Cryptography

Algebraic persistent fault analysis (APFA) combines algebraic analysis with persistent fault analysis, providing a novel approach for examining block cipher implementation security. Since its introduction, APFA has attracted considerable attention. Traditionally, APFA has assumed that fault injection occurs solely within the S-box during the encryption process. Yet, algorithms like PRESENT and AES also utilize S-boxes in the key scheduling phase, sharing the same S-box implementation as encryption. This presents a previously unaddressed challenge for APFA. In this work, we extend APFA’s fault injection and analysis capabilities to encompass the key scheduling stage, validating our approach on PRESENT. Our experimental findings indicate that APFA continues to be a viable approach. However, due to faults arising during the key scheduling process, the number of feasible candidate keys does not converge. To address this challenge, we expanded the depth of our fault analysis without increasing the number of faulty ciphertexts, effectively narrowing the key search space to near-uniqueness. By employing a compact S-box modeling approach, we were able to construct more concise algebraic equations with solving efficiency improvements ranging from tens to hundreds of times for PRESENT, SKINNY and CRAFT block ciphers. The efficiency gains became even more pronounced as the depth of the fault leakage increased, demonstrating the robustness and scalability of our approach. Full article

Virtual reality (VR)/the metaverse is transforming into a ubiquitous technology by leveraging smart devices to provide highly immersive experiences at an affordable price. Cryptographically securing such augmented reality schemes is of paramount importance. Securely transferring the same secret key, i.e., obfuscated, between several parties is the main issue with symmetric cryptography, the workhorse of modern cryptography, because of its ease of use and quick speed. Typically, asymmetric cryptography establishes a shared secret between parties, after which the switch to symmetric encryption can be made. However, several SoTA (State-of-The-Art) security research schemes lack flexibility and scalability for industrial Internet-of-Things (IoT)-sized applications. In this paper, we present the full architecture of the PRIVocular framework. PRIVocular (i.e., PRIV(acy)-ocular) is a VR-ready hardware–software integrated system that is capable of visually transmitting user data over three versatile modes of encapsulation, encrypted—without loss of generality—using an asymmetric-key cryptosystem. These operation modes can be optical character-based or QR-tag-based. Encryption and decryption primarily depend on each mode’s success ratio of correct encoding and decoding. We investigate the most efficient means of ocular (encrypted) data transfer by considering several designs and contributing to each framework component. Our pre-prototyped framework can provide such privacy preservation (namely virtual proof of privacy (VPP)) and visually secure data transfer promptly (<1000 ms), as well as the physical distance of the smart glasses (∼50 cm). Full article

The development of Smart Grids (SGs) is a current trend and an indispensable essential living requirement. Due to economic development and improved quality of life, electricity demand has rapidly increased. However, the power grids in major cities have become outdated, leading to uneven power distribution and frequent power outages. SGs can adjust distribution strategies based on consumers’ real-time electricity demands, which requires continuous transmission of consumer electricity data within the grid. If the privacy and security of these data cannot be ensured, consumers’ habits will be exposed, and unnecessary waste may occur. In this article, we propose a key distribution process based on QKD, enabling entities within the SG to encrypt and authenticate each other’s data, ensuring the security and privacy of communication channels and transmitted data. Full article

We present a new construction of a one-time pad (OTP) with inherent diffusive properties and a redundancy injection mechanism that benefits from them. The construction is based on interpreting the plaintext and key as members of a permutation group in the Lehmer code representation after conversion to factoradic. The so-constructed OTP translates any perturbation of the ciphertext to an unpredictable, metrically large random perturbation of the plaintext. This allows us to provide unconditional integrity assurance without extra key material. The redundancy is injected using Foata’s “pun”: the reading of the one-line representation as the cyclic one; we call this Pseudo Foata Injection. We obtain algorithms of quadratic complexity that implement both mechanisms. Full article

This paper presents a new encryption technique, which combines affine ciphers and the residue number system. This makes it possible to eliminate the shortcomings and vulnerabilities of affine ciphers, which are sensitive to cryptanalysis, using the advantages of the residue number system, i.e., the parallelization of calculation processes, performing operations on low bit numbers, and the linear combination of encrypted residues. A mathematical apparatus and a graphic scheme of affine encryption using the residue number system is developed, and a corresponding example is given. Special cases of affine ciphers such as shift and linear ciphers are considered. The cryptographic strength of the proposed cryptosystem when the moduli are prime numbers is estimated, and an example of its estimation is given. The number of bits and the number of moduli of the residue number system, which ensure the same cryptographic strength as the longest key of the AES algorithm, are determined. Full article

