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Towards post-quantum blockchain: A review on blockchain cryptography resistant to quantum computing attacks

Tiago M. Fernandez-Carames, Paula Fraga-Lamas

arXiv:2402.00922v1cs.CRquant-ph

TL;DR

Quantum computing threatens blockchain public-key cryptography and hash functions through Shor’s and Grover’s algorithms. This article reviews post-quantum cryptosystems and blockchain initiatives, compares promising encryption and signature schemes, and identifies implementation challenges and selection criteria. Its comparisons highlight candidate performance and practical trade-offs, while code-based schemes show larger keys than current ECDSA and RSA-based systems.

  • Problem

    Quantum attacks threaten the public-key cryptography and hash functions that underpin blockchain security, requiring cryptosystems resistant to Shor’s and Grover’s algorithms.

  • Method

    The article reviews post-quantum cryptosystems and blockchain applications, examines initiatives and challenges, and compares promising public-key encryption and digital-signature schemes.

  • Results

    Code-based schemes provide 128 to 256 bits of classical security, while their keys are larger on average than those of current ECDSA and RSA-based systems.

  • Takeaways & Limitations

    Scheme selection should consider node hardware, available memory and speed, required performance, energy use, and the necessary security level.

Abstract

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Blockchain and other Distributed Ledger Technologies (DLTs) have evolved significantly in the last years and their use has been suggested for numerous applications due to their ability to provide transparency, redundancy and accountability. In the case of blockchain, such characteristics are provided through public-key cryptography and hash functions. However, the fast progress of quantum computing has opened the possibility of performing attacks based on Grover's and Shor's algorithms in the near future. Such algorithms threaten both public-key cryptography and hash functions, forcing to redesign blockchains to make use of cryptosystems that withstand quantum attacks, thus creating which are known as post-quantum, quantum-proof, quantum-safe or quantum-resistant cryptosystems. For such a purpose, this article first studies current state of the art on post-quantum cryptosystems and how they can be applied to blockchains and DLTs. Moreover, the most relevant post-quantum blockchain systems are studied, as well as their main challenges. Furthermore, extensive comparisons are provided on the characteristics and performance of the most promising post-quantum public-key encryption and digital signature schemes for blockchains. Thus, this article seeks to provide a broad view and useful guidelines on post-quantum blockchain security to future blockchain researchers and developers.

I. INTRODUCTION

Blockchain provides distributed data sharing, transparency, and resilience through linked blocks, consensus, and cryptographic security primitives. The section motivates post-quantum blockchain research by describing quantum threats to these foundations and the article’s review scope.

  • Blockchain foundations: Blockchain is a distributed ledger that links data blocks by hashes and enables information sharing among parties that may not trust one another.Transactions are verified through consensus and are ideally difficult to remove once stored.
  • Applications: Blockchain has been proposed for applications including smart health, measuring systems, logistics, e-voting, and smart factories.
  • Security foundations: Public-key cryptography authenticates transactions, while hash functions link blocks and support blockchain data integrity.Nodes, miners, and smart contracts provide additional operational components for validating transactions and automating tasks.
  • Motivation and scope: Quantum attacks based on Shor’s and Grover’s algorithms threaten blockchain public-key cryptosystems and hash functions.The article reviews post-quantum cryptosystems, blockchain applications, major challenges, and comparative scheme characteristics and performance.
  • Security properties: Blockchain security features include decentralization, data privacy, integrity, authentication, and transaction immutability.Information remains available across nodes, while cryptography and hashes support privacy, integrity, and authentication.

B. BLOCKCHAIN SECURITY PRIMITIVES

Blockchain security relies on public-key cryptography and hash functions, but quantum algorithms threaten transaction authentication, mining, and block integrity. The section explains these primitives, their quantum vulnerabilities, and the resulting security implications.

