Quantum pseudorandomness is an emerging research area. Ji, Liu, and Song defined pseudorandom states (PRSs) and pseudorandom unitaries (PRUs) as quantum analogs of pseudorandom generators and pseudorandom functions. A unitary oracle separation result between one-way functions and PRSs/PRUs, established by Kretschmer, suggests that certain quantum primitives may remain secure even if classical cryptography is compromised. This insight has spurred extensive work on quantum pseudorandomness and its applications in quantum cryptography. Many constructions of PRSs have been established under standard assumptions, yet building a secure PRU was a long-standing open problem. This dissertation aims to narrow the gap between PRSs and PRUs and presents results that go beyond PRSs. We introduce Pseudorandom State Scramblers (PRSSs), a new primitive that lies between PRSs and PRUs. A PRSS maps any pure state to a pseudorandom state, a property shared with PRUs but not with PRSs. We present a construction of PRSSs inspired by the well-known Kacâs walk, and in particular, we develop a parallel variant that significantly accelerates the mixing time, enabling an efficient construction. PRSSs support cryptographic tasks not known to be achievable from PRSs alone, including a quantum encryption scheme and a succinct quantum state commitment. Additionally, when suitable classical randomness is provided, our construction exhibits a special dispersing property not known to be satisfied by any existing construction of quantum pseudorandom primitives. Our subsequent work shows that, without asymptotically increasing the number of steps, our construction based on the parallel Kacâs walk yields PRUs with standard or even strong security. The proof builds on a recently developed technique for establishing adaptive security, known as the path-recording method. This result provides an alternative construction of PRUs and further showcases the power of this proof technique. In addition, this dissertation includes two side projects. The first revisits the Hidden Subgroup Problem over â¤n, providing a simplified analysis of a known quantum algorithm using elementary lattice tools. The second establishes a quantum analogue of a classical impossibility result for statistical non-interactive zero-knowledge arguments, showing limitations of black-box reductions under classical-query quantum adversaries.
N. Ramanjaneya Reddy, Supriya Suryadevara, K. Guru Raghavendra Reddy, R. Umamaheswari ¡ 6 authors
Quantum computing is an evolution of classical computing, capable of solving problems that are competitive enough to break the existing cryptographic primitives upon which current blockchain systems are based. Popular schemes like RSA, ECDSA, and SHA-256 can be compromised by quantum algorithms (Shor's and Grover's), raising questions about the security and trustworthiness of blockchain-based applications in finance, healthcare, and supply chains. Many current approaches focus on isolated aspects of the blockchain, such as cryptographic primitives or key exchange, without a comprehensive strategy that can guarantee end-to-end security in the face of a quantum threat. Finally, traditional consensus mechanisms such as Proof-of-Work and Proof-of-Stake are vulnerable to Sybil attacks, centralization, and leader-selection bias. When the adversary has access to a quantum computer, these issues become significantly worse. In this paper, we present QuantumShield-BC, a modular blockchain framework incorporating post-quantum cryptographic signatures, quantum key distribution (QKD), and a novel Quantum Byzantine Fault Tolerance (Q-BFT) consensus mechanism driven by quantum random number generation (QRNG) to address these challenges. QKD: The system supports tamper-proof key exchange, quantum-resilient consensus among validator nodes, and secure transaction signing. Experimental evaluation demonstrates that QuantumShield-BC achieves low consensus latency and high throughput, while providing perfect security against simulated attacks from Shor's and Grover's algorithms. The proposed framework eradicates the Sybil attack effectiveness up to 0%, eliminates replay and MITM vulnerabilities, and achieves an average throughput of over 7,000 transactions per second with 100 validators, orders of magnitude better than classical blockchain systems. The importance of each quantum part to the system's robustness is also demonstrated using an ablation study. With its unique ability to provide a post-quantum framework for high-assurance, general-purpose, scalable, and interoperable blockchain networks resistant to quantum-inspired attacks or quantum retrieval, QuantumShield-BC is practical for deployment in critical infrastructure and digital trust ecosystems where performance and a future-proof foundation are essential.
With the emergence of quantum computing, traditional cryptographic methods used in blockchain systems face increasing risk. One such area of concern is the Layer-2 protocols zk-Rollups designed to improve scalability and privacy in platforms like Ethereum, which are heavily dependent on classical zero-knowledge proofs such as zk-SNARKs and zk-STARKs. These systems may be compromised by quantum algorithms. To address this, we propose a quantum-secure zk-Rollup model using Quantum Zero-Knowledge Proofs (QZKPs), implemented with IBMâs Qiskit simulator. The protocol uses quantum features like superposition and random basis selection to verify transactions without leaking private data. Simulation results confirm key properties: valid proofs are reliably accepted, while invalid ones are rejected. This demonstrates both the feasibility and future relevance of integrating QZKPs into blockchain systems for post-quantum security.
