How to make offline transactions in Electrum with Coldcard wallet.
Coldcard is an ‘only-Bitcoin’ hardware wallet mostly recommended for mid-high knowledgeable/experienced bitcoiners. If you are a newbie, I´d recommend you using Trezor as your standard hardware wallet. However, it doesn´t provide the same level of privacy and security.
This is a step by step practical tutorial. I won’t dive into any explanation of the Coldcard wallet itself. For further information about it you can click on the links below:
One of the unique features of the CC wallet is the ability to perform offline transactions through PSBT (Partial signed Bitcoin transaction) with a microSD card.
CC wallet can get started using an external battery with no need to connect it to your computer, unlike Ledger and Trezor which both require to connect them to the computer everytime they’re being used.
1. Connect your CC (coldcard) to an external battery. Enter the Prefix Pin and once you check the 2 words shown on the screen, enter the rest of Pin.
2.Select Advanced option> MicroSd card> Electrum wallet
3. Select a type of address ( I’ve chosen a ‘Native Segwit’ address).And press ok. This will create a file in your microSD. Press ‘ok’ again.
Take out the MicroSD and connect it to the computer.
4. Open a wallet with funds. and go to File> open> and select the file generated in your microSD. Press open. This will open the new wallet created in CC.
5. Press ‘Next’ and when you see the message ‘please insert yout coldcard …’ press “NO”
6. I sent funds to CC wallet generated in the microSD, to be able to make a subsequent offline transaction from the CC.
7. Once the CC wallet has funds we proceed to send it back. But this time offline through the microSD. When you have entered all the necessary data to broadcast the transaction, click on ‘Preview’. Then click on ‘save PSBT’. And save the file in the microSD.
8. Once this is done, you connect the microSD in your CC wallet again.
9. Ready to sign> “Ok to send?” > Press ‘ok’> And you will see “PSBT signed”. After that connect the microSD to the computer again.
10. From Electrum: Tools> Load Transaction> From file> and select the file * .Txn and open> Broadcast.