One of the biggest long-term technological threats to Bitcoin has moved a step closer from theory to practical solution. A researcher from StarkWare conducted a transaction on the main Bitcoin network designed to withstand an attack from a sufficiently powerful quantum computer. The experiment is primarily important because it did not require changes to Bitcoin’s current consensus rules. However, it certainly does not mean that the largest cryptocurrency is safe from the quantum threat.
Table of Contents:
- You Might Be Interested: How to Choose the Right Exchange for Trading Your Cryptocurrencies?
- Why a Quantum Computer Could Threaten Bitcoin
- Not All Bitcoins Are Equally Exposed to the Quantum Threat
- Old bitcoins attributed to Satoshi Nakamoto may also be at stake
- How the first "quantum-safe" bitcoin transaction worked
- The transaction had to be accepted by miner MARA
- This doesn't make Bitcoin quantum-safe
- The biggest problem may ultimately not be technology, but agreement
- Quantum computers don't threaten Bitcoin yet. But time to prepare is not infinite
What would happen if a computer emerged capable of breaking the mathematics protecting a Bitcoin wallet in a short time? A question that just a few years ago seemed more like a sci-fi plot now occupies cryptographers, blockchain developers, and major technology companies.
It is precisely in this area that a significant experiment has now emerged. StarkWare announced that on August 26, 2026, the first transaction using its Quantum-Safe Bitcoin method was mined on the Bitcoin mainnet. The solution is the work of researcher Avihu Levy, who published the concept this spring.
One detail is particularly important – the experiment did not require changing Bitcoin’s fundamental rules or forking the entire network.
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Why a Quantum Computer Could Threaten Bitcoin
Bitcoin’s security is based, among other things, on public and private key cryptography. The private key functions, in simplified terms, as a secret password allowing the owner to manage the bitcoin. From it, a public key can be derived, but the reverse process is practically impossible using current computers.
It is precisely this asymmetry on which the security of digital signatures is based, proving that the coins are truly being managed by their authorized owner.
However, a sufficiently powerful quantum computer could change the situation. Using the so-called Shor’s algorithm, it could theoretically obtain the corresponding private key from the public key much faster than classical computers. An attacker could subsequently create a valid digital signature and transfer the bitcoin without the actual owner authorizing the transaction.
This doesn’t mean something similar can be done today. Even the most advanced current quantum computers don’t have the power and stability needed to practically break Bitcoin cryptography.
However, the technology world takes the threat seriously enough to prepare in advance. The US National Institute of Standards and Technology already completed the first three post-quantum cryptography standards in 2024 and called on organizations to begin transitioning to new algorithms before truly dangerous quantum machines emerge.
Not All Bitcoins Are Equally Exposed to the Quantum Threat
To understand the problem, it’s important to distinguish between a public Bitcoin address and the public key itself. For many types of Bitcoin addresses, the public key is hidden behind a cryptographic hash and only revealed on the blockchain when the user spends the coins. At the moment of sending a transaction, however, the necessary data is published and the transaction waits for a certain time in the so-called mempool until a miner includes it in a block.
It is precisely this time window that an extremely fast quantum attacker could exploit in the future. They would use the published key to derive the private key and attempt to create a competing transaction that would send the coins to themselves.
An even bigger problem is presented by bitcoins whose public keys are already permanently visible on the blockchain.
According to an analysis by Glassnode, the public key was revealed for approximately 6.04 million BTC at the time of its processing, representing 30.2% of Bitcoin’s then-issued supply.
This doesn’t mean these six million bitcoins can be stolen today. It’s only the amount of coins that would be potentially exposed to risk if a quantum computer capable of practically reconstructing the private key from the public key were created.
Glassnode divides this group into approximately 1.92 million BTC exposed due to the type of script used itself, and another 4.12 million BTC whose public keys were revealed, for example, by repeated use of the same address or fund management methods.
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Old bitcoins attributed to Satoshi Nakamoto may also be at stake
The quantum problem has another extremely sensitive dimension. Among old bitcoin outputs, there is a large number of coins stored using the Pay-to-Public-Key format, which publicly exposes the public key directly. Some of these bitcoins come from the very beginnings of the network and are associated with early miners, including Bitcoin’s creator himself, Satoshi Nakamoto.
As CoinDesk pointed out in its analysis of the quantum threat to Bitcoin, approximately 1.7 million BTC are held in about 20 thousand early Pay-to-Public-Key outputs. Some of these may be coins whose original owners no longer have access to them.
