code: def to_der(self):
          
          # Output should be:
          # 0x30 <length> 0x02 <length r> r 0x02 <length s> s
          r, s = self._canonicalize()
  
          total_length = 6 + len(r) + len(s)
          der = bytes([0x30, total_length - 2, 0x02, len(r)]) + r + bytes([0x02, len(s)]) + s
          return der
docs: Encodes this signature using DER
  
          Returns:
              bytes: The DER encoding of (self.r, self.s).