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A Survey and Comparison of Post-quantum and Quantum Blockchains

Zebo Yang, Haneen Alfauri, Behrooz Farkiani, Raj Jain, Roberto Di Pietro, Aiman Erbad

arXiv:2409.01358v1cs.CRquant-ph

TL;DR

Quantum computing threatens the public-key cryptography and hash functions underpinning blockchains. This paper surveys and compares post-quantum cryptographic blockchains with quantum-based blockchain designs, finding hybrid classical-quantum infrastructure a plausible future form while fully quantum approaches remain at an early, largely theoretical stage.

  • Problem

    Quantum computing threatens blockchain cryptography through Shor’s and Grover’s algorithms, while existing surveys lack extensive comparison of post-quantum and quantum blockchains.

    Source: §I · pp. 1–2

  • Method

    The paper reviews and compares post-quantum and quantum blockchain research, including their designs, potential, limitations, and research trends.

    Source: §I · p. 2, §VII · p. 32

  • Results

    The survey identifies hybrid classical-quantum infrastructure as a plausible future network form, while fully quantum blockchain approaches remain impractical and largely theoretical at the current stage.

    Source: §B.3 · p. 25, B. Retrospective of hybrid quantum… · p. 28, C. Retrospective of fully quantum… · p. 28

  • Takeaways & Limitations

    The comparison can help assess the approaches’ strengths, limitations, application fit, and compatibility during a gradual transition to quantum computing.

    Source: §I · p. 2

    Fully quantum blockchain research remains early-stage, with barely available implementations due to limited access to powerful quantum computers.

    Source: C. Retrospective of fully quantum… · p. 28

Abstract

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Blockchains have gained substantial attention from academia and industry for their ability to facilitate decentralized trust and communications. However, the rapid progress of quantum computing poses a significant threat to the security of existing blockchain technologies. Notably, the emergence of Shor's and Grover's algorithms raises concerns regarding the compromise of the cryptographic systems underlying blockchains. Consequently, it is essential to develop methods that reinforce blockchain technology against quantum attacks. In response to this challenge, two distinct approaches have been proposed. The first approach involves post-quantum blockchains, which aim to utilize classical cryptographic algorithms resilient to quantum attacks. The second approach explores quantum blockchains, which leverage the power of quantum computers and networks to rebuild the foundations of blockchains. This paper aims to provide a comprehensive overview and comparison of post-quantum and quantum blockchains while exploring open questions and remaining challenges in these domains. It offers an in-depth introduction, examines differences in blockchain structure, security, privacy, and other key factors, and concludes by discussing current research trends.

I. INTRODUCTION

Quantum computing threatens the public-key cryptography and hash functions that underpin blockchains, motivating both post-quantum cryptography and quantum-based redesigns. The paper surveys and compares these approaches, addressing a gap in reviews that had not extensively covered both.

I. INTRODUCTION

  • Shor’s algorithm threatens public-key cryptography, while Grover’s algorithm threatens the hash functions used in blockchains [6], [7].Post-quantum cryptography uses methods not based on factorization; quantum blockchains explore rebuilding blockchain structures with quantum computers and networks.Source: §I · p. 1
  • The paper provides an in-depth introduction, comparison, and categorization of state-of-the-art post-quantum and quantum blockchains.The authors note that earlier surveys and reviews had not extensively discussed and compared both approaches.Source: §I · p. 2
  • Comparing the approaches can help assess their suitability for applications, security needs, and compatibility during a gradual transition to quantum computing.The paper notes that post-quantum and quantum systems may coexist during the transition.Source: §I · p. 2
  • The paper’s stated contributions include a pedagogical introduction, a survey of potential and limitations, a comparison of key components, and discussion of research trends.Table I presents differing emphases among related reviews, not their superiority or inferiority.Source: §I · p. 2

II. PRELIMINARIES

The preliminaries section introduces classical blockchains, quantum computing, and quantum attacks, then frames post-quantum and quantum blockchains as potential responses.

