Thus group communication systems provide the basic infrastructure for building fault-tolerant distributed systems. The SecureGroup system is a group communication system that provides secure, reliable, totally ordered message delivery for a group of processors communicating over a local-area network. In addition to crash faults, the system also tolerates Byzantine faults. Trojan horses refer to segments of code inserted into a system, that disguise their malicious intent under apparently innocent functionality. They pose an interesting problem simply because their existence is usually revealed only when they exhibit Byzantine behavior.
Detection is made more difficult by the fact that the Byzantine behavior can be transient.
SecureGroup is derived from the Trans and Total suite of protocols and consists of the SecureTrans, SecureTotal and SecureMembership protocols. The SecureTrans protocol uses a combination of message digests and digital signatures to detect and discard messages with modified content or purporting to originate from a different processor. SecureTrans also detects the occurrence of mutants - two or more valid messages from the same processor, with identical sequence numbers but different contents. Byzantine faults, provided a resilience requirement is met. The SecureMembership protocol operates above SecureTotal and supervises processor admittance and removal.