Do Quantum Computers Threaten Blockchain Security?

Quantum computers do not make every cryptographic problem easy, but they may eventually solve some problems far more efficiently than classical machines. That matters for blockchains because public-key signatures are what allow users to prove ownership and authorize transactions.

This explainer draws on a discussion with Dr. Shai Wyborski, whose academic work focuses on quantum and post-quantum cryptography, to examine what the threat is, what would be required to make it practical, and how blockchain networks might migrate.

The Quantum Threat to Blockchain Signatures

The XXIM podcast recently featured Dr. Shai Wyborski, a PhD in quantum cryptography from the Hebrew University of Jerusalem, to discuss a big question: do quantum computers threaten Bitcoin? The answer, of course, is: yes, they do.

Dr. Wyborski has spent much of his academic career focused on post-quantum cryptography, with roughly 60% of his doctoral thesis centered on migrating Bitcoin to a post-quantum world. His perspective is clear: if we woke up twenty years from now and scalable quantum computers were in every garage, all pre-quantum Bitcoin would be vulnerable.

Dr. Wyborski explains quantum computing with a simple analogy. At an abstract level, classical computers can be thought of like machines using pulleys and levers—they manipulate bits (zeros and ones) in predictable ways. Quantum computers, however, introduce a new operation: qubits that can exist in superposition, meaning they're both 0 and 1 at the same time. This allows quantum machines to explore multiple computational paths simultaneously, making them powerful for solving problems that classical computers struggle with. As Dr. Wyborski states: quantum computers "can't increase the type of problems that such a computer can do, but we do believe that it increases the set of problems that such a machine can solve quickly."

One breakthrough example is Shor's Algorithm, which efficiently finds the prime factors of an integer. While this may sound niche, it's critical — because factoring and discrete logarithms form the foundation of public-key cryptography, the technology behind signatures and encryption that proves ownership used in most cryptocurrencies. If those signature schemes break, anyone could forge transactions.

Some forecasts place the arrival of scalable, fault-tolerant quantum computers in the 2030s, but the timing remains uncertain. Estimates discussed in the original interview suggested that an attack on Bitcoin's signature scheme could require thousands of logical qubits and, after accounting for noise and error correction, potentially millions of physical qubits. Progress is steady, but slow.

The straightforward solution is post-quantum signature schemes, which are cryptographic methods designed to withstand quantum attacks. Dr. Wyborski himself worked on a protocol that achieves a 90% accurate blockchain without signatures, pointing toward potential future fixes.

Kaspa as a Case Study

Wyborski's analysis suggests that Kaspa's high-throughput BlockDAG architecture may offer more room for integrating larger or more complex post-quantum signature schemes than slower, linear systems. This is a research argument rather than a deployed capability. Its scalability opens the door to integrating more complex or resilient cryptographic schemes without crippling performance.

Dr. Wyborski is now working on a new project, Tectonic.xyz, focused on building post-quantum blockchain solutions. His work highlights the urgent need for future-proofing crypto — before the quantum era arrives.