xpub-converter.sh

#!/bin/bash

# dependencies: base58

# usage
# ./xpub-converter.sh <ZPUB> xpub

main () {
  local input="$1"
  local prefix="$2"

  declare -A prefixes=(
    ["xpub"]="0488b21e"
    ["ypub"]="049d7cb2"
    ["Ypub"]="0295b43f"
    ["zpub"]="04b24746"
    ["Zpub"]="02aa7ed3"
    ["tpub"]="043587cf"
    ["upub"]="044a5262"
    ["Upub"]="024289ef"
    ["vpub"]="045f1cf6"
    ["Vpub"]="02575483"
  )

  local newPrefix="${prefixes[$prefix]}"

  ### BASE58-CHECK DECODE

  # decode the base58 input to hex
  local decoded=$(echo $input | base58 -d | xxd -p -c 100)
  # remove the last 4 bytes (checksum)
  local payload=${decoded::-8}
  # get the last 4 bytes (checksum)
  local checksum=${decoded:(-8)}
  local computedChecksum=$(echo -n $payload | xxd -r -p | sha256sum | xxd -r -p | sha256sum | xxd -r -p | head -c 4 | xxd -p -c 100)
  # compare the checksums
  if [ "$checksum" != "$computedChecksum" ]; then
    echo "Checksums do not match"
    exit 1
  fi

  ### CHANGE PREFIX
  # remove the first 4 bytes from payload
  local newPayload=${payload:8}
  # add the new prefix
  local newPayloadWithPrefix="$newPrefix$newPayload"

  ### BASE58-CHECK ENCODE
  local newChecksum=$(echo -n $newPayloadWithPrefix | xxd -r -p | sha256sum | xxd -r -p | sha256sum | xxd -r -p | head -c 4 | xxd -p -c 100)
  local newEncoded=$(echo -n "$newPayloadWithPrefix$newChecksum" | xxd -r -p | base58)
  echo $newEncoded
}

main "$@"