# PBFT ## Metadata **Status**:: #x **Zettel**:: #zettel/literature **Created**:: [[2026-01-20]] **Reference**:: [[Castro et al. - Practical Byzantine Fault Tolerance and Proactive Recovery]] ## Synopsis - Guarantee the uniqueness of sequence number to request mapping via QC (quorum certificate). - A QC contains $2f + 1$ signed messages sent by [[Provable Broadcast]]. - Execute requests by sequence number.