Dev Notes

Software Development Resources by David Egan.

Bitcoin Cold Wallet Setup Bash Script


BASH, Bitcoin, Cryptocurrency
David Egan

Update - the script in this article will not work with Bitcoin Core v0.15.0 and higher. Check out my airgap utilities repo on GitHub instead.

If you want to examine a cold wallet in an offline Tails session, you’ll need to reference the Bitcoin binaries in your persistent volume. You’ll also need to move the required wallet into the Bitcoin data directory - which won’t exist until you run bitcoin-qt for the first time in the session.

This gets tedious, so I wrote this script to connect everything up.

#!/bin/bash
# Open a Bitcoin Core cold wallet in an offline Tails session.
# This script runs a simple zenity GUI which prompts the user to select:
# - The cold wallet file
# - The `bitcoin-qt` binary
# Both of these files will probably be on your persistent volume.
# ------------------------------------------------------------------------------
function set_cold_wallet {
  WALLET_FILE=$(zenity --file-selection --title="Select a Cold Wallet to run." --filename=${PWD}/)
  case $? in
    0)
    echo "\"$WALLET_FILE\" selected.";;
    1)
    echo "No file selected.";;
    -1)
    echo "An unexpected error has occurred.";;
  esac
}

function set_bitcoin_binary {
  BITCOIN_CORE=$(zenity --file-selection --title="Select the bitcoin-qt binary." --filename=${PWD}/)
  case $? in
    0)
    echo "\"$BITCOIN_CORE\" selected.";;
    1)
    echo "No file selected.";;
    -1)
    echo "An unexpected error has occurred.";;
  esac
}

function create_symlink {
  BITCOIN_DIR=~/.bitcoin
  if [[ ! -d "${BITCOIN_DIR}" ]]; then
    echo "Creating ${BITCOIN_DIR}"
    echo ""
    mkdir ${BITCOIN_DIR}
  fi

  if [[ -L "${BITCOIN_DIR}"/cold-wallet.dat ]]; then
    echo "Remove exisiting symlink, ${BITCOIN_DIR}/cold-wallet.dat"
    rm ${BITCOIN_DIR}/cold-wallet.dat
  fi

  echo "Make a symlink ${BITCOIN_DIR}/cold-wallet.dat pointing to ${WALLET_FILE}"
  ln -s ${WALLET_FILE} ${BITCOIN_DIR}/cold-wallet.dat
}

function run_wallet {
  echo "Starting Bitcoin Core with wallet ${WALLET_FILE}"
  ${BITCOIN_CORE} -wallet=cold-wallet.dat
}

# Run this script
# ------------------------------------------------------------------------------
echo "ONLY RUN IN A COLD ENVIRONMENT."
read -p "Do you wish to proceed? [y/N]" PROCEED
case $PROCEED in
  [Yy]* )
  set_cold_wallet
  set_bitcoin_binary
  create_symlink
  run_wallet
  ;;
  [Nn]* )
  echo "END"
  ;;
  * ) echo "Please answer yes or no.";;
esac

Update

As of v0.15.0, the Bitcoin Core client does not allow symlinked wallets. As such, the above script no longer works.

You would need to adjust the script so that it copies your specified cold wallet into the default Bitcoin data directory: (~/.bitcoin/cold-wallet.dat). Rather than rewrite the isolated script, I wrote a set of airgap utilities for Bitcoin/Litecoin core that includes loading a cold wallet into an offline session. The scripts are optimised for an offline Tails session and you can access the package here. The package allows you to:

  • Dump private keys into a symmetrically GPG encrypted file - for super paranoid paper backups
  • Load a fresh copy of Bitcoin/Litecoin core (useful for generating new cold wallets)
  • Load a specified cold wallet into an instance of Bitcoin/Litecoin Core
  • Check the passphrase for a specified cold wallet

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