Although nowadays lots of group key agreement schemes have been presented, most of these protocols generate a secret key for a single group. However, in the IoT HCS, more and more communications are involved in multiple groups and users can join multiple groups to communicate at the same time. Therefore, applying the conventional public-key-based one-at-a-time group key establishment protocols has heavy computational cost or suffer from security vulnerabilities. At the same time, in an IoT HCS, a trusted KGC is usually not available and so more...
