Crypto investor Nic Carter's worst-case quantum scenario has a hostile actor recovering the keys to dormant Bitcoin and spending it across 10 blocks. Proposed protections would restrict legacy signatures, and owners who cannot migrate could lose access.
Nic Carter's worst-case quantum scenario consists of a hostile actor recovering the keys to dormant Bitcoin, then broadcasting a wave of spends across 10 blocks. In his Oct. 13 interview with Luke Martin, Carter says early coins moving together could shake confidence in the network.
The scenario assumes a future quantum machine capable of breaking Bitcoin's key cryptography. Google's published research models future resources for such an attack, and Bitcoin key recovery remains undemonstrated in that work.
Can millions of BTC fit in 10 blocks?
A sufficiently powerful quantum computer could use Shor's algorithm to recover private keys from exposed public keys, gaining the ability to authorize spending. Glassnode's May 20 analysis identified 6.04 million BTC, or 30.2% of then-issued supply, with public keys already exposed.
CryptoSlate models an explicitly hypothetical set of 50,000 early outputs holding 50 BTC each, totaling 2.5 million BTC. Those inputs require about 5.7 million bytes, equivalent to 22.8 million weight units before transaction overhead. Ten blocks have an aggregate ceiling of 40 million weight units, and with one compact receiving output per batch, the illustrative set fits beneath it when split into transactions below Bitcoin Core's 400,000-unit standard weight limit.
Fees, competing traffic, and miner decisions still determine inclusion. An actual sweep's block-space demand would depend on its particular outputs and spending requirements.
Proposed fixes trade protection for access
Keeping existing spending rules intact preserves the ability to spend with a valid key, including one a future attacker recovers. Restricting legacy signatures changes that bargain: owners who cannot migrate or meet rescue conditions could lose access.
BIP-361's proposed phases would restrict new vulnerable destinations about three years after activation, then tighten legacy-signature spending through rescue conditions about two years later. Dan Robinson's May 1 PACT concept explores advanced, private timestamps proving address control, though protection depends on the holder preparing before quantum key recovery becomes possible.
The February Hourglass V2 draft takes another approach: one P2PK spend and one BTC of net spending per block. Throttling would slow the outflow while constraining legitimate holders under the same rules.
These remain proposals and research concepts. Bitcoin's community would still have to decide which claims to recognize when an ordinary signature can no longer distinguish an original holder from a quantum attacker.
Source: CryptoSlate
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