Coldcard is a premium hardware wallet for sophisticated users. Unchained Capital is pleased to support Coldcard’s air-gapped functionality, along with maintaining support for Trezor and Ledger.

What you need:

Unchained Capital supports Coldcard for air-gapped data transfer only. This means that additional supplies are required:

  • Initialized Coldcard Mk 2 or Mk 3 with the most recent firmware
  • MicroSD card
  • MicroSD card reader for your computer

Create an Unchained Capital Account

Log in at my.unchained-capital.com and fill out required onboarding information depending on which products you want to use. Tier 2 gives individuals and businesses the ability to use vaults. Tier 3 is required for Bitcoin OTC purchases and for USD loans.

Export the Xpub from the Coldcard

  1. Unlock your Coldcard and insert your MicroSD card
  2. Navigate to Settings
  3. Select Multisig Wallets
  4. Select Export Xpub
  5. Review information about the Xpub and select ok to create your Xpub file
  6. Remove the MicroSD card from your Coldcard and insert it into the MicroSD card reader connected to your computer

Create an Unchained Capital Key

  1. Log into your Unchained Capital Account
  2. Navigate to the keys menu and select create a new key
  3. Name the key – write down the key name on your recovery seed
  4. Select Coldcard
  5. Select Upload Xpub and select the exported file from the MicroSD card, or drag and drop the exported file from the MicroSD card into the Upload Xpub section on Unchained
  6. Your Xpub will appear on Unchained Capital if it has been imported correctly. Select next and then create

Your Coldcard can now sign partially signed bitcoin transactions (PSBTs) produced by the vault. See the full key creation flow below. Click any image to enlarge.

Create a Second Key and Build a Vault

You can either create a second Coldcard key by performing the above steps with a second initialized Coldcard, or upload a second key by using a Trezor or Ledger and following the onscreen instructions.

Once you have 2 keys uploaded, you can build a vault by selecting “create a new vault” from your dashboard or by selecting New Vault from the menu on the side.

Initialize the Multisig Vault on your Coldcard

  1. After you build your vault, select “Configure Coldcard” from the Coldcard Users screen or navigate to the menu in the completed Vault’s transact window and download the Coldcard configuration file. This file will teach your Coldcard about the vault and different keys used to secure it.
  1. Move the Coldcard configuration file onto the MicroSD card plugged into your computer
  2. Remove the MicroSD card from the computer and plug it into your Coldcard
  3. On your Coldcard homescreen, select Settings, then Multisig Wallets
  4. Select Import from SD
  1. The Coldcard will find the file. Select ok, then select the file
  2. Review the multisig wallet and select ok

Now your Coldcard can sign partially signed bitcoin transactions (PSBTs) produced by the vault.

Sign a PSBT from the Vault with a Coldcard

  1. Author a withdrawal from the vault dashboard and select your Coldcard key as one of the signers
  2. In the signing workflow, select the key secured by the Coldcard and select that you are signing from a Coldcard
  3. Download the PSBT file and move it to the SD card. Remove the SD card from your computer and insert it into the Coldcard
  1. On your Coldcard, select ready to sign. Your Coldcard will find the PSBT. Select it and hit ok
  2. Review the transaction details. If they look good, hit ok to sign the transaction. Your Coldcard will produce a new file
  3. Remove the SD card and plug it into your computer. Drag the file from the SD card to the upload PSBT field

You have signed the transaction and can now broadcast it.

Tips and Tricks

  • Keep your SD card clean. We recommend you delete all files after each transaction.
  • If you’re replacing an existing key with a Coldcard, do a key check with any remaining keys first.
  • Delete any PSBTs that are saved in a downloads folder, or set your browser to prompt you where to download files so that you can select the MicroSD card.
  • Keep your firmware updated. Unchained Capital will always officially support the two most recent firmware versions.

Leave a Reply