Henrique Hepp, Murilo V. G. da Silva, Leandro M. Zatesko
The complexity class of the problems that can be solved by a quantum algorithm in a non-adaptive collapse-free model is called naCQP. This class was introduced in 2016 by Aaronson et al. intended to be a slightly larger class than BQP: larger enough to include important NP-intermediate candidate problems, but likely not to include NP-complete problems. Aaronson et al. (2016) showed that there is an oracle A for which NPA â̸ naCQPA; and Hepp et al. (2025) showed that relative to an oracle A chosen uniformly at random, (UP ⊠coUP)A â̸ naCQPA with probability 1, being UP ⊠coUP a subclass of NP. Amongst the NP-intermediate candidate problems in naCQP is the entire class SZK, of the problems that admit a statistical zero-knowledge interactive proof system. The relation between QSZK, which is the class of the problems that admit a quantum zero-knowledge interactive proof system, and naCQP is unknown, with some believing that there is an oracle A for which QSZKA â̸ naCQPA. A promise problem complete for QSZK is the trace distance distinguishability of mixed quantum states. We show that this problem, when restricted to pure quantum states, is in naCQP.
However, with the rapid development of quantum computing cracking the basic security algorithms of the current blockchain system, such as RSA and ECC, is a big threat. To tackle this critical issue, this work is aimed to develop a quantum resilient consensus scheme that combines in general purpose blockchain architectures with lattice based cryptographic primitives. This model is based on the hardness of lattice problems, which are believed to be resistant to even the attack of quantum; securing blockchain data long and immutably. Our contribution is a novel Proof of Work (PoW) and Proof of Stake (PoS) hybrid, combined with three primitives for secure identity management, digital signature and transaction validation, provided by Learning with Errors (LWE) and Ring-LWE. Quantum Resistance, Computational Complexity, Latency and Network Scalability of the proposed system is evaluated with respect to the classical methods and it is demonstrated that the proposed system is superior in all of these aspects. This marks a critical and one important step toward future proofing blockchain ecosystems as they will be forced into the quantum paradigm that will be inevitable.
S. Jagan, B. Girirajan, Manisha Bhimrao Mane, Hussana Johar R B ¡ 6 authors
The convergence of quantum computing and artificial intelligence (AI) has introduced innovative opportunities to accelerate deep learning, particularly within decentralized cloud architectures. This study develops an adaptive quantum AI model leveraging hybrid quantum-classical algorithms to optimize deep learning processes such as training, inference, and resource allocation. The proposed model integrates Variational Quantum Circuits (VQCs) and Quantum Approximate Optimization Algorithms (QAOAs), which enable efficient handling of high-dimensional data and complex optimization tasks inherent in distributed environments. By addressing challenges like latency, energy efficiency, and computational overhead, the quantum AI model demonstrates significant performance gains in decentralized cloud systems.Experimental evaluations on benchmark datasets reveal a 40% reduction in training time, a 30% improvement in resource efficiency, and a 20% increase in prediction accuracy compared to classical deep learning frameworks. This study highlights the transformative potential of quantum computing in AI-driven decentralized cloud architectures, offering insights into its application for computationally intensive tasks across industries such as healthcare, finance, and logistics. Future work will focus on refining quantum hardware compatibility, developing quantum error correction methods, and exploring federated learning applications to expand the scope of quantum AI in privacy-preserving and distributed systems.
Marija MikiÄ, Mihajlo Srbakoski, Strahinja Praska
The integration of privacy-preserving transactions into public blockchains such as Ethereum remains a major challenge. The Stealth Address Protocol (SAP) provides recipient anonymity by generating unlinkable stealth addresses. Existing SAPs, such as the Dual-Key Stealth Address Protocol and the Curvy Protocol, have shown significant improvements in efficiency, but remain vulnerable to quantum attacks. Post-quantum SAPs based on lattice-based cryptography, such as the Module-LWE SAP, on the other hand, offer quantum resistance while achieving better performance. In this paper, we present a novel hybrid SAP that combines the Curvy protocol with the computational advantages of the Module-LWE technique while remaining Ethereum-friendly. In contrast to full post-quantum solutions, our approach does not provide quantum security, but achieves a significant speedup in scanning the ephemeral public key registry, about three times faster than the Curvy protocol. We present a detailed cryptographic construction of our protocol and compare its performance with existing solutions. Our results prove that this hybrid approach is the most efficient Ethereum-compatible SAP to date.
