How to Check the Coldcard Ypub

These instructions describe how to verify that the Ypub you see in Casa App matches the Ypub derived from your Coldcard.
 
1. Obtain the root xpub from your Coldcard:
 
- Insert a microSD card into the Coldcard and turn it on
- Select Advanced > MicroSD > Dump Summary. This will create a public.txt file on the Coldcard.
- Turn the Coldcard off and insert the microSD 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:
 
Screen_Shot_2020-06-25_at_5.02.30_PM.png
 
2. Copy the root xpub and paste it into https://iancoleman.io/bip39/
 
- If you want maximum privacy then you should save the page and open it on an offline machine
- Paste the root xpub into the BIP32 Root Key section
- Scroll down to Derivation Path and click the BIP32 tab
- Select ‘Custom Derivation Path’ for the Client
- Open up the 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.
 
3. Convert the xpub to a Ypub with https://jlopp.github.io/xpub-converter/
 
- If you want maximum privacy then you should save the page and open it on an offline machine
- 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.
 

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