Electrum 2/3 PSBT Multi-sig

Keystone firmware version V1.1.1 (BTC-Only) or newer supports PSBT Muti-signature function. This instruction will show how to create a 2/3 PSBT Multi-signature with 2*Keystone, 1*Coldcard and Electrum V4.1.2 in details.

I. Preparation

1. Firmware version V1.1.1 (BTC-Only) or newer running on Keystone Essential or Pro.

(Please read How to upgrade firmware for more details.)

2. Coldcard upgraded to firmware version V2.1.0 or newer.

3. MicroSD card (≤512GB; Default FAT32 format).

How to Format a MicroSD Card to FAT32?

4. Electrum Wallet (V4.1.2 or newer) running on PC/Mac.

Tips: If you want to switch to [Test Net], please go to "Keystone > Settings > Blockchain > Test Net" and "Coldcard > Settings > Blockchain > Test Net". Then continue with the following steps.

**II. Create a 2/3 multisig wallet with 2Keystone and 1Coldcard**

- Create multisig wallet on Coldcard

1. Export Keystone’s Xpub to microSD card

1) Insert the microSD card into Keystone.

2) Touch [Menu] > [Multisig Wallet] > Press the [•••] button on the top right > [Show/Export XPUB].

3) Touch [Export All] > [Export].

Tips:

① Please repeat this step on 2*Keystone.

② If you were using 1*Keystone and 2*Coldcard to create a 2/3 PSBT Muti-signature wallet, please export Xpubs from 1 Keystone and 2 Coldcard ([Settings] > [Multisig Wallets] > [Export XPUB]).

2. Create multisig wallet on Coldcard

1) Take out the microSD card from Keystone and insert it into Coldcard.

2) [Settings] > [Multisig Wallets] > [Create Airgapped].

3) Set address type (Default-P2WSH) and the number of cosigner (2 of 3).

4) Confirm (√) and complete creating a 2/3 multisig wallet.

3. After the previous steps, you will get 2 files on your microSD card

1) “export-CC-2-of-3.txt” - this is for importing multi-sig wallet to Keystone - allows Keystone to check the genuinity of multisig when signing.

2) “el-CC-2-of-3.json” - this is for creating watch-only wallet on Electrum.

Tips: If you didn’t get these two files, please export manually by following instructions:

1) Export the multisig wallet file (for importing multisig wallet to Keystone) to the microSD card

① Insert the microSD card into Coldcard.

② [Settings] > [Multisig Wallets] > [2/3: CC-2-of-3] > [Coldcard Export] > Export the “export-CC-2-of-3.txt” file to the microSD card.

2) Export the multisig wallet file (for creating watch-only wallet on Electrum) to the microSD card

① Insert the microSD card into Coldcard.

② [Settings] > [Multisig Wallets] > [2/3: CC-2-of-3 > [Electrum Export] > Export the “el-CC-2-of-3.json” file to the microSD card.

- Import multisig wallet file to Keystone

1. Take out the microSD card from Coldcard and insert it into Keystone.

2. Touch [Menu] > [Multisig Wallets] > [Import Multisig Wallet].

3. Select file “export-CC-2-of-3.txt” > Touch [Confirm].

- Import multisig wallet file to Electrum and create watch-only wallet

1. Take out the microSD card from Keystone and insert the it into PC/Mac.

2. Run Electrum and click on [Choose...] > Select file “el-CC-2-of-3.json” > [Open] > [Next] > [No].

Note: As Electrum doesn’t have a Keystone plugin (we are working on that), Keystone can’t generate a Electrum skeleton json file. So you have to export the Electrum skeleton json file from Coldcard to set up the watch-only wallet on Electrum.

III. Sending bitcoin from the 2/3 multisig address (2Keystone & 1Coldcard)

- Generate multisig transaction on watch-only wallet(Electrum) and export unsigned multisig transaction file to MicroSD card.

1. Click [Send] > Enter destination address and amount > [Pay] > [Send].

2. Click [Export] > [For hardware device; include Xpubs] > [Export for file] > [Save].

- Partially sign multisig transaction on Coldcard

1. Take out the microSD card from PC/Mac and insert it into Coldcard.

2. [Ready To Sign] > Confirm and export partially signed multisig transaction file to microSD card.

- Complete sign multisig transation on Keystone

1. Take out the microSD card from Coldcard and insert it into Keystone.

2. Enter Multisig Wallet > Press "microSD card" icon on the top right > Select the partially signed transaction file > Confirm transaction details and press [Sign].