The advent of quantum computers poses a direct threat to the security of traditional digital signature schemes, which are based on the Rivest–Shamir–Adleman (RSA) and Elliptic Curve Cryptography (ECC) cryptosystems. Shor's algorithm allows solving the Discrete Logarithm Problem (DLP) in polynomial time, whereas Grover's algorithm significantly reduces the effort required for brute-force attacks on symmetric hash functions and ciphers. Although many post-quantum solutions have been proposed, such as lattice-based schemes (e.g., CRYSTALS-Dilithium, Falcon) or hash-based schemes (e.g., SPHINCS+), they still have some limitations to overcome, such as large public keys, bulky signatures, high computational costs, and difficulties in integrating into existing Public Key Infrastructures (PKIs). In this paper, we propose a new type of hard problem, defined over a finite prime field, in which the generator is kept secret to prevent any direct Shor attack and is only subject to a limited influence from Grover. Based on this newly proposed hard problem, we construct a post-quantum digital signature scheme that is both Shor-resistant and Grover-resistant, secure against classical attacks, and fully compatible with current PKI infrastructures. Compared with existing post-quantum digital signature schemes, our solution significantly optimizes the size of public keys and signatures while increasing the speed of signing and verification. The newly proposed hard problem cannot be solved by known classical or quantum algorithms, thus ensuring long-term security. Performance evaluation results show that the scheme provides an optimal balance between performance and security, opening up a cost-effective implementation path for the post-quantum cryptography era.
The advent of quantum computers poses a direct threat to the security of traditional digital signature schemes, which are based on the Rivest–Shamir–Adleman (RSA) and Elliptic Curve Cryptography (ECC) cryptosystems. Shor's algorithm allows solving the Discrete Logarithm Problem (DLP) in polynomial time, whereas Grover's algorithm significantly reduces the effort required for brute-force attacks on symmetric hash functions and ciphers. Although many post-quantum solutions have been proposed, such as lattice-based schemes (e.g., CRYSTALS-Dilithium, Falcon) or hash-based schemes (e.g., SPHINCS+), they still have some limitations to overcome, such as large public keys, bulky signatures, high computational costs, and difficulties in integrating into existing Public Key Infrastructures (PKIs). In this paper, we propose a new type of hard problem, defined over a finite prime field, in which the generator is kept secret to prevent any direct Shor attack and is only subject to a limited influence from Grover. Based on this newly proposed hard problem, we construct a post-quantum digital signature scheme that is both Shor-resistant and Grover-resistant, secure against classical attacks, and fully compatible with current PKI infrastructures. Compared with existing post-quantum digital signature schemes, our solution significantly optimizes the size of public keys and signatures while increasing the speed of signing and verification. The newly proposed hard problem cannot be solved by known classical or quantum algorithms, thus ensuring long-term security. Performance evaluation results show that the scheme provides an optimal balance between performance and security, opening up a cost-effective implementation path for the post-quantum cryptography era.
Quantum computing represents one of the most disruptive technological advancements of the 21st century, with profound implications for modern cryptographic systems. Traditional digital signature algorithms—such as RSA, DSA, and Elliptic Curve Cryptography (ECC)—derive their security from mathematical problems like integer factorization and discrete logarithms, which are computationally infeasible for classical computers. However, the advent of quantum algorithms, particularly Shor’s and Grover’s algorithms, poses a direct threat to these cryptographic assumptions by drastically reducing the time required to solve such problems. This development renders existing Digital Signature infrastructures potentially obsolete once large-scale quantum computers become operational. To counter this threat, researchers have proposed a range of post-quantum cryptographic (PQC) algorithms, including lattice-based, hash-based, and multivariate polynomial-based signature schemes, which are designed to resist quantum attacks. This paper critically examines the extent of quantum vulnerability in current Digital Signature systems and evaluates the comparative performance, efficiency, and security trade-offs of post-quantum alternatives. The study aims to provide a structured understanding of the ongoing transition toward quantum-resistant digital authentication and to propose a roadmap for secure implementation in future cryptographic environments.
