What Is Post-Quantum Cryptography?

No. Running Shor's algorithm against a real Bitcoin private key would require several thousand stable, error-corrected qubits held in that state long enough to finish the calculation. The largest quantum computers built as of 2026 have at most a few thousand physical qubits, and none reach the error-corrected scale the attack needs. The threat is real as a long-term planning problem, not as something happening this year.

Shor's algorithm is a method, published by mathematician Peter Shor in 1994, for solving certain math problems on a quantum computer far faster than any classical computer can. Elliptic-curve cryptography, the type securing Bitcoin and Ethereum private keys, relies on exactly the kind of problem Shor's algorithm targets, which is why a sufficiently powerful quantum computer would threaten it.

In August 2024, NIST finalized three post-quantum cryptography standards: FIPS 203 (ML-KEM, for encrypting data), FIPS 204 (ML-DSA, for digital signatures), and FIPS 205 (SLH-DSA, an alternative signature scheme). Each is built on a different math problem believed to resist both classical and quantum attacks, giving software makers a tested foundation instead of an unproven, homegrown design.

No wallet using standard elliptic-curve cryptography is vulnerable to a quantum attack today, because no quantum computer built so far comes close to the scale required. The real question for the years ahead is whether wallets, exchanges, and blockchain protocols adopt post-quantum signature schemes before that scale becomes achievable, not whether an attack is possible this year.

None of the major cryptocurrencies in wide use, including Bitcoin and Ethereum, have switched their default signature scheme to a post-quantum algorithm as of 2026. Some smaller projects market themselves as quantum-resistant, and the credible way to check that claim is looking for an actual NIST-standardized algorithm like ML-DSA or SLH-DSA behind it, rather than taking the label at face value.

It would require a coordinated protocol upgrade, similar in scale to past major changes like Ethereum's move to proof of stake, where every wallet, exchange, and node eventually supports the new signature scheme while a transition period lets existing keys migrate safely. Post-quantum signatures like ML-DSA also produce much larger keys and signatures than today's elliptic-curve ones, so a real migration has to account for bigger transaction sizes and higher fees, not just swap one algorithm for another underneath the hood. Node software would need to accept both old and new signature types during the transition, wallets would need to generate and manage a second kind of key pair, and exchanges would need to support withdrawals to either format. No such upgrade has shipped on either network as of 2026, though both communities have discussed the eventual need, and some newer blockchains launched after 2024 have already built optional post-quantum signature support in from the start rather than retrofitting it later.

Migrating cryptographic infrastructure takes years, and data encrypted today could still be sensitive by the time a capable quantum computer exists, so some institutions are testing quantum-safe systems well ahead of any real threat. Testing early gives them a working system in place long before it's actually needed, rather than reacting once the risk has already arrived.

A physical qubit is one actual quantum bit built into a quantum computer's hardware, and it's inherently noisy and error-prone. A logical qubit is a stable, error-corrected unit built by combining many physical qubits together to cancel out that noise. Current quantum hardware needs many physical qubits for every one reliable logical qubit, which is a big part of why today's machines are still so far from the scale Shor's algorithm needs against a real cryptographic key.