Post-Quantum Blockchains Overview
- Post-quantum blockchains are classical distributed systems enhanced with quantum-resistant cryptography to counteract future quantum computing risks.
- They employ design models such as direct cryptographic substitution, hybrid transitions, and consensus adaptations while retaining familiar blockchain architecture.
- Practical studies highlight challenges like larger transaction sizes, increased verification overhead, and complex migration strategies affecting decentralization.
Post-quantum blockchains (PQB) are blockchain or distributed-ledger systems redesigned so that their cryptographic foundations remain secure even if large-scale quantum computers become practical. Surveys describe PQB as the “cautious upgrade” path: they preserve the classical blockchain architecture—blocks linked by hashes, consensus through PoW, PoS, or variants, and replicated state across nodes—while replacing quantum-vulnerable trust anchors with post-quantum cryptography (PQC). This distinguishes PQB from quantum blockchains, which instead attempt to rebuild blockchain mechanisms using quantum communication, quantum cryptography, or quantum states (Ghosh, 18 Jul 2025, Yang et al., 2024).
1. Definition, scope, and taxonomy
In the survey literature, PQB does not mean “using quantum computers to run the blockchain.” It means keeping the blockchain architecture classical while replacing quantum-vulnerable primitives—especially public-key signatures and, in some cases, hash functions—with post-quantum cryptography. PQB therefore remain computationally secured classical systems rather than quantum-network protocols grounded in entanglement, QKD, or quantum state manipulation (Yang et al., 2024, Fernandez-Carames et al., 2024).
This distinction is central because the two research directions have different feasibility profiles. Quantum blockchains may use QKD, quantum digital signatures, quantum data structures, or even blocks represented as quantum states linked by entanglement, but they depend on fragile qubits, decoherence-limited hardware, specialized channels, and immature quantum networking. PQB, by contrast, can be deployed on existing hardware and networks because they use classical computation plus quantum-resistant algorithms (Ghosh, 18 Jul 2025, Yang et al., 2024).
Surveys further describe several recurring PQB design patterns. A direct cryptographic substitution model replaces ECDSA-style signatures and classical key exchange while keeping the rest of the stack largely unchanged. A hybrid transition model combines PQC with legacy mechanisms during migration. A consensus adaptation model recognizes that changing signatures alone does not address Grover-related effects on mining or randomness, and therefore revisits PoW, PoS, QRNG-assisted mechanisms, or other consensus components (Ghosh, 18 Jul 2025, Al-Janabi, 23 Aug 2025).
A common misconception is that PQB are simply classical blockchains with bigger signatures. The literature repeatedly rejects that reduction. PQB preserve familiar blockchain structure, but their design space spans transaction authorization, wallet ownership, identity verification, ledger verifiability, privacy mechanisms, validator selection, and migration procedures. In that sense, PQB are best understood as a cross-layer redesign problem within a classical distributed-systems envelope (Mallick et al., 15 Dec 2025, Fernandez-Carames et al., 2024).
2. Quantum threat model for blockchain systems
The canonical quantum threat model is organized around Shor’s and Grover’s algorithms. Shor’s algorithm efficiently solves integer factorization and discrete logarithms, compromising cryptographic systems such as RSA, ECDSA, and Diffie–Hellman; surveys and system papers extend that observation to ECDH, DSA, EdDSA, Schnorr, BLS signatures, ECVRF-style constructions, and pairing-based commitments such as KZG when their security rests on elliptic-curve assumptions (Liu et al., 15 May 2026, Mallick et al., 15 Dec 2025).
For blockchains, this is not merely an abstract break of public-key cryptography. Transaction authorization, wallet ownership, validator authentication, membership credentials, and many privacy mechanisms are all exposed once a public key is visible and the corresponding private key can be derived. Some studies emphasize the blockchain-specific severity of this condition: assets are represented by keys, public transaction histories reveal cryptographic material, and there is no general central authority that can revoke a compromised key and rebind ownership without protocol-specific recovery mechanisms (Al-Janabi, 23 Aug 2025, Kikuchi, 2024).
Grover’s algorithm does not outright break symmetric primitives and hash functions, but it gives a quadratic speedup for unstructured search and therefore reduces their effective security margin. In blockchain terms, that affects hash-based mining, preimage search, collision search, block reconstruction attempts, address derivation, and some hash-based signatures. Surveys characterize the consequence as weaker security margins for SHA-256-, Keccak-, or RIPEMD-160-based components and a potential quantum advantage in proof-of-work mining or hash-centric consensus logic (Ghosh, 18 Jul 2025, Fernandez-Carames et al., 2024).