And this is where one of Bitcoin’s most complex future problems arises. An active owner can move their funds to a more secure system before sufficiently powerful quantum computers arrive. The owner of a lost private key cannot do this. If a functional quantum attack were to emerge one day, coins that had been considered lost for decades could theoretically re-enter circulation – but this time in the hands of an attacker.
The Bitcoin community is therefore grappling with a very uncomfortable question: should old and unsecured coins be frozen after a certain date, or would such a step contradict Bitcoin’s fundamental idea that the network should not arbitrarily prevent anyone from managing their property? Even leading cryptographers have yet to agree on the answer.
How the first “quantum-safe” bitcoin transaction worked
StarkWare’s experiment attempts to solve a somewhat different part of the problem – not the millions of bitcoins with long-published keys, but primarily the dangerous period during coin transfers.
The Quantum-Safe Bitcoin (QSB) method adds another layer to current security based on hash functions instead of elliptic curve cryptography.
According to StarkWare’s technical explanation, the solution uses a procedure called “signature grinding.” In this process, the computer performs a vast amount of calculations in advance, searching for a specific form of transaction that meets the required conditions. The resulting security can thus rely on the properties of cryptographic hashes, against which Shor’s algorithm does not pose the same type of threat.
Computationally, this is still a very impractical method. As The Block reports, creating a single transaction can take hours. StarkWare mentions costs in the order of several hundred dollars. This is therefore not a technology that Bitcoin users would start enabling in their wallets in the coming weeks.
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The transaction had to be accepted by miner MARA
The experiment had another complication. QSB uses a non-standard transaction format that regular bitcoin nodes do not automatically forward.
The transaction therefore could not simply pass through the standard mempool like an ordinary payment. The researchers submitted it directly to the miner through the MARA Slipstream service, and MARA subsequently included it in a bitcoin block.
This also demonstrates the difference between what the bitcoin protocol actually allows and what regular nodes standardly accept and distribute.
Technically, it was possible to mine the QSB transaction without changing the consensus rules. For mass adoption, however, the current method would be considerably impractical.
This doesn’t make Bitcoin quantum-safe
This point is the most important for interpreting the news. A successful transaction does not mean that Bitcoin has become resistant to quantum computers.
StarkWare itself emphasizes that QSB in its current form is primarily proof that a certain form of protection can be built on top of the existing bitcoin protocol. It does not automatically address millions of coins whose public keys have already been published in the past, nor does it convert the entire network to post-quantum cryptography.
The solution’s author, Avihu Levy, also supports a longer-term option in the form of changing the bitcoin protocol through a soft fork.
StarkWare CEO Eli Ben-Sasson compared the current solution more to a lifeboat: its existence, he says, shows that certain protection is possible, but it should not be a reason to postpone preparations for systematic defense.
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The biggest problem may ultimately not be technology, but agreement
Bitcoin has one specific characteristic compared to conventional financial systems. There is no central company that could simply announce one day that starting from a new version, all users will use different cryptography.
Significant change requires coordination among developers, miners, node operators, wallet manufacturers, exchanges, and ultimately the users themselves.
And it is precisely the time needed for such a migration that may be more important than the answer to whether the first truly dangerous quantum computer will emerge in five, ten, or twenty years.
A recent academic study, Quantum Horizon, therefore describes the quantum threat to Bitcoin as real but manageable. The authors conclude that with timely transition to new signature mechanisms, most of the problem can be technically solved. The more difficult part may be the decentralized decision-making and moving funds before the new system is actually needed.
Quantum computers don’t threaten Bitcoin yet. But time to prepare is not infinite
For the average bitcoin holder, the current news is therefore not a reason for panic or to move funds.
There is no publicly known quantum computer that could crack bitcoin private keys today. No one knows exactly when the technology will reach a stage where something like this would be possible.
However, StarkWare’s experiment shows why the topic is increasingly appearing among leading cryptographers.
For a digital asset that, according to its proponents, should store value for decades or hundreds of years, the question of whether its security is sufficient today is not enough. What matters more is whether it can change before the technology on which its security rests ceases to be sufficient.
The first quantum-resistant transaction on the bitcoin mainnet has not yet resolved this question. However, it has shown that the path to defense need not begin only when a quantum attack becomes truly possible.
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