Signing a Transaction in Keymaster With Coldcard

After adding your Coldcard to Keymaster, you can use your Coldcard to sign a transaction, or perform a health check on the device. 

The steps detailed below to sign a transaction from your keyset are also the same steps you’ll take to perform a Health Check of your Coldcard in Keymaster (to ensure that it’s been properly added and available for signing outgoing transactions when needed). 

If you haven’t added your Coldcard to Keymaster yet, please see our article Adding Coldcard to Keymaster.

When signing a transaction or performing a health check, you will need:

        - Coldcard device
        - A laptop or desktop computer
        - Micro SD card 
        - Micro SD card adapter (if your computer does not have a micro SD card slot)

First, initiate a transaction, or initiate a Health Check, from within Keymaster.


Next, check your email inbox for an email from Casa with a link. Clicking that link will initiate the signing process. 

Physically insert your SD card into your computer (you may need an adapter for this step). 


When you click the link, you’ll be prompted to download a file onto your computer. Once the file is downloaded, drag and drop the file onto the Coldcard’s SD card.


Next, take the SD card out of your computer and insert it into your Coldcard.


When your Coldcard is powered up and unlocked with your PIN code, navigate to: 

Advanced > MicroSD Card > Sign Text File

Click “Ok” to export the signature text file to the SD card.



Now that the transaction’s signature is copied to the SD card, you’re ready to transfer the signature back to your computer to complete the signing process. 

Remove the SD card from the Coldcard and insert it into your computer. 


Back at the Casa API, click “Next,” then drag and drop the file into the window when prompted.


That’s it! If you’re just doing a health check, you’re all done. 

If you’re signing a transaction, you’ll need to give your other signatures to the transaction, if necessary, and complete the transaction from within Keymaster. 

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