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Carnot avoids the chain reorg problem, making it compatible with PoS schemes
This enhances the robustness of the protocol, making it a valuable addition to the ecosystem of consensus protocols
# The Protocol
The protocol in Carnot operates in two modes: the happy path and the unhappy path.
In Carnot, nodes are arranged in a binary tree overlay committee structure. Moreover, Carnot is a
pipelined consensus protocol where a block contains the proof of attestation of its parent. In happy path the
leader proposes a block that contains a quorum certificate (QC) with votes from more than two-thirds of the root
committee and its child committee/ committees. The voting process begins at the leaf committee where nodes verify
the proposal and send their votes to the parent committee. Once a node in the parent committee receives more than
two-thirds of the votes from its child committee members, it sends its votes to its parent. This process continues
recursively until the root committee members collect votes from its child committee/ committees. The root committee
member builds a QC from the votes and sends it to the next leader. The leader builds a QC and proposes the next block
upon receiving more than two-thirds of votes.
In the unhappy path, if a node does not receive a message within a timeout interval, it will timeout. Only nodes at
the root committee and its child committee/ committees send their timeout messages to the root committee. The root
committee builds a timeout QC from more than two-thirds of messages, recalculates the new overlay, and broadcasts it
to the network. Similar to the happy path, the timeout message moves from leaves to the root. Each parent waits for
more than two-thirds of timeout messages from its child committees and sends its timeout to the parent committee once
the threshold is reached. A node in the root committee builds a QC from timeout messages received from its
child committee/committees and forwards it to the next leader. Upon receiving more than two-thirds of timeout
messages, the next leader builds an aggregated QC and proposes the next block containing the aggregated QC.
It should be noted that while receiving timeout messages, each node also updates its high_qc (the most recent QC)
and passes it to its parent through the timeout message. In this way, the aggregated QC will include the high_qc seen
by the majority of honest nodes. Hence, after the view change, the protocol safety is preserved.
# Carnot Specification
This is the pseudocode specification of the Carnot consensus algorithm.
In this specification we will omit any cryptographic material, block validity and proof checks. A real implementation is expected to check those before hitting this code.