In post-quantum approach, we consider classical (non-quantum) protocols and primitives which are run by honest parties on classical computers and our aim is to keep their security in an environment where the adversary can rely on quantum computers [3].In particular, even a harder goal is set by requiring provable security guaranties in a concurrent running environment as we aim computational UC-security.Unruh [16] conjectured that classical arguments of computational UC-security remain usable in a postquantum world as long as the underlying computational UC-secure primitives are also computationally quantum UC-secure.Our proposed technique (full factorization) aims at reducing the original protocol into a statisticallysecure protocol by turning the protocol into a hybrid one where all cryptographic primitives are substituted by appropriate ideal functionalities.The considered set of primitives consists of secret key and public key encryption as well as digital signature.This way and by applying the Unruh's Quantum Lifting Theorem as well as the Quantum Universal Composition Theorem we gain a computationally quantum UC-secure protocol from a classical UC-secure protocol.We consider quantum standard-security, where the adversary can send only classical inputs to honest algorithms, i.e. honest machines cannot receive quantum superposition of inputs If we add also the practical need of efficiency our example is the class of protocols built from symmetric key primitives.A practical (fast) implementation could be based on AES encryption algorithm with appropriate key size as long as we live with the wide belief that this algorithm is secure against a quantum adversary.
In post-quantum approach, we consider classical (non-quantum) protocols and primitives which are run by honest parties on classical computers and our aim is to keep their security in an environment where the adversary can rely on quantum computers [3].In particular, even a harder goal is set by requiring provable security guaranties in a concurrent running environment as we aim computational UC-security.Unruh [16] conjectured that classical arguments of computational UC-security remain usable in a postquantum world as long as the underlying computational UC-secure primitives are also computationally quantum UC-secure.Our proposed technique (full factorization) aims at reducing the original protocol into a statisticallysecure protocol by turning the protocol into a hybrid one where all cryptographic primitives are substituted by appropriate ideal functionalities.The considered set of primitives consists of secret key and public key encryption as well as digital signature.This way and by applying the Unruh's Quantum Lifting Theorem as well as the Quantum Universal Composition Theorem we gain a computationally quantum UC-secure protocol from a classical UC-secure protocol.We consider quantum standard-security, where the adversary can send only classical inputs to honest algorithms, i.e. honest machines cannot receive quantum superposition of inputs If we add also the practical need of efficiency our example is the class of protocols built from symmetric key primitives.A practical (fast) implementation could be based on AES encryption algorithm with appropriate key size as long as we live with the wide belief that this algorithm is secure against a quantum adversary.
We call quantum security the area of IT security dealing with scenarios where one or more parties have access to quantum hardware. This encompasses both the fields of post-quantum cryptography (that is, traditional cryptography engineered to be resistant against quantum adversaries), and quantum cryptography (that is, security protocols designed to be natively run on a quantum infrastructure, such as quantum key distribution). Moreover, there exist also hybrid models, where traditional cryptographic schemes are somehow `mixed' with quantum operations in certain scenarios. Even if a fully-fledged, scalable quantum computer has yet to be built, recent results and the pace of research in its realization call for attention, lest we suddenly find ourselves one day with an obsolete security infrastructure. For this reason, in the last two decades research in quantum security has experienced an exponential growth in interest and investments. In this work, we propose the first systematic classification of quantum security scenarios, and for each of them we recall the main tools and results, as well as presenting new ones. We achieve this goal by identifying four distinct quantum security classes, or domains, each of them encompassing the security notions and constructions related to a particular scenario. We start with the class QS0, which is `classical cryptography' (meaning that no quantum scenario is considered), where we present some classical constructions and results as a preliminary step. Regarding post-quantum cryptography, we introduce the class QS1, where we discuss in detail the problems arising when designing a classical cryptographic object meant to be resistant against adversaries with local quantum computing power, and we provide a classification of the possible quantum security reductions in this scenario when considering provable security. Moreover, we present results about the quantum security and insecurity of the Fiat-Shamir transformation (a useful tool used to turn interactive identification schemes into digital signatures), and ORAMs (protocols used to outsource a database in a private way). In respect to hybrid classical-quantum models, in the security class QS2 we discuss in detail the possible scenarios where these scenarios arise, and what a correct formalization should be in terms of quantum oracle access. We also provide a novel framework for the quantum security (both in terms of indistinguishability and semantic security) of secret-key encryption schemes, and we give explicit secure constructions, as well as impossibility results. Finally, in the class QS3 we consider all those cryptographic constructions designed to run natively on quantum hardware. We give constructions for quantum encryption schemes (both in the secret- and public-key scenario), and we introduce transformations for obtaining such schemes by conceptually simpler schemes from the class QS2. Moreover, we introduce a quantum version of ORAM, called quantum ORAM (QORAM), aimed at outsourcing in a private way a database composed of quantum data. In proposing a suitable security model and an explicit construction for QORAMs, we also introduce a technique of independent interest which models a quantum adversary able to extract information from a quantum system without disturbing it `too much'. We believe that the framework we introduce in this work will be a valuable tool for the scientific community in addressing the challenges arising when formalizing sound constructions and notions of security in the quantum world.
