Quantum Computers and Bitcoin: Legal Battle Over Stolen or Abandoned Crypto

Quantum Computing Poses a Growing Threat to Bitcoin

Bitcoin’s quantum debate often stalls because discussions conflate two distinct issues: technical feasibility and legal consequences. Technically, Bitcoin’s signature scheme could adapt through new address types, migration rules, and soft forks. However, the legal question is more immediate: if a quantum computer derives a private key from an old wallet and transfers the funds, does the law consider this theft or recovery of abandoned property?

BIP-361 Proposes Freezing 6.5 Million Vulnerable Bitcoins

In April 2026, BIP-361 was proposed to freeze over 6.5 million BTC held in quantum-vulnerable UTXOs, including an estimated 1 million+ coins linked to Satoshi Nakamoto. This proposal shifts the debate from abstract concerns to a real-world fight over ownership, confiscation, and the definition of property in a system that prioritizes control over legal title.

Classical Property Law: Quantum Theft is Still Theft

The critical question is not when quantum computers will break Bitcoin’s encryption but what happens if they do. Classical property law provides a clear answer: deriving a private key via quantum computing to move dormant funds constitutes theft.

This legal stance may frustrate some Bitcoiners, as Bitcoin’s network enforces control rather than legal title. If a transaction is valid, the network accepts it—but this only underscores the need for clarity on the underlying legal implications. The harder Bitcoin relies on control, the more urgent it becomes to define what the law would say about quantum-driven theft.

The Real Quantum Risk: Exposed Public Keys

Not all Bitcoin is equally vulnerable. The primary risk lies in specific address types where the public key is exposed on-chain:

• Pay-to-Public-Key (P2PK) outputs: Early transactions reveal the full public key.
• Taproot outputs: P2TR outputs commit directly to a 32-byte output key, not a hash.
• Address reuse: Spending from an address and leaving funds under the same key material exposes the public key.

Google’s Breakthrough Accelerates the Timeline

On March 31, 2026, Google Quantum AI published research showing that Bitcoin’s secp256k1 curve could be broken with fewer than 500,000 physical qubits—a twenty-fold reduction from prior estimates of nine million. The study also modeled a mempool attack vector, demonstrating how quantum computers could exploit vulnerabilities during transaction propagation.

Key Takeaways

• Quantum computers could derive private keys from exposed public keys, enabling theft of dormant Bitcoin.
• Classical property law classifies such actions as theft, not recovery of abandoned property.
• BIP-361 proposes freezing 6.5 million vulnerable BTC, including coins linked to Satoshi.
• Google’s research reduces the estimated qubit requirement for breaking secp256k1 to under 500,000.

"The harder the network leans on control, the more important it becomes to state clearly what the law would say about the underlying act."