Shor's Algorithm: How Quantum Computing Threatens Bitcoin and Blockchain Security

When you send Bitcoin or lock funds in a smart contract, you’re trusting Shor's algorithm, a quantum computing method that can crack the mathematical foundations of modern encryption. It doesn’t just guess passwords—it mathematically breaks the very codes that make blockchain secure. Right now, your crypto is safe because no quantum computer is powerful enough to run it at scale. But that clock is ticking.

Shor's algorithm targets public-key cryptography, the system behind Bitcoin’s ECDSA signatures and Ethereum’s address generation. It finds prime factors of huge numbers in seconds—something classical computers would take thousands of years to do. That’s a problem because every Bitcoin address is built on the assumption that factoring large numbers is impossible. If a quantum computer runs Shor’s algorithm on a public key, it can derive the private key and steal your coins. This isn’t science fiction. Google, IBM, and China’s quantum labs are already building machines with enough qubits to threaten today’s crypto.

The fix? quantum-resistant cryptography, new encryption methods designed to survive attacks from quantum machines. Projects like NIST are already standardizing algorithms like CRYSTALS-Kyber and Dilithium. Some blockchains, including Ethereum’s long-term roadmap, are planning upgrades to swap out vulnerable math for quantum-safe alternatives. But most existing wallets, exchanges, and smart contracts? They’re still using the same old math. That’s why you’ll find posts here about Merkle trees, formal verification, and blockchain security—they’re part of the same battle. We’re not just tracking coins or exchanges. We’re tracking the race between the old world of crypto and the new world of quantum threats.

Below, you’ll find real-world breakdowns of how blockchains are built, how they’re attacked, and what’s being done to protect them—not just today, but when quantum computers finally arrive.