How to check the Coldcard Ypub

These instructions describe how to verify that the Ypub you see in your Casa app matches the Ypub derived from your Coldcard.

1. Obtain the root xpub from your Coldcard:

• Insert a micro SD card into the Coldcard and turn it on
• Select Advanced > MicroSD > Dump Summary. This will create a public.txt file on the micro SD card.
• Turn the Coldcard off, remove the micro SD card, and insert the card into a computer.
• Open public.txt and look for the line that says ## Top-level, 'master' extended public key ('m/)

Find the root xpub immediately below it:

• If you want maximum privacy, you should save the web page and open it on a computer that is not connected to the internet.
• Paste the root xpub into the BIP32 Root Key section
• Scroll down to Derivation Path and click the BIP32 tab
• Select 'Custom derivation path' on the BIP32 tab for the Client
• Open your Casa app and select the device that corresponds to your Coldcard. Select View Public Keys > BTC Account. Locate the Derivation Path. It should look something like m/49/0/1. The last number may vary depending on your account.
• Enter the derivation path into the BIP32 Derivation Path section of https://iancoleman.io/bip39/
• A BIP 32 Extended Public Key should now be generated. Copy it.

• If you want maximum privacy, you should save the web page and open it on a computer that is not connected to the internet.
• Select Ypub (mainnet P2WSH in P2SH)
• Paste in the extended public key that was obtained from Step 2 and click Convert.
• The Ypub should match the Ypub in your Casa app.