International Association
for Cryptologic Research

Aggregation of message authentication codes (MACs) is a proven and efficient method to preserve valuable bandwidth in resource-constrained environments: Instead of appending a long authentication tag to each message, the integrity protection of multiple messages is aggregated into a single tag. However, while such aggregation saves bandwidth, a single lost message typically means that authentication information for multiple messages cannot be verified anymore. With the significant increase of bandwidth-constrained lossy communication, as applications shift towards wireless channels, it thus becomes paramount to study the impact of packet loss on the diverse MAC aggregation schemes proposed over the past 15 years to assess when and how to aggregate message authentication. Therefore, we empirically study all relevant MAC aggregation schemes in the context of lossy channels, investigating achievable goodput improvements, the resulting verification delays, processing overhead, and resilience to denial-of-service attacks. Our analysis shows the importance of carefully choosing and configuring MAC aggregation, as selecting and correctly parameterizing the right scheme can, e.g., improve goodput by 39% to 444%, depending on the scenario. However, since no aggregation scheme performs best in all scenarios, we provide guidelines for network operators to select optimal schemes and parameterizations suiting specific network settings.

You can now submit your papers to the very first edition of the IACR Communications in Cryptology.

Submission deadline: Jan 8, 2024 at 11:59pm Anywhere on Earth (AoE).

The Lund Crypto and Security Group offers four new PhD positions, two in cryptography and two in computer security.

The research topics include side-channel attacks on symmetric and post-quantum cryptographic algorithms, the mathematical foundations of fully homomorphic encryption (FHE) and its safe implementation, and security for dynamic resource allocation in next-generation mobile networks. Senior researchers will be active in the projects and provide supervision.

The main duties of doctoral students are to devote themselves to their research studies, which includes participating in research projects and third cycle courses. The work duties will also include teaching and other departmental duties (no more than 20%).

Third-cycle studies at LTH consist of full-time studies for 4 years. A doctoral studentship is a fixed-term employment of a maximum of 5 years (including 20% departmental duties).

More information can be found in: https://lu.varbi.com/what:job/jobID:679799/

Closing date for applications:

Contact: Christian Gehrmann (christian.gehrmann@eit.lth.se); Thomas Johansson (thomas.johansson@eit.lth.se)

More information: https://lu.varbi.com/what:job/jobID:679799/

Do you live in the terminal? Do you like programming? Do you enjoy tinkering with rando embedded devices? Do you have a passion for security geared towards one or more of these topics?

• side-channel analysis
• applied cryptography
• software security
• hardware-assisted security

If so, this might be the right opportunity for you! To apply for this fully-funded position, please e-mail your motivation letter, CV, and transcript.

Closing date for applications:

Contact: Billy Brumley (bbbics at rit dot edu)

The Universitat Oberta de Catalunya (UOC) is a leading university of quality online education that is rooted in Barcelona and open to the world. It offers people lifelong learning to help them and society advance, while carrying out research into the knowledge society. It is the 2nd Spanish-speaking online educational institution in the world with more than 80.000 students in the academic year 2022/2023.

KISON is a research group focused on creating technologies for the protection of the security of networks, the information transmitted through them and the privacy of their users. The KISON group research lines focus on the compatibility of the security of decentralized networks (e.g. ad-hoc, IoT networks, 5G/6G) and the protection of information in the Internet (especially multimedia contents) with users' rights to privacy.

Applications are invited for a 3-year predoctoral grant in the Network and Information Technologies doctoral programme. Reserach lines are:

Cybersecurity in 5G/6G networks

Security in Cyber-physical Systems

User-centered privacy-enhancing technologies

Security and Privacy in the Internet of Things

Digital media security, privacy and forensics

Blockchain

Malware Detection Using Machine Learning Algorithms

Tampering detection in multimedia content

Digital Chain of Custody in computer forensics

More details on research lines:
https://www.uoc.edu/portal/en/escola-doctorat/linies-recerca/linies-nit/information-network/index.html

The candidate should have completed his/her master´s degree by July 2024 in computer science, telecommunications, or a related area.
The starting date will be Sept. 2024.

