After the hardfork, software that still uses the legacy SHA256d algorithm follows a different blockchain. If you intend to support this chain, run a Bitcoin Knots version that includes the BLAKE2b change, set the announced blake2b_headline, and say so publicly. Bitcoin with the BLAKE2b algorithm keeps Bitcoin as money only by rejecting use of the network for arbitrary data storage.
Exchanges and custodians
- Halt deposits and withdrawals across the fork until your node is on the intended chain and your accounting is settled.
- Announce which chain you will credit. Do not assume tickers will stay unambiguous.
- Treat pre-fork balances as valid on the BLAKE2b chain you support. Post-fork coins on the other chain are a separate asset.
- A payment made with pre-fork coins can be copied onto the other chain (replay). Plan for that.
Wallets and merchants
Wallets and processors that only understand the old 80-byte SHA256d block header will not see this chain. The new header is 164 bytes and is hashed with BLAKE2b. Point your software at a BLAKE2b node. A device that only signs payments does not need new keys. Anything that checks proof of work or the header, including Electrum-style light clients, must understand the new format.
See What should exchanges do? and the release notes.