In 1994, Peter Shor developed a quantum algorithm that can efficiently solve the factorization and discrete logarithm problems. These problems are the foundation of modern cryptographic algorithms and the existence of an efficient algorithm for solving them threatens their security. Although large-scale quantum computers capable of breaking current cryptographic algorithms are not yet available, advances in quantum technology and the risk of “store now, decrypt later” attacks make it essential to prepare for migration to quantum-safe cryptography today. For the past decade, the cryptographic community has been actively developing algorithms that are not exploitable by Shor’s algorithm; such algorithms are said to be “quantum-safe” or “post-quantum.” However, cryptographic algorithms do not exist in isolation—they are components of larger cryptographic systems, such as protocols or other cryptographic primitives. Migrating these systems to use quantum-safe algorithms is therefore a complex task. This thesis studies the migration of several widely used cryptographic systems to post-quantum cryptography. In particular, we consider the migration of the public-key infrastructure (PKI), the TLS protocol, the XML Encryption and XML Signature standards, the SAML security framework, the Advanced Electronic Signature (AdES) standard, and the password-authenticated public-key encryption (PAPKE) primitive. For each topic, we analyze how the presence of quantum adversaries affects the security of existing constructions and identify components that rely on cryptographic assumptions vulnerable to quantum attacks. Based on this analysis, we propose approaches for adapting these systems to use post-quantum cryptographic algorithms. The proposed solutions are considered in two main forms: purely post-quantum and hybrid post-quantum. Purely post-quantum approaches rely exclusively on post-quantum algorithms, while hybrid post-quantum approaches combine classical and post-quantum mechanisms in order to provide security as long as at least one of the underlying assumptions remains secure. Hybrid post-quantum approaches are primarily motivated by uncertainty regarding the security of post-quantum algorithms. For each proposal, we discuss the advantages and disadvantages of the design, including deployment complexity, compatibility with existing systems, and performance considerations. In several cases, we also provide proof-of-concept implementations and evaluate their performance through benchmarks. We study post-quantum public-key infrastructures, which form a fundamental component of many other cryptographic systems. We show that constructing a purely post-quantum PKI does not fundamentally differ from constructing a classical PKI. For hybrid deployments, we propose two approaches—the composite hybrid and the parallel hybrid—which differ primarily in their implementation complexity. We also survey and analyze existing proposals for post-quantum TLS. In contrast, systems such as XML encryption and XML signatures, the SAML security framework, and the eIDAS-related AdES standard have received little attention in the context of post-quantum migration. For these systems, we outline possible migration approaches and provide proof-of-concept implementations. In addition, we present an example migration plan for a Trust Service Provider that relies on all of the discussed cryptographic systems, together with the methodology used to develop it. Finally, we consider the migration of the cryptographic primitive PAPKE. We propose a novel construction that replaces an ideal cipher with a half-ideal cipher, resulting in more efficient quantum-safe constructions and motivating the study of a new public-key encryption property called decryption robustness.