The threat is therefore multi-layer. At the transaction layer, signatures become forgeable. At the consensus layer, PoW search or timing assumptions may become distorted. At the privacy layer, ECC-based ring signatures, stealth addresses, RingCT, Bulletproofs, and related constructions lose their security basis. At the validator-selection layer, quantum attacks on VRFs or VDFs can bias randomness and leader election. A system-of-knowledge study accordingly frames quantum disruption as reshaping not only authentication, but also consensus fairness, privacy, propagation, throughput, and incentive equilibrium (Mallick et al., 15 Dec 2025).
Several application papers sharpen the temporal aspect of the threat. PQBFL treats federated-learning updates as exposed to “Harvest Now, Decrypt Later” risk because model information can remain valuable across many rounds, while the broader blockchain literature notes that even conditionally hidden public keys become vulnerable once they are exposed in mempool traffic or on chain (GHaravi et al., 20 Feb 2025, Mallick et al., 15 Dec 2025).
3. Cryptographic foundations and transaction-authentication designs
The main cryptographic foundation of PQB is PQC, especially lattice-based, code-based, hash-based, multivariate, and, in older surveys, supersingular isogeny-based families. Surveys repeatedly identify lattice-based constructions as the most practically promising balance of security, key size, and computational efficiency, while hash-based schemes remain attractive for conservative security and code-based schemes remain attractive for conservative hardness assumptions despite very large keys (Fernandez-Carames et al., 2024, Al-Janabi, 23 Aug 2025).
The post-NIST focus in blockchain papers is especially clear. Practical recommendations recurrently point to ML-KEM / CRYSTALS-Kyber for key establishment, ML-DSA / CRYSTALS-Dilithium and FALCON for digital signatures, and SLH-DSA / SPHINCS+ for stateless hash-based signatures. The design trade-offs also recur: Dilithium is treated as a strong general-purpose choice, Falcon as attractive when signature size must be small, and SPHINCS+ as attractive for conservative hash-based security when large signatures are tolerable (Barbaccia et al., 22 Jun 2026, Al-Janabi, 23 Aug 2025).
PQC substitution, however, is only one design pattern. Several works argue that transaction semantics themselves may need to change. A systems paper proposes a hash-based commit–reveal authorization scheme in which a one-way function
is used to derive a public authorization identifier , with a commit transaction
followed by a reveal of . The paper positions this as post-quantum security under standard hash assumptions while keeping each on-chain hash output at a fixed 32 bytes (Finlow-Bates et al., 7 May 2026).
Hybrid authentication is another major pattern. PQFabric redesigns Hyperledger Fabric’s credential-management and signing stack to support one classical and one post-quantum signature, integrates libOQS through a CGO wrapper, and emphasizes complete crypto-agility with live migration and per-node algorithm selection. Its hybrid X.509 format adds Subject-Alt-Public-Key-Info, Alt-Signature-Value, and Alt-Signature-Algorithm so that classical verifiers can ignore the extra extensions while upgraded nodes verify both layers (Holcomb et al., 2020).
The literature also generalizes “cryptographic replacement” beyond signatures alone. In useful-work consensus for decentralized AI economies, the transaction layer is assigned ML-DSA or SLH-DSA, while validation proofs are steered away from pairing-based SNARKs toward STARK-style systems because the latter rely on hash functions rather than elliptic-curve pairings. The same paper is explicit that the ML work layer itself is not the PQC problem; the cryptographic wrappers are (Barbaccia et al., 22 Jun 2026).
4. Protocol architectures, consensus redesign, and application-specific PQB systems
PQB research does not converge on a single canonical protocol. Instead, it spans permissioned ledgers, public ledgers, blockchain-assisted machine learning systems, confidential institutional ledgers, and transition mechanisms tied to smart-contract logic.
One line of work modifies permissioned stacks. PQFabric is a concrete example: it redesigns Fabric’s MSP, BCCSP, and cryptogen to support hybrid signatures, hybrid certificates, and staged migration while preserving backward compatibility in the operational sense that individual nodes and clients need not all use post-quantum keys simultaneously (Holcomb et al., 2020).
A second line treats consensus itself as a PQ design problem. In the decentralized AI-economy proposal, quantum resilience is analyzed through a three-layer architecture: a compute layer for inference and training, a validation layer combining zkML proofs, peer ranking, benchmark injection, and reputation weighting, and an economic coordination layer formalized as a -closed-loop token economy. The paper’s claim is architectural rather than cryptographic: replacing hash puzzles with ML-native work reduces exposure to Grover-style speedups at the work layer, while the transaction layer still requires post-quantum signatures (Barbaccia et al., 22 Jun 2026).