II. PRELIMINARIES

  • The section reviews classical blockchains, quantum computing, and Shor’s and Grover’s impacts on cryptographic systems, then discusses post-quantum and quantum blockchain responses.Source: §II · p. 2

A. Classical Blockchains

The section introduces blockchain structure and transactions through Bitcoin, covering peer addresses, data organization, and consensus. It explains how public-key pairs support transactions and how multiple addresses can help users maintain privacy.

A. Classical Blockchains

  • A blockchain system comprises peer addresses, decentralized data structure, and a consensus mechanism for maintaining and agreeing on new entries.Bitcoin serves as the section’s illustrative example, while many systems retain a shared foundational core.Source: A. Classical Blockchains · pp. 2–3

A.1. Blockchain addresses

  • Addresses are typically derived from public keys, and private-key signatures can be authenticated with the corresponding public keys to verify transaction integrity.A user may hold multiple public- and private-key pairs.Source: §A.1 · p. 3
  • Users may create a new address for each transaction to reduce the risk of identification associated with reusing one address.Most blockchain wallet applications support creating new addresses for this purpose.Source: §A.1 · p. 3

A.2. Blockchain data

Blockchain data is organized into linked blocks whose hash pointers connect each block to its predecessor. This structure supports tamper resistance, while hash functions also underpin the links and have security properties relevant to attacks.

A.2. Blockchain data

  • Each block contains transactions and a header with the preceding block’s hash, linking blocks into a chain.The header also carries metadata such as a timestamp and nonce.Source: §A.2 · p. 3
  • Modifying a block requires recalculating succeeding blocks, which becomes increasingly challenging with proof-of-work consensus.Source: §A.2 · p. 3
  • Hash functions create fixed-length hash pointers; their non-reversibility illustrates preimage resistance, while finding collisions requires searching the full space absent a faster classical algorithm.Source: §A.2 · p. 3

A.3. Blockchain consensus

The section introduces blockchain consensus and quantum-computing basics, then explains how Shor’s and Grover’s algorithms threaten cryptographic keys and proof-of-work. It also describes smart contracts and surveys consensus alternatives.

A.3. Blockchain consensus

  • Consensus ranges from proof-of-work nonce races and confirmation-depth fork selection to Byzantine agreement and stake-, delegate-, capacity-, or authority-based validator selection.Proof-of-work is energy-intensive; the Broadcast protocol has high communication overhead.Source: §A.3 · pp. 3–4
  • The Broadcast protocol assumes fewer than one-third dishonest nodes, reaches Byzantine agreement within m+1 rounds, and incurs considerable communication overhead.Source: §A.3 · p. 4

A.4. Smart contracts

  • Smart contracts automatically trigger coded actions when specified conditions are met, avoiding a trusted third party or arbitrator.Source: §A.4 · p. 5

B. Quantum Computing

  • Qubits use superposition and entanglement; measurement collapses superposition to a classical bit, while qubit instability impedes commercialization.Source: B. Quantum Computing · p. 5

C. Impacts of Quantum Computing

C.1. Shor’s algorithm

  • Shor finds a period with quantum registers and a quantum Fourier transform, then uses classical gcd calculations to factor N.For N=91, the passage reports factors 7 and 13.Source: §C.1 · p. 6
  • 10 minutes on a 10 MHz quantum computer is the cited RSA2048 break estimate; Shor-derived private keys could enable transaction impersonation.Source: §C.1 · p. 6

C.2. Grover’s algorithm

  • Grover reduces unstructured search from O(N) to O(√N), potentially accelerating mining and hash-collision attacks, though large-scale practicality remains undetermined.The passage says Monero’s RandomX proof-of-work makes it safe from Grover’s algorithm.Source: §C.2 · p. 7

D. Solutions to Quantum Threats

This section surveys approaches to quantum threats to blockchains, contrasting post-quantum blockchains with quantum blockchains and covering their cryptographic foundations and applications. Topics include signatures, privacy, decentralized applications, IoT, smart cities, key exchange, proof-of-work, and consensus.

