In June 2010, with Bitcoin trading for less than a cent, someone on @bitcointalk asked what would happen if SHA-256 were cracked tomorrow. A mathematician friend had warned that hardly any hash functions survive 10 years. Satoshi's answer: SHA-256 should "last several decades unless there's some massive breakthrough attack." If it broke suddenly, the community would agree on the honest chain from before the trouble and "continue from there with a new hash function." If it weakened slowly, the software would switch to a new hash at a set block. "Everyone would have to upgrade by that time." He was right about the cryptography. SHA-256 was first published in 2001 and is still standing 25 years later. The plan for replacing it is what aged. Getting everyone to upgrade was a reasonable ask when Bitcoin's whole community could fit inside one forum thread. Today it means miners, exchanges, custodians, ETF issuers and millions of holders agreeing on a change and upgrading in lockstep, with well over a trillion dollars at stake. That's the real shape of the quantum debate. The threat today is mainly to signatures rather than the hash, but the hard question is the one Satoshi answered: when cryptography needs replacing, who has to agree first? CKB was designed so that adding a new signature scheme needs no network-wide agreement. It's a lock script, and each holder moves to it when they choose. No fork, no flag day. From the original thread 👇