We present a detailed analysis of the effect of quantum loss and decoherence in the Bell-CHSH scenario. Adopting a device-independent approach, we study the change in the bipartite conditional probability distribution, i.e., the behavior of the realized nonlocal box pair when the elements of the entangled qubit pair subjected to independent noisy quantum channels modeled by completely positive maps. As the verification of Bell inequalities is crucial in device-independent quantum cryptography, our considerations are instructive from the perspective of quantum realizations of nonlocal box pairs. We find that the impact of quantum channels cannot be described by an equivalent classical noise channel. Full article

Healthcare data is often fragmented across different institutions (hospitals, clinics, research centers), creating data silos. Privacy-enhancing technologies (PETs) play a fundamental role in collaborative healthcare analysis, enabling healthcare providers to improve care while protecting patient privacy. By providing a compliant framework for data sharing and research, PETs facilitate collaboration while adhering to stringent regulations like HIPAA and GDPR. This work conducts a comprehensive survey to investigate PETs in healthcare industry. It investigates the privacy requirements and challenges specific to healthcare, and the key enabling PETs are explored. A review of recent research trends that identify challenges, and AI related concerns is presented. Full article

Threshold Multi-Party Private Set Intersection (TMP-PSI) is a cryptographic protocol that enables an element from the receiver’s set to be included in the intersection result if it appears in the sets of at least $t-1$ other participants, where t represents the threshold. This protocol is crucial for a variety of applications, such as anonymous electronic voting, online ride-sharing, and close-contact tracing programs. However, most existing TMP-PSI schemes are designed based on threshold homomorphic encryption, which faces significant challenges, including low computational efficiency and a high number of communication rounds. To overcome these limitations, this study introduces the Threshold Oblivious Pseudo-Random Function (tOPRF) to fulfill the requirements of threshold encryption and decryption. Additionally, we extend the concept of the Oblivious Programmable Pseudo-Random Function (OPPRF) to develop a novel cryptographic primitive termed the Partially OPPRF (P-OPPRF). This new primitive retains the critical properties of obliviousness and randomness, along with the security assurances inherited from the OPPRF, while also offering strong resistance against malicious adversaries. Leveraging this primitive, we propose the first malicious-secure TMP-PSI protocol, named QMP-PSI, specifically designed for applications like anonymous electronic voting systems. The protocol effectively counters collusion attacks among multiple parties, ensuring robust security in multi-party environments. To further enhance voting efficiency, this work presents a cloud-assisted QMP-PSI to outsource the computationally intensive phases. This ensures that the computational overhead for participants is solely dependent on the set size and statistical security parameters, thereby maintaining security while significantly reducing the computational burden on voting participants. Finally, this work validates the protocol’s performance through extensive experiments under various set sizes, participant numbers, and threshold values. The results demonstrate that the protocol surpasses existing schemes, achieving state-of-the-art (SOTA) performance in communication overhead. Notably, in small-scale voting scenarios, it exhibits exceptional performance, particularly when the threshold is small or close to the number of participants. Full article

Scalability and security restrictions are posing new challenges for blockchain networks, especially in the face of Distributed Denial-of-Service (DDoS) attacks and upcoming quantum threats. Previous research also found that post-quantum blockchains, despite their improved cryptographic algorithms, are still vulnerable to DDoS attacks, emphasizing the need for more resilient architectural solutions. This research studies the use of dynamic sharding, an innovative approach for post-quantum blockchains that allows for adaptive division of the network into shards based on workload and network conditions. Unlike static sharding, dynamic sharding optimizes resource allocation in real time, increasing transaction throughput and minimizing DDoS-induced disruptions. We provide a detailed study using Monte Carlo simulations to examine transaction success rates, resource consumption, and fault tolerance for both dynamic sharding-based and non-sharded post-quantum blockchains under simulated DDoS attack scenarios. The findings show that dynamic sharding leads to higher transaction success rates and more efficient resource use than non-sharded infrastructures, even in high-intensity attack scenarios. Furthermore, the combination of dynamic sharding and the Falcon post-quantum signature technique creates a layered strategy that combines cryptographic robustness, scalability, and resilience. This paper provides light on the potential of adaptive blockchain designs to address major scalability and security issues, opening the path for quantum-resilient systems. Full article