The rise of quantum computing poses a serious threat to the cryptographic backbone of decentralized systems like Ethereum's Plasma chains, which rely on classical cryptography. This paper introduces a novel approach, integrating post-quantum cryptography (PQC) with hybrid frameworks that blend quantum-resistant algorithms with traditional cryptographic techniques. This hybrid approach ensures strong quantum-resistant security while maintaining Plasma's scalability, performance, and compatibility with Ethereum's ecosystem. This study focuses on critical plasma components like state transitions, fraud proofs, and exit strategies, that are most vulnerable to quantum attacks, proposing hybrid cryptography for low risk, high frequency transactions, while leveraging post-quantum solutions like Kyber and NTRU for securing long-term commitments and high-risk processes. By establishing clear decision criteria to determine when hybrid cryptography should take precedence over pure PQC, based on factors such as computational efficiency, security demands, and system interoperability. The insights set a new standard for Plasma's quantum resilience, ensuring it stays secure and adaptable as quantum computing evolves, paving path for decentralized finance to thrive in the face of quantum threats.
We propose a scalable quantum architectures which can improve operation of Blockchain systems. We focus on permissioned blockchains with consensus derived from Practical Byzantine Fault Tolerance (PBFT). We propose multipartite entanglement quantum architectures that can perform PBFT. Further we develop quantum systems and algorithms that can support Proof of Stake (PoS) voting as well as voter election and voting in delegated Proof of Stake systems. Validating nodes within a cluster hold qubits entangled in multipartite structure. Due to maximally connected entanglement they jointly perform voting and calculate voting results. We propose algorithms that can track voter's behavior and detect collusion and voting centralization problem.
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 âno-cloningâ 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.
Bit commitment is a fundamental cryptographic primitive and a cornerstone for numerous two-party cryptographic protocols, including zero-knowledge proofs. However, it has been proven that unconditionally secure bit commitment, both classical and quantum, is impossible. In this work, we demonstrate that imposing a restriction on the committing party to perform only separable operations enables secure quantum bit commitment schemes. Specifically, we prove that in any perfectly hiding bit commitment protocol, an honestly-committing party limited to separable operations will be detected with high probability if they attempt to alter their commitment. To illustrate our findings, we present an example protocol.
Non-interactive zero-knowledge (NIZK) proof systems are a cornerstone of modern cryptography, but their security has received little attention in the quantum settings. Motivated by improving our understanding of this fundamental primitive against quantum adversaries, we propose a new definition of security against quantum adversary. Specifically, we define the notion of quantum simulation soundness (SS-NIZK), that allows the adversary to access the simulator in superposition. We show a separation between post-quantum and quantum security of SS-NIZK, and prove that Sahaiâs construction for SS-NIZK (in the CRS model) can be made quantumly-simulation-sound. As an immediate application of our new notion, we prove the security of the Naor-Yung paradigm in the quantum settings, with respect to a strong quantum IND-CCA security notion. This provides the quantum analogue of the classical dual key approach to prove the security of encryption schemes. Along the way, we introduce a new notion of quantum-query advantage functions, which may be used as a general framework to show classical/quantum separation for other cryptographic primitives, and it may be of independent interest.
As a popular decentralized and distributed database exhibiting transparency and unforgeability, blockchain has received widespread attention. At the time of writing, its security hinges on classical cryptography, which maintains a high grade of security by exploiting the potentially excessive computational complexity of mathematical problems to be solved by state-of-the-art computers. However, as computational technology develops, this encryption philosophy is likely to be challenged and there is a risk of âstore now and decrypt laterâ attacks. A compelling solution to this security threat is to intrinsically integrate blockchain with quantum technology. Against this background, we propose a quantum blockchain scheme relying on quantum secure direct communication (QSDC). Specifically, we conceive QSDC-based blockchain for identity verification, message encryption, and consensus. We also propose an optical network based realization of the proposed QSDC-aided blockchain using present-day technology. Our simulations quantify the benefits of the scheme, especially in terms of its resource utilization. This work provides a new prospect for the intrinsic fusion of quantum information technology and blockchain technology, paving the way for its rapid commercialization.
