firmware/docs/bitcoin-core-usage.md

Using Coldcard with Bitcoin Core

Background

Core has not always supported BIP32 hierarchical keys, and it does not presently support BIP44 derivation. Instead it uses derivation like this:

m/0'/{change}'/{index}'

It will also, as of 0.16, do Segwit in P2SH by default. In time, bech32 will become the default address format.

Setup Steps

• generate a new seed phrase on the Coldcard
• export the xpub file from Coldcard (USB or MicroSD)
• import that xpub as a new wallet in core
• display balances

Day-to-day Operation

• generate unsigned transactions
• get that onto the Coldcard, and sign it there
• use core to broadcast the new txn for confirmation

Use of "dumpwallet" command

• You can do a "dumpwallet" command and get the xprv associated with your wallet. We can import that, and then you'd need to destroy the existing wallet files, backups of those, and so on.

• Our output file, called public.txt, can be compared to dumpwallet's output, but:

  • you must find the section with appropriate derivation path for core
  • core puts the addresses into a random order, not sequential like ours
  • segwit, and p2sh segwit choice has to match