code: def get_public_keys_der_v3(self):
          
  
          if self._v3_signing_data == None:
              self.parse_v3_signing_block()
  
          public_keys = []
  
          for signer in self._v3_signing_data:
              public_keys.append(signer.public_key)
  
          return public_keys
docs: Return a list of DER coded X.509 public keys from the v3 signature block