A. Post-quantum Cryptography

  • Post-quantum cryptography replaces factorization-based public-key schemes with quantum-resistant alternatives, but often entails larger keys and hashes or higher computational complexity.The surveyed families include code-based, multivariate-based, lattice-based, and supersingular elliptic curve isogeny cryptosystems; increasing key size is a straightforward response to Grover’s search, while hash functions are generally not redesigned,, [11]. NIST selected Kyber for encryption and Dilithium, FALCON, and SPHINCS+ for signatures –[65].Source: D. Solutions to Quantum Threats · p. 7, A. Post-quantum Cryptography · p. 8

D. Solutions to Quantum Threats

  • Quantum blockchains combine techniques such as QKD, quantum signatures, teleportation, and bit commitment, but depend on quantum networks that remain under development.Teleportation transmits quantum information between parties while destroying the transmitted qubit on the sender’s side; a global quantum internet is still a way off.Source: D. Solutions to Quantum Threats · p. 7

B. Studies of Post-quantum Blockchains

  • Post-quantum blockchain studies address quantum threats through signature schemes, privacy-enhancing techniques such as ZKPs, and decentralized applications built with smart contracts.The literature review groups these proposals by intended objective.Source: B. Studies of Post-quantum Blockchains · p. 10

B.1.1. Industrial approaches

  • Industrial signature approaches include hash-based signatures in IOTA Tangle and QRL, lattice-based cryptography in Abelian, and an optional SPHINCS scheme for Corda,,,.QRL uses XMSS and claims compatibility with different cryptographic solutions,; Corda offers SPHINCS for long-term contracts but describes its 41 KB signatures and slow signing as impractical for many applications,.Source: §B.1.1 · pp. 10–11

B.1.2. Academic approaches

  • Academic signature proposals use lattice- and hash-based schemes, with work targeting compact keys, signatures, and signing or verification costs,,,,.Examples include bonsai-tree wallets that store a root key, SDS compression trees, BPQS with a fallback for continued signing, and WOTS-S, whose signatures are 59% and 24% shorter than IOTA and QRL, respectively.Source: §B.1.2 · p. 11

B.2. Privacy-enhancing approaches

  • ZKPs can support confidential transactions, but post-quantum properties differ: hash-based zk-STARKs resist quantum attacks, whereas elliptic-curve zk-SNARKs do not,.STARKs generally produce larger proofs and can entail higher verification overhead, but avoid a trusted setup; off-chain provers can perform private transactions with on-chain verification. Zerocash uses zk-SNARKs to conceal unspent-fund commitments.Source: §B.2 · p. 12

B.3. Post-quantum decentralized applications

  • Post-quantum decentralized applications include blockchain e-voting proposals that use code-based or lattice-based cryptography to protect voting integrity and voter privacy,.The Niederreiter-based protocol was evaluated as suitable for small-scale elections; a certificate-less NTRU ring-signature scheme aims to reduce PKI management burdens,.Source: §B.3 · pp. 12–13
  • Other applications use SIDH for quantum-resistant sharing of sensitive industrial data and lattice-based signatures for transaction authentication and decentralized PKI –.The IPFS–Ethereum framework performs encryption off-chain because transparent smart-contract code could expose private variables; QChain’s ring-LWE signature approach was reported to perform similarly to centralized PKI while providing decentralized post-quantum benefits,.Source: §B.3 · p. 13
  • A blockchain-based Social Internet of Things platform uses a multivariate ring signature to hide which group member signed a transaction.The public can verify the signature using the group’s ring public key but cannot identify the signer.Source: §B.3 · p. 13
  • A modified key-exchange protocol for resource-constrained IoT devices reuses keys to reduce computational and communication costs while resisting replay, man-in-the-middle, and impersonation attacks.The passage describes the protocol as maintaining a high level of security while reducing the overhead associated with traditional key exchange methods.Source: §B.3 · p. 13
  • A post-quantum proof-of-work for smart cities replaces Bitcoin’s SHA-256 hashing challenge with solving multivariate quadratic equations, with lightweight transactions built on that consensus.Miners use a Gröbner basis algorithm to solve seeded equations; the transaction design embeds an identity-based signature scheme and IPFS, with efficient performance reported.Source: §B.3 · pp. 13–14
  • Other proposals include a polynomial-equation-based parametric blockchain hash claimed collision-impossible and analysis of IoT, cloud, and blockchain integration in the quantum era.A post-quantum dApp combines Ethereum smart contracts, IPFS, and lattice-based key exchange for encrypted data sharing or storage; another work explores quantum machine learning’s potential impact on classical 5G networks.Source: §B.3 · p. 14
  • Researchers examine interactions between blockchain, machine learning, and quantum technologies,,, while and use concurrent-preprocessing MPC for asynchronous quantum-resistant blockchain consensus.The latter approach achieves quantum resistance through MPC rather than post-quantum cryptography,.Source: §B.3 · p. 14

