Quantum Computers Could Crack Bitcoin Security Sooner Than Expected

A new study warns that the cryptographic foundations of major cryptocurrencies like Bitcoin and Ethereum are more vulnerable to quantum attacks than previously thought. Researchers have developed updated resource estimates showing that a quantum computer with fewer than half a million physical qubits could break the elliptic curve cryptography used in these systems, potentially within minutes. This finding s earlier assumptions about the timeline for quantum threats and underscores the urgent need for the cryptocurrency community to transition to post-quantum cryptography before it's too late.

The researchers focused on the Elliptic Curve Discrete Logarithm Problem (ECDLP), which underpins the security of digital signatures in Bitcoin and Ethereum. They estimated that solving this problem on the secp256k1 curve, used by these cryptocurrencies, requires either 1,200 logical qubits and 90 million Toffoli gates or 1,450 logical qubits and 70 million Toffoli gates. Using a zero-knowledge proof to validate these estimates without disclosing attack details, they demonstrated that on superconducting architectures with 10^-3 physical error rates, these circuits could execute in minutes with fewer than 500,000 physical qubits. This represents a nearly 20-fold reduction over prior estimates, bringing the threat of quantum attacks much closer to reality.

The study distinguishes between 'fast-clock' quantum architectures, such as superconducting and photonic systems, and 'slow-clock' ones like neutral atom and ion trap devices. Fast-clock systems could enable 'on-spend' attacks, where a quantum computer intercepts and forges transactions in real-time, potentially within Bitcoin's 10-minute average block time. In contrast, slow-clock systems might only support 'at-rest' attacks on dormant assets with exposed public keys. This architectural difference informs mitigation strategies, with fast-clock threats requiring immediate action to protect active transactions.

Analysis of cryptocurrency vulnerabilities reveals significant risks. For Bitcoin, over 1.7 million BTC (about 9% of the supply) is secured by Pay-to-Public-Key (P2PK) scripts that expose public keys, making them vulnerable to at-rest attacks. Additionally, address reuse and public mempool exposure create further vulnerabilities, with an estimated 6.9 million BTC across all protocols at risk. Ethereum faces broader threats due to its account model and smart contracts, putting at least 20.5 million ETH in vulnerable accounts and exposing administrative keys for contracts holding 2.5 million ETH and $200 billion in stablecoins. The study also highlights risks to Ethereum's Proof-of-Stake consensus and Data Availability Sampling mechanism.

To mitigate these threats, the researchers urge immediate migration to post-quantum cryptography (PQC), noting that some blockchains like Algorand and Quantum Resistant Ledger have already made progress. However, s include higher resource costs for PQC schemes and the logistical difficulty of migrating dormant assets, such as Bitcoin's P2PK coins. The study proposes policy options like 'digital salvage' to regulate the recovery of abandoned assets and recommends that cryptocurrency communities implement intermediate measures, such as removing vulnerable spending paths and enabling key rotation. Without swift action, the emergence of cryptographically relevant quantum computers could undermine trust in digital currencies and lead to significant financial losses.