Quantum Computers Vs. Bitcoin: Chronicle of a Foretold Threat.
Although the large-scale threat is still on the horizon, a portion of all bitcoins is already theoretically vulnerable.
It’s a technological saga with the feel of a thriller, a silent duel between two of the most disruptive innovations of our time. On one side, Bitcoin, the digital fortress deemed inviolable, guarded by the relentless laws of mathematics. On the other hand, the quantum computer, a machine whose processing power promises to break the codes we thought were eternal. This showdown, long confined to theory, is accelerating dramatically. The milestone set by IBM engineer Steve Tippeconnic in August 2025 confirms a blistering pace of progress that began back in 2023.
The question is no longer if the threat is real, but when it will strike and if Bitcoin will be ready to withstand it.
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The Two Cryptographic Faces of Bitcoin
To grasp what’s at stake in this confrontation, it’s crucial to understand that Bitcoin’s security doesn’t rest on one, but on two distinct cryptographic pillars. Confusing the two means misunderstanding the exact nature of the quantum threat.
1. The Fortress of Mining: SHA-256
The first pillar is the one that powers Bitcoin mining. It relies on a hash function called SHA-256. Imagine it as a kind of mathematical food processor: you can put any amount of data into it (for example, the thousands of transactions in a block), and it will always produce a fixed-size output, a unique digital fingerprint called a “hash.” This hash is nothing more than a very large number.
The miners’ job is a sort of cosmic lottery. They take the data from a block, add a random number to it, and run the whole thing through the SHA-256 processor. Their goal? To find, through trial and error, a hash that is lower than a certain target value set by the network. This is an extraordinarily energy-intensive process. The first miner to succeed validates the block, adds it to the blockchain, and receives new bitcoins as a reward. This Proof of Work mechanism is, for now, considered relatively resistant to quantum computers. The primary threat does not lie here.
2. The Secret of Transactions: Public-Key Cryptography (ECC)
Bitcoin’s true Achilles’ heel in the face of quantum computing lies in its second pillar: the management of wallets and transactions. This system uses a technique called public-key cryptography, specifically the Elliptic Curve Digital Signature Algorithm (ECDSA).
The concept is formidably elegant. When you create a Bitcoin wallet, the software generates a pair of keys: a secret private key and a public key derived from the first. To spend your bitcoins, you must use your private key to “sign” the transaction, thus proving you are the owner. The genius of the system is that it’s trivial to calculate the public key from the private key, but virtually impossible to do the reverse. A classical computer would take billions of years to achieve this. It is this impossibility that guarantees the security of your funds. At least, until the quantum computer arrived.
From Proof of Concept to Acceleration: IBM’s Progress
The quantum threat crossed a decisive threshold in the summer of 2023. It was then that IBM researchers delivered the first concrete proof of concept. Using their 133-qubit IBM_TORINO quantum processor, they first managed to break a 5-bit ECC key in July, followed by a 6-bit key shortly after, using the famous Shor’s algorithm.
Of course, a 6-bit key is cryptographically insignificant. With only 26 (or 64) possibilities, your laptop could brute-force it in a microsecond. In comparison, Bitcoin keys are 256 bits long, a gargantuan scale representing about 2250 times more combinations. The gap to be bridged remained astronomical. However, the key takeaway was something else: the experiment proved that the theoretical attack was practically achievable.
But this proof of concept was just the beginning. The saga took a new turn last month, in August 2025. Engineer Steve Tippeconnic, also at IBM and leveraging a 133-qubit chip, took another step forward by breaking another cryptographic key. This recent success is crucial: it transforms the one-off achievement of 2023 into a measurable and continuous trend of progress. The machine is in motion, and it’s speeding up.
The Race Against Time: Logical Qubits vs. The Clock
To assess the true timeline of the threat, one must distinguish between physical qubits and logical qubits. Physical qubits (like the 133 in IBM’s chip) are unstable and prone to errors. To perform a complex calculation, thousands of them must be grouped to form a single, stable, error-corrected logical qubit. The latter is the true indicator of power.
Experts estimate that it would take over 2,330 logical qubits to have a chance of breaking a Bitcoin key in less than a month. IBM’s roadmap had predicted reaching 200 logical qubits by 2029, but recent progress could accelerate this timeline. IBM believes it could reach the critical threshold as early as 2033. The Pauli Group, an expert collective, estimates the window of danger to be between 2027 and 2033.
Post-Quantum Bitcoin: A Titanic Migration
So, is this the end of Bitcoin? Not at all. With the threat identified, the community can prepare for one of the greatest migrations in its history: the transition to post-quantum cryptography (PQC).
Solutions already exist, such as the Kyber and Dilithium algorithms, which are designed to resist both classical and quantum computers. However, the challenge is colossal:
Technical Constraints: PQC algorithms generate larger signatures and keys, which would reduce the number of transactions per block and could increase fees.
Governance: The Bitcoin protocol is intentionally difficult to change. Reaching a consensus for such a fundamental shift will be a long and complex process.
Ecosystem Migration: All wallets (software and hardware), exchanges, and services will need to be updated. Most importantly, every user will have to manually move their bitcoins to new, post-quantum addresses.
The Present Vulnerability: The Sin of Address Reuse
Although the large-scale threat is still on the horizon, a portion of all bitcoins is already theoretically vulnerable. This weakness stems from a bad practice: address reuse.
Normally, your public key is only revealed on the blockchain at the moment you spend funds from an address. If you never reuse that address, the risk is minimal. However, if you continue to receive funds at an address whose public key is already exposed, a future quantum attacker could scan the blockchain, calculate the corresponding private key, and steal the funds.
The golden rule is therefore simple: generate a new address for every transaction you receive!
It’s estimated that about 33% of all BTC are currently vulnerable, which amounts to approximately 6.36 million bitcoins. Of this total, 4.49 million are at risk due to address reuse. The remainder comes from very old address types, notably those containing Satoshi Nakamoto’s bitcoins.
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