garbling. We use that as a starting point and introduce new techniques tailored towards addressing Free-XOR-based schemes.

Event date: 3 May 2025

Event date: 8 December to 12 December 2025

Event date: 23 June to 26 June 2025
Submission deadline: 15 March 2025
Notification: 20 April 2025

The post-quantum cryptography research group at Monash University, Australia, has a fully funded postdoc opening for a research project funded by Australian Research Council - Discovery Projects 2025, including in particular the following areas:

• Developing tools and techniques for FHE-based private cloud computation applications.
• Theory and applications of zk-SNARKs in FHE-based cloud computation.
• Secure and Efficient Implementations of zk-SNARK and FHE schemes and their applications.

The candidate will have the opportunity to work in an excellent research environment and collaborate with experts in cryptography and with CryptoLab industry partners, as well as contributing to supervision and training of PhD students.

Monash University is among the leading universities in Australia and is located in Melbourne, ranked as Australia's most liveable city and among the most liveable cities in the world.

Applicants should have (or be expected to complete in the next 6 months) a PhD in mathematics, theoretical computer science, cryptography, engineering or closely related areas. Research experience in at least one of lattice-based cryptography, zero-knowledge proofs, or FHE is required.

The candidate should have excellent English verbal and written communication skills. Programming experience and skills, especially in Sagemath, Python, Magma, and/or C/C++, are also highly desirable.

To apply: Please apply by filling in the application form by 21st Apr 2025 at the following URL: https://forms.gle/YYZBb5uGwq4eGpT27

Closing date for applications:

Contact: Ron Steinfeld ([email protected])

We have an opening of multiple PhD and Post-Doc researchers at the Research Institute CODE in Munich, Germany. All positions are available for start from March/April 2025 and are fully funded at federal salary levels TV-ÖD E13/14. The researcher will work closely with Michael Hutter who will start a professorship in Embedded Systems Security. The candidate will have the opportunity to travel and tackle cutting-edge challenges currently facing the industry (e.g., PQShield). Candidates will also gain experience with supporting teaching activities.

We are seeking talented researchers with a strong interest and relevant experience in any of the following research areas:

• Applied cryptography with a focus on hardware and embedded systems security
• Physical attacks, side-channel leakage detection, fault analysis, hardware tampering, machine learning/deep learning/AI-driven techniques for SCA
• Secure and efficient implementations of cryptography, Post-Quantum Cryptography (PQC), privacy-preserving computing (MPC, FHE)
• ASIC/FPGA design security

Requirements:

• Master's degree or PhD in Computer Science, Information Security, etc.
• PostDoc candidates must have a strong track record
• High motivation for research work and ability to work independently
• Eager to disseminate research results through publications and presentations at top-tie conferences.
• Fluency in written and spoken English (German desirable but not required)

How to apply?
Send an email to Michael Hutter with subject "Application CODE" including your motivation letter, CV, transcripts of grades, and references.

Closing date for applications:

Contact: Prof. Michael Hutter (michutte [AT] gmail dot com)

Applications will be processed continuously until the positions are filled.

More information: https://www.unibw.de/code

We are recruiting one PhD student to conduct research in privacy-preserving post-quantum cryptography. The position is fully funded for up to four years, with attractive stipends and travel grants. Applicants are expected to have a Master's degree in cryptography (or a closely related field) and proficiency in English. Applications will be processed continuously until the position is filled.

Closing date for applications:

Contact: Please send your applications (CV, transcripts, contacts for references) to Dr Khoa Nguyen ([email protected]).

Temporary contract, 24 months, Esch-sur-Alzette/Belval, Luxembourg

Are you passionate about research? So are we! Come and join us
The Luxembourg Institute of Science and Technology (LIST) is a Research and Technology Organization (RTO) active in the fields of IT, materials and environment. By transforming scientific knowledge into technologies, smart data and tools, LIST empowers citizens in their choices, public authorities in their decisions and businesses in their strategies.
Do you want to know more about LIST? Check our website: https://www.list.lu/

How will you contribute?
We are looking for a motivated research engineer to support a project in the context of semi-autonomous cyber-range training and exercise scenario generation.
You will be mainly in charge of, but not limited to:

