A quorum certificate (QC) is a bundle of validator signatures showing that enough validators voted for the same block. In DiemBFT, the next round’s leader collects these votes and uses the QC to extend the blockchain. section 12.4.2
A round creates a QC in a few practical steps:
- A designated leader proposes a transaction block extending a previously seen block. section 12.4.2
- Validators vote by signing the proposed block and sending their signatures to the next round’s leader. section 12.4.2
- The next leader bundles enough signatures into a QC and proposes a new block containing it. section 12.4.2
- With 3f + 1 validators, the QC requires at least 2f + 1 votes, allowing safety and progress despite up to f malicious validators. section 12.4.3
Figure 12.9 Each round of DiemBFT starts with the designated leader proposing a block that extends the last one they’ve seen. Other validators can then vote on this block by sending their vote to the next round’s leader. If the next round’s leader gathers enough votes to form a quorum certificate (QC), they can propose a new block containing the QC, effectively extending the previously seen block.
Follow the round-by-round flow from proposal and validator votes to QC formation and the next block. section 12.4.2
