Bitcoin Vulnerability to Quantum Threat Sparks 'Freeze' Debate: Ownership vs. Security

The Bitcoin community is increasingly debating whether to limit the spending of coins vulnerable to quantum computer threats, raising questions about how far consensus rules can be altered. The debate extends beyond adopting new cryptographic technology to encompass how much existing ownership rights should be preserved and how network security should be maintained.

According to Bitcoin Magazine, current ECDSA and Schnorr signatures used by Bitcoin could be threatened if sufficiently powerful quantum computers emerge. Specifically, older P2PK outputs, taproot outputs with exposed public keys, and addresses reusing public keys are considered vulnerable.

The concern is that if quantum computers are used for attacks, attackers could calculate private keys from public keys to steal coins. The article estimates that even after migrating to quantum-resistant methods, at least 2.6 million BTC would remain exposed, with approximately 1.7 million BTC in older P2PK outputs.

Some developers argue that simply adding new quantum-resistant addresses is insufficient, as vulnerable coins left active could be stolen and dumped on the market, potentially affecting both price and network trust if large amounts move simultaneously.

Others counter that forcibly freezing existing coins would undermine Bitcoin's core principles. Restricting transactions for coins that can still be signed normally is seen as limiting ownership rights, especially since distinguishing between long-held coins, inheritance assets, or inactive wallets from those at risk remains difficult.

A leading proposal, BIP-361, suggests restricting new coins from moving to vulnerable addresses after quantum-resistant addresses are introduced, with a grace period before blocking spending of ECDSA and Schnorr-dependent coins. However, experts note this requires sufficient preparation time due to potential increases in on-chain costs from larger key sizes and the possibility that future cryptographic changes may be needed.

Compromise solutions include restricting only new vulnerable outputs, temporarily locking coins for a period, or limiting daily spending of older P2PK coins. The central issue is not when quantum computers will threaten Bitcoin but how to agree on response rules before then. Current consensus leans toward reducing address reuse while researching quantum-resistant signatures and recovery methods, preparing for long-term migration.