A third line is application-specific blockchain integration. In blockchain-based federated learning, one proposal combines XMSS transaction signatures with Dilithium or Falcon certification of the XMSS tree, and adds VRF-based role selection and miner selection to improve fairness and reduce manipulation. Another, PQBFL, uses a hybrid off-chain/on-chain architecture in which the blockchain records hashed registration artifacts, task publication, model-update hashes, feedback, and reputation events, while confidentiality-critical traffic uses Kyber plus ECDH and ratcheting to provide forward secrecy and post-compromise security across many learning rounds (Gurung et al., 2023, GHaravi et al., 20 Feb 2025).
A fourth line addresses highly regulated settings. QSET proposes an Encrypted Table-based Ledger for financial institutions, built from Module-LWE / Module-SIS assumptions and a suite of zero-knowledge proofs. Its explicit objectives are confidentiality, auditability, and public verifiability rather than anonymous cash-like transfer. The protocol supports customizable auditor keys, multi-asset transactions, and a new equality-proof technique for showing that two commitment messages are equal without opening one commitment during re-commitment; the appendix gives a rough estimate that total proving time per participant per asset can be brought down to around $120$ ms (Zhu et al., 5 Mar 2026).
More radical consensus redesign appears in smart-city PQB work. That paper replaces hash-only PoW with a multivariate-quadratic-equation-based mining puzzle, solved via Gröbner-basis methods and paired with an identity-based Rainbow-derived signature for lightweight transactions. Its stated goals are both quantum resistance and “memory mining,” in deliberate contrast to Bitcoin’s mostly memory-light SHA-256 mining (Chen et al., 2020).
Transition logic itself can also be encoded on chain. An Ethereum-based proposal generates trapdoor-free factorization puzzles as “locks” and uses successful factorization as a publicly verifiable proof of cryptographic quantum supremacy, after which a smart-contract-controlled account switches from classical signatures to Lamport signatures. The mechanism is explicitly designed to delay fallback “as long as possible” because quantum-secure signatures are larger, costlier, and more complex (Papadopoulos, 9 Jan 2026).
5. Systems costs: size, throughput, verification, and replication overhead
A dominant theme of PQB research is that migration is a systems problem because blockchains are globally replicated systems. One paper makes the point as an explicit cost model:
Every additional byte is copied, relayed, stored, and validated by many nodes, so cryptographic overhead becomes network-wide infrastructure overhead rather than a local implementation detail (Finlow-Bates et al., 7 May 2026).
Representative measurements vary by scheme and workload, but they consistently show that artifact size is a first-order blockchain parameter rather than a secondary benchmark statistic.
| Context | Reported finding | Source |
|---|---|---|
| Transaction footprint | ECDSA: bytes; Dilithium: bytes; SPHINCS+: bytes | (Finlow-Bates et al., 7 May 2026) |
| 1000-transaction block size | ML-DSA-44: 5,092,084 bytes; Falcon-512: 2,497,118 bytes; Hawk-512: 2,651,084 bytes | (Jain, 25 Jan 2026) |
| Theoretical throughput loss with ML-DSA-44 | Bitcoin: about 84%; Monero: about 59%; Algorand: about 92%; XRPL: about 85% | (Mallick et al., 15 Dec 2025) |
These size effects propagate into validation latency, propagation delay, archival burden, and decentralization pressure. The same systems paper argues that direct adoption of Dilithium or SPHINCS+ could push Bitcoin full validation into the tens of terabytes and Ethereum archive-style operation into tens or hundreds of terabytes, and warns that naive PQ substitution can concentrate the network by making full-node operation more expensive (Finlow-Bates et al., 7 May 2026).
Blockchain prototypes further show that size interacts with verification cost in non-obvious ways. The single-node account-based prototype comparing ML-DSA, Falcon, Hawk, and HAETAE reports that Falcon and Hawk produce substantially smaller transactions and blocks than ML-DSA, and that Hawk-512 has the fastest signing and verification in the integrated benchmark. The paper’s central architectural lesson is that a modular, pluggable signature interface is essential because no single scheme dominates all deployment priorities (Jain, 25 Jan 2026).
