Quantum Computing
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Quantum computing is a type of computation that uses quantum-mechanical phenomena — such as superposition and entanglement — to process information in ways classical computers cannot. While still in early stages, quantum computers are advancing rapidly and raise concerns about the long-term security of current cryptographic systems.
Threat to blockchain cryptography
Most blockchains rely on two cryptographic primitives that quantum computers could eventually break:
- ECDSA (Elliptic Curve Digital Signature Algorithm) — used to generate and verify wallet signatures. A sufficiently powerful quantum computer could derive a private key from a public key using Shor's algorithm, allowing an attacker to steal funds from any address whose public key has been exposed.
- SHA-256 (hash function) — used in Bitcoin's proof-of-work. Grover's algorithm could theoretically speed up hash brute-forcing, but the speedup is only quadratic — making this a far less urgent concern than ECDSA.
Current risk level
Today's quantum computers are far too small and error-prone to threaten real-world cryptography. Breaking Bitcoin's 256-bit elliptic curve keys would require millions of stable logical qubits — current machines have hundreds to thousands of noisy physical qubits. Most researchers estimate a meaningful threat is at least 10–20 years away.
Post-quantum cryptography
Post-quantum cryptography (PQC) refers to cryptographic algorithms designed to resist quantum attacks. NIST finalized its first post-quantum standards in 2024. Blockchain projects are beginning to evaluate migration paths, though no major chain has switched yet.
Reusing Bitcoin addresses (so the public key is never exposed on-chain until spending) is one practical step users can take now to reduce exposure.
