Blockchain Safety in the Era of Quantum Computing: Preparing for Q-Day

The security of the likes of Bitcoin and Ethereum relies on cryptographic algorithms designed for classical computing power. But with the rise of Quantum Computing, that cryptographic foundation could be at serious risk.

Once Quantum algorithms run on sufficiently advanced machines, they could unravel the cryptography protecting blockchain networks, digital banking, and even the integrity of everyday credit card transactions. The impact of Quantum Computers on trust will be profound, and the clock is already ticking.

QuantumBasel, as a hub for applied Quantum Computing and AI, is working at the forefront of this challenge. We’re helping organizations prepare for the Quantum era.

Quantum Computing vs Cryptography: The Risk to Blockchain Networks

Quantum Computers exploit the principles of Quantum mechanics, such as superposition and entanglement, to solve problems beyond classical reach. Peter Shor’s algorithm, for example, can factor large numbers exponentially faster than any existing machine, breaking RSA and elliptic curve cryptography (ECC) the tools securing blockchain signatures, web authentication, and secure messaging.

The concern is not theoretical. Companies like IBM, IonQ, and D-Wave are already demonstrating advances in scalable Quantum technology. While IBM focuses on superconducting qubits, IonQ are building ion-trapped qubits, and D-Wave has pioneered annealing systems that showcase Quantum problem-solving for real-world applications such as logistics and portfolio optimization. Early breakthroughs highlight that Quantum supremacy is no longer a theoretical concept; while still years off, its arrival is now a matter of when, not if.

For blockchain architecture, this matters deeply. Most cryptocurrencies, including Bitcoin, depend on ECDSA, a cryptographic system that Quantum computers could one day crack.

In Bitcoin, once funds are spent from an address, the public key becomes exposed. A Quantum adversary could then derive the private key and drain the wallet.

Migrating Bitcoin would require a disruptive hard fork, forcing all users (including inactive addresses like those belonging to the mysterious creator of Bitcoin, Satoshi Nakamoto) to move funds into Quantum-secure wallets. 

Even in 2024, Deloitte sounded the alarm that up to 25% of Bitcoins would soon be vulnerable to hacks. That’s $500bn as of late 2024, or $562bn at time of writing. The governance and technical challenges for blockchains and cryptocurrencies are immense.

Q-Day: A Quantum Reckoning

Q-Day is the moment when Quantum Computers first crack today’s encryption. Experts estimate a 33% chance by 2035.

Unlike Y2K, Q-Day won’t be a single visible event. It may emerge as unexplained breaches, suspicious financial outputs, or geopolitical leaks. As Damir Bogdan, Chief Strategy and Alliances Officer of QuantumBasel states: “It will be the start of a completely new era, where no one and nothing can be trusted anymore.”

This is the existential threat: not just stolen crypto, but a collapse of digital trust in finance, governance, and communications.

Harvest Now, Decrypt Later

Adversaries don’t need to wait for Q-Day. Through Harvest Now, Decrypt Later (HNDL), they are already intercepting encrypted data today, stockpiling it, and planning to decrypt it once Quantum systems mature.

In fact, a 2025 report by The Federal Reserve described HNDL as an “active threat model” and “current and ongoing risk”. 

“A bad actor can obtain a distributed ledger replica, harvest the data, and in the fullness of time reveal previously obfuscated and confidential data using a sufficiently powerful quantum computer,” the report concluded. 

Data with long-term value such as healthcare records, biometric identifiers, legal contracts, remains vulnerable decades after creation. Once decrypted, the damage is irreversible. This is why Quantum-secure planning is essential now, not later.

Post-Quantum Cryptography and Global Action

To prepare, the U.S. NIST finalized its first PQC standards in 2024: CRYSTALS-Kyber (encryption), CRYSTALS-Dilithium, and SPHINCS+ (signatures). A fifth algorithm, HQC, was added in 2025.

The UK’s NCSC set a 2035 deadline for full PQC migration, while U.S. directives mandate readiness across federal agencies on similar timelines. Yet academic studies show nearly half of enterprises are not ready. With cryptographic transitions historically taking 10–20 years, this is dangerously close to the Q-Day horizon.

For blockchain architecture, the challenge is greater still. Decentralization slows upgrades, and introducing PQC often means rethinking consensus, digital signatures, and even proof of Quantum work mechanisms. Some projects are exploring Quantum blockchain concepts, including native ledgers built with PQC or Quantum-resistant primitives (cryptographic building blocks, such as signature schemes, key exchanges, or hash-based proofs), but mainstream blockchains have yet to commit to such radical overhauls.

Strategic Imperative for Businesses

For business leaders, the takeaway is clear: the risk isn’t investing in Quantum preparation, but rather in not investing. Companies that act now will be seen as Quantum-secure leaders, offering long-term trust in an uncertain future. Those that delay risk obsolescence when real-world applications of Quantum decryption suddenly make headlines. As with so much of contemporary physics education, the ‘boiling frog theory’ abounds in both AI and the Quantum domains.

As Bogdan puts it: “In the Quantum world, if you are on time, you’re already too late. To be on time, one must be early.”

Practical Steps to Prepare

1. Audit cryptography across systems, including networks and IoT.
2. Track standards from NIST, NSA, and UK NCSC.
3. Push vendors, including IBM, cloud providers, and blockchain developers, for PQC roadmaps.
4. Experiment early with hybrid PQC-classical deployments.
5. Prioritize long-term data like financial records, healthcare, and IP.
6. Educate executives, framing Quantum risk as a trust and business continuity issue.

QuantumBasel actively supports organizations in building this roadmap, helping them become Quantum-secure before the threat becomes urgent.

Quantum Security Systems as the Shield Against Q-Day

The impact of Quantum Computing on cryptography, and by extension, the security of blockchain-based systems, will be profound whether skeptics choose to believe it or not.

Whether through Shor’s algorithm breaking signatures, annealing machines optimizing attack vectors, or adversaries exploiting HNDL, the threat is looming, it is large, and it is unavoidable.

The solution is equally clear: adopt Quantum-secure methods early. Businesses that prepare will lead the next iteration of the global economy. Those that delay will risk being the first casualties on the beaches of Q-Day.

QuantumBasel stands ready to guide you through this transition. Let’s ensure your systems, your data, and your business remain secure in the Quantum age.