Permissioned blockchain Sample Clauses

Permissioned blockchain. Permissioned chains rely on a trusted authority that can appoint a set of consensus nodes. These consensus nodes could be each operated by a different company, public institution or other reputable entity. Because one needs permission from the trusted authority to become a new consensus node, these systems are called “permissioned” or “distributed” (as opposed to decentralized) systems. In a setting where a relatively small number of pre-defined consensus nodes exist, consensus can be achieved efficiently and securely using a so-called Byzantine-fault tolerant (BFT) consensus protocol. The term Byzantine- fault means that some of the nodes can deviate from the correct protocol execution in arbitrary ways, which covers node compromise by an external attacker, malicious inside administrator and other similar attacks. BFT consensus protocols have been studied for decades. A classical theoretical work by Xxxxxxx et al. from the early 1980’s shows that there are solutions to the BFT consensus problem only when there are less than 1/3 faulty nodes [11]. This is why any BFT consensus protocol can tolerate at maximum 1/3 compromised nodes. Another classical work in this field is an efficient and formally-proven BFT consensus protocol called Practical BFT (PBFT) by Xxxxxx et al. [12]. This protocol is commonly used in modern permissioned blockchain systems. Recently, there has been significant research into more optimized BFT consensus protocols that can have slightly better scalability or other improvements. The research community has peer-reviewed widely available public proofs of schemes such as Practical BFT and HotStuff and determined that these schemes indeed have this tolerance. There have been many new BFT-based schemes introduced in the past few years that modify the BFT protocol to increase performance, but many of these schemes either do not have a published mathematical proof or have not gone through a peer review process. The trust assumptions of BFT protocols, and thus permissioned blockchains, are simple and well-understood. To violate consensus, the adversary needs to compromise at least 1/3 of the consensus nodes. For example, when 30 consensus nodes are used, the adversary needs to gain control of 10 different organizations. If each organization protects their consensus node appropriately, this is a difficult task for an external adversary. The other possible way to violate consensus is to have at least 1/3 of the organizations collude. If the org...