code: def footer_length(header):
      
      footer_length = 0
      if header.algorithm.signing_algorithm_info is not None:
          footer_length += 2  # Signature Length
          footer_length += header.algorithm.signature_len  # Signature
      return footer_length
docs: Calculates the ciphertext message footer length, given a complete header.
  
      :param header: Complete message header object
      :type header: aws_encryption_sdk.structures.MessageHeader
      :rtype: int