B.4. Summary of post-quantum blockchains

The survey reviews post-quantum blockchain approaches across cryptographic families and applications, alongside their trade-offs and research maturity. It reports a lack of recent updates to blockchain-specific post-quantum signatures and notes that many proposals remain theoretical.

B.4. Summary of post-quantum blockchains

  • Post-quantum blockchain designs span lattice-, hash-, code-, multivariate-, and isogeny-based cryptography, with trade-offs including security, efficiency, and key size.The survey also covers privacy-enhancing zero-knowledge proofs and applications such as IoT.Source: §B.4 · p. 14
  • Blockchain-specific post-quantum signature work had no reported update after Corda's 2018 proposal.The paper also notes that Bitcoin Post-Quantum had ceased operation by the time of revision.Source: §B.4 · p. 15
  • Several surveyed proposals are conceptual rather than implemented, including work on lightweight wallets, double signatures, Bitcoin security, and decentralized applications.The cited studies focus on theoretical aspects or security analysis rather than experiments or implementations.Source: §B.4 · pp. 15–16
  • SDS reduces hash-tree creation time and key and signature sizes through a key-compression tree, and its testbed outperformed two XMSS instances in efficiency.The tree replaces direct use of XMSS.Source: §B.4 · p. 15
  • BPQS is reported to compare favorably with classical and post-quantum signatures and to outperform XMSS on signature size.The surveyed approach is based on XMSS and includes a prototype.Source: §B.4 · p. 15
  • Replacing ECDSA with Rainbow did not affect blockchain processes or performance in experiments using Ethereum.Source: §B.4 · p. 15
  • Zerocash transactions are reported as smaller than 1 kB and verifiable in under 6 ms, comparable to plain Bitcoin in efficiency.The scheme uses zk-SNARKs and hides commitments of unspent funds.Source: §B.4 · pp. 15–16
  • The surveyed code-based voting scheme is reported as suitable for small-scale elections and settings with limited voter numbers.Source: §B.4 · p. 16

A.1. Quantum key distribution

The section introduces quantum communication and cryptographic protocols, then describes how quantum techniques can support blockchain designs. It covers QKD, quantum signatures, teleportation, bit commitment, and a hybrid blockchain using QKD-generated keys.

A.1. Quantum key distribution

  • QKD lets two parties share a secret key using quantum states, and BB84 detects possible interception through mismatches while requiring trust and an authenticated classical channel.In BB84, parties keep measurements made in matching bases and discard the rest.Source: §A.1 · pp. 16–17

A.2. Quantum signature

  • Quantum signatures use quantum states derived from private bit strings, but swap tests cannot always distinguish unequal states and distributing copies is limited by Holevo's theorem.The text contrasts these constraints with classical signatures.Source: §A.2 · p. 18

A.3. Quantum teleportation

  • Teleportation transfers an unknown qubit using a shared entangled pair, a Bell-state measurement, and classical communication; measurement destroys Alice's original state.Bob applies gates based on Alice's transmitted measurement result.Source: §A.3 · p. 18

A.4. Bit commitment

  • The described bit-commitment protocol aims to conceal a committed bit until reveal and bind the sender afterward, but unconditional security is impossible in classical and quantum settings.The text notes cheat-sensitive quantum protocols as an alternative.Source: §A.4 · p. 19