Abstract Blockchain technology ensures accountability, transparency, and redundancy, but its reliance on publicâkey cryptography makes it vulnerable to quantum computing threats. This article addresses the urgent need for quantumâsafe blockchain solutions by integrating postâquantum cryptography (PQC) into blockchain frameworks. Utilizing algorithms from the NIST PQC standardization process, it is aimed to fortify blockchain security and resilience, particularly for IoT and embedded systems. Despite the importance of PQC, its implementation in blockchain systems tailored for embedded environments remains underexplored. A quantumâsecure blockchain architecture is proposed, evaluating various PQC primitives and optimizing transaction sizes through techniques such as publicâkey recovery for Falcon, achieving up to 17% reduction in transaction size. The analysis identifies Falconâ512 as the most suitable algorithm for quantumâsecure blockchains in computerâbased environments and XMSS as a viable but unsatisfactory stateful alternative. However, for embeddedâbased blockchains, Dilithium demonstrates a higher transactionsâperâsecond (TPS) rate compared to Falcon, primarily due to Falcon's slower signing performance on ARM CPUs. This highlights the signing time as a critical limiting factor within embedded blockchains. Additionally, smart contract functionality is integrated, assessing the impact of PQC on smart contract authentication. The findings demonstrate the feasibility and practicality, paving the way for robust and futureâproof IoT applications.
Atoms and photons, two things so different but yet so alike. The former, the building block of matter, something we learn about in school and imagine it as some tiny marbles encircled by other tinier marbles. The latter, an electromagnetic wave, a light particle or an excitation of the electromagnetic field. Quantum mechanics tells us about the properties of these two entities. And even if it sounds, looks and writes counter-intuitive, it has proven right for over a century now. In this work, I elaborate on how we tested the laws of quantum mechanics and how we used them learn more about the tiny building blocks of nature and the fields they use to talk to each other. The atoms we use, are artificial. Superconducting qubits, small electrical circuits with quantized energy levels behave like electrons that transition between different orbitals in an atom. One of the qubits' advantages, is also a big disadvantage. We design the circuits' energy levels and fabricate them in a cleanroom. This allows for arbitrary spaced energy levels but in contrast to real atoms, prevents two superconducting qubits from being alike. Still, this qubit platform is one of the frontrunners for future quantum computing technology and testing fundamental physics due to their scalability. We interface superconducting qubits, which operate in the GHz regime, with microwave photons. We use 3D aluminum cavities as mediators between qubits and photons. The cavities allow for non-destructive readout of the qubit state, they shield the qubits from noise at the qubit frequency and they give us an easy way to frequency-tune these joint systems. We need to operate superconducting qubits and their cavities at millikelvin temperatures in dilution refrigerators. At higher temperatures, superconductivity suffers and even worse, the environment is filled with thermal noise photons. This poses a fundamental limitation on the scalability of superconducting qubit devices. Also connecting multiple devices in different fridges does not work over room temperature links because the microwave photons used for this purpose will be covered in noise and the quantum information they carry, will be unusable. Infrared photons do not suffer from this noise problem since there are close to zero thermal noise photons at their frequencies at room temperature. We cannot simply interface superconducting devices with optical photons due their frequency mismatch and the destructive effect of optical photons on superconductors. Therefore, we use microwave-to-optics transducers that allow to convert microwave photons into optical ones and vice-versa. The transducers that we use are macroscopic electro-optic transducers using the Pockels effect in a disk-shaped Lithium Niobate whispering gallery mode resonator. By using a strong optical pump, photons from the two frequency domains experience a beam-splitter interaction and get converted from one to the other. We measure the generated optical photons using elaborate optical setups, optical heterodyning and single photon detectors to gain knowledge about the qubit state or the converted microwave photons. Bridging the microwave and the optical world allows us to take advantage of both of their strengths but it also requires deep knowledge about both of their working principles. In this work, we describe two experiments that our group conducted to showcase the opportunities that arise from interfacing superconducting qubits with optical photons but also the pitfalls, one may encounter on the way. In the first experiment, we managed to all-optically read out a superconducting qubit. We show that the assignment fidelity, the probability that a measurement of the qubit state matches the prepared state, is close to equal for all-optical, microwave-to-optics and conventional microwave readout. We show T1 and T2 measurements for all three readout types and give an analysis of the noise caused by the optics. Finally, we show that the infrared light does not affect the qubit performance in a negative way but that the heating it causes does. This is an important insight that we used in the next experiment. The second experiment is the upconversion of itinerant single microwave photons to the optical domain. We show that we can generate single microwave photons from a qubit-cavity system. We upconvert these single photons, measure them with a single photon detector and reconstruct their shape. By conducting a single photon Rabi measurement, we show correlations between the microwave and the optical domain. And by thorough signal-to-noise measurements and noise analysis, we find that we can generate single infrared photons with high signal-to-noise ratio 5.1 and low transducer added noise (<0.012 quanta). We show that this measurement creates a path towards entanglement of a superconducting qubit and an optical photon and what parameters need to be improved to achieve it. Additionally, this experiment is a proof of principle for an on-demand infrared single photon source. More generally, it allows to link microwave quantum technology in general to the optical domain.
