One of the main challenges of securing multicast communication is source authentication, or enabling receivers of multicast data to verify that the received data originated with the claimed source and was not modified en-route. The problem becomes more complex in common settings where other receivers of the data are not trusted, and where lost packets are not retransmitted. EMSS EMSS is an efficient protocol to sign data streams. The main idea is to ammortize an expensive digital signature operation over a large number of data packets.
Confidentiality is the main purpose of secure group communication.
The general approach is to establish a secret group key shared by all members to encrypt all confidential communication. Dealing with dynamic membership is a challenging problem since secure group communication requires forward and backward secrecy. Forward secrecy guarantees that a passive adversary who knows a contiguous subset of old group keys cannot discover subsequent group keys. Similarly, backward secrecy guarantees that a passive adversary who knows a contiguous subset group keys cannot discover preceding group keys. In this setting, every member is usually a sender and a receiver.