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Currently, with the threat of quantum computer attacks, the idea of combining several same-type primitives has reemerged. This is also the case for cryptographic keys where a hybrid quantum key exchange combination allows for preserving the security guarantees of pre-quantum schemes and achieving quantum resistance of post-quantum schemes. In this article, we present a concrete 3-key combiner system implemented on a Field Programmable Gate Arrays (FPGA) platform. Our system involves a pre-quantum Key EXchange scheme (KEX), a post-quantum key encapsulation mechanism, and a Quantum Key Distribution (QKD) algorithm. The proposed 3-key combiner is proven to be secure in the quantum standard model and it is INDistinguishable under a Chosen-Ciphertext Attack (IND-CCA). Our combiner can run in small FPGA platforms due to its relatively low resources usage. In particular, the key combiner without QKD is able to output up to 1 624 keys per second and the key combiner with QKD is able to output up to 9.2 keys per second.

As the ongoing standardization process of postquantum schemes yields initial outcomes, it is important not only to focus on optimization of standalone implementations but also to explore the possibilities of combining multiple schemes into one unified architecture. In this paper, we focus on exploring the combination of two NIST selected schemes, namely the CRYSTALS-Dilithium digital signature scheme and the CRYSTALS-Kyber key encapsulation scheme. We present optimized designs of unified hardware components that can be used as building blocks for these schemes. All implemented components outperform state-of-the-art implementations in both hardware utilization and performance.

With increasing digitalization and omnipresent data sensing, security and users’ privacy become essential requirements in new digital services. Group Signatures (GS) or also known as Anonymous Digital Signatures (ADS) are often used as a core Privacy-Enhancing Technology (PET) in order to keep users’ privacy during their access and/or authentication phases within ensuring the security of provided services. In this work, we provide a comprehensive assessment of group signatures on various small computing platforms typically used in modern digital services. Based on our analysis of well-established GS schemes and their libraries, we implement and evaluate chosen schemes on both well-known smartphone platforms (i.e., Android, iOS) and on a single-board computer. Our results indicate that current handheld devices can already effectively perform main group signatures’ phases and make these schemes practical for deployment in various privacy-requiring scenarios.

Threshold signatures have gained increased attention especially due to their recent applications in blockchain technologies. In fact, current cryptocurrencies such as Bitcoin, and Cardano started to support multi-signature transactions. Even if the Schnorr-based threshold signatures improve the blockchain's privacy and scalability, these schemes do not provide post-quantum security. In this paper, we propose the optimization of the DS2 lattice-based $(n,n)$-threshold signature scheme and present its practical implementation. Moreover, we evaluate our optimized implementation of the DS2 scheme on different platforms. The results demonstrate that our implementation is easily portable and executable on constrained devices based on ARM Cortex-A53, ARM Cortex-M3, and ESP32 architectures.

As quantum-safe algorithms are increasingly implemented in security protocols used in current and emerging digital services, there is also a corresponding need to map the current state of security protocols and applications and their preparedness for the post-quantum era. In this paper, we review current security recommendations, existing security libraries, and the support of Post-Quantum Cryptography (PQC) in widely-used security protocols. We also present a practical assessment of recently selected PQC algorithms by the National Institute of Standards and Technologies (NIST) PQC standardization on typical platforms that can be deployed in intelligent infrastructures (e.g., smartphones and single-boards), and recently recommended hash-based signatures for software/firmware signing. Finally, we discuss how incoming post-quantum migration affects selected areas in intelligent infrastructures.

The recent COVID-19 pandemic situation highlights the importance of digital vaccine certificates. In response, the European Union (EU) developed EU Digital Vaccine Certificates to enable proof of non-infectivity and completed vaccinations. However, these solutions suffer from several shortcomings, such as ineffective certificate holder identification and a high violation of user privacy with the disclosure of sensitive information. In this work, we present a novel solution for privacy-preserving EU Digital Vaccine Certificates. Our solution solves the aforementioned privacy and security shortcomings and is in line with current EU legislation, i.e., the General Data Protection Regulation (GDPR), the upcoming revision of the electronic IDentification, Authentication, and trust Services (eIDAS), called regulation eIDAS 2.0, and the new tools that it envisages to be led by European digital identity. This identity is intended to allow citizens to prove their identity to access online services, share digital documents, or simply prove specific personal characteristics such as age without revealing their identity or other personal information. The core of our proposal is built on our novel attribute-based credential scheme, which can be easily implemented on various handheld devices, especially on Android smartphones and smartwatches. However, due to the lightweight nature of our scheme, it can also be implemented on constrained devices such as smart cards. In order to demonstrate the security, privacy, and practicality inherent in our proposal, we provide the security analysis of the cryptographic core along with a set of experimental results conducted on smartphones and smart cards.

