Sixteen years ago, Satoshi Nakamoto answered a doubter on a forum in 2010, and the reply still guides how the network defends its money today. Satoshi Nakamoto Predicted Bitcoin's Hash Defense 16 Years Before Quantum Fears Key Takeaways - Satoshi Nakamoto defended SHA-256 in a July 16, 2010 Bitcointalk forum post. - Google Quantum AI cut its 2026 estimate for breaking Bitcoin’s curve to 500,000 qubits. - Developers have proposed BIP-360 and other ideas in 2026 to prepare quantum-resistant addresses. A Forum Post That Set the Rules On July 16, 2010, a user named bdonlan questioned Bitcoin’s double SHA-256 hashing on the Bitcointalk forum. He asked whether the design weakened security. Satoshi answered directly. Bitcoin’s inventor compared SHA-256 to the jump from 32-bit to 64-bit computing, not a small step up in bit length. Computers ran out of 32-bit address space at 4 gigabytes, he said, but nobody expects to run out of 64-bit space anytime soon. SHA-256 works the same way, and the math gives Bitcoin room to spare. Satoshi also gave the network an exit plan. If SHA-256 ever weakened, developers could soft fork to a new hash function at a set block height. Old and new hashes would run side by side until every node upgraded. Bitcoin’s market capitalization has since grown past a trillion, and the network settles hundreds of billions of dollars in value daily. Every dollar of that activity still depends on the hash function Satoshi defended in a single forum reply sixteen years ago. Why Bitcoin Runs Two Hashes Instead of One Bitcoin’s code hashes data twice: SHA256(SHA256(data)), a method developers call SHA256d. Cryptographers Niels Ferguson and Bruce Schneier recommended the approach to block length extension attacks, a flaw in the Merkle-Damgard structure SHA-2 uses. Miners hash block headers twice to meet the