new_contents: from .charset import charset_to_int, int_to_charset
  
  # https://en.bitcoin.it/wiki/Base58Check_encoding
  B58_CHARS = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
  
  def b58_to_int(s):
      return charset_to_int(s, B58_CHARS)
  
  def int_to_b58(val):
      return int_to_charset(val, B58_CHARS)
  
  def is_b58(s):
      for char in s:
          if char not in B58_CHARS:
              return False
      return True
  
subject: add base 58 encoding