Bitcoin & Quantum Computing
Quick take on Levy's "QSB white paper" & Bitcoin resilience
OVERVIEW
A meaningful technical paper was published on April 9, 2026, by a credentialed cryptographer at StarkWare, a respected blockchain infrastructure firm. The “Quantum-Safe Bitcoin Transactions Without Softforks” white paper by Avihu Levy presents the first known method for making Bitcoin transactions quantum-resistant on the existing network, requiring no changes to Bitcoin itself.
While the paper is not an immediate call to action, it presents a development worth understanding. For those of us who aren’t computer scientists or engineers, this memo is intended to address questions about quantum risk and Bitcoin’s vulnerability. Those questions have been on the rise and this memo hopes to provide a grounded basis for conversations with clients who hold bitcoin. I am far from qualified to provide any technical support or challenge to Mr. Levy’s white paper; my objective is merely to provide some context for those who hold bitcoin and for those of us who advise them.
THE QUANTUM RISK — “SIMPLY” STATED
Bitcoin’s security rests on a mathematical problem that today’s computers cannot solve in any practical timeframe: deriving a private key from a public key. That one-way relationship provides the cryptographic security that makes Bitcoin ownership meaningful.
A sufficiently powerful quantum computer running a specific algorithm (Shor’s algorithm) could solve that problem and with it, forge the digital signatures that authorize Bitcoin transactions. This would be a total break of Bitcoin’s security protocol. A bad actor with that capability could steal any Bitcoin whose public key has been exposed.
Two important clarifications help calibrate the risk:
Timeline is genuinely uncertain. No credible source can precisely predict when quantum computers will in fact reach the scale needed to threaten Bitcoin’s security. Current machines are orders of magnitude too small. Most serious estimates place the threat in the range of a decade or more, although the field of quantum computing is certainly advancing. The Bitcoin developer community is working on this now; they aren’t waiting. It’s a feature – not a bug – that changes are made only slowly and incrementally with Bitcoin’s code. But Bitcoin code developers have historically demonstrated the ability to achieve consensus to solve major challenges to the network.
Not all Bitcoin is equally exposed. UTXOs (Bitcoin holdings) whose public key has never been revealed in a prior transaction are in a substantially better position than those that have. This distinction – which maps to how and when wallets have been used – matters for owner-specific risk assessment. A sufficiently-capable quantum computer running Shor’s algorithm would need the public key in order to derive the private key.
Critically, even Bitcoin held behind quantum-safe spending conditions can be vulnerable if the transaction authorizing the spend is itself forged. The quantum risk runs through the transaction layer, not just the wallet layer. Levy’s QSB paper directly addresses this issue.
WHAT THE QSB PAPER INDICATES
The paper introduces Quantum-Safe Bitcoin (QSB): a method for constructing a Bitcoin spending transaction whose authorization cannot be forged by a quantum computer, even one running Shor’s algorithm. Its security rests on hash functions rather than the vulnerable signature mathematics, and hash functions are far more resistant to quantum attack. Crucially, it works within Bitcoin’s existing rules today with no softfork or protocol change required.
The headlines:
QSB method works on the live network today. No Bitcoin consensus changes are needed. The method operates within rules that have existed since Bitcoin’s earliest days.
Designed for high-value cold storage. Spending a QSB-protected UTXO requires roughly $75–$200 in off-chain computing costs (GPU time). That’s immaterial for a multi-million-dollar holding; it’s not designed for everyday or Lightning transactions.
Computationally intensive but non-custodial. The heavy computational work (grinding through transaction variants) can be outsourced to cloud computing without ever exposing private keys. The sensitive cryptographic material never leaves the holder’s secure device.
Operationally complex today. QSB transactions require submission directly to mining pools rather than the normal Bitcoin network. To our knowledge, no major custodian currently supports this workflow as a standard product.
Levy is explicit that QSB is a bridge, not a destination. He calls it a ‘last-resort measure’ and continues to advocate for protocol-level changes through Bitcoin’s normal softfork process that would make quantum-safe transactions efficient, standard, and user-friendly for all Bitcoin holders. (QSB doesn’t do that.) QSB demonstrates that a solution path exists within Bitcoin’s current design; it is not that solution in its final form.
WHAT THIS MEANS FOR BITCOINERS
No immediate portfolio action is warranted. The quantum threat to Bitcoin is real in principle and uncertain in timeline. Levy’s paper provides evidence that Bitcoin’s technical community is solving this problem proactively and ahead of the threat. Amid unfounded or vague “quantum FUD” that hits the Bitcoin community from time to time, the paper should affirm that a quantum-resistant solution is viable.
Relevant takeaways:
Bitcoin has a credible quantum migration path. Unlike some legacy financial infrastructure where post-quantum upgrades require replacing entire systems, Bitcoin has a demonstrated softfork upgrade mechanism and a community of cryptographers actively working on the problem.
The threat is not today’s threat. Current quantum hardware is not remotely close to the scale needed. The window for protocol-level upgrades to occur before the threat matures is measured in years, not months.
Custody matters. Clients with significant cold storage holdings should be asking their custodians about quantum readiness: address type support, UTXO segmentation by exposure level, and protocol upgrade preparedness. Bespoke has developed a specific questionnaire for this purpose.
This is a watch item, not a crisis. We are monitoring the protocol development trajectory, custodian readiness, and regulatory guidance. We will flag any material change.
TLDR: Quantum computing is probably coming. Bitcoin’s house is not on fire.