Bitcoin

Researchers from the quantum startup Alice & Bob posted a paper on 28 October estimating that a fault-tolerant quantum computer could solve the elliptic-curve discrete logarithm problem behind secp256k1, Bitcoin's signature scheme, with at most 30,000 cat qubits in about an hour (IACR ePrint 2026/2665). It follows Google Quantum AI's estimate in March of fewer than 500,000 physical qubits for the same attack (CryptoBriefing).

What the paper estimates

The paper, "Shor's algorithm compiled on cat qubits", gives end-to-end resource estimates for Shor's algorithm on superconducting cat qubits, with the same compilation reused for secp256k1: factoring RSA-2048 needs about 23,000 cat qubits and 3.14 days, while solving secp256k1's discrete logarithm problem needs at most 30,000 and one hour (IACR ePrint 2026/2665). ForkLog reported the same figures as 29,588 physical qubits forming 1,462 logical qubits for 61.8 minutes, about 17 times lower than the sub-500,000 qubit benchmark Google researchers presented in March, though the comparison is conditional because the studies use different hardware architectures and assumptions.

Google's paper put the attack at 9 to 23 minutes on 1,200 to 1,450 logical qubits (CryptoBriefing), so the new estimate needs fewer qubits but runs several times longer. It also assumes a 1 microsecond error-correction cycle, a phase-flip error probability of 0.0005 and no bit-flips, which the authors equate to a bit-flip time of about 100 years. Relaxing that with an extra layer of error correction raises the RSA-2048 figure to about 45,000 cat qubits (IACR ePrint 2026/2665).

What is not settled

The estimates are theoretical resource calculations, not a demonstration (Bitcoin.com), and no machine with these characteristics has been built (CryptoBriefing). Bitcoin.com noted that a one-hour attack would still exceed Bitcoin's roughly ten-minute block interval, which limits its immediate use against ordinary transactions awaiting confirmation, but leaves coins with already-exposed public keys more exposed, and cited earlier estimates that about 6.9 million BTC could face exposure (Bitcoin.com).

Cointelegraph reported Stacks founder Muneeb Ali saying on its Chain Reaction podcast that quantum risks are already discouraging institutional investment, that Bitcoin needs a credible roadmap with meaningful progress by 2028, and that 2030 is the target drawn from National Institute of Standards and Technology guidance.

What to watch

• A post-quantum signature BIP. BIP 361, the draft that would sunset legacy ECDSA and Schnorr signatures, lists the signature BIP it requires as still to be determined.

Bitcoin is in the news because Bitcoin Core changed how it discloses security flaws. On 22 October developer Antoine Poinsot told the Bitcoin development mailing list that bugs judged easy to find would have fixes backported to every maintained release and shipped as soon as possible, because language models have drastically lowered the bar to finding some classes of bugs (the mailing list post). A flaw that can be found with a single prompt to a language model is no longer protected by secrecy, so Core will stop holding it under embargo (Bitcoin Core's security advisories page).

The change matters for who waits for a fix. Core previously reserved such fixes for major releases, so users of older versions waited for the next one; now they get a point release of their own (the mailing list post).

Bitcoin Core rewrote its disclosure rules

Core's own policy page sets out the mechanism. A vulnerability judged "easily discoverable", which the page defines as one that can be discovered "with minimal effort, such as through a simple LLM prompt", will get a point release carrying the fix for each maintained major version as soon as possible, published alongside a security advisory and without the standard embargo (Bitcoin Core).

Everything else keeps the old timetable. Low severity bugs are disclosed two weeks after the release of a major version containing the fix. Medium and high severity bugs are disclosed two weeks after the last affected release reaches End of Life, roughly a year after that fix ships. Critical bugs sit outside the standard policy and would be handled case by case (Bitcoin Core).

Poinsot's argument is about backports. While details were embargoed, a fix could not be shipped to an older release, so users of that version waited for the next major one. "The embargo period achieves little but it delays the availability of a fixed release," he wrote (Cointelegraph).

The pressure was already visible

The change follows a summer in which automated tools found flaws faster than disclosure could contain them. Core Lightning developers urged operators to upgrade or take their nodes offline after receiving multiple AI-generated vulnerability reports, withholding technical detail for two weeks. In August the volunteer Bitcoin Red Team reported nearly 5,000 potential issues across 390 projects, with around a fifth reproduced at the time (Cointelegraph).

The ETF inflow streak broke

The same day, US spot bitcoin ETFs recorded $635 million of net outflows, their largest single-day outflow since 25 June, ending a three-day streak that had attracted $1.08 billion and pushing October's net outflows to $175 million (Cointelegraph). Bitcoin traded between $80,996 and $82,551 on 22 October, down from an intraday high of $84,777 on 21 October (Cointelegraph).

What to watch

• Whether Bitcoin Core's first "easily discoverable" point releases ship across all maintained major versions at once, which is the practical test of the new rule. As of 27 October the advisories page lists none under the new policy (Bitcoin Core).
• Whether ETF flows recover before October closes on 31 October, which decides whether it ends as a net outflow month (Cointelegraph).