Can a quantum computer break Bitcoin?

The topic of quantum computers and Bitcoin security is a hot topic among cryptocurrencies and scientists. Here's what we know today:

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Can a quantum computer break Bitcoin?

Yes - theoretically, but not today and not anytime soon. Bitcoin is based on, among others:

SHA-256 (hashing for block mining),

ECDSA (Elliptic Curve Digital Signature Algorithm) - used when signing transactions.

It is ECDSA that is vulnerable to quantum attack - especially using Shor's algorithm.

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When will it be possible?

For a quantum computer to actually break ECDSA, it would need:

At least 10 million logical qubits,

Extremely stable quantum error correction,

Gigantic computing power operating in real time.

Currently (2025) we are dealing with quantum computers of the order of several hundred qubits, and we are a whole decade or more away from breaking Bitcoin.

Experts (e.g. from MIT or IBM) estimate that computers capable of such an attack may be created after 2035–2040, if they are created at all.

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What will Bitcoin do?

Bitcoin community:

Already investigating a transition to algorithms more resistant to quanta (post-quantum crypto).

Possible soft-fork or hard-fork update to new mechanisms (e.g. Schnorr + Lamport signatures or other PQCs).

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Summary:

BTC cracked by quanta in 2025? No.

Real threat? Yes – but only in a dozen or so years.

Will Bitcoin adapt? Yes – and it has time for that.

Let's play "what if..." - namely:

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Scenario: A quantum computer is created suddenly and attacks Bitcoin before the network reacts

Year: 2033

Unexpectedly, one of the government agencies (or a private company from Asia) creates a working quantum computer with 10+ million stable qubits, ready to run Shor's algorithm in real time.

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Step by step - what happens:

1. Attack on ECDSA signatures

The attacker selects Bitcoin addresses that have already had their public keys exposed (i.e.... practically all active addresses). Thanks to Shor's algorithm, he recovers the private key within minutes.

2. Theft of funds

From these addresses, he sends BTC to his new, freshly created quantum addresses. If he does it quickly - even thousands of transactions can go unnoticed in the first blocks.

3. Chaos on the market

The price of BTC starts to fall rapidly.

People are losing trust.

Exchanges are freezing withdrawals.

The media is announcing the “end of cryptocurrencies”.

4. Community reaction

Programmers and core developers are holding a global crisis call.

Decision: Hard fork to a post-quantum signature system (e.g. XMSS, SPHINCS+, Rainbow).

Bitcoin Q (BTCQ) is created – “the safe one”.

5. Old vs. new

Some of the network (and people) stay with the old chain (like with BCH), but most migrate to BTCQ.

The new chain ignores transactions with quantum signatures.

The losses of some users are unrecoverable – this is the “crypto war of 2033”.

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Long-term effect:

The price of BTC drops to several hundred dollars... and then BTCQ grows to a new ATH.

Trust returns, but it takes years.

Cryptocurrencies are accelerating the adoption of PQC (post-quantum cryptography) worldwide.

Quantum computers are becoming part of the new cold war.

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