Modern Intelligent Infrastructures (II) are highly complex, interconnected systems that are now emerging. For instance, II can integrate technologies and processes to provide citizens with faster services and better goods. An average II can include many technologies, e.g., Cloud applications and IoT devices, under different environments, e.g., industry 4.0 production plants and smart buildings. Although II bring concrete benefits to all of these contexts, they also carry security concerns. Reasoning about threats and security exposures that might affect II is non trivial. This is only partially due to their inherent complexity. As a matter of fact, real II are typically in charge of some critical operations that cannot be interrupted or compromised for experimental purposes. An alternative solution is to rely on digital replicas which can provide a good trade off between realism and usability. These assets represent a strategic and highly demanded resource for the security community. In this paper we present HArMoNICS, a case study infrastructure meant to provide a playground for security experts interested in II security. HArMoNICS revolves around a digital replica of a real Smart Polygeneration Microgrid (SPM) located in Italy. Although most of the components are based on or inspired to the real system, HArMoNICS has been enriched with further security-relevant features. As a result, the case study includes vertical uses cases focusing on specific security topics. Security researchers can use it to assess the effectiveness of new methodologies, to carry out security training activities, or even to extend it with new elements.

Kyber is one of the three finalists of the National Institute of Standards and Technology (NIST) post-quantum cryptography competition. This article presents an optimized Very High Speed Integrated Circuit Hardware Description Language (VHDL)-based implementation of the main components of the Kyber scheme, namely Number-Theoretic Transform (NTT) and Keccak. We focus specifically on NTT, Keccak and their derivatives since they largely determine Kyber's performance due to their wide involvement in each step of the scheme. Our high-speed implementation also takes into account the trade-off between the degree of parallelization and the resources utilization. The NTT component is more than 27\% faster than the state-of-the-art implementations. Furthermore, the optimization helps the algorithm to achieve 1 572 839 NTT operations per second.

In the last decades, several signcryption schemes have been developed for different privacy-enhancing purposes. In this paper, we propose a new privacy-enhancing group signcryption schemethat provides: unforgeability, confidentiality, ciphertext and sender anonymity, traceability, unlinkability,exculpability, coalition-resistance, and unforgeable tracing verification. It is important to notice that theproposed scheme allows a signer to anonymously signcrypt a message on the group’s behalf (i.e., sender’sanonymity). The security analysis of the scheme is also provided. Our proposal is proven to be stronglyexistentially unforgeable under an adaptive chosen message attack, indistinguishable under an adaptivechosen ciphertext attack, and to provide ciphertext anonymity under an adaptive chosen ciphertext attack.Furthermore, the scheme is extended to work in a multi-receiver scenario, where an authorized group ofreceivers is able to unsigncrypt the ciphertext. The experimental results show that our scheme is efficienteven on computationally restricted devices and can be therefore used in many IoT applications. TheSigncryptprotocol on smart cards takes less than 1 s (including communication overhead). The timeof theUnsigncryptprotocol on current ARM devices is negligible (less than 40 ms).

As we move into a new decade, the global world of Intelligent Infrastructure (II) services integrated into the Internet of Things (IoT) are at the forefront of technological advancements. With billions of connected devices spanning continents through interconnected networks, security and privacy protection techniques for the emerging II services become a paramount concern. In this paper, an up-to-date privacy method mapping and relevant use cases are surveyed for II services. Particularly, we emphasize on post-quantum cryptography techniques that may (or must when quantum computers become a reality) be used in the future through concrete products, pilots, and projects. The topics presented in this paper are of utmost importance as (1) several recent regulations such as Europe's General Data Protection Regulation (GDPR) have given privacy a significant place in digital society, and (2) the increase of IoT/II applications and digital services with growing data collection capabilities are introducing new threats and risks on citizens' privacy. This in-depth survey begins with an overview of security and privacy threats in IoT/IIs. Next, we summarize some selected Privacy-Enhancing Technologies (PETs) suitable for privacy-concerned II services, and then map recent PET schemes based on post-quantum cryptographic primitives which are capable of withstanding quantum computing attacks. This paper also overviews how PETs can be deployed in practical use cases in the scope of IoT/IIs, and maps some current projects, pilots, and products that deal with PETs. A practical case study on the Internet of Vehicles (IoV) is presented to demonstrate how PETs can be applied in reality. Finally, we discuss the main challenges with respect to current PETs and highlight some future directions for developing their post-quantum counterparts.