Can a sufficiently powerful quantum computer forge the signatures used to authorize Bitcoin and Ethereum transactions? What would it take to upgrade both networks before that happens? In this new lecture, Stanford cryptographer @danboneh explores why blockchains may turn to signatures built from hash functions. He also presents new research on threshold signing. The talk ends with the questions Bitcoin still has to answer, including whether post-quantum signatures will require larger blocks, what happens to abandoned coins, and how someone such as Satoshi could prove ownership after Bitcoin’s current signatures have been retired. 00:00 Why blockchains need to prepare for quantum computers 03:05 Why Bitcoin may bet on hash-based signatures 06:25 The “big footgun” in stateful signatures 08:58 A quantum-safe signature that takes one billion hashes 14:13 Inside SLH-DSA’s virtual tree 20:30 How Bitcoin and Ethereum could make the switch 23:48 What happens when a wallet loses its state? 32:47 Can threshold signing survive the quantum transition? 36:39 How to hide lattice cryptography from the blockchain 38:49 Why threshold one-time signatures seem impossible 45:36 How context prevents forged signatures 49:37 The forgotten idea behind Winternitz signatures 54:50 Turning one-time signatures into threshold signatures 1:04:27 Will quantum-safe signatures require bigger Bitcoin blocks? 1:06:26 Abandoned bitcoin and Satoshi’s recovery problem(a16z crypto)