Public debate on the quantum threat to blockchains—and much of the survey literature—is dominated by chain-level claims that mislocate the risk. We relocate the problem to the level at which an algorithm actually acts, showing that the post-quantum fate of any chain decomposes into three layers: which hardness assumption secures its signatures (Shor-vulnerable discrete-log/factoring, hash, or lattice); that assumption's status under the physically-realizable computational model (classical BPP vs quantum BQP); and the physical floor beneath it—unstructured-search lower bounds and serial-depth constraints, not a claim of unconditional security. At ground zero, the abelian-hidden-subgroup atom is efficiently broken under BQP (Shor), while no efficient BQP break is known for hash or lattice; hash security rests on the most conservative, best-tested conjecture; discrete-log rests on exploitable algebraic structure; and lattice assumptions, though buttressed by worst-case reductions unevenly across the lattice family, carry a much shorter cryptanalytic record. We locate the vulnerability in a single object—the exposed public key—and formalize compromise as a conjunction of exposure, feasibility, and non-revocation. Under a floor assumption (generic, unstructured search stays infeasible) this factors into four conjuncts answering to four distinct authorities—mathematics, the ledger, engineering, and the owner or protocol—with feasibility entailing brokenness. Each per-asset cryptanalytic defense we survey denies the primary one of these four conjuncts—an accounting identity over the four predicates (some defenses touch more than one; we classify by the primary), not a claim of exhaustiveness over an open-ended literature. We give an exposure taxonomy checked against the reference implementations and a first-party, reproducible measurement of the full Bitcoin UTXO set (block 957,269, July 2026): 1.93M BTC (≈9.6% of supply) carries a standing exposed public key—the defensible, structurally unambiguous figure—rising to 5–7M BTC (25–35%) once key-reuse is included, the range's width set by the P2SH/P2WSH script-hash upper bound. This decomposes exactly along the taxonomy's structural-versus-operational axis and quantifies Taproot's hidden-key regression (a directional shift on the exposure axis, minor by value); current resource estimates and a CRQC timeline; and a per-chain migration survey. A recurring result: account and governance architectures migrate most easily while immutable/UTXO chains are hardest—the property prized as a security virtue is the migration handicap. No unconditional security exists; all verdicts are contingent on unproven conjectures and the assumption that BQP is the physical ceiling of computation.
Public debate on the quantum threat to blockchains—and much of the survey literature—is dominated by chain-level claims that mislocate the risk. We relocate the problem to the level at which an algorithm actually acts, showing that the post-quantum fate of any chain decomposes into three layers: which hardness assumption secures its signatures (Shor-vulnerable discrete-log/factoring, hash, or lattice); that assumption's status under the physically-realizable computational model (classical BPP vs quantum BQP); and the physical floor beneath it—unstructured-search lower bounds and serial-depth constraints, not a claim of unconditional security. At ground zero, the abelian-hidden-subgroup atom is efficiently broken under BQP (Shor), while no efficient BQP break is known for hash or lattice; hash security rests on the most conservative, best-tested conjecture; discrete-log rests on exploitable algebraic structure; and lattice assumptions, though buttressed by worst-case reductions unevenly across the lattice family, carry a much shorter cryptanalytic record. We locate the vulnerability in a single object—the exposed public key—and formalize compromise as a conjunction of exposure, feasibility, and non-revocation. Under a floor assumption (generic, unstructured search stays infeasible) this factors into four conjuncts answering to four distinct authorities—mathematics, the ledger, engineering, and the owner or protocol—with feasibility entailing brokenness. Each per-asset cryptanalytic defense we survey denies the primary one of these four conjuncts—an accounting identity over the four predicates (some defenses touch more than one; we classify by the primary), not a claim of exhaustiveness over an open-ended literature. We give an exposure taxonomy checked against the reference implementations and a first-party, reproducible measurement of the full Bitcoin UTXO set (block 957,269, July 2026): 1.93M BTC (≈9.6% of supply) carries a standing exposed public key—the defensible, structurally unambiguous figure—rising to 5–7M BTC (25–35%) once key-reuse is included, the range's width set by the P2SH/P2WSH script-hash upper bound. This decomposes exactly along the taxonomy's structural-versus-operational axis and quantifies Taproot's hidden-key regression (a directional shift on the exposure axis, minor by value); current resource estimates and a CRQC timeline; and a per-chain migration survey. A recurring result: account and governance architectures migrate most easily while immutable/UTXO chains are hardest—the property prized as a security virtue is the migration handicap. No unconditional security exists; all verdicts are contingent on unproven conjectures and the assumption that BQP is the physical ceiling of computation.