The emergence of quantum computing is a serious threat to the principles of modern crypto-logical mathematics. The classical public-key cryptography, including Rivest-Shamir-Adleman (RSA), Elliptic Curve Cryptography (ECC), and Diffie-Hellman are very safe against classical adversaries yet become susceptible to quantum algorithms, including the Shor algorithm, which can easily solve the underlying mathematical problems. This weakness is jeopardizing confidentiality and integrity of the world-wide systems of communication, money transactions, and essential structures, and requires the immediate creation of safe alternatives. The current literature on post-quantum cryptography (PQC) has covered various classes of algorithm, such as lattice-based, code-based, multivariate schemes, and isogeny-based schemes. Although lattice-based approaches like Nth Degree Truncated Polynomial Ring Unit (NTRU) and FrodoKEM can be highly theoretically resistant, they can be computationally and memory-intensive. Cryptosystems based on code such as Classic McEliece are secure but not practicable because they have huge public key sizes. Multivariate schemes like Rainbow, and isogeny-based schemes like Super singular Isogeny Key Encapsulation (SIKE) have been attacked recently by cryptanalytic attacks, and broken completely. Such restrictions open the necessity to find more efficient and secure quantum-resistant solutions.This research study postulates a hybrid post-quantum cryptographic (PQC) system that combines CRYSTALS-Kyber for encryption with CRYSTALS-Dilithium for digital signatures both of which are approved through the National Institute of Standards and Technology (NIST) PQC standardization program. The model will be such that it ensures quantum resistance but at the same time it will be scalable, efficient and compatible with the existing infrastructures. The test outcomes indicate that the hybrid PQC model is 35-45 percent faster to encrypt and decrypt, signature performance is enhanced by up to 40 percent, and the throughput is 20 times higher (98.7 Mbps) than the same base PQC scheme including Nth Degree Truncated Polynomial Ring Unit (NTRU), McEliece and Rainbow. These enhancements affirm that the suggested model provides a viable trade-off between the security, speed, and efficiency in terms of key size, which makes it a viable and a sound base to ensure secure communication in the quantum age.
The rapid advancement of quantum computing poses a fundamental threat to classical cryptographic mechanisms that underpin modern digital security. Shor’s algorithm can efficiently solve integer factorization and discrete logarithm problems, thereby breaking widely used public-key cryptosystems such as RSA, ECC, and Diffie–Hellman. Grover’s algorithm also reduces the effective security of symmetric encryption and hash functions by half. This paper provides a systematic analysis of the impact of quantum attacks on current cryptographic infrastructures, including TLS, digital signatures, and blockchain. We then review the state of post-quantum cryptography (PQC) as standardized by NIST, focusing on three leading candidates: CRYSTALS-Kyber for key encapsulation, and CRYSTALS-Dilithium and FALCON for digital signatures. Through simulation using the Open Quantum Safe (liboqs) library on a standard x86_64 platform, we measure key generation time, encryption/signing speed, decryption/verification latency, and key/signature sizes. Our results show that Kyber-768 achieves key generation in <0.1 ms and produces public keys of about 1.2 KB, while Dilithium-3 generates signatures of ~2.7 KB with verification times under 0.3 ms. Compared to RSA-2048 and ECDSA-P256, PQC algorithms offer competitive performance at the cost of larger key and signature sizes. Based on these findings, we propose a hybrid transition roadmap that combines classical and PQC algorithms in parallel, minimizing risk while maintaining backward compatibility. The paper concludes that organizations should begin immediate preparations for the post-quantum era, especially for data requiring long-term confidentiality.
Digital signatures are indispensable for security on the Internet, because they guarantee authenticity, integrity, and non-repudiation, of namely e-mails, software updates, and in the Transport Layer Security (TLS) protocol which is used for secure data transfer, for example. Most signature schemes that are currently in use such as the RSA signature scheme, are considered secure as long as the integer factorization problem or the discrete logarithm (DL) problem are computationally hard. At present, no algorithms have yet been found to solve these problems on conventional computers in polynomial time. However, in 1997, Shor published a polynomial-time algorithm that uses quantum computation to solve the integer factorization and the DL problem. In particular, this means that RSA signatures are considered broken as soon as large-scale quantum computers exist. Due to significant advances in the area of quantum computing, it is reasonable to assume that within 20 years, quantum computers that are able to break the RSA scheme, could exist. In order to maintain authenticity, integrity, and non-repudiation of data, cryptographic schemes that cannot be broken by quantum attacks are required. In addition, these so-called post-quantum secure schemes should be sufficiently efficient to be suitable for all established applications. Furthermore, solutions enabling a timely and secure transition from classical to post-quantum schemes are needed. This thesis contributes to the above-mentioned transition. In this thesis, we present the two lattice-based digital signature schemes TESLA and qTESLA, whereby lattice-based cryptography is one of five