Full details:
https://www.uoc.edu/portal/en/escola-doctorat/beques/beques-uoc-escola-doctorat/index.html
Deadline: 12/02/2024

Closing date for applications:

Contact: Helena Rifà-Pous

More information: https://www.uoc.edu/en/studies/doctorates/doctorate-technologies-information-networks

We are looking for a Doctoral researcher in lattice-based cryptography located at the Aalto University Otaniemi campus.

Broadly, the PhD study may include the following depending on the skills and interests of the candidate: studying the hardness and relations of underlying mathematical problems, constructing and analysing lattice-based cryptographic schemes, proving theoretical impossibilities, implementing software libraries, performing concrete efficiency evaluation, etc.

We are looking for candidates who have recently completed, or will soon complete, a Master’s degree in cryptography, mathematics, computer science, or other relevant fields of studies. The success candidate will have strong background in mathematics and computer science, especially in areas relevant to the position. Good communication skills and fluent written and spoken English are required.

To apply, please visit:
https://aalto.wd3.myworkdayjobs.com/aalto/job/Otaniemi-Espoo-Finland/Doctoral-Researcher-in-Lattice-based-Cryptography_R38062

Closing date for applications:

Contact:
Russell Lai, e-mail "firstname.lastname@aalto.fi" (research related information)
Susanna Holma, e-mail "firstname.lastname@aalto.fi" (recruitment process)

More information: https://aalto.wd3.myworkdayjobs.com/aalto/job/Otaniemi-Espoo-Finland/Doctoral-Researcher-in-Lattice-based-Cryptography_R38062

In this work, we introduce FANNG-MPC, a versatile secure multi-party computation framework capable to offer active security for privacy preserving machine learning as a service (MLaaS). Derived from the now deprecated SCALE-MAMBA, FANNG is a data-oriented fork, featuring novel set of libraries and instructions for realizing private neural networks, effectively reviving the popular framework. To the best of our knowledge, FANNG is the first MPC framework to offer actively secure MLaaS in the dishonest majority setting, specifically two parties.

FANNG goes beyond SCALE-MAMBA by decoupling offline and online phases and materializing the dealer model in software, enabling a separate set of entities to produce offline material. The framework incorporates database support, a new instruction set for pre-processed material, including garbled circuits and convolutional and matrix multiplication triples. FANNG also implements novel private comparison protocols and an optimized library supporting Neural Network functionality. All our theoretical claims are substantiated by an extensive evaluation using an open-sourced implementation, including the private evaluation of popular neural networks like LeNet and VGG16.

Private computation of nonlinear functions, such as Rectified Linear Units (ReLUs) and max-pooling operations, in deep neural networks (DNNs) poses significant challenges in terms of storage, bandwidth, and time consumption. To address these challenges, there has been a growing interest in utilizing privacy-preserving techniques that leverage polynomial activation functions and kernelized convolutions as alternatives to traditional ReLUs. However, these alternative approaches often suffer from a trade-off between achieving faster private inference (PI) and sacrificing model accuracy. In particular, when applied to much deeper networks, these methods encounter training instabilities, leading to issues like exploding gradients (resulting in NaNs) or suboptimal approximations. In this study, we focus on PolyKervNets, a technique known for offering improved dynamic approximations in smaller networks but still facing instabilities in larger and more complex networks. Our primary objective is to empirically explore optimization-based training recipes to enhance the performance of PolyKervNets in larger networks. By doing so, we aim to potentially eliminate the need for traditional nonlinear activation functions, thereby advancing the state-of-the-art in privacy-preserving deep neural network architectures.

In this brief note, we flesh out some details of the recently proposed Simplex atomic broadcast protocol, and modify it so that leaders disperse blocks in a more communication efficient fashion, while maintaining the simplicity and excellent latency characteristics of the protocol.