• Design and development of the architecture of a minimal testing platform for cyber range scenarios execution
• Design, development and integration of the semi-autonomous scenario generator tool
• Integration of threat intelligence sources for scenarios definition
• Prepare the tools and platform for deployment: running tests, designing, and developing APIs
• Contribution in design and develop cyber range training and exercise scenarios
• Test and validate the tools and platform on base of the selected scenarios
• Contribute to the writing of technical reports/project deliverables

Nationality/Eligibility
Due to the nature of this position the applicant must be from a NATO member country, from an EU EEA/EFTA country or from one of the following NATO Indo-Pacific partners: Australia, Japan, Republic of South Korea and New Zealand

Closing date for applications:

Contact: Carolina DE LEON

More information: https://app.skeeled.com/offer/c/67af2e8a307a1c35c03a5ccb?lang=en&show_description=true

We show a black box barrier against constructing public key quantum money from obfuscation for evasive functions. As current post-quantum obfuscators based on standard assumptions are all evasive, this shows a fundamental barrier to achieving public key quantum money from standard tools. Our impossibility applies to black box schemes where (1) obfuscation queries made by the mint are classical, and (2) the verifier only makes (possibly quantum) evaluation queries, but no obfuscation queries. This class seems to capture any natural method of using obfuscation to build quantum money.

The study of fine-grained cryptography has proliferated in recent years due to its allure of potentially relying on weaker assumptions compared to standard cryptography. As fine-grained cryptography only requires polynomial gaps between the adversary and honest parties, it seems plausible to build primitives relying upon popular hardness assumptions about problems in $\mathbf{P}$ such as $k$-$\mathsf{SUM}$ or $\mathsf{Zero}$-$k$-$\mathsf{Clique}$. The ultimate hope is that fine-grained cryptography could still be viable even if all current cryptographic assumptions are false, such as if $\mathbf{P} = \mathbf{NP}$ or if we live in Pessiland where one-way functions do not exist.

In our work, we consider whether this approach is viable by studying fine-grained complexity when all standard cryptographic assumptions are false. As our main result, we show that many popular fine-grained complexity problems are easy to solve in the average-case when one-way functions do not exist. In other words, many candidate hardness assumptions for building fine-grained cryptography are no longer options in Pessiland. As an example, we prove that the average-case $k$-$\mathsf{SUM}$ and $\mathsf{Zero}$-$k$-$\mathsf{Clique}$ conjectures are false for sufficiently large constant $k$ when no one-way functions exist. The average-case $\mathsf{Zero}$-$k$-$\mathsf{Clique}$ assumption was used to build fine-grained key-exchange by Lavigne et al. [CRYPTO'19].

We also show that barriers for reductions in fine-grained complexity may be explained by problems in cryptography. First, we show that finding faster algorithms for computing discrete logarithms is equivalent to designing average-case equivalence between $k$-$\mathsf{SUM}$ and $k$-$\mathsf{CYC}$ (an extension of $k$-$\mathsf{SUM}$ to cyclic groups). In particular, finding such a reduction from $k$-$\mathsf{CYC}$ to $k$-$\mathsf{SUM}$ could potentially lead to breakthrough algorithms for the discrete logarithm, factoring, RSA and quadratic residuosity problems. Finally, we show that discrete logarithms with preprocessing may be reduced to the $k$-$\mathsf{CYC}$-$\mathsf{Index}$ problem, and we present faster algorithms for average-case $k$-$\mathsf{SUM}$-$\mathsf{Index}$ and $k$-$\mathsf{CYC}$-$\mathsf{Index}$.

Broadcast encryption allows a user to encrypt a message to $N$ recipients with a ciphertext whose size scales sublinearly with $N$. The natural security notion for broadcast encryption is adaptive security which allows an adversary to choose the set of recipients after seeing the public parameters. Achieving adaptive security in broadcast encryption is challenging, and in the plain model, the primary technique is the celebrated dual-systems approach, which can be implemented over groups with bilinear maps. Unfortunately, it has been challenging to replicate the dual-systems approach in other settings (e.g., with lattices or witness encryption). Moreover, even if we focus on pairing-based constructions, the dual-systems framework critically relies on decisional (and source-group) assumptions. We do not have constructions of adaptively-secure broadcast encryption from search (or target-group) assumptions in the plain model.

