The paper presents a new reliable multicast protocol that tolerates arbitrary faults, including Byzantine faults. This protocol is developed using a novel way of designing secure protocols which is based on a well-founded hybrid failure model. Despite our claim of arbitrary failure resilience, the protocol need not necessarily incur the cost of "Byzantine agreement", in number of participants and round/message complexity. It can rely on the existence of a simple distributed security kernel-the TTCB-where the participants only execute crucial parts of the protocol operation, under the protection of a crash failure model. Otherwise, participants follow an arbitrary failure model. The TTCB provides only a few basic services, which allow our protocol to have an efficiency similar to that of accidental fault-tolerant protocols: for f faults, our protocol requires f+2 processes, instead of 3f+1 in Byzantine systems. Besides, the TTCB (which is synchronous) allows secure operation of timed protocols, despite the unpredictable time behavior of the environment (possibly due to attacks on timing assumptions).