Andrew Chow

Tales from the Crypt #127: Andrew Chow

- Andrew Chow developed the PSBT (Partially Signed Bitcoin Transaction) standard to enable hardware wallets to work seamlessly with Bitcoin Core, replacing incompatible ad-hoc formats used by different software. - PSBT is a well-defined, extensible standard that packages all transaction information needed for signing into one portable string, simplifying coordination between wallets and hardware devices. - Coin selection is a hard computational problem requiring balance between minimizing current fees, avoiding future dust, and maintaining privacy—branch and bound algorithm uses tree pruning to optimize combinations efficiently. - CoinJoins improve privacy but remain difficult to coordinate at scale; manual coordination is cumbersome, and merchant adoption barriers (like BTCPay's operational complexity) limit payjoin's viability. - Hardware wallets each implement transaction signing differently despite solving the same problem, creating implementation burdens; Cold Card's adoption of PSBT simplified hardware wallet support in HWI. - Descriptor wallets and hardware wallet script managers represent long-term refactoring of Bitcoin Core's wallet to separate concerns and support arbitrary scripts, multisig, and future protocols like Taproot.