Gentry and Waters (EUROCRYPT 2009) described a compiler that takes any semi-statically-secure broadcast encryption scheme and transforms it into an adaptively-secure scheme in the random oracle model. While semi-static security is easier to achieve and constructions are known from witness encryption as well as search (and target-group) assumptions on pairing groups, the transformed scheme relies on random oracles. In this work, we show that using publicly-sampleable projective PRGs, we can achieve adaptive security in the plain model. We then show how to build publicly-sampleable projective PRGs from many standard number-theoretic assumptions (e.g., CDH, LWE, RSA).

Our compiler yields the first adaptively-secure broadcast encryption scheme from search assumptions as well as the first such scheme from witness encryption in the plain model. We also obtain the first adaptively-secure pairing-based scheme in the plain model with $O_\lambda(N)$-size public keys and $O_\lambda(1)$-size ciphertexts (where $O_\lambda(\cdot)$ suppresses polynomial factors in the security parameter $\lambda$). Previous adaptively-secure pairing-based schemes in the plain model with $O_\lambda(1)$-size ciphertexts required $O_\lambda(N^2)$-size public keys.

In many areas of cybersecurity, we require access to Personally Identifiable Information (PII), such as names, postal addresses and email addresses. Unfortunately, this can lead to data breaches, especially in relation to data compliance regulations such as GDPR. An IP address is a typical identifier which is used to map a network address to a person. Thus, in applications which are privacy-aware, we may aim to hide the IP address while aiming to determine if the address comes from a blacklist. One solution to this is to use homomorphic encryption to match an encrypted version of an IP address to a blacklisted network list. This matching allows us to encrypt the IP address and match it to an encrypted version of a blacklist. In this paper, we use the OpenFHE library \cite{OpenFHE} to convert network addresses into the BFV homomorphic encryption method. In order to assess the performance impact of BFV, it implements a matching method using the OpenFHE library and compares this against the partial homomorphic methods of Paillier, Damgard-Jurik, Okamoto-Uchiyama, Naccache-Stern and Benaloh. The main findings are that the BFV method compares favourably against the partial homomorphic methods in most cases.

The Pointer Authentication Code ($\textsf{PAC}$) feature in the Arm architecture is used to enforce the Code Flow Integrity ($\textsf{CFI}$) of running programs. It does so by generating a short $\textsf{MAC}$ - called the $\textsf{PAC}$ - of the return address and some additional context information upon function entry, and checking it upon exit. An attacker that wants to overwrite the stack with manipulated addresses now faces an additional hurdle, as they now have to guess, forge, or reuse $\textsf{PAC}$ values. $\textsf{PAC}$ is deployed on billions of devices as a first line of defense to harden system software and complex programs against software exploitation.

The original version of the feature uses a 12-round version the $\textsf{QARMA-64}$ block cipher. The output is then truncated to between 3 and 32 bits, in order to be inserted into unused bits of 64-bit pointers. A later revision of the specification allows the use of an 8-round version of $\textsf{QARMA-64}$. This reduction may introduce vulnerabilities such as high-probability distinguishers, potentially enabling key recovery attacks. The present paper explores this avenue.

A cryptanalysis of the $\textsf{PAC}$ computation function entails restricting the inputs to valid virtual addresses, meaning that certain most significant bits are fixed to zero, and considering only the truncated output. Within these constraints, we present practical attacks on various $\textsf{PAC}$ configurations. These attacks, while not presenting immediate threat to the $\textsf{PAC}$ mechanism, show that some versions of the feature do miss the security targets made for the original function. This offers new insights into the practical security of constructing $\textsf{MAC}$ from truncated block ciphers, expanding on the mostly theoretical understanding of creating PRFs from truncated PRPs.

We note that the results do not affect the security of $\textsf{QARMA-64}$ when used with the recommended number of rounds for general purpose applications.

