After the BIP-110 softfork, software that still uses the legacy SHA256d algorithm follows a different blockchain. If you intend to support this chain, run a Bitcoin Knots 29.4.2 node that includes the BLAKE2b change 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
- If deposits and withdrawals are still open, halt them until your node is on the intended chain and your accounting is settled.
- Announce which chain you credit. Do not assume tickers 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). Ordinary signatures stay valid and still copy. Wallets that spend on both chains should opt in to
SIGHASH_UNIFIED(PR 357). That new message also means the spend does not copy onto a chain that does not implement it. If a customer intends to sell, gift, or spend the fake “bitcoins” on the SHA256d altcoin launched by former miners, they should first send their bitcoins to themselves with that format on this chain and wait for the payment to confirm.
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 how it works.