Decentralized runtime verification of message sequences in message-based systems

Message-based systems are usually distributed in nature, and distributed components collaborate via asynchronous message passing. In some cases, particular ordering among the messages may lead to violation of the desired properties such as data confidentiality. Due to the absence of a global clock and usage of off-the-shelf components, such unwanted orderings can be neither statically inspected nor verified by revising their codes at design time. We propose a choreography-based runtime verification algorithm that given an automata-based specification of unwanted message sequences detects the formation of the unwanted sequences. Our algorithm is fully decentralized in the sense that each component is equipped with a monitor, as opposed to having a centralized monitor, and also the specification of the unwanted sequences is decomposed among monitors. In this way, when a component sends a message, its monitor inspects if there is a possibility for the formation of unwanted message sequences. As there is no global clock in message-based systems, monitors cannot determine the exact ordering among messages. In such cases, they decide conservatively and declare a sequence formation even if that sequence has not been formed. We prevent such conservative declarations in our algorithm as much as possible and then characterize its operational guarantees. We evaluate the efficiency and scalability of our algorithm in terms of the communication overhead, the memory consumption, and the latency of the result declaration through simulation.