Substitution boxes (S-Boxes) function as essential nonlinear elements in contemporary cryptographic systems, offering robust protection against cryptanalytic attacks. This study presents a novel technique for generating compact 8-bit S-Boxes based on multiplication in the Galois Field $GF\left(2^4\right)$. The goal of this method is to create S-Boxes with low hardware implementation cost while ensuring cryptographic properties. Experimental results indicate that the suggested S-Boxes achieve a nonlinearity value of 112, matching the AES S-Box. They also maintain other cryptographic properties, such as the Bit Independence Criterion (BIC), the Strict Avalanche Criterion (SAC), Differential Approximation Probability, and Linear Approximation Probability, within acceptable security thresholds. Notably, compared to existing studies, the proposed S-Box architecture demonstrates enhanced hardware efficiency, significantly reducing resource utilization in implementations. Specifically, the implementation cost of the S-Box consists of 31 XOR gates, 32 two-input AND gates, 6 two-input OR gates, and 2 MUX21s. Moreover, this work provides a thorough assessment of the S-Box, covering cryptographic properties, side channel attacks, and implementation aspects. Furthermore, the study estimates the quantum resource requirements for implementing the S-Box, including an analysis of CNOT, Toffoli, and NOT gate counts. Full article

Popular technologies such as blockchain and zero-knowledge proof, which have already entered the enterprise space, heavily use cryptography as the core of their protocol stack. One of the most used systems in this regard is Elliptic Curve Cryptography, precisely the point multiplication operation, which provides the security assumption for all applications that use this system. As this operation is computationally intensive, one solution is to offload it to specialized accelerators to provide better throughput and increased efficiency. In this paper, we explore the use of Field Programmable Gate Arrays (FPGAs) and the High-Level Synthesis framework of AMD Vitis in designing an elliptic curve point arithmetic unit (point adder) for the secp256k1 curve. We show how task-level parallel programming and data streaming are used in designing a RISC processor-like architecture to provide pipeline parallelism and increase the throughput of the point adder unit. We also show how to efficiently use the proposed processor architecture by designing a point multiplication scheduler capable of scheduling multiple batches of elliptic curve points to utilize the point adder unit efficiently. Finally, we evaluate our design on an AMD-Xilinx Alveo-family FPGA and show that our point arithmetic processor has better throughput and frequency than related work. Full article

CRYSTALS-Kyber has been standardized as a general public-key post-quantum algorithm under the name of ML-KEM after NIST released its first three final post-quantum standards in August 2024. The resilience of post-quantum cryptography to side-channel attacks has been an important research endeavor, and there have been many attacks designed, including basic Correlation Power Analysis. This paper adapts existing Correlation Power Analysis attacks to the most recent ARM Cortex M4 optimized implementation that uses Plantard arithmetic. It also demonstrates an improved version of a CPA that results in a 50% speedup compared to the original attack. Data are gathered and the mathematical model is tested using a ChipWhisperer-Lite board. Full article

Authenticated encryption with associated data (AEAD) schemes based on stream ciphers, such as ASCON and MORUS, typically use nonlinear feedback shift registers (NFSRs) and linear feedback shift registers (LFSRs) to generate variable-length key streams. While these methods ensure message confidentiality and authenticity, they present challenges in security analysis, especially when automated evaluation is involved. In this paper, we present MLOL, a novel AEAD algorithm based on the LOL framework. MLOL combines authenticated encryption with optimizations to the LFSR structure to enhance both security and efficiency. The cost evaluation demonstrates that on specialized CPU platforms without SIMD instruction set support, MLOL achieves better performance in authenticated encryption speed compared to LOL-MINI with GHASH. Our security analysis confirms that MLOL provides 256-bit security against current cryptanalytic techniques. Experimental results demonstrate that MLOL not only inherits the excellent performance of LOL but also reduces the time complexity of the authenticated encryption process, providing more reliable security guarantees. It significantly simplifies security evaluation, making it suitable for automated analysis tools, and offers a feasible new approach for AEAD algorithm design. Full article

With the rise in applications of artificial intelligence (AI) across various sectors, security concerns have become paramount. Traditional AI systems often lack robust security measures, making them vulnerable to adversarial attacks, data breaches, and privacy violations. Cryptography has emerged as a crucial component in enhancing AI security by ensuring data confidentiality, authentication, and integrity. This paper presents a comprehensive bibliometric review to understand the intersection between cryptography, AI, and security. A total of 495 journal articles and reviews were identified using Scopus as the primary database. The results indicate a sharp increase in research interest between 2020 and January 2025, with a significant rise in publications in 2023 and 2024. The key application areas include computer science, engineering, and materials science. Key cryptographic techniques such as homomorphic encryption, secure multiparty computation, and quantum cryptography have gained prominence in AI security. Blockchain has also emerged as an essential technology for securing AI-driven applications, particularly in data integrity and secure transactions. This paper highlights the crucial role of cryptography in safeguarding AI systems and provides future research directions to strengthen AI security through advanced cryptographic solutions. Full article

