Question

In Practical Byzantine Fault Tolerance (PBFT), what is the minimum fraction of nodes that must act honestly for the system to reach consensus and ensure liveness?

Accepted Answer

In Practical Byzantine Fault Tolerance, the system requires a minimum of two-thirds of the nodes to act honestly. This means that if the total number of nodes in the system is denoted as n, the number of faulty or malicious nodes, denoted as f, must satisfy the inequality n is greater than or equal to 3f plus 1. Byzantine Fault Tolerance refers to a system&#x27;s ability to reach a correct consensus even when some components fail or act maliciously by sending conflicting information. Liveness ensures that the system continues to make progress and provide responses to client requests despite these failures. To guarantee both safety, which is the assurance that all honest nodes agree on the same sequence of operations, and liveness, the system requires a supermajority of honest participants. Specifically, out of 3f plus 1 nodes, at most f nodes can be faulty. This allows the system to receive enough identical responses to form a quorum, which is the minimum number of votes required to validate an action, while ensuring that the votes of faulty nodes cannot override the honest majority. For example, in a system with 4 nodes, where f equals 1, at least 3 nodes must be honest to ensure that even if one node provides false data or goes offline, the remaining 3 nodes provide a consistent and reliable consensus.

Home → All Courses → Engineering and Technology Courses → Blockchain Systems Development → Flashcard

In Practical Byzantine Fault Tolerance (PBFT), what is the minimum fraction of nodes that must act honestly for the system to reach consensus and ensure liveness?