  • Public-key cryptography: Public-key cryptography authenticates blockchain transactions through signatures generated with private keys and verified with public keys.Wallets associate users with public addresses and private keys used to sign transactions.
  • Hash functions: Hash functions support digital signatures, chronological block linking, mining conditions, and the generation or shortening of user addresses.Common examples include SHA-256 and Scrypt.
  • Quantum threats: Shor’s algorithm can break public-key systems based on integer factorization, elliptic curves, and discrete logarithms on sufficiently powerful quantum computers.The cited estimates include 160-bit elliptic curves requiring a 1000-qubit quantum computer and 1024-bit RSA roughly 2,000 qubits.
  • Quantum threats: Current quantum computers are not yet powerful enough for these attacks, but the article cites estimates that capable systems could emerge within 20 years.The most powerful claimed system described has 79 qubits.
  • Quantum threats: Grover’s algorithm accelerates hash brute-force attacks quadratically and can target collisions or mining nonces, threatening block replacement and blockchain integrity.One cited result concludes that a hash output must contain 3*n bits to provide n-bit security against collision attacks.
  • Consequences: Quantum attacks can also enable signature forgery, user impersonation, and theft of blockchain assets.

C. POST-QUANTUM BLOCKCHAIN INITIATIVES

Post-quantum blockchain work spans broad cryptographic research, standardization efforts, and blockchain-specific implementations. The section identifies operational requirements and frames scheme selection as a trade-off involving resource constraints, performance, security, and standardization.

  • Research and standardization: Post-quantum cryptography has been studied through research projects, standardization initiatives, workshops, and the NIST call for proposals.
  • Blockchain initiatives: Blockchain-specific initiatives include Bitcoin Post-Quantum, Ethereum 3.0, Abelian, and Corda experiments using post-quantum components or algorithms.Examples include post-quantum signatures, zk-STARKs, lattice-based cryptosystems, and SPHINCS.
  • Design requirements: Efficient post-quantum blockchain schemes should combine small keys and signatures, fast execution, low computational complexity, and low energy consumption.These properties are especially relevant for resource-constrained IoT devices and high-throughput transaction processing.
  • Design requirements: Fast execution on one processor does not imply low computational complexity on another, so evaluations must consider hardware-dependent trade-offs.Schemes using AVX2-enabled Intel processors may perform differently on ARM-based microcontrollers.
  • Cryptosystem taxonomy: The article distinguishes four main post-quantum cryptosystem types plus a hybrid category and reviews their use for encryption, decryption, and transaction signing.Figure 1 summarizes the categories with example encryption and digital-signature implementations.
  • Scope: Detailed algorithm descriptions are outside the article’s scope, which directs readers to cited references and broader cryptosystem texts.

A. PUBLIC-KEY POST-QUANTUM CRYPTOSYSTEMS

The review surveys five post-quantum public-key cryptosystem families and compares their security, key sizes, performance, and blockchain-relevant trade-offs. Code-based and lattice-based schemes offer practical advantages but also impose substantial storage or execution costs.

  • Code-based cryptosystems: Code-based cryptosystems rely on error-correction codes; McEliece offers fast encryption and relatively fast decryption but uses 100-kilobyte-to-several-megabyte key matrices.Matrix compression and alternative codes are identified as directions for reducing this burden on resource-constrained devices.
  • Code-based cryptosystems: 128–256 bits of classical security are reported for evaluated code-based schemes, while their keys range from 320 bits to 15.5 KB and generally exceed current ECDSA and RSA key sizes.The reported classical security is reduced significantly in quantum-security terms.
  • Other cryptosystem families: Multivariate, isogeny-based, and hybrid cryptosystems provide additional post-quantum options but retain practical challenges involving decryption speed, key size, signatures, or protection against weaknesses in post-quantum schemes.SIKEp434 uses a 2,640-bit public key and a 2,992-bit private key at 128-bit classical security.
  • Lattice-based cryptosystems: Lattice-based schemes can execute blockchain transactions efficiently, but they require large keys and introduce substantial ciphertext overheads.Their security relies on lattice problems such as SVP, CVP, and SIVP, which are not efficiently solvable by current quantum computers.
  • Lattice-based cryptosystems: Round5 KEM IoT appears to have the smallest keys among schemes offering roughly 100-bit quantum security and is also reported to execute quickly.The comparison uses parameter sets selected for the smallest keys at NIST’s 128-, 192-, and 256-bit security levels.

B. POST-QUANTUM SIGNING ALGORITHMS

The review compares post-quantum digital-signature families for blockchain use, emphasizing trade-offs among key size, signature length, speed, and quantum-security assumptions. Lattice-based schemes appear comparatively balanced, while isogeny- and multivariate-based approaches retain notable size or performance drawbacks.