Several measurements complicate the simplistic view that “PQC is always slower.” A benchmarking study across ARM, x64, and desktop platforms reports that PQC algorithms introduce only minor overhead at security level 1 and that ML-DSA can outperform ECDSA in verification at higher security levels; one cited example is ML-DSA verification of 0.14 ms on an ARM-based laptop at level 5 versus 0.88 ms for ECDSA. The same study’s blockchain simulation shows ML-DSA substantially reducing block-verification time relative to ECDSA in some environments (Schemitt et al., 10 Oct 2025).
Likewise, a cryptocurrency-exchange prototype reports that Dilithium-based wallets and signatures were faster than ECDSA in the measured implementation, while Falcon had the fastest signature verification among the tested PQ schemes. Yet this does not remove the systems-level overhead from larger public keys and signatures (Chen, 2024).
Permissioned-ledger experiments underline precisely that point. PQFabric benchmarks show that long public keys and signatures increase hashing time inside the block-processing path and that this hashing overhead can become comparable to the time spent signing or verifying messages themselves. The paper treats this as a new and potentially significant issue in post-quantum blockchain migration (Holcomb et al., 2020).
Finally, application-specific results indicate that cryptographic micro-cost is not always the practical bottleneck. In PQS-BFL, average ML-DSA-65 sign and verify times remain sub-millisecond, while blockchain transaction latency and gas dominate round time; the paper concludes that PQC performance is not the bottleneck in that blockchain-based federated-learning setting, even though on-chain PQC verification is roughly nine times more gas-expensive than ECDSA in its reported estimates (Commey et al., 3 May 2025).
6. Migration, governance, sustainability, and open research problems
The literature converges on a strong negative claim: PQB migration is not a drop-in replacement exercise. It affects transaction formats, address derivation, validator selection, consensus timing, block-size limits, gas schedules, wallet compatibility, archival storage, and incentive design. A system-of-knowledge study therefore argues that quantum resilience requires architectural redesign rather than simple algorithm substitution (Mallick et al., 15 Dec 2025).
Migration strategy is itself a research topic. Surveys discuss hard forks, soft forks, hybrid cryptosystems, staged adoption roadmaps, and address-migration procedures. PQFabric provides one of the clearest operational plans: deploy upgraded software while remaining classical, upgrade the certificate authority, add alternate-signature fields to certificates, roll out post-quantum keys node by node, and later upgrade clients. The paper’s stated objective is live migration under crypto-agility rather than instantaneous cutover (Holcomb et al., 2020).
Governance is a recurrent concern because decentralized systems do not have a single operator who can impose a cryptographic transition. The interactive demonstration platform “Quantum Futures Interactive” is notable precisely because it treats PQB migration as a socio-technical process involving quantum threat education, sentiment capture, technology prioritization, infrastructure tradeoff exploration, and generation of demonstrative cryptographic artifacts. Its serverless platform explicitly incorporates distributed trust, governance, transparency, sustainability, and stakeholder consensus rather than presenting migration as a purely cryptographic replacement (Liu et al., 15 May 2026).
Sustainability appears less frequently in PQB papers, but where it does appear it is unusually explicit. “Quantum Futures Interactive” compares environmental impact across simulators, trapped-ion QPUs, superconducting QPUs, and neutral-atom analog quantum systems, tying the comparison to execution duration, regional carbon intensity, hardware infrastructure demands, and long-term deployment feasibility. This suggests that some strands of PQB research are broadening the migration question from security and performance to sustainable distributed trust (Liu et al., 15 May 2026).
Open problems remain substantial. Surveys and recent system papers repeatedly call for realistic deployment studies, mature incentive and game-theoretic analysis, cross-layer integration of cryptography, consensus, and network assumptions, testbeds and open benchmarks, practical PQ VRFs, post-quantum privacy mechanisms with acceptable proof size and verification cost, and migration frameworks that preserve decentralization under large-artifact overheads (Ghosh, 18 Jul 2025, Fernandez-Carames et al., 2024). In specialized domains, further gaps are identified even more sharply: useful-work consensus lacks a formal post-quantum security game and a quantum reduction for its honest-majority assumption, while blockchain-based federated-learning systems still leave model privacy, secure aggregation, and end-to-end post-quantum chain security unresolved (Barbaccia et al., 22 Jun 2026, Commey et al., 3 May 2025).
Across the literature, the most stable conclusion is therefore pragmatic. PQB are the most deployable near- to medium-term response to quantum risk because they do not require quantum channels or quantum processors. But their practicality depends on solving the systems consequences of PQC—artifact size, verification cost, storage growth, network propagation, protocol governance, and migration coordination—without undermining the decentralization and trust model that blockchains were meant to provide (Ghosh, 18 Jul 2025, Mallick et al., 15 Dec 2025).