A.5.1. Hybrid quantum blockchain overview

  • Hybrid quantum blockchains use QKD-generated secret keys for a mostly symmetric-cryptography, private or permissioned network.Their deployment phase establishes keys and authenticates nodes; block production uses consensus and keyed hashing.Source: §A.5.1 · p. 19
  • In the hybrid design, nodes authenticate transactions by comparing keyed hashes, while the described BFT consensus reaches consistency when dishonest nodes are fewer than one third.The survey cautions that this consensus becomes exponentially data-heavy with many dishonest or non-operational nodes.Source: §A.5.1 · p. 19

A.5.2. Fully quantum blockchain overview

The fully quantum blockchain model represents blocks as temporally entangled quantum states, with creation times serving as timestamps. The survey contrasts this design with more prevalent hybrid systems, noting major practical constraints on fully quantum implementations.

A.5.2. Fully quantum blockchain overview

  • A fully quantum chain is built by appending temporally entangled states, with each block carrying two-bit data and its creation time serving as a timestamp.The first two blocks can be merged into a four-photon GHZ state.Source: §A.5.2 · p. 20
  • The described consensus design uses a quantum random number generator to select a block producer and distributed verification tests.Source: §A.5.2 · p. 20

B.1. Designing quantum blockchains

  • Fully quantum blockchains are described as infeasible to implement currently because quantum computers are limited, and most proposals lack practical implementation or experimental validation.The survey says hybrid approaches are more numerous and offer adequate, though lower, security against quantum attacks.Source: §B.1 · p. 20

B.1.1. QKD-based hybrid quantum blockchains

The section surveys hybrid blockchains that combine quantum mechanisms with classical blockchain components, including QKD-based key exchange and quantum signatures. It also describes constraints on QKD deployment and limitations in several proposed designs.

B.1.1. QKD-based hybrid quantum blockchains

  • JPMorgan’s hybrid proof-of-concept keeps the blockchain classical while using multiplexed QKD for key exchange, supporting data rates up to 800 Gbps.Source: §B.1.1 · p. 20
  • A two-layer QKD blockchain shares secret keys in one layer and uses Toeplitz-hash authentication tags in another, with Broadcast consensus forming blocks and preventing forks.The system was experimentally tested using an urban-fiber QKD network; its Toeplitz hash remains vulnerable to Grover’s algorithm.Source: §B.1.1 · pp. 20–21
  • QKD networks require dedicated quantum channels and have low key-generation rates, limiting their suitability for large-scale systems.A quantum key pool of pregenerated shared keys is proposed to support secure key management.Source: §B.1.1 · p. 21
  • A QKD- and QSDC-based design uses qulogicoins, classical and quantum certificates, and QHBA consensus to validate transactions.The authors claim QHBA is more efficient than classical Byzantine protocols when many nodes are dishonest.Source: §B.1.1 · p. 21
  • QSYAC combines QKD-distributed keys, Toeplitz group signatures, and three-phase peer voting, assuming at least three-quarters of peers are honest.The survey notes that the hash function for verified blocks is unspecified and questions the lottery’s ideal-protocol properties.Source: §B.1.1 · pp. 21–22

B.1.2. Other hybrid quantum blockchains

  • A hybrid design combines QSCDff-based quantum signatures with DPoSB, which ranks block producers using stake, behavior, and Borda-count voting.Source: §B.1.2 · p. 22
  • Quantum transaction signing requires users to distribute public keys to miners and generate a key set for each transaction, which the survey considers impractical for public blockchains.The survey also raises unresolved concerns about malicious miners and the handling of teleportation results.Source: §B.1.2 · p. 22

B.1.3. Fully quantum blockchains

The section reviews designs that build blockchains from quantum states or use quantum mechanisms to replace blockchain components. These approaches include time-entangled chains, quantum identity and cash systems, quantum hashes, and measurement-based consensus, but fully quantum systems have limited data capacity.