Quantum computing poses distinct risks to blockchain security: Shor’s algorithm threatens signatures associated with exposed public keys, while Grover’s algorithm reduces the security margin of hash-based mechanisms. This systematic mapping study examines quantum-resistant blockchain defenses and the evidence supporting their practical use. A total of 387 peer-reviewed primary studies published between 2018 and 2026 were identified through IEEE Xplore, the MDPI journal collection, and citation searching, and classified by contribution type and evidence maturity. The findings show that post-quantum cryptographic constructions dominate the literature (56.1%), followed by quantum-native designs (26.6%) and hybrid migration approaches (13.7%). Despite substantial research on these defenses, only 16.0% of the studies report real-platform laboratory experiments, and 1.3% reach public-testnet evaluation. Hybrid migration studies demonstrate greater progress toward platform-level evaluation than other defense categories, but practical validation remains limited. These findings highlight the gap between proposed quantum-resistant mechanisms and their evaluation under realistic blockchain conditions, emphasizing the need for reproducible system-level testing and migration strategies addressing interoperability, governance, and operational continuity.
As quantum computing advances, classical cryptographic systems - signature schemes, key exchange protocols, public-key encryption, and certain hash constructions - that secure most blockchain platforms come under threat, raising serious concerns about their long-term security and integrity. Transitioning to post-quantum primitives is rarely straightforward: their larger sizes and higher computation costs can have unintended consequences, and in some cases make such a transition impractical. We examine the impact of post-quantum migration on blockchain systems across three dimensions. First, we dissect the cryptographic primitives most vulnerable to quantum attacks within the consensus, identity, and transaction-validation layers. Next, we survey proposed post-quantum adaptations and evaluate their practical feasibility. Finally, we assess how substituting classical primitives with post-quantum alternatives affects system performance, protocol behavior, and the underlying incentive and trust structures. Our findings show that PQ adoption is far from a drop-in replacement: it demands careful architectural reconsideration, as naive substitution risks destabilizing core protocol operations and weakening the security and efficiency guarantees blockchains rely upon.
Quantum computing poses a real, broad-based, but bounded and substantially mitigable threat to Bitcoin and Ethereum. We separate the two quantum algorithms that public discussion routinely conflates: Shor's algorithm breaks the elliptic-curve signatures (ECDSA over secp256k1, BLS over BLS12-381) that authorize spending, whereas Grover's algorithm does not meaningfully threaten proof-of-work mining, which is protected by a merely quadratic speedup, fault-tolerant per-operation costs, a square-root parallelization wall, and difficulty adjustment. Folding hardware scaling, the falling resource requirement, a fault-tolerance readiness lag, and expert surveys into a single Monte-Carlo forecast yields a wide, bimodal arrival distribution for a cryptographically relevant quantum computer: about a one-in-six chance by 2035, near 30% by 2040, and about 60% by 2050. Exposure is concentrated and mostly migratable: of Bitcoin's roughly six million quantum-exposed coins only about 2.3 million are irreducibly at risk, while 50 to 65% of Ether sits at key-revealed accounts that can adopt post-quantum signatures. A timely migration beats even an optimistic 2035 machine, so the binding constraint is governance, not technology. A survey of the top twenty cryptocurrencies finds none fully post-quantum. Reproducible models accompany every quantitative claim.
The advent of Quantum Computing (QC) poses significant threats to the cryptographic foundations of Blockchain (BC) systems, as quantum algorithms like Shor’s and Grover’s undermine the security of public-key cryptography and hash functions. This research conducts a comprehensive risk assessment of quantum vulnerabilities across critical BC components, including consensus mechanisms, smart contracts, and digital wallets. Leveraging the STRIDE threat modeling framework, we analyze threat vectors specific to QC, identifying key areas most susceptible to quantum-enabled attacks, such as private key compromise, consensus disruptions, and smart contract integrity risks. Our contributions provide actionable mitigation strategies, including a detailed security blueprint for quantum resilience, encompassing the integration of Post-Quantum Cryptography (PQC) and the adoption of quantum-resistant hash functions. We offer implementation best practices, focusing on key management, secure coding, and network security to strengthen BC components against quantum threats. To mitigate the risk of QC during transition from classical to quantum-resistant BCs, we present two hybrid BC architectures. As part of a comprehensive quantum resilience strategy, these architectures facilitate a secure and scalable migration by integrating platform-specific adaptations that balance security, adaptability, and operational efficiency. Our analysis extends to major BC platforms, including Bitcoin, Ethereum, Ripple, Litecoin, and Zcash, providing platform-specific vulnerability assessments and highlighting unique weaknesses in the quantum era. By identifying vulnerabilities, developing proactive defense strategies, and adopting a structured hybrid migration approach, this research equips BC stakeholders with a robust framework to achieve long-term quantum resilience. Finally, we explore challenges and research directions for integrating emerging technologies, including quantum machine learning, Artificial Intelligence (AI), and Web3, with BC systems, and discuss new threats that may arise from this convergence in the QC era.