Recent applications and attacks have highlighted the need for authenticated encryption (AE) schemes to achieve the so-called committing security beyond privacy and authenticity. As a result, several generic solutions have been proposed to transform a non-committing AE scheme to a committing one, for both basic unique-nonce security and advanced misuse-resistant (MR) security. We observe that all existing practical generic transforms are subject to at least one of the following limitations: (i) not committing to the entire encryption context, (ii) involving non-standard primitives, (iii) not being a black-box transform, (iv) providing limited committing security. Furthermore, so far, there has been no generic transform that can directly elevate a basic AE scheme to a committing AE scheme that offers MR security. Our work fills these gaps by developing black-box generic transforms that crucially rely on hash functions, which are well standardized and widely deployed.

First, we construct three basic transforms that combine AE with a single hash function, which we call $\mathsf{HtAE}, \mathsf{AEaH}$ and $\mathsf{EtH}$. They all guarantee strong security, and $\mathsf{EtH}$ can be applied to both AE and basic privacy-only encryption schemes. Next, for MR security, we propose two advanced hash-based transforms that we call $\mathsf{AEtH}$ and $\mathsf{chaSIV}$. $\mathsf{AEtH}$ is an MRAE-preserving transform that adds committing security to an MR-secure AE scheme. $\mathsf{chaSIV}$ is the first generic transform that can directly elevate basic AE to one with both committing and MR security; moreover, $\mathsf{chaSIV}$ also works with arbitrary privacy-only encryption schemes. Both of them feature a simple design and ensure strong security.

For performance evaluation, we compare our transforms to similar existing ones, both in theory and through practical implementations. The results show that our $\mathsf{AEaH}$ achieves the highest practical efficiency among basic transforms, while $\mathsf{AEtH}$ excels in MRAE-preserving transforms. Our MRAE-lifting transform $\mathsf{chaSIV}$ demonstrates comparable performance to MRAE-preserving ones and surpasses them for messages larger than approximately $360$ bytes; for longer messages, it even outperforms the benchmark, non-committing standardized $\mathsf{AES}\text{-}\mathsf{GCM}\text{-}\mathsf{SIV}$.

This paper presents a novel single-trace side-channel attack on FALCON—a lattice-based post-quantum digital signature protocol recently approved for standardization by NIST. We target the discrete Gaussian sampling operation within the FALCON key generation scheme and use a single power measurement trace to succeed. Notably, negating the ‘shift right 63-bit’ operation (for 64-bit values) leaks critical information about the ‘-1’ vs. ‘0’ assignments to intermediate coefficients. These leaks enable full recovery of the generated secret keys. The proposed attack is simulated on the ELMO simulator running both reference and optimized software implementation from FALCON’s NIST Round 3 package. Statistical analysis with 20k tests reveals a full key-recovery success rate of 100% for FALCON-512. This work highlights the vulnerability of current software solutions to single-trace attacks and underscores the urgent need to develop single-trace resilient software for embedded systems in the presilicon phase.

A secret sharing scheme allows a trusted dealer to divide a secret among multiple parties so that a sufficient number of them can recover the secret, while a smaller group cannot. In CRYPTO'21, Goyal, Song, and Srinivasan introduced Traceable Secret Sharing (TSS), which enhances traditional secret sharing by enabling the identification of parties involved in secret reconstruction, deterring malicious behavior like selling shares. Recently, Boneh, Partap, and Rotem (CRYPTO'24) presented two more efficient TSS schemes. However, these existing TSS schemes assume that all distributed shares are valid and shareholders act honestly during the secret reconstruction phase. In this paper, we introduce Traceable Verifiable Secret Sharing (TVSS), a concept designed to ensure both traceability and verifiability in the face of malicious actions by either the dealer or shareholders. We propose a general strategy for transforming a Shamir-based, computationally secure Verifiable Secret Sharing (VSS) scheme into an efficient TVSS scheme. Building on this strategy, we construct two practical TVSS schemes in the honest-majority setting, based on well-known VSS schemes proposed by Feldman (SFCS'87) and Pedersen (CRYPTO'91). Our proposed TVSS schemes retain public shareholder indexes, enhancing flexibility in designing accountable threshold protocols (e.g., Distributed Key Generation protocols) using TVSS. Compared to the original VSS schemes, the individual share size in the new TVSS schemes increases by only a single field element and is just two or three times the size of the main secret. Motivated by a recent study on Accountable Threshold Cryptosystems (ATCs) by Boneh, Partap, and Rotem (CRYPTO'24), and by leveraging our proposed Feldman-based TVSS scheme, we also introduce an efficient ATC based on ElGamal cryptosystem. This new ATC enables a tracer to uniquely identify the parties involved in the decryption process while introducing minimal overhead to existing actively secure (and/or robust) threshold protocols built on the ElGamal cryptosystem.

