Progress in quantum technologies has reached a new level: Google predicts that mass production of quantum computers could become a reality by 2029. In the crypto community, these prospects are raising serious concerns: will the blockchain be able to withstand the new threats posed by quantum computing power? In this article, we look at whether these concerns are justified and what post-quantum solutions can secure the blockchain in the future.


 

Quantum vs. classical: what makes the new computers unique?
 

Quantum computing is based on mechanisms that are very different from the classical computing scheme. Standard computers use binary code and control data with bits that can be either 0 or 1. Quantum computers, on the other hand, use qubits — special elements that can be in multiple states at the same time (superposition) and exchange information with each other instantaneously (entanglement). This allows parallel computation at scales inaccessible to classical systems.
 

Quantum computers have already shown enormous potential in solving problems that are beyond the capabilities of conventional devices. This poses a likely threat to the traditional encryption methods that underpin the security of many modern systems, including blockchain. To date, blockchain cryptographic algorithms have been successful in preventing errors and protecting against hacking. However, with the development of quantum technologies that can perform calculations in a split second, selecting private keys — 32-byte numbers — is no longer a difficult task.
 

The threat of quantum computers to cryptocurrencies

The emergence of quantum computers poses several threats to the security of the cryptocurrency ecosystem at once:
 

1. Risk #1. Centralisation.

Blockchain systems, including bitcoin, use the Proof-of-Work consensus algorithm, which requires significant computing power. Quantum computers can provide this power, giving them an advantage over traditional miners and creating the risk of centralisation — a situation where control of the network is concentrated in the hands of a few participants.
 

2. Risk #2. Vulnerability of digital signatures.

Blockchain uses public key cryptography, including digital signatures, to validate transactions and protect user funds. Quantum computers are able to solve factorisation and discrete logarithm problems much faster, opening up the possibility of cracking digital signatures and revealing private keys in the future.
 

How real is the quantum threat?

Despite the risks described above, the practical threat of a quantum attack is still far from reality. Modern quantum computers are still very unstable and require special conditions, such as ultra-low temperatures, which limit their potential to break cryptographic algorithms. There are also limits to the number of qubits: successfully cracking encryption keys requires far more computing resources than current prototypes can provide.
 

Prominent members of the crypto community, such as Vitalik Buterin, point out that blockchain networks such as Ethereum can adapt and use hardforks to protect users' funds. As a result, many experts believe that while quantum computing may reach a level that threatens crypto in the future, the current risks are greatly exaggerated.
 

Quantum computers on guard of cryptocurrencies

Paradoxically, quantum computers may be the solution that allows blockchain to effectively counter new threats. Quantum cryptography uses the principles of quantum mechanics, such as entanglement and superposition, to create unbreakable keys that cannot be intercepted or deciphered by traditional methods.
 

One promising direction is the use of quantum key distribution (QKD) to exchange secret keys between network participants. These keys, which are reliably protected, are beyond the control of even the most powerful quantum computers. Today, QKD technologies are being actively tested and applied in various fields to protect data, and in the future they could be integrated into blockchains, creating a stable and quantum-secure cryptographic environment.
 

How to protect the blockchain from quantum threats?

Today, the crypto community is actively working on solutions that can protect the blockchain from quantum threats:
 

• Improving hashing algorithms.

Moving to more sophisticated algorithms, such as SHA-512, can significantly increase the resilience of the system.
 

• Increase the size of the private key.

The longer the key, the harder it is to crack, and current approaches involve implementing longer keys that are resistant to quantum attacks.
 

• Post-quantum cryptography.

The most promising post-quantum cryptographic schemes are NTRU, SIDH and LWE. They are currently being actively researched and considered for implementation in blockchain.
 

Given the existing technological limitations of quantum computers, the threat to blockchain remains purely hypothetical at the moment. The industry is actively developing defence mechanisms, such as post-quantum cryptography, which opens up new prospects for the security of digital currencies and blockchain technologies.