This paper examines the growing threat that quantum computing presents to blockchain security. Core blockchain cryptographic frameworks, specifically the Elliptic Curve Digital Signature Algorithm and the Secure Hash Algorithm 256, are vulnerable to quantum algorithms. Both the Shor algorithm and the Grover algorithm are capable of breaking the Elliptic Curve Digital Signature Algorithm, enabling attackers to calculate private keys from public keys, while the Grover algorithm can also compromise hash-based systems that depend on brute-force methods, such as Proof-of-Work. On-chain analysis indicates that billions of dollars’ worth of crypto-assets are held in addresses susceptible to these quantum attacks. A proposed countermeasure is migration to Post-Quantum Cryptography, which incorporates quantum-resistant algorithms, such as CRYSTALS-Dilithium and Falcon. However, this migration introduces a trilemma among network security, decentralization, and performance. Post-Quantum Cryptography algorithms significantly increase transaction sizes and computational costs, which pose economic and technical challenges for large blockchain networks. The paper further discusses how the timeline for quantum advancements will be shaped by geopolitical competition, and how the catch-the-crop, decrypt-later strategy puts current data at risk from future quantum decryption. It emphasizes that active migration to Post-Quantum Cryptography is urgent, calling on stakeholders to prioritize system audits, transition to cryptographically flexible infrastructures, promote research into quantum-resistant solutions, and establish governance frameworks that enable prompt and decentralized upgrades.
Classical cryptography has been around for a long time in the documented human history, but most classical ciphers were broken and even solved by hand. Shannon introduced the notion of perfect secrecy that formally defines confidentiality in the information-theoretic sense, which is only possible in the restricted scenarios where the message is no longer than the encryption key. The invention of public-key cryptography (the Diffie-Hellman key exchange protocol in 1976 and the RSA crypto-system in 1977) marks the birth of modern cryptography, allowing parties to exchange messages securely without sharing any secrets in advance. Furthermore, it provides computational security based on the conjectured hardness of mathematical problems such as factorization and the discrete logarithm. Public-key cryptography has found numerous applications in the Internet, financial and banking industry, and blockchains, and it plays a crucial role in protecting information security and asset safety. Unfortunately, in the 1990s, Shor proposed efficient quantum algorithms that solve number-theoretic problems, including factorization and discrete logarithms in polynomial time. Once a quantum computer of a particular scale becomes a reality, it will cause a devastating blow to the existing public-key infrastructure. To deal with such a ‘quantum crisis’, academia and industry are looking into the design, analysis and standardization of cryptographic algorithms that can resist quantum computers referred to as post-quantum cryptography (PQC). The National Institute of Standards and Technology (NIST) has been soliciting proposals for the post-quantum public-key algorithms since 2016. More recently, the Chinese Association for Cryptologic Research (CACR) held a competition on designing cryptographic algorithms whose public-key cryptography track focused on post-quantum cryptographic algorithms. Lattice-based cryptography is considered by most to be the mainstream technical route of post-quantum cryptography, which is reflected in the number of proposals (and their percentage of the total) received in the NIST PQC process. To reflect the status quo of post-quantum cryptography, we invite leading experts in this area to contribute three technical perspectives that aim to help readers understand the algorithms, the underlying basic techniques and different technical routes to achieve quantum resistance. The first perspective, presented by Lu and Zhang, introduces public-key cryptographic algorithms whose quantum security is reducible from the conjectured quantum hardness of lattice problems. In particular, they mainly focus on public-key encryption (PKE) and the key encapsulation mechanism (KEM), which are essential building blocks for securing the confidentiality of communication without pre-shared secrets. Both types of crypto-systems are solicited by the NIST PQC standardization and the CACR algorithm design competition. This perspective gives a comprehensive survey on practical lattice-based PKEs/KEMs, and their best-known quantum and classical attacks. Another important post-quantum crypto-system is digital signature, which ensures that three goals of information security are met other than confidentiality, namely, integrity, authentication and non-repudiation. The second perspective is on lattice-based signature by Lyubashevsky. In this perspective, he surveys different techniques in building lattice-based post-quantum crypto-systems, discusses the challenges in overcoming performance issues and gives us state-of-the-art digital signature schemes. In addition to ensuring the ‘static’ security of information in storage and transmission, advanced cryptographic algorithms and protocols can guarantee information security during the computation process (possibly among multiple parties), referred to as privacy-preserving computation. Cryptographic techniques involved in privacy-preserving computation include secure multi-party computation, zero-knowledge proof and fully homomorphic encryption. There is a pressing need to migrate them to the post-quantum era. The third perspective, by Yu and Xie, presents practical instantiations of these algorithms and discusses possible ways to migrate them to their quantum-resistant counterparts. To summarize, post-quantum cryptography has received widespread attention and made significant progress in recent years. Some post-quantum cryptographic algorithms, such as the lattice-based candidate, also have other advantages (e.g., computational efficiency and full homomorphism) over their classical counterparts. Lattice-based cryptography is an emerging field with high theoretical value and wide application, and we encourage young researchers to enter and explore this new and exciting field.