Blockchain technology has revolutionized secure and decentralized digital transactions. However, the emergence of quantum computing presents a significant threat to traditional cryptographic protocols, particularly public-key encryption mechanisms such as RSA and Elliptic Curve Cryptography (ECC). Quantum computers, leveraging Shorâs and Groverâs algorithms, can efficiently break these encryption schemes, compromising blockchain security. This paper explores quantum-secure blockchain protocols that integrate post-quantum cryptographic (PQC) techniques such as lattice-based, hash-based, and code-based cryptography to resist quantum attacks. Additionally, we evaluate quantum-resistant consensus mechanisms like Quantum-Secure Proof of Stake (QS-PoS) and Quantum-Protected Byzantine Fault Tolerance (Q-BFT). Through simulation-based performance analysis, we demonstrate that quantum-safe blockchain models can achieve robust security while maintaining efficient transaction processing. Our findings suggest that a hybrid approach, combining classical cryptographic elements with post-quantum algorithms, provides the best balance between security, performance, and scalability.
Adeshina Akin Ajayi, Igba Emmanuel, Adesola Dorcas Soyele, Joy Onma Enyejo
This paper explores the integration of quantum cryptography and blockchain technology to address two pressing challenges: securing financial transactions in Central Bank Digital Currencies (CBDCs) and combating the spread of misinformation during U.S. elections through decentralized social media platforms. As quantum computing advances, traditional encryption methods may become obsolete, posing significant risks to digital financial systems. Quantum cryptography, with its quantum-resistant algorithms, offers enhanced protection for CBDC transactions, ensuring long-term security and privacy. Simultaneously, blockchain-based social media platforms provide a decentralized structure that can prevent the dissemination of false information by ensuring transparency and authenticity through cryptographic verification and consensus mechanisms. These platforms also facilitate decentralized identity management, empowering users to verify content without relying on centralized authorities. By combining quantum cryptographyâs secure framework with blockchainâs decentralized transparency, this dual approach creates a more secure digital ecosystem that not only safeguards financial transactions but also strengthens democratic processes. The paper further addresses the regulatory and technical challenges associated with implementing these technologies and their potential to shape a more secure, transparent, and accountable future.
A Zero-Knowledge Proof basically is a protocol between two parties, the Prover and the Verifier, that allows the Prover to convince the Verifier about the truthness of a non trivial statement without revealing any additional information. Zero Knowledge Proofs have found a lot of practical applications covering most of the protocols concerning about data privacy and protocol verification. Examples of that are anonymous cash or electronic voting. The possibility to have real quantum computers with a reasonable size in a near future is forcing the cryptographic community to devise new methods to provide security that resist quantum attacks. Most of the zero-knowledge protocols used nowadays are based on computational problems like the discrete logarithm problem that can no longer be considered hard, since there are known efficient ways to solve them with quantum algorithms. Cryptographic research about the quantum security of zero knowledge proofs started nearly 20 years ago in a very theoretical approach, but not many papers on that topic appeared since then. The goal of this thesis is writing a survey including the main concepts about quantum secure zero-knowledge protocols, the state-of-the-art both from the theoretical and practical approaches, and an exploration of their potential application areas. The survey will be a good starting document for further students willing to do research in this topic.
Private set intersection (PSI) has important application value, however, current quantum PSI protocols are either unsuitable for multi-party scenarios or inefficient. Recently, Imran (arXiv: 2303.17196v3 , 2023) proposed two quantum secure multi-party greatest common divisor (GCD) protocols that can be used for PSI, but with the downside of information leakage and resource consumption. In this paper, we propose a novel quantum secure multi-party GCD protocol that has higher security and lower complexity. To hide privacy, each party randomly selects a coefficient within a range determined by his input integer, and with the assistance of a semi-honest third party TP, all parties secretly calculate the linear combination of their inputs under these coefficients. Once enough linear combinations are collected, TP calculates the GCD of these combinations, which is equal to the GCD of all input integers. To verify the honesty of participants, a quantum zero-knowledge proof sub-protocol is designed. Analysis shows that our GCD protocol is correct and has security against malicious attacks. Moreover, its complexity is polynomial level and lower than Imranâs. Furthermore, we demonstrate the scalability of our GCD protocol in private set operations, such as private set intersection, private set intersection cardinality, private multi-set intersection, etc.