  • Code-based cryptosystems: Code-based signatures provide short signatures and fast verification, but they retain the large-key-size disadvantage associated with McEliece-like cryptosystems.Fiat–Shamir variants may outperform CFS in some cases, but are not known to be completely quantum-secure except under certain circumstances.
  • Multivariate-based cryptosystems: Multivariate signatures usually combine large public keys with very small signatures, while their keys still require further reduction and often occupy several tens of thousands of bytes.MQDSS has small keys but among the largest signatures in the comparison; other schemes use several-kilobyte keys and short signatures.
  • Lattice-based cryptosystems: Lattice-based signature keys are generally smaller than multivariate-based keys, although their generated signatures are slightly larger.FALCON provides the smallest key sizes and signature lengths among the compared lattice schemes.
  • Lattice-based cryptosystems: qTESLA is reported as fast, but its major drawback is large key sizes.Other lattice-based schemes use SIS-based designs and have been developed specifically for blockchain and blind-signature applications.
  • Supersingular elliptic curve isogeny cryptosystems: Isogeny-based signature schemes remain limited by poor performance and scarce literature, despite examples with small keys and relatively efficient signing and verification.One 128-bit-quantum-security scheme uses a 336-byte public key and a 48-byte private key but produces 122,880-byte signatures.
  • Hash-based signature schemes: Hash-based signatures derive security from the underlying hash function, but XMSS and SPHINCS are considered impractical for some blockchain applications because of performance.Blockchain adaptations include single authentication paths and limited keys to preserve anonymity and minimize user tracking.

A. PUBLIC-KEY ENCRYPTION SCHEMES

The paper compares post-quantum encryption schemes on hardware representing regular and full blockchain nodes, while accounting for processor differences. Execution-time results favor some lightweight schemes but vary with hardware and implementation.

  • Evaluation setup: Tables 6 and 7 compare key-generation, encapsulation/encryption, and decapsulation/decryption cycles for regular and full blockchain nodes.The evaluation distinguishes nodes that interact with the blockchain from nodes that also store, update, and validate it.
  • Evaluation setup: The comparisons use Intel x64 processors with Turbo Boost and Hyper-Threading disabled, but processor-generation differences affect performance interpretation.Table 9 reports processor characteristics to support fairer analysis across the compared cryptosystems.
  • Execution-time comparison: Lightweight NTRU Prime, Three Bears, and SABER variants achieve very fast average execution times in the compared evaluations.Three Bears and SABER use low-power laptop processors, whereas NTRU Prime was evaluated on a powerful Intel Xeon server processor.
  • Execution-time comparison: SIKE is the overall slowest compared scheme, while Classic McEliece has slow key generation despite reduced decapsulation/decryption and encapsulation/encryption times.The paper notes that architectural optimization could reduce the execution times of slower schemes.

VI. POST-QUANTUM BLOCKCHAIN PROPOSALS

The reviewed proposals adapt existing blockchains and distributed systems with post-quantum cryptography, spanning SIDH, multivariate, hash-based, code-based, and lattice-based approaches. Examples target industrial data sharing, Bitcoin, Ethereum, e-voting, transaction authentication, and cryptocurrency systems.

  • Proposed blockchain systems: A proposed industrial-data framework combines IPFS and Ethereum with Diffie-Hellman key exchange based on SIDH.The framework is designed for sharing sensitive industrial data in public distributed networks.
  • Proposed blockchain systems: Other proposals modify Ethereum with a multivariate-based cryptosystem and improve Bitcoin’s ECDSA-based process with TESLA#, BLAKE2, and SHA-3.The Bitcoin proposal addresses a system using secp256k1 and SHA-256 during ECDSA signature processing.
  • Proposed blockchain systems: A blockchain-based transparent e-voting protocol uses Niederreiter’s code-based cryptosystem to address quantum attacks.The proposal is presented as a blockchain-based voting system rather than a general-purpose cryptocurrency.
  • Proposed blockchain systems: Quantum-safe blockchain proposals include lattice-based transaction authentication and a standard transaction model, as well as lattice-based signatures for cryptocurrency implementation.These approaches are presented as methods for preventing quantum attacks in blockchain transactions.
  • Commercial blockchains: IOTA’s Tangle claims greater resistance than Bitcoin to quantum attacks affecting nonce search and uses one-time hash-based Winternitz signatures instead of ECC.IOTA is also expected to use ternary hardware and a new hash function, according to the reviewed discussion.

