A technique for key sharing among multiple key servers connected to one another over a communication network is provided herein. Each key sever of the multiple key servers stores respective cryptographic keys, and provides the keys to a local device group connected with the key server, to enable the device group to encrypt messages with the keys. Each key server acts as a proxy for the other key servers in order to receive other keys from the other key servers over the network, and provide the other keys to the device group for use to decrypt messages received from other local device groups respectively connected with the other key servers that were encrypted with the other keys and to check message integrity. The multiple key servers may share keys with each other directly, or alternatively, indirectly through a central key server, as needed to support secure communications between their respective device groups.