NERC CIP CIP-012 R1.1: CIP-012-2 R1.1: Mitigate unauthorized disclosure and modification of real-time data between Control Centers

What does CIP-012 R1.1 require?

Under a documented plan implemented except under CIP Exceptional Circumstances (oral communications excluded), identify the methods used to mitigate the risks of unauthorized disclosure and unauthorized modification of Real-time Assessment and Real-time monitoring data while it is transmitted between Control Centers.