Bitcoin Faces ‘Q-Day’ Threat From Quantum Computers

Recent advancements in quantum computing from Google and IBM are raising concerns about a potential “Q-Day,” the moment when a quantum computer could crack older Bitcoin addresses and expose over $711 billion in vulnerable wallets. While current quantum computers are too small and unstable to pose an immediate threat, the gap is closing faster than anticipated.

Bitcoin’s signatures use elliptic-curve cryptography, which exposes public keys when an address is spent. Older addresses, particularly those from Satoshi’s era, are most at risk. A successful attack would involve a quantum computer using Shor’s algorithm to calculate the private key tied to an exposed public key, allowing an attacker to move funds.

Experts estimate that $180 billion worth of Bitcoin, including roughly $100 billion believed to belong to Satoshi, is currently at risk due to abandoned wallets and lost private keys. While no one can freeze Bitcoin directly, practical defenses focus on migrating vulnerable funds and adopting post-quantum addresses.

Significant progress in quantum computing was made in 2025, including Google’s Willow chip, Microsoft’s Majorana 1 platform, and IBM’s targets for logical qubits. However, post-quantum digital signature schemes come with performance costs, as they are significantly larger than current signatures, creating a challenge for blockchain storage and fees.

Several Bitcoin Improvement Proposals (BIPs) are being explored to prepare for the quantum threat. These range from quick fixes like P2TRH to full network migrations, each with its own advantages and drawbacks. The decentralized nature of Bitcoin complicates these upgrades, requiring broad community agreement.

To mitigate risk, users are advised to avoid reusing addresses and using modern wallet formats. While a quantum attack isn’t imminent, ongoing investments could accelerate the timeline, and the community must proactively address the threat to protect Bitcoin’s long-term security.

Disclaimer: What is written here is not investment advice. Cryptocurrency investments are high-risk investments. Every investment decision is under the individual’s own responsibility.