B.1.3. Fully quantum blockchains

  • Fully quantum blockchains chain quantum states, but their data-storage capacity is limited compared with classical blockchains [49].Source: §B.1.3 · p. 22
  • A time-entangled design uses temporally ordered entangled qubits to form a chain whose alteration would collapse the states and reveal tampering.Source: §B.1.3 · p. 22
  • QBIF applies a time-entangled quantum-state chain to decentralized identity authentication, with QRNG block-producer selection and distributed θ-protocol verification.The design combines quantum-network nodes with classical off-chain communication and is described as having various limitations and challenges.Source: §B.1.3 · p. 23
  • In qbitcoin, coins pair a classical transaction record with a quantum state, and teleportation transfers the quantum part so the former owner no longer possesses it.The survey says the mapping between the classical and quantum parts is unspecified, leaving coin validity difficult to check.Source: §B.1.3 · p. 23
  • Other designs replace blockchain components with a quantum-walk hash function or quantum-weighted hypergraph states, using relative phases for consensus,.The quantum-walk design does not explain why nodes omit a consensus algorithm.Source: §B.1.3 · p. 23
  • Quantum-server mining uses a Byzantine fault-tolerant consensus design, while a separate measurement-based proposal uses quantum randomness and quantum ZKP,.The survey notes that the mining design leaves hashes and signatures unimproved, and the ZKP verification mechanism is not clearly explained.Source: §B.1.3 · pp. 23–24

B.2. Building quantum blockchain applications

The section surveys quantum-blockchain applications in voting, lotteries, auctions, and other domains. The proposals use QKD or quantum protocols in different ways, and the survey identifies unresolved vulnerabilities and deployment details.

B.2. Building quantum blockchain applications

  • A QKD-backed voting application encrypts stored block hashes but leaves the blockchain’s cryptographic design vulnerable to quantum attacks.Source: §B.2 · p. 24
  • A quantum voting protocol combines QKD, QBC, and QHBA and claims to satisfy anonymity, binding, non-reusability, verifiability, eligibility, fairness, and self-tallying requirements.The survey notes that the protocol does not explain how the system determines the total number of voters or detects non-voters.Source: §B.2 · p. 24
  • Lottery and sealed-bid auction protocols use QKD and QBC, with miners reaching consensus on outcomes.The survey notes that cheating-node sensitivity was not analyzed and that QBC and consensus may be susceptible to cheating nodes.Source: §B.2 · pp. 24–25
  • Other proposed applications combine quantum cryptography with classical blockchains for vehicles, smart contracts, and healthcare, including simulated healthcare scenarios,,.Source: §B.2 · p. 25
  • Hybrid quantum-classical payment systems pair classical blockchains and smart contracts with quantum lightning or quantum money,.One design uses a classical blockchain as a timestamped dictionary linking quantum-money serial numbers to users’ public keys.Source: §B.2 · p. 25

B.3. Summary of quantum blockchains

The summary identifies QKD as central to quantum-blockchain designs and notes that many reviewed approaches retain classical hash functions. It distinguishes hybrid from fully quantum systems and characterizes fully quantum chains as promising but currently impractical.

B.3. Summary of quantum blockchains

  • QKD is central to reviewed quantum-blockchain designs because it lets nodes generate shared secret keys, while quantum signatures, hashes, and consensus algorithms are also used [48].Few reviewed approaches replace classical hash functions; the survey says doubling hash sizes can mitigate quantum threats to them.Source: §B.3 · p. 25
  • Fully quantum designs often chain quantum states through graph states or entanglement, but the survey considers them impractical at the current stage of quantum-computing development [60].Source: §B.3 · p. 25
  • The reviewed studies include a QKD-based urban-fiber blockchain experiment and a multiplexed-QKD proof-of-concept network [25], [48].Source: §B.3 · p. 26
  • One proposal uses a time-entangled quantum-state blockchain for identity management, with QRND-based consensus and quantum-state verification tests; another designs cryptocurrency using teleportation and quantum signatures but omits coin mapping and public-key distribution.Source: §B.3 · p. 26
  • Other proposals explore quantum hashes, hypergraph-state chains, mining, and measurement-based consensus, with reported implementation evidence ranging from a five-qubit proof-of-concept to an interferometer demonstration [196], [197], [198], [199].The survey also flags missing consensus details, vulnerable hash and signature components, or unclear quantum-ZKP verification in these studies.Source: §B.3 · pp. 26–27

V. COMPARISON

  • The survey separates hybrid blockchains, which use classical and quantum systems, from fully quantum blockchains, which assume quantum systems and networks [90].Source: §V · p. 27

A. Retrospective of post-quantum blockchains

Post-quantum blockchains retain compatibility with existing infrastructure, but their cryptographic security remains theoretical and they may leave hash functions exposed to quantum brute-force attacks.

