What Is Q-Day? The Quantum Threat to Bitcoin Explained

Experts warn that quantum computers could eventually forge Bitcoin's digital signatures, leading to unauthorized transactions. Currently, quantum computers are not powerful enough to threaten existing cryptography, but advancements from tech giants suggest the threat is closer than anticipated. Q-Day refers to the moment when a sufficiently advanced quantum computer could exploit vulnerabilities in Bitcoin’s encryption, particularly affecting early wallets with exposed public keys. If a quantum computer can calculate a private key from a public key, an attacker could authorize transactions without the owner's consent. As of 2025, significant progress has been made in quantum computing, with companies achieving milestones in qubit stability and error reduction. This raises concerns over old Bitcoin wallets that are susceptible to exploitation due to their published public keys. Developers are proposing various Bitcoin Improvement Proposals that explore options for transitioning to quantum-resistant signatures. The urgency to prepare for quantum threats is amplified by the potential loss of millions in abandoned coins, making proactive steps crucial as the community debates how to safeguard Bitcoin's integrity.

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