code: def verify_relayable_signature(public_key, doc, signature):
      
      sig_hash = _create_signature_hash(doc)
      cipher = PKCS1_v1_5.new(RSA.importKey(public_key))
      return cipher.verify(sig_hash, b64decode(signature))
docs: Verify the signed XML elements to have confidence that the claimed
      author did actually generate this message.