Challenges and opportunities for post-quantum blockchain security

Blockchain, the technology behind digital currencies, faces a looming crisis as quantum computing advances threaten its core cryptographic foundations. A new study by Sufyan Al-Janabi from the College of Computer Science and IT, University of Anbar, Iraq, delivers a stark warning about the vulnerability of classical blockchain systems and outlines the path forward through quantum-resistant innovations.

The paper, “Post-Quantum Blockchain: Challenges and Opportunities” (arXiv, 2025), reviews how emerging quantum algorithms could break widely used blockchain security protocols such as RSA, SHA-256, and Elliptic Curve Digital Signature Algorithm (ECDSA). It further explores the promise and limitations of Post-Quantum Cryptography (PQC) and the development of Post-Quantum Blockchains (PQBs) as a way to safeguard digital assets in the quantum era.

Why quantum computing threatens blockchain integrity

Blockchain security relies heavily on cryptographic primitives like public-key encryption, digital signatures, and hash functions. In current systems, techniques such as RSA and elliptic curve cryptography ensure that only authorized users can approve transactions. However, quantum algorithms such as Shor’s and Grover’s pose a direct threat to these systems.

Shor’s algorithm, if run on a sufficiently powerful quantum computer, can efficiently break the mathematical problems underpinning RSA and ECDSA. This would allow malicious actors to forge digital signatures and hijack blockchain transactions. Meanwhile, Grover’s algorithm accelerates brute-force search, significantly reducing the strength of hash functions and enabling faster detection of hash collisions. Together, these capabilities undermine the immutability and trust that form the backbone of blockchain technology.

The research notes that while today’s quantum computers remain limited, the trajectory of development suggests that quantum machines capable of breaking RSA-2048 could emerge within the next decade. This creates an urgent need for blockchain ecosystems to prepare defenses before critical vulnerabilities are exposed.

How post-quantum cryptography provides a path forward

To counter these risks, the author points to Post-Quantum Cryptography (PQC) as the most viable near-term solution. Unlike quantum cryptography, which requires entirely new infrastructures, PQC schemes can be implemented on classical systems but are based on mathematically hard problems resistant to quantum attacks.

The study identifies five major classes of PQC approaches:

• Lattice-based cryptography, including NIST-endorsed standards such as CRYSTALS-Kyber, Dilithium, and FALCON, which balance strong security with efficiency.
• Code-based cryptography, exemplified by McEliece, known for robustness but hindered by large key sizes.
• Hash-based cryptography, including SPHINCS+, offering long-term digital signatures anchored in hash function resilience.
• Multivariate-based cryptography, which leverages the difficulty of solving complex polynomial equations.
• Supersingular isogeny cryptography, a newer approach based on elliptic curve isogenies, though less mature compared with others.

These PQC algorithms are already being standardized by organizations such as the U.S. National Institute of Standards and Technology (NIST), which has recommended Kyber for key encapsulation and Dilithium for digital signatures. Their adoption into blockchain systems would lay the foundation for Post-Quantum Blockchains (PQBs) capable of resisting quantum-based attacks.

The paper highlights several blockchain initiatives already experimenting with PQC. Bitcoin offshoots are testing quantum-resistant mining protocols, while Ethereum’s roadmap includes zk-STARKs to bolster security and scalability. Platforms such as Algorand, IoTeX, and Cardano are preparing for quantum-era upgrades, while dedicated PQB ecosystems like Nexus, Komodo, QRL, Tidecoin, and QANplatform are operational and designed specifically to withstand quantum threats.

What challenges stand in the way of post-quantum blockchains?

Despite the promise of PQC, the research reveals that significant hurdles must be overcome before PQBs can achieve mainstream adoption. A central challenge lies in the large key and signature sizes of many PQC algorithms, which slow transaction speeds and reduce block capacity. For resource-constrained devices, particularly in the Internet of Things (IoT), these inefficiencies make implementation difficult.

Another obstacle is computational cost and energy consumption. PQC algorithms often demand greater storage and processing power, intensifying concerns in blockchain systems already criticized for energy use. This becomes particularly critical in consensus protocols like Proof of Work (PoW), which are highly vulnerable to Grover’s algorithm. Unless new consensus mechanisms, such as Proof of Stake (PoS) or other quantum-resistant designs, are adopted, quantum-equipped miners will always hold an advantage over classical miners.

PQCs are not immune to other vulnerabilities. Threats such as double spending, Sybil attacks, denial-of-service exploits, and smart contract flaws remain relevant even in quantum-resistant frameworks. This means PQBs must be designed with layered defenses to address both quantum and non-quantum risks.

Looking forward, the paper identifies several research priorities:

• Developing hybrid cryptosystems that combine classical and quantum-safe methods to ensure resilience.
• Exploring quantum cryptography-based blockchains using Quantum Key Distribution (QKD) for ultra-secure communication.
• Enhancing PQC efficiency through compression techniques to reduce ciphertext and execution overhead.
• Integrating advanced cryptographic tools such as ring signatures, aggregate signatures, homomorphic encryption, zero-knowledge proofs, and secure multi-party computation.
• Innovating adaptive consensus mechanisms that balance decentralization, security, and performance under quantum-resistant conditions.