casa-helper.sh

#!/bin/bash -eu

# NO WARRANTY PROVIDED OR IMPLIED.  USE AT YOUR OWN RISK.

###########
## Paths ##
###########
# This is the keypath provided in the Casa recovery email minus the "m"
KEYPATH="/49/0/0"

# Sub-paths.  This not provided by Casa in their recovery
# instructions but seems to follow the Electrum v4 default, which is
# - External: /0/*
# - Internal (change): /1/*
EXTERNAL_SUBPATH="/0/*"
INTERNAL_SUBPATH="/1/*"

###########
## Xpubs ##
###########
# All operations with this script require you to enter the extended
# pubkeys (xpubs) for all five signing keys.  If you want to use the
# descriptors for address verification or signing, you will also need to
# provide their fingerprints (FPs).
#
# The Casa recovery email includes ypubs (not xpubs) for the mobile and
# recovery keys.  You will need to convert those ypubs to xpubs, which
# can be done with the following tool:
#
#     https://jlopp.github.io/xpub-converter/
#
# Note: you can use that page offline for additional privacy, although
# the operator of that website is currently Casa's CTO, so I ran it
# online

MOBILE_FP=FILL_THIS_IN
MOBILE_XPUB=FILL_THIS_IN

RECOVERY_FP=FILL_THIS_IN
RECOVERY_XPUB=FILL_THIS_IN

# For HW wallets, use HWI to get the xpubs.  E.g., plug in the device,
# enter its pin (or use `hwi promptpin`), use `hwi enumerate` to get
# it's fingerprint, and use something like this to get its xpub:
#    hwi -t ledger getxpub m$KEYPATH

HW1_FP=FILL_THIS_IN
HW1_XPUB=FILL_THIS_IN

HW2_FP=FILL_THIS_IN
HW2_XPUB=FILL_THIS_IN

HW3_FP=FILL_THIS_IN
HW3_XPUB=FILL_THIS_IN

############################## END CONFIGURATION ###################################
## You shouldn't need to edit anything below this point, except for special cases ##
####################################################################################

# sh: P2SH, wsh: witness script hash, sortedmulti: multisig with keys in
# BIP67 order, 3: 3-of-n multisig
external_descriptor="sh(wsh(sortedmulti(3,"
internal_descriptor="sh(wsh(sortedmulti(3,"

# The five fingerprints and xpubs
external_descriptor="${external_descriptor}[$MOBILE_FP$KEYPATH]$MOBILE_XPUB$EXTERNAL_SUBPATH,"
internal_descriptor="${internal_descriptor}[$MOBILE_FP$KEYPATH]$MOBILE_XPUB$INTERNAL_SUBPATH,"

external_descriptor="${external_descriptor}[$RECOVERY_FP$KEYPATH]$RECOVERY_XPUB$EXTERNAL_SUBPATH,"
internal_descriptor="${internal_descriptor}[$RECOVERY_FP$KEYPATH]$RECOVERY_XPUB$INTERNAL_SUBPATH,"

external_descriptor="${external_descriptor}[$HW1_FP$KEYPATH]$HW1_XPUB$EXTERNAL_SUBPATH,"
internal_descriptor="${internal_descriptor}[$HW1_FP$KEYPATH]$HW1_XPUB$INTERNAL_SUBPATH,"

external_descriptor="${external_descriptor}[$HW2_FP$KEYPATH]$HW2_XPUB$EXTERNAL_SUBPATH,"
internal_descriptor="${internal_descriptor}[$HW2_FP$KEYPATH]$HW2_XPUB$INTERNAL_SUBPATH,"

external_descriptor="${external_descriptor}[$HW3_FP$KEYPATH]$HW3_XPUB$EXTERNAL_SUBPATH"
internal_descriptor="${internal_descriptor}[$HW3_FP$KEYPATH]$HW3_XPUB$INTERNAL_SUBPATH"

# Close the sh/wsh/sortedmulti parens
external_descriptor="${external_descriptor})))"
internal_descriptor="${internal_descriptor})))"

# Validate the descriptors and update them to include a checksum
external_descriptor=$( bitcoin-cli getdescriptorinfo "$external_descriptor" | jq -r .descriptor )
if [ "$external_descriptor" == "" ]; then
  echo "Error parsing external descriptor.  Check fingerprints and keys for typos.  Terminating script..."
  exit 1
fi
internal_descriptor=$( bitcoin-cli getdescriptorinfo "$internal_descriptor" | jq -r .descriptor )
if [ "$internal_descriptor" == "" ]; then
  echo "Error parsing internal descriptor.  Check fingerprints and keys for typos.  Terminating script..."
  exit 1
fi

case "$1" in
  get_descriptors)
    echo "$external_descriptor"
    echo "$internal_descriptor"
  ;;

  derive_receiving_addresses)
    # Only derive receiving (external) addresses
    bitcoin-cli deriveaddresses "$external_descriptor" 1000
  ;;

  # Note, if you get a "ripemd160 not supported error", see https://github.com/bitcoin-core/HWI/issues/656
  verify_receive_address)
    shift
    if [ $# -lt 1 ] ; then
      echo "$0 verify_receive_address <address> <hwi_arguments>"
      exit 1
    fi
    ADDRESS="$1" ; shift

    index=$( $0 derive_receiving_addresses | jq 'index("'$ADDRESS'")' )
    if ! echo "$index" | grep -q '^[0-9]\+$' ; then
      echo "Address not found: $ADDRESS"
      exit 1
    fi

    # Our original ranged descriptor looks like:
    #    sh(wsh(sortedmulti(3,[.../49/0/0]xpub.../0/*,....
    # We need a single-address descriptor that looks like:
    #    sh(wsh(sortedmulti(3,[.../49/0/0/]xpub.../0/$index,....
    address_descriptor=$( echo "$external_descriptor" | sed """
       # Remove the checksum
       s/#.*//;
       # Replace the range "*" with the particular index
       s/\*/$index/g;
    """ )
    # Give the individual descriptor a checksum
    address_descriptor=$( bitcoin-cli getdescriptorinfo "$address_descriptor" | jq -r .descriptor )

    derived_address=$( bitcoin-cli deriveaddresses "$address_descriptor" | jq -r '.[]' )
    if [ "$ADDRESS" != "$derived_address" ] ; then
      echo "Something went wrong.  Provided address $ADDRESS not the same as computed address $derived_address.  Exiting..."
      exit 1
    fi

    echo "Press enter to run the following command to verify address $ADDRESS:"
    echo
    echo "    hwi" "$@" displayaddress --desc "$address_descriptor"
    echo
    echo "Press CTRL-C if any necessary parameters to hwi, like -t and -d, are missing"
    echo "Also remember to unlock your device with its pin before pressing enter"
    read

    hwi "$@" displayaddress --desc "$address_descriptor"

  ;;

  scan_utxos)
    # NB: increase the ranges if you've sent or received more than that
    # number of payments using your Casa wallet.
    bitcoin-cli scantxoutset start '[{"desc": "'"$internal_descriptor"'", "range": 1000}, {"desc": "'"$external_descriptor"'", "range": 1000}]'
  ;;

  *)
    echo "Unknown command: $1"
    exit 1
  ;;
esac