A. QUANTUM COMPUTING FAST EVOLUTION

The paper identifies evolving technical and deployment constraints for post-quantum blockchains, including future attacks, large keys and signatures, computational cost, energy use, and standardization uncertainty. These constraints require balancing security, efficiency, storage, hardware compatibility, and migration needs.

  • Quantum computing evolution: New attacks may emerge against post-quantum cryptosystems, so researchers must continue monitoring advances in quantum computing.The paper frames quantum computing as an active research area whose development could expose further cryptosystem vulnerabilities.
  • Size constraints: Post-quantum cryptosystems usually require keys much larger than current public-key cryptosystems, typically spanning 128 to 4,096 bits.Larger key material is identified as a general post-quantum design characteristic.
  • Size constraints: Supersingular-isogeny signatures can use 2,688-bit public keys and 384-bit private keys yet produce 120 KB signatures, challenging blockchain storage.The cited 128-bit quantum-security example illustrates the trade-off between compact keys and large signatures.
  • Size constraints: Hash-based schemes often exceed 40 KB signatures, whereas DILITHIUM versions use roughly 1,500-byte keys and 2,701-byte signatures.The comparison also notes that some multivariate schemes have short signatures but keys occupying several kilobytes.
  • Performance and security trade-offs: Optimized Round5 versions offer good performance on current blockchain-node hardware with a 2,736-bit public key and 128-bit private key, but key-size and security trade-offs remain unresolved.The paper calls for further research into post-quantum encryption schemes for blockchain use.
  • Performance and deployment constraints: Some schemes limit messages per signing key, requiring continuous key generation that consumes resources and slows blockchain processes.The paper also links post-quantum execution, storage, and computational demands to increased energy consumption and hardware constraints.
  • Deployment constraints: Because post-quantum standardization remains ongoing, blockchain developers must avoid non-standard, discarded, or broken schemes during compatibility decisions.Migration proposals may require a hard fork, although a soft-fork mechanism has been suggested to avoid it.

I. QUANTUM BLOCKCHAIN

The article reviews post-quantum blockchain research, cryptosystems, projects, and performance, finding that no single algorithm currently combines all desirable properties. It identifies promising candidates while emphasizing hardware-, resource-, performance-, and security-dependent selection.

  • Review scope: The review covers post-quantum blockchain projects, standardization initiatives, cryptosystem types, performance comparisons, and future challenges.Its recommendations are presented as guidance for blockchain and DLT researchers and developers.
  • Research landscape: No large academic initiative applying post-quantum security to blockchain was found despite substantial post-quantum security projects.
  • Open challenges: No current post-quantum blockchain algorithm simultaneously provides small keys, short signatures or hashes, fast execution, low complexity, and low energy consumption.These constraints are especially important for resource-constrained Internet-of-Things devices.
  • Deployment considerations: Selecting a blockchain post-quantum cryptosystem depends on node hardware, available memory and speed, required performance, and necessary security level.The authors also advise monitoring NIST developments because many compared schemes were still under consideration for standardization.
  • Cryptosystem findings: Code-based schemes require large keys and substantial resources, while multivariate schemes need faster decryption and smaller keys despite fast AVX2-optimized signatures.
  • Cryptosystem findings: Lattice-based schemes are among the most promising candidates, with Three Bears and SABER reported as fast and optimized DILITHIUM and qTESLA signatures among the fastest compared.Round5 KEM IoT is described as suitable for much current blockchain-node hardware and lower-security applications.
  • Cryptosystem findings: Hybrid schemes may precede pure post-quantum blockchains but require hardware for two security mechanisms and large payloads; hash-based signatures generally perform poorly.Supersingular isogeny schemes remain promising but need smaller signatures, while newer hash-based algorithms may be practical.
  • DLT scope: Applying the recommendations to DAG- and Hashgraph-based DLTs is described as straightforward, but claimed post-quantum readiness of existing implementations still requires thorough evaluation.

IX. CONCLUSION

The article analyzes quantum attacks on blockchain cryptography, reviews post-quantum schemes and blockchain applications, and compares promising candidates. It concludes with guidance on challenges, implementation choices, and future research.

  • Conclusion: The article studies Grover- and Shor-based attacks on blockchain cryptography and reviews post-quantum schemes for mitigating them.It also examines their application to blockchain and compares their characteristics and performance.
  • Conclusion: The review provides guidance on applying post-quantum cryptosystems to blockchain and identifies associated challenges and future research directions.
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