Cryptocurrency networks crucially rely on digital signature schemes, which are used as an authentication mechanism for transactions. Unfortunately, most major cryptocurrencies today, including Bitcoin and Ethereum, employ signature schemes that are susceptible to quantum adversaries, i.e., an adversary with access to a quantum computer can forge signatures and thereby spend coins of honest users. In cryptocurrency networks, signature schemes are typically not executed in isolation, but within a so-called cryptographic wallet. In order to achieve security against quantum adversaries, the signature scheme and the cryptographic wallet must withstand quantum attacks.

In this work, we advance the study on post-quantum secure signature and wallet schemes. That is, we provide the first formal model for deterministic threshold wallets and we show a generic post-quantum secure construction from any post-quantum secure threshold signature scheme with rerandomizable keys. We then instantiate our construction from the isogeny-based signature scheme CSI-FiSh and we show that our instantiation significantly improves over prior work.

In this work, we present the first low-latency, second-order masked hardware implementation of Ascon that requires no fresh randomness using only $d+1$ shares. Our results significantly outperform any publicly known second-order masked implementations of AES and Ascon in terms of combined area, latency and randomness requirements. Ascon is a family of lightweight authenticated encryption and hashing schemes selected by NIST for standardization. Ascon is tailored for small form factors. It requires less power and energy while attaining the same or even better performance than current NIST standards. We achieve the reduction of latency by rearranging the linear layers of the Ascon permutation in a round-based implementation. We provide an improved technique to achieve implementations without the need for fresh randomness. It is based on the concept of changing of the guards extended to the second-order case. Together with the reduction of latency, we need to consider a large set of additional conditions which we propose to solve using a SAT solver. We have formally verified both, our first- and second-order implementations of Ascon using CocoAlma for the first two rounds. Additionally, we have performed a leakage assessment using t-tests on all 12 rounds of the initial permutation. Finally, we provide a comparison of our second-order masked Ascon implementation with other results.

In this report, we perform an in-depth analysis of the RSA authentication feature used in the secure boot procedure of Xilinx Zynq-7000 SoC device. The First Stage Boot Loader (FSBL) is a critical piece of software executed during secure boot, which utilizes the RSA authentication feature to validate all the hardware and software partitions to be mounted on the device. We analyzed the implementation of FSBL (provided by Xilinx) for the Zynq-7000 SoC and identified a critical security flaw, whose exploitation makes it possible to load an unauthenticated application onto the Zynq device, thereby bypassing RSA authentication. We also experimentally validated the presence of the vulnerability through a Proof of Concept (PoC) attack to successfully mount an unauthenticated software application on an RSA authenticated Zynq device. The identified flaw is only present in the FSBL software and thus can be easily fixed through appropriate modification of the FSBL software. Thus, the first contribution of our work is the identification of a critical security flaw in the FSBL software to bypass RSA authentication.

Upon bypassing RSA authentication, an attacker can mount any unauthenticated software application on the target device to mount a variety of attacks. Among the several possible attacks, we are interested to perform recovery of the encrypted bitstream in the target boot image of the Zynq-7000 device. To the best of our knowledge, there does not exist any prior work that has reported a practical bitstream recovery attack on the Zynq-7000 device. In the context of bitstream recovery, Ender et al. in 2020 proposed the Starbleed attack that is applicable to standalone Virtex-6 and 7-series Xilinx FPGAs. The design advisory provided by Xilinx as a response to the Starbleed attack claims that the Zynq-7000 SoC is resistant “due to the use of asymmetric and/or symmetric authentication in the boot/configuration process that ensures configuration is authenticated prior to use". Due to the security flaw found in the FSBL, we managed to identify a novel approach to mount the Starbleed attack on the Zynq-7000 device for full bitstream recovery. Thus, as a second contribution of our work, we present the first practical demonstration of the Starbleed attack on the Zynq-7000 SoC. We perform experimental validation of our proposed attacks on the PYNQ-Z1 platform based on the Zynq-7000 SoC.

