A group key, also known as the global key is shared by all the sensor nodes within the network.
The base station uses this key to encrypt data that is transmitted to all the nodes within the
group. Since the entire group of nodes is sharing this key, it eliminates the need for a base
station to separately encrypt the same message to individual nodes with individual keys.
Confidentiality is invoked as long as the key is updated every once a while in case one of the
nodes stops functioning and is removed from the group or network. A special case of a group
key is known as the cluster key