approaches to construct post-quantum secure schemes. Furthermore, we prove that our signature schemes are secure as long as the so-called Learning With Errors (LWE) problem is computationally hard to solve. It is presumed that even quantum computers cannot solve the LWE problem in polynomial time. The security of our schemes is proven using security reductions. Since our reductions are tight and explicit, efficient instantiations are possible that provably guarantee a selected security level, as long as the corresponding LWE instance provides a certain hardness level. Since both our reductions (as proven in the quantum random oracle model) and instantiations, take into account quantum attackers, TESLA and qTESLA are considered post-quantum secure. Concurrently, the run-times for generating and verifying signatures of qTESLA are similar (or faster) than those of the RSA scheme. However, key and signature sizes of RSA are smaller than those of qTESLA. In order to protect both the theoretical signature schemes and their implementations against attacks, we analyze possible vulnerabilities against implementation attacks. In particular, cache-side-channel attacks resulting from observing the cache behavior and fault attacks, which recover secret information by actively disrupting the execution of an algorithm are focused. We present effective countermeasures for each implementation attack we found. Our analyses and countermeasures also influence the design and implementation of qTESLA. Although our schemes are considered (post-quantum) secure according to state-of-the-art LWE attacks, cryptanalysis of lattice-based schemes is still a relatively new field of research in comparison to RSA schemes. Hence, there is a lack of confidence in the concrete instantiations and their promised security levels. However, due to developments within the field of quantum computers, a transition to post-quantum secure solutions seems to be more urgently required than ever. To solve this dilemma, we present an approach to combine two schemes, e.g., qTESLA and the RSA signature scheme, so that the combination is secure as long as one of the two combined schemes is secure. We present several of such combiners to construct hybrid signature schemes and hybrid key encapsulation mechanisms to ensure both authenticity and confidentiality in our Public-Key Infrastructure (PKI). Lastly, we also demonstrate how to apply the resulting hybrid schemes in standards such as X.509 or TLS. To summarize, this work presents post-quantum secure candidates which can, using our hybrid schemes, add post-quantum security to the current classical security in our PKI.
The emergence of quantum computing introduces unprecedented risks to classical cryptographic schemes, particularly digital signatures that safeguard authentication, confidentiality, and data integrity across digital ecosystems. To address these concerns, this paper investigates the adoption of Post-Quantum Cryptography (PQC) within Public Key Infrastructure (PKI) frameworks, emphasizing its role in strengthening electronic signature (eSign) systems against quantum threats. Traditional PKI implementations rely on algorithms such as RSA and ECC in combination with Hardware Security Modules (HSMs) for secure key management; however, these methods are vulnerable to quantum algorithms like Shor's. We examine how quantum-resistant alternatives-including lattice-based, hash-based, and multivariate polynomial-based schemes standardized by NIST-can be integrated into PKI without compromising interoperability and compliance. A comparative evaluation highlights trade-offs in performance, storage, and computational complexity while demonstrating the feasibility of embedding PQC into existing eSign infrastructures. Our findings underscore the urgency of transitioning towards quantum-safe digital signatures to ensure resilience, regulatory alignment, and long-term trust in national-scale digital services.
The boom of quantum computing has brought both benefits and threats to cyber-physical systems. The primary purpose of the paper is to highlight the possible threats by quantum computers, and to provide a comparative study of the on-going quantum-resistant post-quantum cryptography suitable for current network infrastructure. Asymmetric key cryptography, mainly the widely adopted RSA and ECC algorithms, has been compromised by quantum algorithms such as the Shor’s algorithm. Moreover, symmetric algorithms such as AES are weakened by brute force attacks using Grover’s algorithm. Thus, researchers are developing public key algorithms based on hard mathematical models that provide resistance against quantum attacks and can be deployed in classical hardware. We categorize the well-known post-quantum schemes based on (1) their security goals: confidentiality and integrity, and (2) their mathematical problems: code-based, lattice-based, super-singular elliptic curve isogeny based, multivariate and hash-based algorithm. Hash-based post- quantum cryptography is further categorized into two: stateless and stateful signature scheme. Furthermore, the chapter compares the algorithms based on the key sizes, ciphertext sizes, signature sizes, computation, and time cost. The paper also presents the challenges faced by the post-quantum algorithms, and it outlines directions for further research to improve the algorithms. Moreover, various cyber-physical fields, including industrial control systems, mainly nuclear power plants, water management plants, and even space stations and their infrastructure, rely on classical cryptography. Thus, the paper presents a generic hybrid cryptosystem based on classical and post-quantum cryptography to enhance resistance against classical and quantum attacks.