The privacy-preserving machine learning (PPML) has gained growing importance over the last few years. One of the biggest challenges is to improve the efficiency of PPML so that the communication and computation costs of PPML are affordable for large machine learning models such as deep learning. As we know, linear algebra such as matrix multiplication occupies a significant part of the computation in the deep learning such as deep convolutional neural networks (CNN). Thus, it is desirable to propose the MPC protocol specialized for the matrix operations. In this work, we propose a dishonest majority MPC protocol over matrix rings which supports matrix multiplication and addition. Our MPC protocol can be seen as a variant of SPDZ protocol, i.e., the MAC and global key of our protocol are vectors of length $m$ and the secret of our protocol is an $m\times m$ matrix. Compared to the classic SPDZ protocol, our MPC protocol reduces the communication complexity by at least $m$ times. We also show that our MPC protocol is as efficient as [11] which also presented a dishonest majority MPC protocol specialized for matrix operations. The MPC protocol [11] resorts to the homomorphic encryption scheme (BFV scheme) to produce the matrix triples in the preprocessing phase. This implies that their protocol only supports the matrix operations over integer rings or prime fields of large size. On the contrary, we resort to vector oblivious linear evaluations and random vector oblivious linear evaluations to generate correlated randomness in the preprocessing phase. Thus, the matrices of our MPC protocol can be defined over any finite field or integer ring. Due to the small size of our MAC, the communication complexity of our MPC protocol remains almost the same regardless of the size of the field or the ring.

We introduce protocols for classical verification of quantum depth (CVQD). These protocols enable a classical verifier to differentiate between devices of varying quantum circuit depths, even in the presence of classical computation. The goal is to demonstrate that a classical verifier can reject a device with a quantum circuit depth of no more than $d$, even if the prover employs additional polynomial-time classical computation to deceive. Conversely, the verifier accepts a device with a quantum circuit depth of $d'>d$.

Previous results for separating hybrid quantum-classical computers with various quantum depths require either quantum access to oracles or interactions between the classical verifier and the quantum prover. However, instantiating oracle separations can significantly increase the quantum depth in general, and interaction challenges the quantum device to keep the qubits coherent while waiting for the verifier's messages. These requirements pose barriers to implementing the protocols on near-term devices.

In this work, we present a two-message protocol under the quantum hardness of learning with errors and the random oracle heuristic. An honest prover only needs classical access to the random oracle, and therefore any instantiation of the oracle does not increase the quantum depth. To our knowledge, our protocol is the first non-interactive CVQD, the instantiation of which using concrete hash functions, e.g., SHA-3, does not require additional quantum depth.

Our second protocol seeks to explore the minimality of cryptographic assumptions and the tightness of the separations. To accomplish this, we introduce an untrusted quantum machine that shares entanglements with the target machine. Utilizing a robust self-test, our protocol certifies the depth of the target machine with information-theoretic security and nearly optimal separation.

A failed hypothesis is reported here. The hope was that large matrices over small non-standard arithmetic are likely to have infeasible division, and furthermore be secure for use in Rabi–Sherman associative cryptography.