A. Retrospective of post-quantum blockchains

  • Post-quantum blockchains are easier to implement and adopt while preserving compatibility and existing performance, but rely on cryptographic algorithms whose effectiveness remains theoretical.They also do not fully harness quantum technologies.Source: A. Retrospective of post-quantum… · p. 27
  • Powerful future quantum computers may break even large-key hash functions, a threat most post-quantum blockchains do not address.The paper identifies post-quantum hash functions and hybrid-quantum or fully quantum blockchains as possible alternatives in that case.Source: A. Retrospective of post-quantum… · p. 27
  • Fully quantum blockchains may remain decades away because current quantum systems are small-scale and unstable.The paper presents this as a constraint on their adoption, not a settled timeline.Source: A. Retrospective of post-quantum… · p. 27

B. Retrospective of hybrid quantum blockchains

Hybrid quantum blockchains combine classical systems with quantum components, often using QKD, and may serve as a transition toward fully quantum blockchains. Fully quantum designs promise quantum-specific capabilities but remain theoretical and face substantial infrastructure and compatibility barriers.

B. Retrospective of hybrid quantum blockchains

  • Hybrid systems combine classical and quantum algorithms for gradual adoption, but integration can be complex and may introduce new attack vectors.The challenges depend on the quantum component’s role; quantum-based consensus, for example, is less feasible and reliable owing to quantum noise, as illustrated by an energy-efficient block-production protocol.Source: B. Retrospective of hybrid quantum… · pp. 27–28
  • QKD-based hybrid blockchains are more practical than fully quantum blockchains but less efficient than post-quantum blockchains.They use QKD for key exchange in a classical blockchain, then nodes communicate using symmetric keys,.Source: B. Retrospective of hybrid quantum… · p. 28
  • QKD-based designs use mostly Byzantine-agreement consensus, which is effective but carries relatively high message overhead.The paper notes follow-up work on optimizing consensus algorithms [194],,.Source: B. Retrospective of hybrid quantum… · p. 28
  • Hybrid quantum blockchains may provide a transition from classical blockchains to fully quantum systems and fit a plausible future hybrid network infrastructure,.Source: B. Retrospective of hybrid quantum… · p. 28

C. Retrospective of fully quantum blockchains

  • Fully quantum blockchains are designed from scratch around quantum computing and communication, with potential performance gains and novel applications.Their implementation requires major advances in quantum infrastructure and is complex and costly, with limited compatibility with existing systems.Source: C. Retrospective of fully quantum… · p. 28
  • Fully quantum blockchain research remains theoretical, with few implementations or developed simulations and designs that typically chain one-qubit states as blocks.The approach is far from competitive with classical blockchains; foundational components such as quantum broadcast networks remain open issues, leaving the field confined to laboratories.Source: C. Retrospective of fully quantum… · p. 28

D. Comparisons of the technologies

The comparison presents post-quantum blockchains as more accessible, hybrid systems as a balance, and fully quantum systems as potentially most beneficial but dependent on major advances. It also identifies early-stage research challenges spanning cryptographic trade-offs, integration, quantum hardware, and awareness.