The formal study of computer malware was initiated in the seminal work of Fred Cohen in the mid-80s, who applied elements of Computation Theory in the investigation of the theoretical limits of using the Turing Machine formal model of computation in detecting viruses. Cohen gave a simple but realistic formal definition of the characteristic actions of a computer virus as a Turing Machine that replicates itself and proved that detecting this behaviour, in general, is an undecidable problem. In this paper, we complement Cohen’s approach by providing a simple generalization of his definition of a computer virus so as to model any type of malware behaviour and showing that the malware/non-malware classification problem is, again, undecidable. Most importantly, beyond Cohen’s work, our work provides a generic theoretical framework for studying anti-malware applications and identifying, at an early stage, before their deployment, several of their inherent vulnerabilities which may lead to the construction of zero-day exploits and malware strains with stealth properties. To this end, we show that for any given formal system, which can be seen as an anti-malware formal model, there are infinitely many, effectively constructible programs for which no proof can be produced by the formal system that they are either malware or non-malware programs. Moreover, infinitely many of these programs are, indeed, malware programs which evade the detection powers of the given formal system. Full article

Field-programmable gate arrays (FPGAs) are widely used in cloud servers as an acceleration solution for compute-intensive tasks. Cloud FPGAs are typically multi-tenant, enabling resource sharing among multiple users but are vulnerable to power side-channel analysis (SCA) attacks due to their programmability and runtime dynamic reconfigurability. It is well-known that the clock frequencies of the circuits on multi-tenant FPGAs affect power consumption, but their impact on remote correlation power analysis (CPA) attacks has largely been ignored in the literature. This work systematically evaluates how clock frequency variations influence the effectiveness of remote CPA attacks on multi-tenant FPGAs. We develop a theoretical model to quantify this impact and validate our findings through the CPA attacks on processors running AES-128 and SM4 cryptographic algorithms. Our results demonstrate that the runtime clock frequency significantly affects the performance of remote CPA attacks. Our work provides valuable insights into the security implications of frequency scaling in multi-tenant FPGAs and offers guidance on selecting clock frequencies to mitigate power side-channel risks. Full article

This paper explores advancements in the Gentry-Sahai-Waters (GSW) fully homomorphic encryption scheme (FHE), addressing challenges related to message data range limitations and ciphertext size constraints. We leverage the well-known parallelizing technology—the Chinese Remainder Theorem (CRT)—to tackle the message decomposition, significantly expanding the allowable input message range to the entire plaintext space. This approach enables unrestricted message selection in the GSW scheme and supports parallel homomorphic operations without intermediate decryption. Additionally, we adapt existing ciphertext compression techniques, such as the PVW-like scheme, to reduce the memory overhead associated with ciphertexts. Our experimental results demonstrate the effectiveness of combining the proposed CRT-based decomposition with the PVW-like compression in increasing the upper bound of message values and improving the scheme’s capacity for consecutive homomorphic operations. However, compression introduces a trade-off, necessitating a reduced message range due to error accumulation in successive HE operations. This research contributes to enhancing the practicality and efficiency of the GSW encryption scheme for complex computational scenarios while managing the balance between expanded message range, computational complexity, and storage requirements. Full article

Private information retrieval (PIR) enables a client to retrieve a specific element from a server’s database without disclosing the index that was queried. This work introduces three improvements to the efficient single-server PIR protocol Spiral. We found that performing a modulus switching towards expanded ciphertexts can improve the server throughput. Secondly, we apply two techniques called the composite $\mathsf{NTT}$ algorithm and approximate decomposition to Spiral to further improve it. We conduct comprehensive experiments to evaluate the concrete performance of our protocol, and the results confirm an approximately 1.7 times faster overall throughput than Spiral. Full article

A group signature scheme allows a user to sign a message anonymously on behalf of a group and provides accountability by using an opening authority who can “open” a signature and reveal the signer’s identity. Group signature schemes have been widely used in privacy-preserving applications, including anonymous attestation and anonymous authentication. Fully dynamic group signature schemes allow new members to join the group and existing members to be revoked if needed. Symmetric-key based group signature schemes are post-quantum group signatures whose security rely on the security of symmetric-key primitives, and cryptographic hash functions. In this paper, we design a symmetric-key based fully dynamic group signature scheme, called DGMT, that redesigns DGM (Buser et al. ESORICS 2019) and removes its two important shortcomings that limit its application in practice: (i) interaction with the group manager for signature verification, and (ii) the need for storing and managing an unacceptably large amount of data by the group manager. We prove security of DGMT (unforgeability, anonymity, and traceability) and give a full implementation of the system. Compared to all known post-quantum group signature schemes with the same security level, DGMT has the shortest signature size. We also analyze DGM signature revocation approach and show that despite its conceptual novelty, it has significant hidden costs that makes it much more costly than using the traditional revocation list approach. Full article