Enhancing privacy on smart contract-enabled blockchains has garnered much attention in recent research. Zero-knowledge proofs (ZKPs) is one of the most popular approaches, however, they fail to provide full expressiveness and fine-grained privacy. To illustrate this, we underscore an underexplored type of Miner Extractable Value (MEV), called Residual Bids Extractable Value (RBEV). Residual bids highlight the vulnerability where unfulfilled bids inadvertently reveal traders’ unmet demands and prospective trading strategies, thus exposing them to exploitation. ZKP-based approaches failed to ad- dress RBEV as they cannot provide post-execution privacy without some level of information disclosure. Other MEV mitigations like fair-ordering protocols also failed to address RBEV. We introduce Ratel, an innovative framework bridging a multi-party computation (MPC) prototyping framework (MP-SPDZ) and a smart contract language (Solidity), harmonizing the privacy with full expressiveness of MPC with Solidity ’s on-chain programmability. This synergy empowers developers to effortlessly craft privacy-preserving decentralized applications (DApps). We demonstrate Ratel’s efficacy through two distinguished decentralized finance (DeFi) applications: a decentralized exchange and a collateral auction, effectively mitigating the potential RBEV issue. Furthermore, Ratel is equipped with a lightweight crash-reset mechanism, enabling the seamless recovery of transiently benign faulty nodes. To prevent the crash-reset mechanism abused by malicious entities and ward off DoS attacks, we incorporate a cost-utility analysis anchored in the Bayesian approach. Our performance evaluation of the applications developed under the Ratel framework underscores their competency in managing real-world peak-time workloads.

Stablecoins are digital assets designed to maintain a consistent value relative to a reference point, serving as a vital component in Blockchain, and Decentralized Finance (DeFi) ecosystem. Typical implementations of stablecoins via smart contracts come with important downsides such as a questionable level of privacy, potentially high fees, and lack of scalability. We put forth a new design, PARScoin, for a Privacy-preserving, Auditable, and Regulation-friendly Stablecoin that mitigates these issues while enabling high performance both in terms of speed of settlement and for scaling to large numbers of users. Our construction is blockchain-agnostic and is analyzed in the Universal Composition (UC) framework, offering a secure and modular approach for its integration into the broader blockchain ecosystem.

In this work we introduce algebraic transition matrices as the basis for a new approach to integral cryptanalysis that unifies monomial trails (Hu et al., Asiacrypt 2020) and parity sets (Boura and Canteaut, Crypto 2016). Algebraic transition matrices allow for the computation of the algebraic normal form of a primitive based on the algebraic normal forms of its components by means of well-understood operations from linear algebra. The theory of algebraic transition matrices leads to better insight into the relation between integral properties of $F$ and $F^{−1}$. In addition, we show that the link between invariants and eigenvectors of correlation matrices (Beyne, Asiacrypt 2018) carries over to algebraic transition matrices. Finally, algebraic transition matrices suggest a generalized definition of integral properties that subsumes previous notions such as extended division properties (Lambin, Derbez and Fouque, DCC 2020). On the practical side, a new algorithm is described to search for these generalized properties and applied to Present, resulting in new properties. The algorithm can be instantiated with any existing automated search method for integral cryptanalysis.

Isogeny-based cryptography is an instance of post-quantum cryptography whose fundamental problem consists of finding an isogeny between two (isogenous) elliptic curves $E$ and $E'$. This problem is closely related to that of computing the endomorphism ring of an elliptic curve. Therefore, many isogeny-based protocols require the endomorphism ring of at least one of the curves involved to be unknown. In this paper, we explore the design of isogeny based protocols in a scenario where one assumes that the endomorphism ring of all the curves are public. In particular, we identify digital signatures based on proof of isogeny knowledge from SIDH squares as such a candidate. We explore the design choices for such constructions and propose two variants with practical instantiations. We analyze their security according to three lines, the first consists of attacks based on KLPT with both polynomial and superpolynomial adversary, the second consists of attacks derived from the SIDH attacks and finally we study the zero-knowledge property of the underlying proof of knowledge.

In "Oops, I did it again" - Security of One-Time Signatures under Two-Message Attacks, Bruinderink and Hülsing analyzed the effect of key reuse for several one time signature systems. When they analyzed the Winternitz system, they assumed certain probabilities were independent when they weren't, leading to invalid conclusions. This paper does a more correct characterization of the Winternitz scheme, and while their ultimate conclusion (that key reuse allows for practical forgeries) is correct, the situation is both better and worse than what they concluded.