D. Comparisons of the technologies

  • Post-quantum blockchains offer greater compatibility, hybrid systems balance classical and quantum technologies, and fully quantum systems have greater potential but require substantial advances.Table VIII presents a general comparison that may omit nuances.Source: D. Comparisons of the technologies · p. 28, Table VIII · p. 29
  • Fully quantum blockchains have limited compatibility and are difficult and costly to adopt and scale, requiring substantial infrastructure advances and new standards and protocols.Source: D. Comparisons of the technologies · p. 29
  • Fully quantum systems promise exceptional security from quantum properties, but practical security has not been demonstrated; performance gains remain theoretical and depend on quantum-system deployment.The cited potential applications include faster transactions and secure computation.Source: D. Comparisons of the technologies · p. 29
  • Table IX compares blockchain components and other factors; fully quantum blockchain privacy has no explicit research yet, though blind quantum computation is expected to support it.Source: Table IX · p. 29, D. Comparisons of the technologies · p. 29

VI. LESSONS LEARNED AND RESEARCH TRENDS

A.1. Critical challenges in these fields

  • Because both fields remain early-stage, post-quantum research must balance security, efficiency, and key sizes, while hybrid designs must integrate quantum components without disrupting classical systems or performance.The paper gives hash-based and lattice-based cryptography as examples of security-practicality trade-offs.Source: §A.1 · p. 30
  • Fully quantum blockchain work faces scarce, inadequate hardware and a lack of implementations; raising awareness through education and collaboration is another stated challenge.The paper calls for collaboration among academia, industry, and policy-makers.Source: §A.1 · p. 30

A.2. Lessons learned

The survey distills lessons from post-quantum and quantum blockchain research and identifies unresolved design trade-offs, application needs, and infrastructure questions. It concludes that quantum-resistant blockchains are necessary, while both research directions retain open challenges.

A.2. Lessons learned

  • Quantum computing’s blockchain impact remains uncertain, post-quantum approaches are currently most practical, and some demonstrated signature schemes still lack blockchain integration and use-case analysis.Increasing current hash-function key sizes can mitigate attacks at the cost of computation and storage; quantum breakthroughs may improve throughput, but concepts promising millions of TPS have no practical implementations. Proof-of-work may resist major near-term acceleration, while long-term post-quantum security remains uncertain.Source: §A.2 · pp. 30–31

B.1. Ideal Post-quantum Cryptography

  • No ideal post-quantum cryptographic scheme yet balances efficiency, quantum resistance, and blockchain-suitable key and signature sizes.Hash-based signatures may offer stronger quantum security but be less practical than lattice-based schemes; lattice security may change, and multivariate security remains unclear.Source: §B.1 · p. 31

B.2. Post-quantum blockchain paradigms

  • Post-quantum blockchain research targets signature integration, consensus mechanisms, quantum-resistant proof-of-work, and balancing security with performance.Interactive signature processes may require new blockchain procedures and can negatively affect performance.Source: §B.2 · p. 31

B.3. Post-quantum blockchain applications

  • Post-quantum applications require adapting smart-contract dApps and developing infrastructure such as access control, authentication, and standards.The security of storing identity data such as ZKPs depends on post-quantum hash functions and public-key schemes.Source: §B.3 · p. 31

B.4. Hybrid quantum blockchains

  • Hybrid quantum blockchains commonly layer classical chains over QKD, but symmetric-key exchange overhead limits scalability and efficiency.Research also considers quantum cryptography beyond QKD, compatibility with established systems, and interoperability across classical, post-quantum, and quantum chains.Source: §B.4 · pp. 31–32

B.5. Quantum blockchain paradigms

  • Current quantum blockchains remain simplified and difficult to scale, with transaction handling, user identification, and asset-account links unresolved.Fully quantum blockchains require substantial quantum advantage; theoretical analysis and useful simulators are research needs given limited hardware.Source: §B.5 · p. 32

B.6. Post-Quantum and quantum supporting infrastructure

  • Different adoption paths may produce isolated internets, motivating discussion of infrastructure that supports heterogeneous legacy, post-quantum, and quantum systems.The proposed infrastructure would support a long-term transition toward a full post-quantum or quantum world.Source: §B.6 · p. 32

VII. CONCLUSION

  • The conclusion presents a comprehensive comparison of post-quantum and quantum blockchain approaches, their open challenges, and research trends.It argues that developing quantum-resistant blockchains is necessary for decentralized-system security and integrity as quantum computing advances.Source: §VII · p. 32

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