The accelerated advancements in quantum computing substantially threaten classical cryptographic systems, particularly those that rely on RSA, ECC, and other public key encryption methods. Particularly Shor's method shows how easily conventional cryptographic techniques might be broken; therefore quick development of quantum resistant substitutes is necessary. Rising as a potential answer with cryptographic algorithms meant to resist quantum attacks is post quantum cryptography (PQC). Nonetheless, performance trade-offs, compatibility problems, and the absence of standardized implementations make the shift to completely quantum-safe cryptographic systems very difficult. Hybrid PQC systems that combine conventional and quantum resistant cryptographic mechanisms have been suggested as a workable method for tackling these difficulties so guaranteeing security in the post quantum future. Emphasizing their security, performance, and practical implementations, this review article offers a thorough study of hybrid PQC methods. The resistance of many hybrid cryptographic models including lattice-based, code-based, and multivariate cryptographic techniques against quantum attacks is comprehensively investigated in this work methodologically, we review current PQC hybrid models, evaluate their computing efficiency, and examine security criteria grounded on recent research and standardizing initiatives like those under NIST. Our results show that hybrid PQC models create difficulties in terms of key management, computational overhead, and implementation complexity even if they improve security by reducing risks related with both conventional and quantum attacks. A comparative study shows among several hybrid systems the trade-offs in terms of encryption speed, key sizes, and resource use. Moreover showing the feasibility of PQC hybridizing in IoT, cloud computing, and block chain security are pragmatic uses of PQC hybridizing in which case appropriate protocols are needed for broad acceptance. At last, our work emphasizes the significant contribution hybrid PQC models provide in the transitional period producing a quantum secure environment. To enable basic integration into the present digital infrastructure, future research should focus on improving the efficiency of hybrid cryptosystems, optimizing key exchange mechanisms, and regulating standardization concerns. The findings of this study support the present discussion on post quantum security and provide data for academics and corporate leaders aiming for the next generation of cryptographic solutions. https://doi.org/10.5281/zenodo.17873992
With the dawn of quantum computing in scale, current secure classical primitives are at risk. Protocols with immediate risk of breach are those built on the advanced encryption standard (AES) and Rivest-Shamir-Adleman (RSA) algorithms. To secure classical data against a quantum adversary, a secure communications ciphersuite must be developed. The ciphersuite developed in this work contains components that do not necessarily rely on quantum key distribution (QKD), due to recent insecurities found when a QKD-based protocol is faced with a quantum eavesdropper. A set of quantum-classical ciphersuite primitives were developed using less common mathematical methods where a quantum adversary will take a non-deterministic polynomial-time to find a solution, but still easy enough for communicating classical computers to evaluate. The methods utilized for this work were created from random walks, lattices, symplectic mappings, combinatorics, and others. The hardware methods developed in this work rely on either classical laser-light, or entangled quantum states, with matching optimization developed from global optimization theories. The result of this work is the creation of non-QKD hybrid quantum-classical set of secure ciphersuite primitives, built and expanded from existing classical and post-quantum security schemes, for both classical and quantum information. In the tight integration between quantum and classical computers, the security of classical systems with quantum interaction is essential.
The emergence of quantum computing has provided new paradigms for cryptography. On the one hand, it poses significant new threats to existing classically cryptographic systems, requiring the community to define new security models that capture what a quantum adversary can do. On the other hand, it gives us new tools to design cryptographic protocols, with weaker assumptions than in the classical world, or even protocols that are impossible classically. In this survey, we first give an overview of new security definitions for classical cryptography, considering quantum adversaries who can either only use local quantum computation (post-quantum security), or even send quantum messages and in particular have access to oracle in superposition (quantum security). We explore these new notions through the examples of commitments, zero-knowledge proofs, encryption, and signatures. Then, we present what is arguably the most famous application of quantum cryptography: quantum key distribution (QKD) protocols that take advantage of unique properties of quantum mechanics to provide secure communication unconditionally. We also explore cryptography beyond QKD, focusing on unclonable cryptography: a family of cryptographic functionalities, built with quantum states, and designed to be resistant to counterfeit by leveraging the “no-cloning” theorem. We examine in particular quantum money, but also the recent notions of unclonable encryption and copy-protection, including related variants. By presenting a comprehensive survey of these topics, this paper aims to provide a thorough understanding of the current landscape and future potential of quantum cryptography.
The rapid development of quantum computing presents a substantial threat to traditional cryptographic algorithms, particularly those relying on mathematical problems such as integer factorization and elliptic curve operations. As a response, the cryptographic community has accelerated the design of post-quantum cryptographic schemes that can withstand attacks from both classical and quantum computers. However, many of these new schemes exhibit inherent trade-offs between performance, key sizes, and implementation complexity. To address this, we propose a novel hybrid cryptographic framework tailored for secure and efficient data transmission in future quantum-aware environments. The proposed system combines three algorithmic paradigms: a lattice-based encryption method for fast and lightweight data protection, a hash-based signature mechanism for authenticity, and a code-based key exchange method to ensure session confidentiality. This layered integration is designed to capitalize on each algorithm’s strengths while mitigating individual limitations. The system is implemented using modular components in a testbed simulating real-world deployments, and its performance is benchmarked across multiple metrics including encryption latency, signature generation time, key sizes, and throughput. Comparative results indicate that the hybrid approach outperforms monolithic schemes in critical areas such as execution time and cryptographic strength under quantum adversary models. The findings support the practicality of using multiple post-quantum primitives in tandem to build robust communication systems. This research contributes a realistic implementation and evaluation of post-quantum security models and highlights key directions for future research and standardization efforts as the global transition to quantum-safe infrastructure begins.