def to_payload
      version.htb << [depth].pack('C') <<
          parent_fingerprint.htb << [number].pack('N') << chain_code << pub.htb
    end
def to_payload
      version.htb << [depth].pack('C') <<
          parent_fingerprint.htb << [number].pack('N') << chain_code << pub.htb
    end
serialize extended pubkey