We present PIR protocols for offline/online two-server setting where a client $C$ wants to privately retrieve a batch of entries from database of size $N$ by interacting with a servers $S_1$. The client has interacted with a server $S_2$ ahead of time, not colluding with $S_1$. We present simple protocols based on one-way functions that substantially improve on the query complexity or runtime over existing works. Concrete instantiations of our general paradigm lead to batch PIR protocols with the following parameters: - A protocol for batches of $\sqrt{N}$, where $C,S_1$, and $S_2$ each spend a total of $\tilde{O}(N)$ work and exchange $\tilde{O}(\sqrt{N})$ bits of communication. This yields an amortized complexity of $\tilde{O}(\sqrt{N})$ work and $\tilde{O}(1)$ communication per query in the batch. - A more balanced protocol for batches of size $N^{1/3}$ in which $C$ spends a total of $\tilde{O}(N^{2/3})$ work, $S_1$ and $S_2$ spend $\tilde{O}(N)$ work, and the total communication is of size $\tilde{O}(N^{2/3})$. Our protocols have immediate applications such as Private Set Intersection (PSI) in the two-server setting with preprocessing and unbalanced set sizes.

We introduce $\mathsf{Zinc}$, a hash-based succinct argument for integer arithmetic. $\mathsf{Zinc}$'s goal is to provide a practically efficient scheme that bypasses the arithmetization overheads that many succinct arguments present. These overheads can be of orders of magnitude in many applications. By enabling proving statements over the integers, we are able to arithmetize many operations of interest with almost no overhead. This includes modular operations involving any moduli, not necessarily prime, and possibly involving multiple moduli in the same statement. In particular, $\mathsf{Zinc}$ allows to prove statements for the ring $\mathbb{Z}/n\mathbb{Z}$ for arbitrary $n\geq 1$. Importantly, and departing from prior work, our schemes are purely code and hash-based, and do not require hidden order groups. In its final form, $\mathsf{Zinc}$ operates similarly to other hash-based schemes using Brakedown as their PCS, and at the same time it benefits from the arithmetization perks brought by working over $\mathbb{Z}$ (and $\mathbb{Q}$) natively.

At its core, $\mathsf{Zinc}$ is a succinct argument for proving relations over the rational numbers $\mathbb{Q}$, even though when applied to integer statements, an honest prover and verifier will only operate with small integers. $\mathsf{Zinc}$ consists of two main components: 1) $\mathsf{Zinc}$-$\mathsf{PIOP}$, a framework for proving algebraic statements over the rationals by reducing modulo a randomly chosen prime $q$, followed by running a suitable PIOP over $\mathbb{F}_q$ (this is similar to the approach taken in prior works, with the difference that we use localizations of $\mathbb{Q}$ to enable prime modular projection); and 2) $\mathsf{Zip}$, a Brakedown-type polynomial commitment scheme built from an IOP of proximity to the integers, a novel primitive that we introduce. The latter primitive guarantees that a prover is using a polynomial with coefficients close to being integral. With these two primitives in place, one can use a lookup argument over the rationals to ensure that the witness contains only integer elements.

SCARF is a tweakable block cipher dedicated to cache address randomization, proposed at the USENIX Security conference. It has a 10-bit block, 48-bit tweak, and 240-bit key. SCARF is aggressively optimized to meet the harsh latency constraints of cache address randomization, and uses a dedicated model for its security claim. The full version of SCARF has 8 rounds, and its designers claim security up to $2^{40}$ queries and $2^{80}$ computations. In this work we present a distinguisher against 6-round SCARF under the collision model with time and query complexity $2^{30}$, and a key-recovery attack against the full 8-round SCARF under the encryption-decryption model with $2^{39}$ queries and time $2^{76.2}$. As part of the attack, we present a novel method to compute the minimal number of right pairs following a differential characteristic when the input pairs are restricted to a subspace of the domain of the primitive.